RESUMEN
Background: Opioids are efficacious and safe analgesic drugs in short-term use for acute pain but chronic use can lead to tolerance and dependence. Opioid-induced microglial activation may contribute to the development of tolerance and this process may differ between males and females. A link is suggested between this microglial activation and inflammation, disturbances of circadian rhythms, and neurotoxic effects. We set out to further delineate the effects of chronic morphine on pain behaviour, microglial and neuronal staining, and the transcriptome of spinal microglia, to better understand the role of microglia in the consequences of long-term high-dose opioid administration. Experimental Approach: In two experiments, we administered increasing subcutaneous doses of morphine hydrochloride or saline to male and female rats. Thermal nociception was assessed with the tail flick and hot plate tests. In Experiment I, spinal cord (SC) samples were prepared for immunohistochemical staining for microglial and neuronal markers. In Experiment II, the transcriptome of microglia from the lumbar SC was analysed. Key Results: Female and male rats had similar antinociceptive responses to morphine and developed similar antinociceptive tolerance to thermal stimuli following chronic increasing high doses of s.c. morphine. The area of microglial IBA1-staining in SC decreased after 2 weeks of morphine administration in both sexes. Following morphine treatment, the differentially expressed genes identified in the microglial transcriptome included ones related to the circadian rhythm, apoptosis, and immune system processes. Conclusions: Female and male rats showed similar pain behaviour following chronic high doses of morphine. This was associated with decreased staining of spinal microglia, suggesting either decreased activation or apoptosis. High-dose morphine administration also associated with several changes in gene expression in SC microglia, e.g., those related to the circadian rhythm (Per2, Per3, Dbp). These changes should be considered in the clinical consequences of long-term high-dose administration of opioids.
Asunto(s)
Analgésicos Opioides , Morfina , Ratas , Masculino , Femenino , Animales , Morfina/uso terapéutico , Analgésicos Opioides/farmacología , Analgésicos Opioides/uso terapéutico , Microglía , Transcriptoma/genética , Analgésicos/farmacología , Dolor/metabolismo , Médula Espinal/metabolismoRESUMEN
Opioids are effective analgesics in the management of severe pain. However, tolerance, leading to dose escalation and adverse effects are significant limiting factors in their use. The role of peripheral opioid receptors in analgesia has been discussed especially under inflammatory conditions. The results from pharmacological and conditional knockout studies together do not provide a clear picture of the contribution of peripheral opioid receptors on antinociceptive tolerance and this needs to be evaluated. Therefore, we studied whether the peripherally restricted opioid receptor antagonist, methylnaltrexone (MNTX), could prevent morphine tolerance without attenuating the antinociceptive effect of morphine. Male Sprague-Dawley rats were treated for 7 days with increasing subcutaneous doses of morphine (5-30 mg/kg) and were coadministered saline, MNTX (0.5 or 2 mg/kg), or naltrexone (NTX; 2 mg/kg). Nociception was assessed with tail-flick, hotplate, and von Frey tests. Morphine, MNTX, and NTX concentrations in the plasma, brain, and spinal cord were measured by liquid chromatography-tandem mass spectrometry. In acute coadministration, NTX, but not MNTX, abolished the acute antinociceptive effects of morphine in all nociceptive tests. The antinociceptive tolerance after repeated morphine administration was also prevented by NTX but not by MNTX. MNTX penetrated to the spinal cord and the brain to some extent after repeated administration. The results do not support the use of MNTX for preventing opioid tolerance and also suggest that morphine tolerance is mediated by central rather than peripheral opioid receptors in the rat.
Asunto(s)
Morfina , Naltrexona , Analgésicos Opioides/farmacología , Animales , Relación Dosis-Respuesta a Droga , Tolerancia a Medicamentos , Masculino , Morfina/farmacología , Naltrexona/análogos & derivados , Naltrexona/farmacología , Antagonistas de Narcóticos/farmacología , Compuestos de Amonio Cuaternario , Ratas , Ratas Sprague-Dawley , Receptores Opioides , Receptores Opioides muRESUMEN
Descending facilitatory circuitry that involves the rostroventromedial medulla (RVM) exerts a significant role in the development of antinociceptive tolerance and hyperalgesia following chronic morphine treatment. The role of the RVM in the development of antinociceptive tolerance to oxycodone, another clinically used strong opioid, is not yet known. Ketamine, an N-methyl-d-aspartate (NMDA) receptor antagonist, attenuates opioid antinociceptive tolerance, but its effect on RVM cell discharge in opioid-tolerant animals is not known. Here, we compared chronic effects of morphine and oxycodone on the discharge properties of RVM cells and attempted to attenuate chronic treatment-induced changes with ketamine. Parallel recordings of RVM cell discharge and limb withdrawal response were performed under light pentobarbital anesthesia in male rats following sustained systemic treatment with morphine or oxycodone at equianalgesic doses. Ongoing activity and the response to noxious heat and pinch were determined in pronociceptive RVM ON-cells and antinociceptive OFF-cells on the sixth treatment day. Proportions of RVM cell types were not changed. Chronic oxycodone induced antinociceptive tolerance both in limb withdrawal and RVM cell activity. Chronic morphine induced antinociceptive tolerance in limb withdrawal that was accompanied by pronociceptive heat response changes in RVM ON- and OFF-cells. A behaviorally subantinociceptive dose of acute ketamine reversed antinociceptive tolerance both to morphine and oxycodone in limb withdrawal and reversed the chronic morphine-induced pronociceptive discharge changes in RVM cells. The results indicate that an NMDA receptor-dependent descending pronociceptive circuitry involving the RVM has an important role in behavioral antinociceptive tolerance to morphine but not oxycodone.NEW & NOTEWORTHY Morphine and oxycodone are two clinically used strong opioids. Chronic treatment with oxycodone as well as morphine can lead to analgesic tolerance and paradoxical hyperalgesia. Here we show that an N-methyl-d-aspartate receptor-dependent pronociceptive change in discharge properties of rostroventromedial medullary neurons controlling spinal nociception has an important role in antinociceptive tolerance to morphine but not oxycodone. Interestingly, chronic oxycodone did not induce pronociceptive changes in the rostroventromedial medulla.
