RESUMO
In rodents, cortical information is transferred to the substantia nigra pars reticulata (SNr) through motor and medial prefrontal (mPF) basal ganglia (BG) circuits implicated in motor and cognitive/motivational behaviors, respectively. The serotonergic 5-HT2A receptors are located in both of these neuronal networks, displaying topographical differences with a high expression in the associative/limbic territories, and a very low expression in the subthalamic nucleus. This study investigated whether the stimulation of 5-HT2A receptors could have a specific signature on the dynamic regulation of BG circuits, preferentially modulating the mPF information processing through trans-striatal pathways. We performed in vivo single-unit extracellular recordings to assess the effect of the 5-HT2A agonist TCB-2 on the spontaneous and cortically evoked activity of lateral and medial SNr neurons in male rats (involved in motor and mPF circuits, respectively). TCB-2 (50-200 µg/kg, i.v.) increased the basal firing rate and enhanced the cortically evoked inhibitory response of medial SNr neurons (transmission through the direct striato-nigral pathway). A prior administration of the preferential 5-HT2A receptor antagonist MDL11939 (200 µg/kg, i.v.) did not modify any electrophysiological parameter, but occluded TCB-2-induced effects. In animals treated with the 5-HT synthesis inhibitor pCPA (4-chloro-dl-phenylalanine methyl ester hydrochloride), TCB-2 failed to induce the above-mentioned effects, thus suggesting the contribution of endogenous 5-HT. However, the mobilization of 5-HT induced by the acute administration of fluoxetine (10 mg/kg, i.p.) did not mimic the effects triggered by TCB-2. Overall, these data suggest that 5-HT2A receptors have a preferential modulatory action on the dynamic regulation of BG circuitry.SIGNIFICANCE STATEMENT Motor and medial prefrontal (mPF) basal ganglia (BG) circuits play an important role in integrative brain functions like movement control or cognitive/motivational behavior, respectively. Although these neuronal networks express 5-HT2A receptors, the expression is higher in associative/limbic structures than in the motor ones. We show a topographical-dependent dissociation in the effects triggered by the 5HT2A agonist TCB-2, which specifically increases the medial substantia nigra pars reticulata neuron activity and has a preferential action on mPF information processing through the striato-nigral direct pathway. These are very likely to be 5-HT2A receptor-mediated effects that require mobilization of the endogenous 5-HT system. These findings provide evidence about the specific signature of 5-HT2A receptors on the dynamic regulation of BG circuits.
Assuntos
Receptor 5-HT2A de Serotonina , Serotonina , Ratos , Masculino , Animais , Serotonina/metabolismo , Receptor 5-HT2A de Serotonina/metabolismo , Ratos Sprague-Dawley , Gânglios da Base/fisiologia , Corpo Estriado/fisiologia , Substância Negra/metabolismoRESUMO
Cortical information is transferred to the substantia nigra pars reticulata (SNr) and the entopeduncular nucleus (EP), the output structures of the basal ganglia (BG), through three different pathways: the hyperdirect trans-subthalamic and the direct and indirect trans-striatal pathways. The nigrostriatal dopamine (DA) and the activation of 5-HT1A receptors, distributed all along the BG, may modulate cortical information transmission. We aimed to investigate the effect of buspirone (5-HT1A receptor partial agonist) and WAY-100635 (5-HT1A receptor antagonist) on cortico-nigral and cortico-entopeduncular transmission in normal and DA loss conditions. Herein, simultaneous electrical stimulation of the motor cortex and single-unit extracellular recordings of SNr or EP neurons were conducted in urethane-anesthetized sham and 6-hydroxydopamine (6-OHDA)-lesioned rats before and after drug administrations. Motor cortex stimulation evoked monophasic, biphasic, or triphasic responses, combination of an early excitation, an inhibition, and a late excitation in both the SNr and EP, while an altered pattern of evoked response was observed in the SNr after 6-OHDA lesion. Systemic buspirone potentiated the direct cortico-SNr and cortico-EP transmission in sham animals since increased duration of the inhibitory response was observed. In DA denervated animals, buspirone administration enhanced early excitation amplitude in the cortico-SNr transmission. In both cases, the observed effects were mediated via a 5-HT1A-dependent mechanism as WAY-100635 administration blocked buspirone's effect. These findings suggest that in control condition, buspirone potentiates direct pathway transmission and DA loss modulates responses related to the hyperdirect pathway. Overall, the results may contribute to understanding the role of 5-HT1A receptors and DA in motor cortico-BG circuitry functionality.
