Spinal dopaminergic D1-and D2-like receptors have a sex-dependent effect in an experimental model of fibromyalgia.

There is evidence about the importance of sex in pain. The purpose of this study was to investigate the effect of sex in the antiallodynic activity of spinal dopamine D1-and D2-like receptors in a model of fibromyalgia-type pain in rats. Reserpine induced the same extent of tactile allodynia in female and male rats. Intrathecal injection of SCH-23390 (3-30 nmol, D1-like receptor antagonist), pramipexole (0.15-15 nmol) or quinpirole (1-10 nmol D2-like receptor agonists) increased withdrawal threshold in reserpine-treated female rats. Those drugs induced a greater antiallodynic effect in female rats. Sex-difference was also observed in a nerve injury model. Ovariectomy abated the antiallodynic effect of SCH-23390 (30 nmol) in reserpine-treated rats, while systemic reconstitution of 17ß-estradiol levels or intrathecal injection of estrogen receptor-α agonist protopanaxatriol in ovariectomized reserpine-treated females restored the antiallodynic effect of SCH-23390. Intrathecal administration of ICI-182,780 (estrogen receptor-α/ß antagonist) or methyl-piperidino-pyrazole hydrate (estrogen receptor-α antagonist) abated 17ß-estradiol-restored antiallodynic effect of SCH-23390 in rats. In contrast, ovariectomy slightly reduced the effect of pramipexole (15 nmol) or quinpirole (10 nmol) in reserpine-treated rats, whereas systemic reconstitution of 17ß-estradiol levels did not modify the antiallodynic effect of both drugs. Combination 17ß-estradiol/progesterone, but not 17ß-estradiol nor progesterone alone, restored the antiallodynic effect of pramipexole and quinpirole in the rats. Mifepristone (progesterone receptor antagonist) abated 17ß-estradiol + progesterone restoration of the antiallodynic effect of pramipexole and quinpirole. These data suggest that the antiallodynic effect of dopamine D1-and D2-like receptors in fibromyalgia-type pain depends on spinal 17ß-estradiol/estrogen receptor-α and progesterone receptors, respectively.

Neurophysiopathological Aspects of Paclitaxel-induced Peripheral Neuropathy.

Chemotherapy is widely used as a primary treatment or adjuvant therapy for cancer. Anti-microtubule agents (such as paclitaxel and docetaxel) are used for treating many types of cancer, either alone or in combination. However, their use has negative consequences that restrict the treatment's ability to continue. The principal negative effect is the so-called chemotherapy-induced peripheral neuropathy (CIPN). CIPN is a complex ailment that depends on diversity in the mechanisms of action of the different chemotherapy drugs, which are not fully understood. In this paper, we review several neurophysiological and pathological characteristics, such as morphological changes, changes in ion channels, mitochondria and oxidative stress, cell death, changes in the immune response, and synaptic control, as well as the characteristics of neuropathic pain produced by paclitaxel.

Chemotherapy-induced neuropathic pain characteristics in Mexico's National Cancer Center pain clinic.

Introduction: Chemotherapy (CT) is one of the most commonly used pharmacological approaches in cancer treatment. However, CT induces damage to several tissues causing significant deleterious effects in cancer survivors being chemotherapy-induced neuropathic pain (CINP) among the most commonly reported. CINP is thought to be present in up to 68.1% of the patients within 1 month of receiving CT. Due to the fact that reliable statistic information is scarce in several Latin American countries' diagnosis and treatment of this side-effect may be delayed directly affecting patients. Therefore, the aim of the present study was to determine and present the incidence and features of CINP in patients with cancer attending the Pain Management Clinic at Mexicos' National Institute of Cancerology in Mexico City. Methods: We performed a retrospective, file-based analysis of all the patients treated in the Pain Management Clinic at the National Institute at Cancer in Mexico from January 2016 to January 2017. Results: CINP was found in 30.9% of the patients. The basal VAS was on average 2.5 upon arrival to the Pain Management Unit and 2.4 at the end of treatment (p>0.05). The patients with the highest risk of developing CINP were those treated with paclitaxel Odds ratio 8.3 (p<0.01), followed by platins OR 4 (p<0.01), vincristine OR 1.5 (p=0.01) and thalidomide OR 1.1 (p=0.01). Conclusion: Incidence of CINP was similar to previous reports; however, the number of variables related to this type of pain in our cohort may open a new line of research and highlight the importance of this particular issue to our health system. It is necessary to develop a mechanism to predict the risk of patients to suffer CINP and to search the mechanism to control and reduce the suffering related to the current treatments.