Asunto(s)
Analgésicos Opioides/farmacología , Tolerancia a Medicamentos , Hiperalgesia/inducido químicamente , Ketamina/farmacología , Bulbo Raquídeo/efectos de los fármacos , Morfina/farmacología , Nocicepción/efectos de los fármacos , Oxicodona/farmacología , Receptores de N-Metil-D-Aspartato/antagonistas & inhibidores , Analgésicos Opioides/administración & dosificación , Animales , Conducta Animal/efectos de los fármacos , Antagonistas de Aminoácidos Excitadores , Ketamina/administración & dosificación , Masculino , Morfina/administración & dosificación , Oxicodona/administración & dosificación , Ratas , Ratas Sprague-DawleyRESUMEN
The glial cell line-derived neurotrophic factor (GDNF) family ligands (GFLs) alleviate symptoms of experimental neuropathy, protect and stimulate regeneration of sensory neurons in animal models of neuropathic pain, and restore their functional activity. However, clinical development of GFL proteins is complicated by their poor pharmacokinetic properties and multiple effects mediated by several receptors. Previously, we have identified a small molecule that selectively activates the major signal transduction unit of the GFL receptor complex, receptor tyrosine kinase RET, as an alternative to GFLs, for the treatment of neuropathic pain. We then introduced a series of chemical changes to improve the biological activity of these compounds and tested an optimized compound named BT44 in a panel of biological assays. BT44 efficiently and selectively stimulated the GFL receptor RET and activated the intracellular mitogene-activated protein kinase/extracellular signal-regulated kinase pathway in immortalized cells. In cultured sensory neurons, BT44 stimulated neurite outgrowth with an efficacy comparable to that of GFLs. BT44 alleviated mechanical hypersensitivity in surgery- and diabetes-induced rat models of neuropathic pain. In addition, BT44 normalized, to a certain degree, the expression of nociception-related neuronal markers which were altered by spinal nerve ligation, the neuropathy model used in this study. Our results suggest that the GFL mimetic BT44 is a promising new lead for the development of novel disease-modifying agents for the treatment of neuropathy and neuropathic pain.
Asunto(s)
Biomimética/métodos , Neuralgia/tratamiento farmacológico , Proteínas Proto-Oncogénicas c-ret/agonistas , Proteínas Proto-Oncogénicas c-ret/metabolismo , Células Receptoras Sensoriales/efectos de los fármacos , Transducción de Señal/efectos de los fármacos , Nervios Espinales/efectos de los fármacos , Animales , Escala de Evaluación de la Conducta , Línea Celular , Neuropatías Diabéticas/tratamiento farmacológico , Factor Neurotrófico Derivado de la Línea Celular Glial/metabolismo , Receptores del Factor Neurotrófico Derivado de la Línea Celular Glial/metabolismo , Factores Neurotróficos Derivados de la Línea Celular Glial , Inmunohistoquímica , Masculino , Proteínas del Tejido Nervioso/metabolismo , Neuralgia/metabolismo , Nocicepción/efectos de los fármacos , Fosforilación , Ratas , Ratas Wistar , Células Receptoras Sensoriales/metabolismo , Nervios Espinales/lesionesRESUMEN
Stimulation of the secondary somatosensory cortex (S2) has attenuated pain in humans and inflammatory nociception in animals. Here we studied S2 stimulation-induced antinociception and its underlying mechanisms in an experimental animal model of neuropathy induced by spinal nerve ligation (SNL). Effect of S2 stimulation on heat-evoked limb withdrawal latency was assessed in lightly anesthetized rats that were divided into three groups based on prior surgery and monofilament testing before induction of anesthesia: 1) sham-operated group and 2) hypersensitive and 3) nonhypersensitive (mechanically) SNL groups. In a group of hypersensitive SNL animals, a 5-HT1A receptor agonist was microinjected into the rostroventromedial medulla (RVM) to assess whether autoinhibition of serotonergic cell bodies blocks antinociception. Additionally, effect of S2 stimulation on pronociceptive ON-cells and antinociceptive OFF-cells in the RVM or nociceptive spinal wide dynamic range (WDR) neurons were assessed in anesthetized hypersensitive SNL animals. S2 stimulation induced antinociception in hypersensitive but not in nonhypersensitive SNL or sham-operated animals. Antinociception was prevented by a 5-HT1A receptor agonist in the RVM. Antinociception was associated with decreased duration of heat-evoked response in RVM ON-cells. In spinal WDR neurons, heat-evoked discharge was delayed by S2 stimulation, and this antinociceptive effect was prevented by blocking spinal 5-HT1A receptors. The results indicate that S2 stimulation suppresses nociception in SNL animals if SNL is associated with tactile allodynia-like hypersensitivity. In hypersensitive SNL animals, S2 stimulation induces antinociception mediated by medullospinal serotonergic pathways acting on the spinal 5-HT1A receptor, and partly through reduction of the RVM ON-cell discharge.NEW & NOTEWORTHY Stimulation of S2 cortex, but not that of an adjacent cortical area, induced descending heat antinociception in rats with the spinal nerve ligation-induced model of neuropathy. Antinociception was bilateral, and it involved suppression of pronociceptive medullary cells and activation of serotonergic pathways that act on the spinal 5-HT1A receptor. S2 stimulation failed to induce descending antinociceptive effect in sham-operated controls or in nerve-ligated animals that had not developed mechanical hypersensitivity.