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BACKGROUND AND PURPOSE: l-DOPA prolonged treatment leads to disabling motor complications as dyskinesia that could be decreased by drugs acting on 5-HT1A receptors. Since the internal segment of the globus pallidus, homologous to the entopeduncular nucleus in rodents, seems to be involved in the etiopathology of l-DOPA-induced dyskinesia, we investigated whether the entopeduncular nucleus is modulated by the 5-HT1A receptor partial and full agonists, buspirone, and 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) in control and 6-hydroxydopamine (6-OHDA)-lesioned rats with or without long-term l-DOPA treatment. EXPERIMENTAL APPROACH: Extracellular single-unit electrocorticogram and local field potential recordings under anaesthesia, immunostaining assays and optogenetic manipulation coupled to electrophysiological recordings were performed. KEY RESULTS: Systemic buspirone reduced the entopeduncular nucleus firing rate in the sham animals and burst activity in the 6-OHDA-lesioned rats (with or without l-DOPA treatment), while local administration reduced entopeduncular nucleus activity in all the groups, regardless of DA integrity. Systemic 8-OH-DPAT also induced inhibitory effects only in the sham animals. Effects triggered by buspirone and 8-OH-DPAT were reversed by the 5-HT1A receptor antagonist, WAY-100635. Neither buspirone nor 8-OH-DPAT modified the low-frequency oscillatory activity in the entopeduncular nucleus or its synchronization with the motor cortex. Buspirone did not alter the response induced by subthalamic nucleus opto-stimulation in the entopeduncular nucleus. CONCLUSION AND IMPLICATIONS: Systemic 5-HT1A receptor activation elicits different effects on the electrophysiological properties of the entopeduncular nucleus depending on the integrity of the nigrostriatal pathway and it does not alter the relationship between subthalamic nucleus and entopeduncular nucleus neuron activity.
Assuntos
Núcleo Entopeduncular , Receptor 5-HT1A de Serotonina , 8-Hidroxi-2-(di-n-propilamino)tetralina/farmacologia , Animais , Buspirona/farmacologia , Levodopa/farmacologia , Oxidopamina/toxicidade , Ratos , Ratos Sprague-DawleyRESUMO
The subthalamic nucleus (STN) houses a dense cluster of glutamatergic neurons that play a central role in the functional dynamics of the basal ganglia, a group of subcortical structures involved in the control of motor behaviors. Numerous anatomical, electrophysiological, neurochemical and behavioral studies have reported that serotonergic neurons from the midbrain raphe nuclei modulate the activity of STN neurons. Here, we describe this serotonergic innervation and the nature of the regulation exerted by serotonin (5-hydroxytryptamine, 5-HT) on STN neuron activity. This regulation can occur either directly within the STN or at distal sites, including other structures of the basal ganglia or cortex. The effect of 5-HT on STN neuronal activity involves several 5-HT receptor subtypes, including 5-HT1A, 5-HT1B, 5-HT2C and 5-HT4 receptors, which have garnered the highest attention on this topic. The multiple regulatory effects exerted by 5-HT are thought to be modified under pathological conditions, altering the activity of the STN, or due to the benefits and side effects of treatments used for Parkinson's disease, notably the dopamine precursor l-DOPA and high-frequency STN stimulation. Originally understood as a motor center, the STN is also associated with decision making and participates in mood regulation and cognitive performance, two domains of personality that are also regulated by 5-HT. The literature concerning the link between 5-HT and STN is already important, and the functional overlap is evident, but this link is still not entirely understood. The understanding of this link between 5-HT and STN should be increased due to the possible importance of this regulation in the control of fronto-STN loops and inherent motor and non-motor behaviors.