Procesamiento central del dolor neuropático: una aproximación integrativa / Central processing of neuropathic pain: an integrative approach

The term pain matrix refers to the structures and pathways in the central nervous system that play a role in pain processing and integration. For the last several years, our group has been studying the mechanisms that are involved in the establishment of long-term pain. Our research focus has been the study of the different nuclei and corticolimbic pathways that are involved in the affective-cognitive component of pain. In addition, we have also explored painful processes and memory. The pain matrix is constituted by the ventral tegmental area (VTA), anterior cingulate cortex (ACC), and insular cortex, among others. VTA is a predominantly dopaminergic area and has projections to ACC and the insular cortex. Stimulation of this region can reduce nociception, whereas its lesion has the opposite effect. In the ACC, it has been studied how excitatory aminoacids, such as glutamate, increase nociception while inhibitory ones decrease it. Moreover, this cortex is associated with mechanisms of pain memory. In this sense, we have seen that blocking cholinergic receptors diminishes the acquisition of pain-related memories. Nociceptive stimuli increase the expression of inhibitory muscarinic M2 receptors. In relation with insular cortex, the focus of study has been on the dopaminergic system. We have found that blocking dopaminergic D2 receptors significantly reduces neuropathic nociception. In response to an inflammatory process there is a decrease in the extracellular levels of dopamine and in the expression of mRNA for excitatory dopamine D1 receptors, while there is an increase in mRNA expression for inhibitory D2 receptors. Despite current progress in this research area, more studies are needed in order to integrate the relationship among the different neurotransmission systems. This will contribute to the proposal of novel therapeutic alternatives to the conventional treatments for pain.

El término "matriz del dolor" se refiriere a todas las estructuras y vías del Sistema Nervioso Central relacionadas con la integración del dolor. Nuestro grupo estudia desde hace varios años los principales mecanismos involucrados en el desarrollo del dolor a largo plazo. Nos hemos enfocado en el estudio de diferentes núcleos y vías cortico-límbicas que están relacionadas con la parte afectiva-cognitiva, así como en la memoria de los procesos dolorosos. Dentro de estos núcleos se encuentra el área tegmental ventral (ATV), la corteza anterior del cíngulo (CAC) y la corteza insular. El ATV es una estructura principalmente dopaminérgica con proyecciones a la CAC y a la corteza insular. Como se verá más adelante, estimular este núcleo disminuye la nocicepción, mientras que el lesionarlo, la aumenta. En la CAC se ha estudiado cómo aminoácidos excitadores como el glutamato aumentan la nocicepción y cómo, por el contrario, los aminoácidos inhibitorios como la taurina, la disminuyen. Además esta corteza está relacionada con mecanismos de memoria dolorosa. Hemos visto que el bloqueo de receptores colinérgicos disminuye la adquisición de la memoria relacionada al dolor. Además, un estímulo nociceptivo aumenta la expresión de los receptores muscarínicos inhibitorios M2. En el caso de la corteza insular, se ha estudiado principalmente el papel del sistema dopaminérgico. Hemos encontrado que el bloqueo de receptores dopaminérgicos D2 disminuye de manera significativa la nocicepción neuropática. Encontramos también que los niveles extracelulares de dopamina en esta región disminuyen a consecuencia de un proceso inflamatorio, además de que disminuye la expresión del RNAm de los receptores excitadores D1 y aumenta la de los receptores inhibidores D2. A pesar del avance que se ha obtenido en esta área de investigación, se necesitan más estudios para integrar la relación entre los diferentes sistemas de neurotransmisión y poder proponer alternativas a los tratamientos convencionales para las diferentes patologías que cursan con una experiencia dolorosa.

Systemic amantadine diminishes inflammatory and neuropathic nociception in the rat / La amantadina sistémica disminuye la nocicepción inflamatoria y neuropática en la rata

The role of dopamine as a possible central inhibitory mediator of pain processes has been demonstrated. The administration of L-Dopa diminishes pain perception in humans as well as the response to nociceptive stimuli in animals. Also, the intracerebral microinjection of dopamine in inflammatory and neuropathic pain models (formalin test and deafferentation, respectively) reduces nociceptive response. In this sense, the selective activation of dopamine D2 receptors and the blockade of D1 in the insular cortex and spinal cord diminish nociception. Furthermore, the microinjection of dopamine or amantadine (dopamine releaser) in the anterior cingulate cortex (ACC) also reduces chronic nociception. The efficacy of amantadine has been tested in the treatment of neuropathic pain, even when given as a single dose. There is evidence of the role of amantadine as a releaser of dopamine (DA) calcium channel (N type) dependent in the striatum as well as a low affinity non-competitive antagonist of blockade/non-blockade kinetics of the NMDA receptor. This compound has also been described as a DA agonist and an inhibitor of its reuptake. With this background, we decided to test if the effects of systemically given amantadine related to acute nociception, hyperalgesia and neuropathic nociception can be reverted by a dopaminergic blockade (using haloperidol) within the ACC. The experiments were conducted in agreement with the Ethics Committee of the International Association for the Study of Pain and the approval of the Projects Commission of the Instituto Nacional de Psiquiatría Ramón de la Fuente (INPRF). Male Wistar rats (250-300 g) were housed in the INPRF. During the observation period, the animals were maintained in transparent acrylic individual cages with light-dark cycles of 12 X 12 h, with feeding and hydration ad libitum. For all surgical procedures, rats were anaesthetised with halothane 2% mixed with O2 98%. In order to test the dopaminergic effect of amantadine within the ACC in nociception, we used the hyperalgesia model as well as a neuropathic nociception model induced by denervation. In the model of hyperalgesia, carrageenan was injected in the plantar region (50 µl at 1%), followed by a thermonociception test in which paw withdrawal latency was measured. In the neuropathic nociception model, the right sciatic nerve was denervated and chronic nociception was measured as autotomy behaviour. Moreover, in another series of experiments, haloperidol (3 mg/ 200 nl) was microinjected into the ACC before the induction of hyperalgesia and neuropathic nociception. Amantadine was then injected (90 mg/kg i.p.) and the behavioural development was observed in both models. Systemic amantadine was able to reduce both neuropathic nociception and hyperalgesia. Also, the results show, on the one hand, that haloperidol significantly decreases the antinociceptive effect of amantadine measured as paw withdrawal latency. On the other hand, amantadine can reduce nociception when administered systemically and, according to what has been published previously, when administered directly into the ACC. Our results show that amantadine is effective in diminishing hyperalgesia and nociception induced by deafferentation. This suggests that amantadine can be a therapeutic alternative for the treatment and prevention of neuropathic pain such as phantom limb pain or pain due to deafferentation, among others.