Asunto(s)
Estimulación Eléctrica , Neuralgia/terapia , Serotonina/metabolismo , Transducción de Señal/fisiología , Corteza Somatosensorial/fisiología , Médula Espinal/metabolismo , Nervios Espinales , 8-Hidroxi-2-(di-n-propilamino)tetralin/farmacología , Potenciales de Acción/fisiología , Animales , Modelos Animales de Enfermedad , Lateralidad Funcional , Hiperalgesia/fisiopatología , Bulbo Raquídeo/citología , Neuronas/fisiología , Ratas , Ratas Wistar , Tiempo de Reacción/efectos de los fármacos , Receptor de Serotonina 5-HT1A/metabolismo , Agonistas de Receptores de Serotonina/farmacología , Médula Espinal/citologíaRESUMEN
Among brain structures receiving efferent projections from the histaminergic tuberomammillary nucleus is the pontine locus coeruleus (LC) involved in descending noradrenergic control of pain. Here we studied whether histamine in the LC is involved in descending regulation of neuropathic hypersensitivity. Peripheral neuropathy was induced by unilateral spinal nerve ligation in the rat with a chronic intracerebral and intrathecal catheter for drug administrations. Mechanical hypersensitivity in the injured limb was assessed by monofilaments. Heat nociception was assessed by determining radiant heat-induced paw flick. Histamine in the LC produced a dose-related (1-10µg) mechanical antihypersensitivity effect (maximum effect at 15min and duration of effect 30min), without influence on heat nociception. Pretreatment of LC with zolantidine (histamine H2 receptor antagonist), but not with pyrilamine (histamine H1 receptor antagonist), and spinal administration of atipamezole (an α2-adrenoceptor antagonist), prazosine (an α1-adrenoceptor antagonist) or bicuculline (a GABAA receptor antagonist) attenuated the antihypersensitivity effect of histamine. The histamine-induced antihypersensitivity effect was also reduced by pretreatment of LC with fadolmidine, an α2-adrenoceptor agonist inducing autoinhibition of noradrenergic cell bodies. Zolantidine or pyrilamine alone in the LC failed to influence pain behavior, while A-960656 (histamine H3 receptor antagonist) suppressed hypersensitivity. A plausible explanation for these findings is that histamine, due to excitatory action mediated by the histamine H2 receptor on noradrenergic cell bodies, promotes descending spinal α1/2-adrenoceptor-mediated inhibition of neuropathic hypersensitivity. Blocking the autoinhibitory histamine H3 receptor on histaminergic nerve terminals in the LC facilitates release of histamine and thereby, increases descending noradrenergic pain inhibition.
Asunto(s)
Histamina/fisiología , Hiperalgesia/fisiopatología , Locus Coeruleus/fisiología , Neuralgia/fisiopatología , Neuronas Adrenérgicas/fisiología , Antagonistas de Receptores Adrenérgicos alfa 1/farmacología , Agonistas de Receptores Adrenérgicos alfa 2/farmacología , Animales , Benzotiazoles/farmacología , Bicuculina/farmacología , Antagonistas de Receptores de GABA-A/farmacología , Antagonistas de los Receptores H2 de la Histamina/farmacología , Calor , Imidazoles/farmacología , Indanos/farmacología , Masculino , Fenoxipropanolaminas/farmacología , Estimulación Física , Piperidinas/farmacología , Prazosina/farmacología , Ratas , Receptores Adrenérgicos alfa 1/fisiología , Receptores Adrenérgicos alfa 2/fisiología , Receptores Histamínicos/fisiología , Nervios Espinales/lesionesRESUMEN
OBJECTIVES: The aim was to compare the effects of high-frequency spinal cord stimulation (HF-SCS) at subparesthetic intensity with conventional SCS in rat models of different types of pain. In addition, microrecordings of afferent activity in the dorsal columns during both types of SCS were performed to elucidate their mode of action. MATERIALS AND METHODS: Miniature SCS electrodes were implanted in all rats. One group was submitted to the spared nerve injury procedure (SNI) and another to inflammatory pain after carrageenan injection into a hind paw. All animals were tested for hypersensitivity to normally innocuous tactile and thermal stimuli. One group of normal healthy rats was submitted to acute nociceptive (pinch, heat) pain. Microrecording of afferent activity in the gracile nucleus (GN) was performed in a group of nerve-lesioned rats responding to conventional SCS. RESULTS: HF-SCS at 500, 1,000, or 10,000 Hz at subparesthetic amplitudes produced similar reductions in hypersensitivity due to nerve lesion as did conventional SCS at 50 Hz. HF-SCS showed no effect on thermal pain. A trial to rescue non-responders to conventional SCS using HF-SCS was not successful. There were no effects either of conventional or of HF-SCS on acute or inflammatory pain. Conventional SCS produced massive activation in the GN but no activation during HF-SCS, though normal peripherally evoked afferent activity remained. CONCLUSIONS: Conventional SCS proved equally effective to HF-SCS in various pain models. As no activity is conveyed rostrally in subparesthetic HF-SCS, we hypothesize that its mechanisms of action are primarily segmental.
Asunto(s)
Modelos Animales de Enfermedad , Manejo del Dolor/métodos , Dolor/fisiopatología , Estimulación de la Médula Espinal/métodos , Vías Aferentes/fisiopatología , Animales , Carragenina/toxicidad , Frío/efectos adversos , Desnervación , Electrodos Implantados , Pie , Calor/efectos adversos , Hiperalgesia/inducido químicamente , Hiperalgesia/terapia , Inflamación/fisiopatología , Masculino , Bulbo Raquídeo/fisiopatología , Microelectrodos , Dolor/clasificación , Dolor/etiología , Presión/efectos adversos , Ratas , Ratas Wistar , Nervio Ciático/fisiopatología , Nervio Ciático/cirugía , Asta Dorsal de la Médula Espinal/fisiopatologíaRESUMEN
First-line pharmacotherapy for peripheral neuropathic pain (NP) of diverse pathophysiology consists of antidepressants and gabapentinoids, but only a minority achieve sufficient analgesia with these drugs. Opioids are considered third-line analgesics in NP due to potential severe and unpredictable adverse effects in long-term use. Also, opioid tolerance and NP may have shared mechanisms, raising further concerns about opioid use in NP. We set out to further elucidate possible shared and separate mechanisms after chronic morphine treatment and oxaliplatin-induced and diabetic polyneuropathies, and to identify potential diagnostic markers and therapeutic targets. We analysed thermal nociceptive behaviour, the transcriptome of dorsal root ganglia (DRG) and the metabolome of cerebrospinal fluid (CSF) in these three conditions, in rats. Several genes were differentially expressed, most following oxaliplatin and least after chronic morphine treatment, compared with saline-treated rats. A few genes were differentially expressed in the DRGs in all three models (e.g. Csf3r and Fkbp5). Some, e.g. Alox15 and Slc12a5, were differentially expressed in both diabetic and oxaliplatin models. Other differentially expressed genes were associated with nociception, inflammation, and glial cells. The CSF metabolome was most significantly affected in the diabetic rats. Interestingly, we saw changes in nicotinamide metabolism, which has been associated with opioid addiction and withdrawal, in the CSF of morphine-tolerant rats. Our results offer new hypotheses for the pathophysiology and treatment of NP and opioid tolerance. In particular, the role of nicotinamide metabolism in opioid addiction deserves further study.