Assuntos
Núcleo Subtalâmico , Gânglios da Base , Humanos , Neurônios , Doença de Parkinson/terapia , SerotoninaRESUMO
The basal ganglia (BG) are involved in cognitive/motivational functions in addition to movement control. Thus, BG segregated circuits, the sensorimotor (SM) and medial prefrontal (mPF) circuits, process different functional domains, such as motor and cognitive/motivational behaviours, respectively. With a high presence in the BG, the CB1 cannabinoid receptor modulates BG circuits. Furthermore, dopamine (DA), one of the principal neurotransmitters in the BG, also plays a key role in circuit functionality. Taking into account the interaction between DA and the endocannabinoid system at the BG level, we investigated the functioning of BG circuits and their modulation by the CB1 receptor under DA-depleted conditions. We performed single-unit extracellular recordings of substantia nigra pars reticulata (SNr) neurons with simultaneous cortical stimulation in sham and 6-hydroxydopamine (6-OHDA)-lesioned rats, together with immunohistochemical assays. We showed that DA loss alters cortico-nigral information processing in both circuits, with a predominant transmission through the hyperdirect pathway in the SM circuit and an increased transmission through the direct pathway in the mPF circuit. Moreover, although DA denervation does not change CB1 receptor density, it impairs its functionality, leading to a lack of modulation. These data highlight an abnormal transfer of information through the associative/limbic domains after DA denervation that may be related to the non-motor symptoms manifested by Parkinson's disease patients.
Assuntos
Gânglios da Base/metabolismo , Dopamina/metabolismo , Sistema Límbico/metabolismo , Córtex Motor/metabolismo , Neurônios/metabolismo , Parte Reticular da Substância Negra/metabolismo , Receptor CB1 de Canabinoide/metabolismo , Potenciais de Ação/fisiologia , Animais , Gânglios da Base/efeitos dos fármacos , Modelos Animais de Doenças , Eletrodos , Imuno-Histoquímica , Sistema Límbico/efeitos dos fármacos , Masculino , Córtex Motor/efeitos dos fármacos , Vias Neurais/efeitos dos fármacos , Vias Neurais/metabolismo , Neurônios/efeitos dos fármacos , Oxidopamina/toxicidade , Doença de Parkinson/metabolismo , Parte Reticular da Substância Negra/citologia , Parte Reticular da Substância Negra/efeitos dos fármacos , Córtex Pré-Frontal/efeitos dos fármacos , Córtex Pré-Frontal/metabolismo , Ratos , Receptor CB1 de Canabinoide/fisiologia , Simpatectomia Química , Simpatolíticos/toxicidadeRESUMO
The search for experimental models mimicking an early stage of Parkinson's disease (PD) before motor manifestations is fundamental in order to explore early signs and get a better prognosis. Interestingly, our previous studies have indicated that 6-hydroxydopamine (6-OHDA) is a suitable model to induce an early degeneration of the nigrostriatal system without any gross motor impairment. Considering our previous findings, we aim to implement a novel system to monitor rats after intrastriatal injection of 6-OHDA to detect and analyze physiological changes underlying prodromal PD. Twenty male Sprague-Dawley rats were unilaterally injected with 6-OHDA (n = 10) or saline solution (n = 10) into the right striatum and placed in enriched environment cages where the activity was monitored. After 2 weeks, the amphetamine test was performed before the sacrifice. Immunohistochemistry was developed for the morphological evaluation and western blot analysis to assess molecular changes. Home-cage monitoring revealed behavioral changes in response to 6-OHDA administration including significant hyperactivity and hypoactivity during the light and dark phase, respectively, turning out in a change of the circadian timing. A preclinical stage of PD was functionally confirmed with the amphetamine test. Moreover, the loss of tyrosine hydroxylase expression was significantly correlated with the motor results, and 6-OHDA induced early proapoptotic events. Our findings provide evidence for a novel prodromal 6-OHDA model following a customized monitoring system that could give insights to detect non-motor deficits and molecular targets to test neuroprotective/neurorestorative agents.