Se ha demostrado el papel de la dopamina como posible mediador inhibitorio central de procesos dolorosos. La administración de L-dopa disminuye la percepción de dolor en los seres humanos, así como la respuesta ante estímulos nociceptivos en los animales. Además, la microinyección intracerebral de dopamina en modelos de dolor inflamatorio y neuropático (prueba de formalina y deaferentación) reduce la respuesta nociceptiva. En este sentido, la activación selectiva de los receptores dopaminérgicos D2 y el bloqueo de los receptores D1 en la corteza insular y la médula espinal disminuyen la nocicepción. La microinyección de dopamina o de amantadina (liberador dopaminérgico) en la corteza anterior del cíngulo (CAC) reduce también la nocicepción crónica. Se ha probado la eficacia de la amantadina en el tratamiento del dolor neuropático, incluso cuando se administra en una sola dosis. También se ha demostrado el papel de la amantadina como liberador de dopamina dependiente del canal del calcio (tipo N) en el estriado, así como el de antagonista no competitivo de baja afinidad de cinética de bloqueo y desbloqueo rápido del receptor de NMDA. Este compuesto también se ha descrito como un agonista de dopamina e inhibidor de su recaptura. Con estos antecedentes decidimos probar si los efectos de la amantadina sistémica relacionados con la nocicepción aguda, la hiperalgesia y la nocicepción neuropática, pueden ser revertidos por el bloqueo dopaminérgico mediante la micro inyección de haloperidol en la corteza anterior del cíngulo. Los experimentos se realizaron de acuerdo con las normas del Comité de Ética de la Asociación Internacional para el Estudio del Dolor y con la aprobación de la Comisión de Proyectos del Instituto Nacional de Psiquiatría Ramón de Fuente (INPRF). Se utilizaron ratas Wistar macho (250-300 g) mantenidas en el bioterio del INPRF. Durante el periodo de observación, los animales se mantuvieron en jaulas individuales de acrílico transparente, con ciclos de luz-oscuridad de 12 X 12 h, con alimentación e hidratación ad libitum. Para todos los procedimientos quirúrgicos, las ratas se anestesiaron con halotano al 2%, mezclado con 98% de O2. Para probar el efecto dopaminérgico de la amantadina en la nocicepción en la corteza anterior del cíngulo, utilizamos un modelo de hiperalgesia y un modelo de nocicepción neuropática inducida por denervación. En el modelo de hiperalgesia, se inyectó carragenina en la región plantar (50 µl al 1%), seguida por una prueba de termonocicepción para posteriormente medir la latencia de retiro de la pata. En el modelo de nocicepción neuropática, se denervó el ciático derecho y se midió la nocicepción crónica mediante la conducta de autotomía. Asimismo, en otra serie experimental se microinyectó haloperidol (3mg/200nl) en la CAC antes de la inducción de la hiperalgesia y de la nocicepción neuropática, y posteriormente se inyectó amantadina (90 mg/kg i.p.) y se observó el desarrollo conductual en ambos modelos. La administración sistémica de amantadina logró reducir tanto la nocicepción neuropática como la hiperalgesia. Además, los resultados muestran, por un lado, que el haloperidol disminuye significativamente el efecto antinociceptivo de la amantadina medido como la latencia de retiro de la pata. Por otro, la amantadina puede reducir la nocicepción cuando se administra sistémicamente y, según lo publicado previamente, directamente en la CAC. Nuestros resultados muestran que la amantadina es efectiva en la reducción de la hiperalgesia y la nocicepción por deaferentación. Este hecho sitúa a la amantadina como una alternativa terapéutica para el tratamiento y prevención del dolor neuropático, como el miembro fantasma doloroso o el dolor por deaferentación.