RESUMEN
Peripheral diabetic neuropathy (PDN) is a devastating complication of diabetes mellitus (DM). Here we test the hypothesis that the transient receptor potential ankyrin 1 (TRPA1) ion channel on primary afferent nerve fibers is involved in the pathogenesis of PDN, due to sustained activation by reactive compounds generated in DM. DM was induced by streptozotocin in rats that were treated daily for 28 days with a TRPA1 channel antagonist (Chembridge-5861528) or vehicle. Laser Doppler flow method was used for assessing axon reflex induced by intraplantar injection of a TRPA1 channel agonist (cinnamaldehyde) and immunohistochemistry to assess substance P-like innervation of the skin. In vitro calcium imaging and patch clamp were used to assess whether endogenous TRPA1 agonists (4-hydroxynonenal and methylglyoxal) generated in DM induce sustained activation of the TRPA1 channel. Axon reflex induced by a TRPA1 channel agonist in the plantar skin was suppressed and the number of substance P-like immunoreactive nerve fibers was decreased 4 weeks after induction of DM. Prolonged treatment with Chembridge-5861528 reduced the DM-induced attenuation of the cutaneous axon reflex and loss of substance P-like immunoreactive nerve fibers. Moreover, in vitro calcium imaging and patch clamp results indicated that reactive compounds generated in DM (4-hydroxynonenal and methylglyoxal) produced sustained activations of the TRPA1 channel, a prerequisite for adverse long-term effects. The results indicate that the TRPA1 channel exerts an important role in the pathogenesis of PDN. Blocking the TRPA1 channel provides a selective disease-modifying treatment of PDN.
Asunto(s)
Diabetes Mellitus Experimental/tratamiento farmacológico , Nefropatías Diabéticas/prevención & control , Fibras Nerviosas/efectos de los fármacos , Neuronas Aferentes/efectos de los fármacos , Fármacos del Sistema Sensorial/farmacología , Piel/inervación , Canales Catiónicos TRPC/antagonistas & inhibidores , Animales , Canales de Calcio/genética , Canales de Calcio/metabolismo , Señalización del Calcio/efectos de los fármacos , Diabetes Mellitus Experimental/complicaciones , Diabetes Mellitus Experimental/metabolismo , Diabetes Mellitus Experimental/fisiopatología , Nefropatías Diabéticas/etiología , Nefropatías Diabéticas/metabolismo , Nefropatías Diabéticas/fisiopatología , Células HEK293 , Humanos , Masculino , Potenciales de la Membrana , Fibras Nerviosas/metabolismo , Proteínas del Tejido Nervioso/antagonistas & inhibidores , Proteínas del Tejido Nervioso/genética , Proteínas del Tejido Nervioso/metabolismo , Conducción Nerviosa/efectos de los fármacos , Neuronas Aferentes/metabolismo , Umbral del Dolor/efectos de los fármacos , Ratas , Reflejo/efectos de los fármacos , Sustancia P/metabolismo , Canal Catiónico TRPA1 , Canales Catiónicos TRPC/agonistas , Canales Catiónicos TRPC/genética , Canales Catiónicos TRPC/metabolismo , Factores de Tiempo , Transfección , Canales de Potencial de Receptor Transitorio/antagonistas & inhibidores , Canales de Potencial de Receptor Transitorio/genética , Canales de Potencial de Receptor Transitorio/metabolismoRESUMEN
OBJECTIVE: During inflammation in the joint, normal joint movements are usually painful. A neuronal mechanism for this form of mechanical hyperalgesia is the persistent sensitization of joint nociceptors to mechanical stimuli. Because tumor necrosis factor (TNF) is a major mediator of joint inflammation, we undertook the present study both to explore the potential of TNF to sensitize joint nociceptors to mechanical stimuli and to address the cellular mechanism involved. METHODS: In anesthetized rats, action potentials (APs) were recorded from sensory nociceptive Aδ fibers and C fibers supplying the knee joint. We monitored responses to rotation of the knee joint at innocuous and noxious intensities. TNF, etanercept, and a p38 inhibitor were injected into the knee joint, and the cyclooxygenase (COX) inhibitor diclofenac was administered intraperitoneally. APs were also recorded in isolated cultured dorsal root ganglion (DRG) neurons in order to test for changes in neuronal excitability induced by TNF. RESULTS: A single application of TNF into the normal knee joint caused a significant persistent sensitization of nociceptive sensory fibers to mechanical stimuli applied to the joint. This effect was dose dependent. It was prevented by coadministration of etanercept or by an inhibitor of p38, and it was attenuated by systemic application of a COX inhibitor. Patch clamp recordings from isolated DRG neurons showed a rapid increase in neuronal excitability induced by TNF. CONCLUSION: TNF can induce a long-lasting sensitization of joint nociceptors to mechanical stimuli and thus can induce long-lasting mechanical hyperalgesia in joints. TNF can act directly on neurons, underscoring its role as a sensitizing pain mediator.