RESUMO
BACKGROUND AND PURPOSE: l-DOPA-induced dyskinesia (LID) is considered a major complication in the treatment of Parkinson's disease (PD). Buspirone (5-HT1A partial agonist) have shown promising results in the treatment of PD and LID, however no 5-HT-based treatment has been approved in PD. The present study was aimed to investigate how the substantia nigra pars reticulata (SNr) is affected by buspirone and whether it is a good target to study 5-HT antidyskinetic treatments. EXPERIMENTAL APPROACH: Buspirone was studied using in vivo single-unit, electrocorticogram, local field potential recordings along with microdialysis and immunohistochemistry in naïve/sham, 6-hydroxydopamine (6-OHDA)-lesioned or 6-OHDA-lesioned and l-DOPA-treated (6-OHDA/l-DOPA) rats. KEY RESULTS: Local buspirone inhibited SNr neuron activity in all groups. However, systemic buspirone reduced burst activity in 6-OHDA-lesioned rats (with or without l-DOPA treatment), whereas 8-OH-DPAT, a full 5-HT1A agonist induced larger inhibitory effects in sham animals. Neither buspirone nor 8-OH-DPAT markedly modified the low-frequency oscillatory activity in the SNr or synchronization within the SNr with the cortex. In addition, local perfusion of buspirone increased GABA and glutamate release in the SNr of naïve and 6-OHDA-lesioned rats but no effect in 6-OHDA/l-DOPA rats. In the 6-OHDA/l-DOPA group, increased 5-HT transporter and decreased 5-HT1A receptor expression was found. CONCLUSIONS AND IMPLICATIONS: The effects of buspirone in SNr are influenced by dopamine loss and l-DOPA treatment. The present results suggest that the regulation of burst activity of the SNr induced by DA loss may be a good target to test new drugs for the treatment of PD and LID.
Assuntos
Levodopa , Parte Reticular da Substância Negra , Animais , Antiparkinsonianos/farmacologia , Buspirona/farmacologia , Dopamina , Oxidopamina , Ratos , Substância NegraRESUMO
Parkinson's disease (PD) is characterized by the degeneration of dopaminergic neurons in the substantia nigra, the depletion of striatal dopamine and the presence of Lewy aggregates containing alpha-synuclein. Clinically, there are motor impairments involving cardinal movement symptoms, bradykinesia, resting tremor, muscle rigidity, and postural abnormalities, along with non-motor symptoms such as sleep, behavior and mood disorders. The current treatment for PD focuses on restoring dopaminergic neurotransmission by l-3,4-dihydroxyphenylalanine (levodopa), which loses therapeutic efficacy and induces disabling abnormal involuntary movements known as levodopa-induced dyskinesia (LID) after several years. Evidence indicates that the pathophysiology of both PD and LID disorders is also associated with the dysfunctional activity of the serotonergic (5-HT) neurons that may be responsible for motor and non-motor disturbances. The main population of 5-HT neurons is located in the dorsal raphe nuclei (DRN), which provides extensive innervation to almost the entire neuroaxis and controls multiple functions in the brain. The degeneration of DRN 5-HT neurons occurs in early PD. These neurons can also take exogenous levodopa to transform it into dopamine, which may disturb neuron activity. This review will provide an overview of the underlying mechanisms responsible for 5-HT dysfunction and its clinical relevance in PD and dyskinesia.