Asunto(s)
Articulación de la Rodilla/efectos de los fármacos , Nociceptores/efectos de los fármacos , Estrés Mecánico , Factor de Necrosis Tumoral alfa/farmacología , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/fisiología , Animales , Antiinflamatorios no Esteroideos/farmacología , Células Cultivadas , Diclofenaco/farmacología , Relación Dosis-Respuesta a Droga , Etanercept , Ganglios Espinales/citología , Ganglios Espinales/efectos de los fármacos , Ganglios Espinales/fisiología , Inmunoglobulina G/farmacología , Inyecciones Intraarticulares , Articulación de la Rodilla/metabolismo , Masculino , Modelos Animales , Nociceptores/metabolismo , Técnicas de Placa-Clamp , Ratas , Ratas Wistar , Receptores del Factor de Necrosis Tumoral , Factor de Necrosis Tumoral alfa/administración & dosificación , Proteínas Quinasas p38 Activadas por Mitógenos/antagonistas & inhibidoresRESUMEN
BACKGROUND: Early patient contacts are considered important in medical education. AIMS: We studied the influence of a real patient trigger on study motivation and learning in problem-based study groups of first-year medical and dentistry students. METHODS: 156 eligible students were allocated into 17 groups. Six randomly selected groups received both the real patient and paper trigger, and 11 groups received only the paper trigger. The immediate and later effects of the trigger were assessed with qualitative and quantitative questionnaires and exam scores. The tutors answered questionnaires concerning learning outcomes. RESULTS: The students reported that the real patient trigger significantly improved their study motivation, understanding of the learning objectives and confidence in future patient encounters. The real patient trigger was considered significantly more interesting than the paper case. No statistically significant difference was observed in the exam scores. The tutors observed that groups with poor previous performance gained better results in study sessions. CONCLUSIONS: Real patient triggers motivate students to learn basic medical sciences. Ways to present real patients to students should be considered in medical curricula from early on.
Asunto(s)
Anatomía/educación , Curriculum , Motivación , Atención al Paciente/métodos , Aprendizaje Basado en Problemas/métodos , Estudiantes de Medicina/psicología , Enseñanza/métodos , Actitud del Personal de Salud , Distribución de Chi-Cuadrado , Educación de Pregrado en Medicina/métodos , Humanos , Mentores , Investigación Cualitativa , Encuestas y CuestionariosRESUMEN
We studied whether stimulation of the primary motor cortex (M1) attenuates pain-related spinal withdrawal responses of neuropathic and healthy control rats, and whether the descending antinociceptive effect is relayed through the noradrenergic locus coeruleus (LC). The assessments of the noxious heat-evoked limb withdrawals reflecting spinal nociception and recordings of single LC units were performed in spinal nerve-ligated neuropathic and sham-operated control rats under light pentobarbital anesthesia. Electric stimulation of M1 produced equally strong spinal antinociception in neuropathic and control rats. Following microinjection into M1, a group I metabotropic glutamate receptor agonist (DHPG; 10 nmol) and a high (25 nmol) but not low (2.5 nmol) dose of glutamate slightly increased on-going discharge rates of LC neurons in neuropathic but not in control animals. Influence of electric stimulation of M1 on LC neurons was studied only in the neuropathic group, in which discharge rates of LC neurons were increased by electric M1 stimulation. Lidocaine block of the LC or block of descending noradrenergic influence by intrathecal administration of a alpha(2)-adrenoceptor antagonist failed to produce a significant attenuation of the spinal antinociceptive effect induced by electric M1 stimulation in the neuropathic or the sham group. The results indicate that stimulation of the rat M1 induces spinal antinociception in neuropathic as well as control conditions. While M1 stimulation may activate the LC, particularly in the neuropathic group, the contribution of coeruleospinal noradrenergic pathways may not be critical for the spinal antinociceptive effect induced by M1 stimulation.
Asunto(s)
Terapia por Estimulación Eléctrica/métodos , Locus Coeruleus/fisiopatología , Corteza Motora/fisiología , Manejo del Dolor , Dolor/fisiopatología , Enfermedades del Sistema Nervioso Periférico/fisiopatología , Enfermedades del Sistema Nervioso Periférico/terapia , Antagonistas de Receptores Adrenérgicos alfa 2 , Antagonistas Adrenérgicos alfa/farmacología , Anestésicos Locales/administración & dosificación , Anestésicos Locales/farmacología , Animales , Vías Autónomas/fisiología , Electrofisiología , Agonistas de Aminoácidos Excitadores/farmacología , Glicina/análogos & derivados , Glicina/farmacología , Calor , Inyecciones Espinales , Lidocaína/administración & dosificación , Lidocaína/farmacología , Ligadura , Masculino , Microinyecciones , Ratas , Ratas Wistar , Receptores Adrenérgicos alfa 2/efectos de los fármacos , Receptores Adrenérgicos alfa 2/fisiología , Reflejo/efectos de los fármacos , Reflejo/fisiología , Resorcinoles/farmacología , Médula Espinal , Nervios Espinales/patologíaRESUMEN
Morphine-3-glucuronide (M3G), the main metabolite of morphine, has been implicated in the development of tolerance and of opioid-induced hyperalgesia, both limiting the analgesic use of morphine. We evaluated the acute and chronic effects of M3G and morphine as well as development of antinociceptive cross-tolerance between morphine and M3G after intrathecal administration and assessed the expression of pain-associated neurotransmitter substance P in the spinal cord. Sprague-Dawley rats received intrathecal M3G or morphine twice daily for 6 days. Nociception and tactile allodynia were measured with von Frey filaments after acute and chronic treatments. Substance P levels in the dorsal horn of the spinal cord were determined by immunohistochemistry after 4-day treatments. Acute morphine caused antinociception as expected, whereas acute M3G caused tactile allodynia, as did both chronic M3G and morphine. Chronic M3G also induced antinociceptive cross-tolerance to morphine. M3G and morphine increased substance P levels similarly in the nociceptive laminae of the spinal cord. This study shows that chronic intrathecal M3G sensitises animals to mechanical stimulation and elevates substance P levels in the nociceptive laminae of the spinal cord. Chronic M3G also induces antinociceptive cross-tolerance to morphine. Thus, chronic M3G exposure might contribute to morphine-induced tolerance and opioid-induced hyperalgesia.