Assuntos
Encéfalo/fisiologia , Encéfalo/fisiopatologia , Discinesia Induzida por Medicamentos/fisiopatologia , Doença de Parkinson/fisiopatologia , Neurônios Serotoninérgicos/fisiologia , Animais , Humanos , Levodopa/efeitos adversos , Modelos NeurológicosRESUMO
Parkinson's disease (PD) as a motor disorder is pathologically featured by the loss of dopaminergic neurons of the substantia nigra compacta (SNc) and the consequent depletion of dopamine in the striatum. However, motor signs are detectable when the loss of dopaminergic striatal terminals exceeds to the dopaminergic neuronal degeneration in SN. Hence, recent evidences about the topological organization of the nigrostriatal system could provide novel insights about the progression of the neurodegenerative process as well as the correct application of the novel therapeutic strategies. Though dopaminergic drugs and different routes of administration have been proposed to treat PD, most of the effects are symptomatic with temporary effects resorting to invasive procedures to ameliorate the side effects. Since the blood-brain barrier (BBB) is the main obstacle for most of molecules to access to the brain, ongoing research is focused on halting the progression of PD through the use of those technologies that allow the effective delivery and diffusion of therapeutic molecules to the central nervous system for bypassing BBB and avoiding the side effects. In this context, nanotechnology is emerging as a promising tool for drug delivery. In fact, nanodelivery of restorative treatments in PD, such as gene therapy increased the effectiveness of neurotrophic factors for restoring the dopamine deficit and improving motor deficit in rodent models. Therefore, the present review is focused on the description and identification of the available nanotherapies developed in experimental models of PD which could suppose an important advance for controlled delivery of nanobioactive components into the brain and one more step for the clinical projection.
Assuntos
Antioxidantes/administração & dosagem , Barreira Hematoencefálica , Dopaminérgicos/administração & dosagem , Nanomedicina/métodos , Fatores de Crescimento Neural/administração & dosagem , Fármacos Neuroprotetores/administração & dosagem , Doença de Parkinson/tratamento farmacológico , Animais , HumanosRESUMO
Schizophrenia is a mental disorder characterized by psychosis, negative symptoms and cognitive impairment. Cognitive deficits are enduring and represent the most disabling symptom but are currently poorly treated. N-methyl D-aspartate receptor (NMDAR) hypofunction hypothesis has been notably successful in explaining the pathophysiological findings and symptomatology of schizophrenia. Thereby, NMDAR blockade in rodents represents a useful tool to identify new therapeutic approaches. In this regard, enriched environment (EE) could play an essential role. Using a multilevel approach of behavior, electrophysiology and protein analysis, we showed that a short-term exposure to EE in adulthood ameliorated spatial learning and object-place associative memory impairment observed in postnatally MK-801-treated Long Evans rats. Moreover, EE in adult life restored long-term potentiation (LTP) in hippocampal-medial prefrontal pathway abolished by MK-801 treatment. EE in adulthood also induced a set of modifications in the expression of proteins related to glutamatergic neurotransmission. Taken together, these findings shed new light on the neurobiological effects of EE to reverse the actions of MK-801 and offer a preclinical testing of a therapeutic strategy that may be remarkably effective for managing cognitive symptoms of schizophrenia.
Assuntos
Maleato de Dizocilpina/toxicidade , Hipocampo/metabolismo , Plasticidade Neuronal/fisiologia , Córtex Pré-Frontal/metabolismo , Receptores de N-Metil-D-Aspartato/biossíntese , Esquizofrenia/metabolismo , Fatores Etários , Animais , Cognição/efeitos dos fármacos , Cognição/fisiologia , Meio Ambiente , Antagonistas de Aminoácidos Excitatórios/toxicidade , Expressão Gênica , Hipocampo/efeitos dos fármacos , Vias Neurais/efeitos dos fármacos , Vias Neurais/metabolismo , Plasticidade Neuronal/efeitos dos fármacos , Córtex Pré-Frontal/efeitos dos fármacos , Ratos , Ratos Long-Evans , Receptores de N-Metil-D-Aspartato/genética , Esquizofrenia/induzido quimicamente , Esquizofrenia/terapiaRESUMO
BACKGROUND AND PURPOSE: In the sensorimotor (SM) and medial prefrontal (mPF) basal ganglia (BG) circuits, the cortical information is transferred to the substantia nigra pars reticulata (SNr) through the hyperdirect trans-subthalamic pathway and through the direct and indirect trans-striatal pathways. The cannabinoid CB1 receptor, which is highly expressed in both BG circuits, may participate in the regulation of motor and motivational behaviours. Here, we investigated the modulation of cortico-nigral information transmission through the BG circuits by cannabinoids. EXPERIMENTAL APPROACH: We used single-unit recordings of SNr neurons along with simultaneous electrical stimulation of motor or mPF cortex in anaesthetized rats. KEY RESULTS: Cortical stimulation elicited a triphasic response in the SNr neurons from both SM and mPF-BG circuits, which consisted of an early excitation (hyperdirect transmission pathway), an inhibition (direct transmission pathway), and a late excitation (indirect transmission pathway). In the SM circuit, after Δ9 -tetrahydrocannabinol or WIN 55,212-2 administration, the inhibition and the late excitation were decreased or completely lost, whereas the early excitation response remained unaltered. However, cannabinoid administration dramatically decreased all the responses in the mPF circuit. The CB1 receptor antagonist AM251 (2 mg·kg-1 , i.v.) did not modify the triphasic response, but blocked the effects induced by cannabinoid agonists. CONCLUSIONS AND IMPLICATIONS: CB1 receptor activation modulates the SM information transmission through the trans-striatal pathways and profoundly decreases the cortico-BG transmission through the mPF circuit. These results may be relevant for elucidating the involvement of the cannabinoid system in motor performance and in decision making or goal-directed behaviour.
Assuntos
Gânglios da Base/efeitos dos fármacos , Canabinoides/farmacologia , Rede Nervosa/efeitos dos fármacos , Córtex Pré-Frontal/efeitos dos fármacos , Córtex Sensório-Motor/efeitos dos fármacos , Animais , Gânglios da Base/fisiologia , Masculino , Rede Nervosa/fisiologia , Córtex Pré-Frontal/fisiologia , Ratos , Ratos Sprague-Dawley , Córtex Sensório-Motor/fisiologiaRESUMO
Omega-3 polyunsaturated fatty acids (n-3 PUFAs) have been widely associated to beneficial effect over different neurodegenerative diseases. In the present study, we tested the potential therapeutic effect of docohexanoic acid (DHA) and its hydroxylated derivate, DHAH, in a partial lesion model of Parkinson's disease (PD). One month before and four months after the striatal lesion with 6-OHDA was made, the animals were daily treated with DHA (50â¯mg/kg), DHAH (50â¯mg/kg), vehicle or saline, by intragastric administration. Animal groups under n-3 PUFA treatments exhibited a trend to improve in amphetamine-induced rotations and cylinder test. The beneficial effect seen in behavioral studies were confirmed with TH immunostaining. TH+ fibers and TH+ neurons increased in the experimental groups treated with both n-3 PUFAs, DHA and DHAH. Moreover, the n-3 PUFAs administration decreased the astrogliosis and microgliosis, in both the striatum and substantia nigra (SN), with a higher decrease of GFAP+ and Iba-1+ cells for the DHAH treated group. This experimental group also revealed a positive effect on Nrf2 pathway regulation, decreasing the positive Nrf2 immmunostaining in the striatum and SN, which revealed a potential antioxidant effect of this compound. Taking together, these data suggest a positive effect of n-3 PUFAs administration, and more concretely of DHAH, for PD treatment as it exhibited positive results on dopaminergic system, neuroinflammation and oxidative stress.