Asunto(s)
Estimulantes del Sistema Nervioso Central/farmacología , Hiperalgesia/inducido químicamente , Derivados de la Morfina/farmacología , Morfina/farmacología , Nocicepción/efectos de los fármacos , Animales , Modelos Animales de Enfermedad , Esquema de Medicación , Tolerancia a Medicamentos , Humanos , Hiperalgesia/diagnóstico , Inyecciones Espinales , Masculino , Morfina/metabolismo , Derivados de la Morfina/metabolismo , Dimensión del Dolor , Ratas , Médula Espinal/efectos de los fármacos , Médula Espinal/metabolismo , Sustancia P/metabolismoRESUMEN
We determined the role of the dopamine D2 receptor in or adjacent to the dopaminergic A11 cell group in descending modulation of neuropathic hypersensitivity. Moreover, we determined the spinal neurotransmitter receptors mediating the modulatory effect. Neuropathy was produced by spinal nerve ligation in the rat that had a chronic cannula for drug delivery into A11 or a control site in the locus coeruleus, and a catheter for spinal drug delivery. Hypersensitivity was assessed by a withdrawal response to monofilaments. Quinpirole (a dopamine D2/D3 receptor agonist) in A11 attenuated hypersensitivity, without influencing thermal nociception in the uninjured tail. Quinpirole in the locus coeruleus failed to influence hypersensitivity. L-741,626 (a dopamine D2 receptor antagonist), raclopride (a dopamine D2/D3 receptor antagonist) and bicuculline (a GABA(A) receptor antagonist) in A11 reversed the antihypersensitivity effect of quinpirole. Raclopride or bicuculline alone in A11 had no effects, whereas muscimol (a GABA(A) receptor agonist) alone in A11 suppressed hypersensitivity. Spinal administration of atipamezole (an alpha(2)-adrenoceptor antagonist) or marginally also WAY-100635 (a 5-HT(1A) receptor antagonist), but not raclopride or bicuculline, reduced the antihypersensitivity effect induced by quinpirole in A11. Electrical stimulation of A11 produced thermal antinociception following intrathecal administration of saline but not raclopride. The results indicate that activation of the dopamine D2 receptor in A11 may selectively suppress neuropathic hypersensitivity, due to mechanisms that involve GABA(A) receptors in the hypothalamus and descending noradrenergic pathways acting on spinal alpha(2)-adrenoceptors, possibly together with a slight contribution of descending serotoninergic pathways acting on spinal 5-HT(1A) receptors.
Asunto(s)
Vías Eferentes/fisiopatología , Hipotálamo/fisiopatología , Dolor/fisiopatología , Enfermedades del Sistema Nervioso Periférico/fisiopatología , Receptores de Dopamina D2/fisiología , Animales , Antagonistas de los Receptores de Dopamina D2 , Hipotálamo/efectos de los fármacos , Masculino , Dimensión del Dolor , Estimulación Física , Ratas , Ratas Endogámicas , Receptor de Serotonina 5-HT1A/fisiología , Receptores Adrenérgicos alfa 2/fisiología , Receptores de Dopamina D2/agonistas , Receptores de GABA-A/fisiología , Médula Espinal/metabolismoRESUMEN
Ketamine and its primary metabolite norketamine attenuate morphine tolerance by antagonising N-methyl-d-aspartate (NMDA) receptors. Ketamine is extensively metabolized to several other metabolites. The major secondary metabolite (2S,6S;2R,6R)-hydroxynorketamine (6-hydroxynorketamine) is not an NMDA antagonist. However, it may modulate nociception through negative allosteric modulation of α7 nicotinic acetylcholine receptors. We studied whether 6-hydroxynorketamine could affect nociception or the effects of morphine in acute or chronic administration settings. Male Sprague Dawley rats received subcutaneous 6-hydroxynorketamine or ketamine alone or in combination with morphine, as a cotreatment during induction of morphine tolerance, and after the development of tolerance induced by subcutaneous minipumps administering 9.6 mg morphine daily. Tail flick, hot plate, paw pressure and rotarod tests were used. Brain and serum drug concentrations were quantified with high-performance liquid chromatography-tandem mass spectrometry. Ketamine (10 mg/kg), but not 6-hydroxynorketamine (10 and 30 mg/kg), enhanced antinociception and decreased rotarod performance following acute administration either alone or combined with morphine. Ketamine efficiently attenuated morphine tolerance. Acutely administered 6-hydroxynorketamine increased the brain concentration of morphine (by 60%), and brain and serum concentrations of 6-hydroxynorketamine were doubled by morphine pre-treatment. This pharmacokinetic interaction did not, however, lead to altered morphine tolerance. Co-administration of 6-hydroxynorketamine 20 mg/kg twice daily did not influence development of morphine tolerance. Even though morphine and 6-hydroxynorketamine brain concentrations were increased after co-administration, the pharmacokinetic interaction had no effect on acute morphine nociception or tolerance. These results indicate that 6-hydroxynorketamine does not have antinociceptive properties or attenuate opioid tolerance in a similar way as ketamine.