Assuntos
Corpo Estriado/efeitos dos fármacos , Neurônios Dopaminérgicos/efeitos dos fármacos , Ácidos Graxos Ômega-3/administração & dosagem , Neuroglia/efeitos dos fármacos , Estresse Oxidativo/efeitos dos fármacos , Doença de Parkinson/metabolismo , Anfetamina/administração & dosagem , Animais , Antioxidantes/administração & dosagem , Corpo Estriado/metabolismo , Dopamina/metabolismo , Dopaminérgicos/administração & dosagem , Neurônios Dopaminérgicos/metabolismo , Masculino , Atividade Motora/efeitos dos fármacos , Fator 2 Relacionado a NF-E2/metabolismo , Neuroglia/metabolismo , Oxidopamina/administração & dosagem , Doença de Parkinson/prevenção & controle , Ratos Sprague-Dawley , Tirosina 3-Mono-Oxigenase/metabolismoRESUMO
Pain affects both sensory and emotional aversive responses, often provoking depression and anxiety-related conditions when it becomes chronic. As the opioid receptors in the locus coeruleus (LC) have been implicated in pain, stress responses, and opioid drug effects, we explored the modifications to LC opioid neurotransmission in a chronic constriction injury (CCI) model of short- and long-term neuropathic pain (7 and 30 days after nerve injury). No significant changes were found after short-term CCI, yet after 30 days, CCI provoked an up-regulation of cAMP (cyclic 5'-adenosine monophosphate), pCREB (phosphorylated cAMP response element binding protein), protein kinase A, tyrosine hydroxylase, and electrical activity in the LC, as well as enhanced c-Fos expression. Acute mu opioid receptor desensitization was more intense in these animals, measured as the decline of the peak current caused by [Met5]-enkephalin and the reduction of forskolin-stimulated cAMP produced in response to DAMGO. Sustained morphine treatment did not markedly modify certain LC parameters in CCI-30d animals, such as [Met5]-enkephalin-induced potassium outward currents or burst activity and c-Fos rebound after naloxone precipitation, which may limit the development of some typical opioid drug-related adaptations. However, other phenomena were impaired by long-term CCI, including the reduction in forskolin-stimulated cAMP accumulation by DAMGO after naloxone precipitation in morphine dependent animals. Overall, this study suggests that long-term CCI leads to changes at the LC level that may contribute to the anxiodepressive phenotype that develops in these animals. Furthermore, opioid drugs produce complex adaptations in the LC in this model of chronic neuropathic pain.
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Analgésicos Opioides/uso terapêutico , Dor Crônica/tratamento farmacológico , Locus Cerúleo/patologia , Neuralgia/tratamento farmacológico , Analgésicos Opioides/farmacologia , Animais , Dor Crônica/fisiopatologia , Constrição Patológica , Locus Cerúleo/efeitos dos fármacos , Locus Cerúleo/fisiopatologia , Masculino , Modelos Biológicos , Morfina/farmacologia , Morfina/uso terapêutico , Naloxona/farmacologia , Naloxona/uso terapêutico , Neuralgia/fisiopatologia , Limiar da Dor/efeitos dos fármacos , Ratos Sprague-DawleyRESUMO
Accumulating evidence indicates that the antidepressant effects of ketamine are, in part, mediated by an increase in the AMPA receptor-mediated neurotransmission in depression related areas, such as the prefrontal cortex (PFC). Therefore, activity in PFC-projecting areas related to major depression, such as the dorsal raphe nucleus (DR), may also be modulated by ketamine. We used whole-cell patch-clamp recordings and western blot experiments to determine whether ketamine promotes acute and maintained alterations in glutamatergic transmission and mTOR pathway in the DR. Bath perfusion of ketamine, but not the NMDA receptor antagonist D-AP5, increased the frequency of AMPA receptor-mediated spontaneous EPSCs (sEPSCs) in DR neurons. However, ketamine did not affect evoked EPSCs or spontaneous inhibitory currents (sIPSCs). Pre-incubation of DR slices with the mTOR inhibitor PP242 decreased the frequency of sEPSCs and prevented the effect of ketamine. The results also show that while no electrophysiological effects were detected 24â¯h after ketamine administration, phosphorylation levels of mTOR were significantly increased in the DR. Nevertheless, expression levels of synaptic proteins were unaffected at that time. Altogether, the present data demonstrate that ketamine transiently increases spontaneous AMPA receptor-mediated neurotransmission in the DR.