Asunto(s)
Analgésicos Opioides/farmacología , Anestésicos Disociativos/farmacología , Conducta Animal/efectos de los fármacos , Encéfalo/efectos de los fármacos , Tolerancia a Medicamentos , Ketamina/análogos & derivados , Morfina/farmacología , Dolor Nociceptivo/prevención & control , Analgésicos Opioides/sangre , Analgésicos Opioides/farmacocinética , Anestésicos Disociativos/sangre , Anestésicos Disociativos/farmacocinética , Animales , Encéfalo/metabolismo , Encéfalo/fisiopatología , Modelos Animales de Enfermedad , Interacciones Farmacológicas , Ketamina/sangre , Ketamina/farmacocinética , Ketamina/farmacología , Masculino , Morfina/sangre , Morfina/farmacocinética , Actividad Motora/efectos de los fármacos , Nocicepción/efectos de los fármacos , Dolor Nociceptivo/sangre , Dolor Nociceptivo/fisiopatología , Dolor Nociceptivo/psicología , Umbral del Dolor/efectos de los fármacos , Ratas Sprague-DawleyRESUMEN
Development of tolerance is a well known pharmacological characteristic of opioids and a major clinical problem. In addition to the known neuronal mechanisms of opioid tolerance, activation of glia has emerged as a potentially significant new mechanism. We studied activation of microglia and astrocytes in morphine tolerance and opioid-induced hyperalgesia in rats using immunohistochemistry, flow cytometry and RNA sequencing in spinal- and supraspinal regions. Chronic morphine treatment that induced tolerance and hyperalgesia also increased immunoreactivity of spinal microglia in the dorsal and ventral horns. Flow cytometry demonstrated that morphine treatment increased the proportion of M2-polarized spinal microglia, but failed to impact the number or the proportion of M1-polarized microglia. In the transcriptome of microglial cells isolated from the spinal cord (SC), morphine treatment increased transcripts related to cell activation and defense response. In the studied brain regions, no activation of microglia or astrocytes was detected by immunohistochemistry, except for a decrease in the number of microglial cells in the substantia nigra. In flow cytometry, morphine caused a decrease in the number of microglial cells in the medulla, but otherwise no change was detected for the count or the proportion of M1- and M2-polarized microglia in the medulla or sensory cortex. No evidence for the activation of glia in the brain was seen. Our results suggest that glial activation associated with opioid tolerance and opioid-induced hyperalgesia occurs mainly at the spinal level. The transcriptome data suggest that the microglial activation pattern after chronic morphine treatment has similarities with that of neuropathic pain.
Asunto(s)
Analgésicos Opioides/farmacología , Encéfalo/efectos de los fármacos , Morfina/farmacología , Neuroglía/efectos de los fármacos , Médula Espinal/efectos de los fármacos , Animales , Encéfalo/metabolismo , Encéfalo/patología , Tolerancia a Medicamentos , Hiperalgesia/metabolismo , Hiperalgesia/patología , Masculino , Modelos Animales , Neuroglía/metabolismo , Neuroglía/patología , Dolor Nociceptivo/tratamiento farmacológico , Dolor Nociceptivo/metabolismo , Dolor Nociceptivo/patología , Ratas Sprague-Dawley , Médula Espinal/metabolismo , Médula Espinal/patología , Transcriptoma/efectos de los fármacosRESUMEN
Here we studied whether and through which mechanisms spinal administration of histamine dihydrochloride (histamine) attenuates pain behavior in neuropathic animals. Experiments were performed in rats with spinal nerve ligation-induced neuropathy and a chronic intrathecal catheter for spinal drug delivery. Mechanical hypersensitivity was assessed with monofilaments while radiant heat was used for assessing nociception. Ongoing neuropathic pain and its attenuation by histamine was assessed using conditioned place-preference test. Following spinal administration, histamine at doses 0.1-10µg produced a dose-related mechanical antihypersensitivity effect. With prolonged treatment (twice daily 10µg for five days), the antihypersensitivity effect of spinal histamine was reduced. In place-preference test, neuropathic animals preferred the chamber paired with histamine (10µg). Histamine (10µg) failed to influence heat nociception in neuropathic animals or mechanically induced pain behavior in a group of healthy control rats. Histamine-induced mechanical antihypersensitivity effect was prevented by spinal pretreatment with zolantidine (histamine H2 receptor antagonist), prazosine (α1-adrenoceptor antagonist) and bicuculline (γ-aminobutyric acid subtype A, GABA(A), receptor antagonist), but not by pyrilamine (histamine H1 receptor antagonist), atipamezole (α2-adrenoceptor antagonist), or raclopride (dopamine D2 receptor antagonist). A-960656, a histamine H3 receptor antagonist alone that presumably increased endogenous histamine levels reduced hypersensitivity. Additionally, histamine prevented central (presumably postsynaptically-induced) facilitation of hypersensitivity induced by N-methyl-d-aspartate. The results indicate that spinal histamine at the dose range of 0.1-10µg selectively attenuates mechanical hypersensitivity and ongoing pain in neuropathy. The spinal histamine-induced antihypersensitivity effect involves histamine H2 and GABA(A) receptors and (presumably neuropathy-induced) co-activation of spinal α1-adrenoceptors.
Asunto(s)
Histamina/farmacología , Hiperalgesia/tratamiento farmacológico , Hiperalgesia/etiología , Neuralgia/tratamiento farmacológico , Neuralgia/etiología , Médula Espinal , Nervios Espinales/cirugía , Animales , Modelos Animales de Enfermedad , Relación Dosis-Respuesta a Droga , Histamina/administración & dosificación , Histamina/uso terapéutico , Hiperalgesia/metabolismo , Ligadura/efectos adversos , Masculino , Neuralgia/metabolismo , Ratas , Ratas Wistar , Receptores de Neurotransmisores/antagonistas & inhibidores , Receptores de Neurotransmisores/metabolismo , Nervios Espinales/efectos de los fármacos , Factores de TiempoRESUMEN
Activation of the dorsomedial nucleus of the hypothalamus (DMH) by galanin (GAL) induces behavioural hyperalgesia. Since DMH neurones do not project directly to the spinal cord, we hypothesized that the medullary dorsal reticular nucleus (DRt), a pronociceptive region projecting to the spinal dorsal horn (SDH) and/or the serotoninergic raphe-spinal pathway acting on the spinal 5-HT3 receptor (5HT3R) could relay descending nociceptive facilitation induced by GAL in the DMH. Heat-evoked paw-withdrawal latency (PWL) and activity of SDH neurones were assessed in monoarthritic (ARTH) and control (SHAM) animals after pharmacological manipulations of the DMH, DRt and spinal cord. The results showed that GAL in the DMH and glutamate in the DRt lead to behavioural hyperalgesia in both SHAM and ARTH animals, which is accompanied particularly by an increase in heat-evoked responses of wide-dynamic range neurons, a group of nociceptive SDH neurones. Facilitation of pain behaviour induced by GAL in the DMH was reversed by lidocaine in the DRt and by ondansetron, a 5HT3R antagonist, in the spinal cord. However, the hyperalgesia induced by glutamate in the DRt was not blocked by spinal ondansetron. In addition, in ARTH but not SHAM animals PWL was increased after lidocaine in the DRt and ondansetron in the spinal cord. Our data demonstrate that GAL in the DMH activates two independent descending facilitatory pathways: (i) one relays in the DRt and (ii) the other one involves 5-HT neurones acting on spinal 5HT3Rs. In experimental ARTH, the tonic pain-facilitatory action is increased in both of these descending pathways.
Asunto(s)
Galanina/química , Hiperalgesia/inducido químicamente , Hipotálamo/metabolismo , Núcleo Talámico Mediodorsal/metabolismo , Precursores de Proteínas/química , Animales , Artritis/inducido químicamente , Conducta Animal , Modelos Animales de Enfermedad , Electrofisiología , Ácido Glutámico/química , Lidocaína/química , Masculino , Neuronas/metabolismo , Nocicepción , Ondansetrón/química , Dolor , Presión , Ratas , Ratas Wistar , Receptores de Serotonina 5-HT3/metabolismo , Serotonina/química , Médula Espinal/metabolismoRESUMEN
Transient receptor potential ankyrin 1 (TRPA1) channel antagonists have suppressed mechanical hypersensitivity in peripheral neuropathy, while their effect on ongoing neuropathic pain is not yet known. Here, we assessed whether blocking the TRPA1 channel induces place-preference, an index for the relief of ongoing pain, in two experimental rat models of peripheral neuropathy. Diabetic neuropathy was induced by streptozotocin and spared nerve injury (SNI) model of neuropathy by ligation of two sciatic nerve branches. Conditioned place-preference (CPP) paradigm involved pairing of the drug treatment with one of the chambers of a CPP device once or four times, and the time spent in each chamber was recorded after conditioning sessions to reveal place-preference. The mechanical antihypersensitivity effect was assessed by the monofilament test immediately after the conditioning sessions. Intraperitoneally (30mg/kg; diabetic and SNI model) or intrathecally (10µg; diabetic model) administered Chembridge-5861528 (CHEM) was used as a selective TRPA1 channel antagonist. In diabetic and SNI models of neuropathy, CHEM failed to induce CPP at a dose that significantly attenuated mechanical hypersensitivity, independent of the route of drug administration or number of successive conditioning sessions. Intrathecal clonidine (an α2-adrenoceptor agonist; 10µg), in contrast, induced CPP in SNI but not control animals. The results indicate that ongoing pain, as revealed by CPP, is less sensitive to treatment by the TRPA1 channel antagonist than mechanical hypersensitivity in peripheral neuropathy.
Asunto(s)
Condicionamiento Psicológico/fisiología , Hiperalgesia/fisiopatología , Hiperalgesia/psicología , Enfermedades del Sistema Nervioso Periférico/fisiopatología , Enfermedades del Sistema Nervioso Periférico/psicología , Canales Catiónicos TRPC/antagonistas & inhibidores , Acetanilidas/administración & dosificación , Agonistas de Receptores Adrenérgicos alfa 2/administración & dosificación , Animales , Clonidina/administración & dosificación , Neuropatías Diabéticas/tratamiento farmacológico , Neuropatías Diabéticas/fisiopatología , Neuropatías Diabéticas/psicología , Modelos Animales de Enfermedad , Hiperalgesia/tratamiento farmacológico , Masculino , Neuralgia/tratamiento farmacológico , Neuralgia/fisiopatología , Neuralgia/psicología , Enfermedades del Sistema Nervioso Periférico/tratamiento farmacológico , Purinas/administración & dosificación , Ratas , Ratas Wistar , Canal Catiónico TRPA1RESUMEN
We studied in rats with a spinal nerve ligation-induced neuropathy whether dopamine D2 receptors (D2Rs) play a role in descending control of pain induced by stimulation of the primary motor cortex (M1). Noxious heat-evoked responses were determined in spinal dorsal horn wide-dynamic range (WDR) and nociceptive-specific (NS) neurons, with and without electrical M1 stimulation. A D2R antagonist, raclopride, was administered into the dorsal striatum or spinally in attempts to reverse spinal antinociception induced by M1 stimulation. Moreover, influence of M1 stimulation on the noxious heat-induced limb withdrawal reflex was determined following block of spinal D2Rs with raclopride or a lidocaine-induced block of the hypothalamic A11 cell group, the main source of spinal dopamine. Striatal administration of raclopride enhanced the heat-evoked baseline responses of WDR but not NS neurons and reversed the M1 stimulation-induced suppression of the heat response in WDR neurons. Following spinal administration of raclopride, M1 stimulation failed to suppress the heat response of WDR neurons, whereas the heat response of NS neurons was enhanced by M1-stimulation. After blocking the A11 with lidocaine or spinal D2Rs with raclopride, M1 stimulation failed to suppress the noxious heat-evoked withdrawal reflex. The results indicate that descending pain control induced by stimulation of the M1 cortex in neuropathic animals involves supraspinal (presumably striatal) and, through A11, spinal D2Rs. Supraspinal and spinal D2Rs have partly dissociative effects on spinal dorsal horn WDR and NS neurons, possibly reflecting differential roles and wirings that these sensory neurons have in pain-processing circuitries.