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Núcleo Dorsal da Rafe/efeitos dos fármacos , Núcleo Dorsal da Rafe/metabolismo , Antagonistas de Aminoácidos Excitatórios/farmacologia , Ketamina/farmacologia , Receptores de AMPA/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Animais , Interações Medicamentosas , Estimulação Elétrica , Antagonistas GABAérgicos/farmacologia , Elevação dos Membros Posteriores , Resposta de Imobilidade Tônica/efeitos dos fármacos , Indóis/farmacocinética , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Técnicas de Patch-Clamp , Fosforilação/efeitos dos fármacos , Picrotoxina/farmacologia , Purinas/farmacocinética , Transdução de Sinais/efeitos dos fármacos , Serina-Treonina Quinases TOR/metabolismoRESUMO
Oxidative stress is a common feature in neurodegenerative diseases associated with neuroinflammation, and therefore, has been proposed as a key target for novel therapies for these diseases. Recently, adipose-derived stem cell (ASC)-based cell therapy has emerged as a novel strategy for neuroprotection. In this study, we evaluate the therapeutic role of ASC-conditioned medium (ASC-CM) against H2O2-induced neurotoxicity in a new in vitro model of ec23/brain-derived neurotrophic factor (BDNF)-differentiated human SH-SY5Y neuron-like cells (SH-SY5Yd). In the presence of ASC-CM, stressed SH-SY5Yd cells recover normal axonal morphology (with an almost complete absence of H2O2-induced axonal beading), electrophysiological features, and cell viability. This beneficial effect of ASC-CM was associated with its antioxidant capacity and the presence of growth factors, namely, BDNF, glial cell line-derived neurotrophic factor, and transforming growth factor ß1. Moreover, the neuroprotective effect of ASC-CM was very similar to that obtained from treatment with BDNF, an essential factor for SH-SY5Yd cell survival. Importantly, we also found that the addition of the antioxidant agent N-acetyl cysteine to ASC-CM abolished its restorative effect; this was associated with a strong reduction in reactive oxygen species (ROS), in contrast to the moderate decrease in ROS produced by ASC-CM alone. These results suggest that neuronal restorative effect of ASC-CM is associated with not only the release of essential neurotrophic factors, but also the maintenance of an appropriate redox state to preserve neuronal function.
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Acetilcisteína/toxicidade , Adipócitos/efeitos dos fármacos , Meios de Cultivo Condicionados/farmacologia , Células-Tronco Mesenquimais/efeitos dos fármacos , Fármacos Neuroprotetores/farmacologia , Adipócitos/fisiologia , Diferenciação Celular/efeitos dos fármacos , Diferenciação Celular/fisiologia , Linhagem Celular Tumoral , Sobrevivência Celular/efeitos dos fármacos , Sobrevivência Celular/fisiologia , Células Cultivadas , Técnicas de Cocultura/métodos , Humanos , Células-Tronco Mesenquimais/fisiologia , Estresse Oxidativo/efeitos dos fármacos , Estresse Oxidativo/fisiologia , Espécies Reativas de Oxigênio/antagonistas & inibidores , Espécies Reativas de Oxigênio/metabolismoRESUMO
The link between the anti-Parkinsonian drug L-3,4-dihydroxyphenylalanine (L-DOPA) and the serotonergic (5-HT) system has been long established and has received increased attention during the last decade. Most studies have focused on the fact that L-DOPA can be transformed into dopamine (DA) and released from 5-HT terminals, which is especially important for the management of L-DOPA-induced dyskinesia. In patients, treatment using L-DOPA also impacts 5-HT neurotransmission; however, few studies have investigated the mechanisms of this effect. The purpose of this review is to summarize the electrophysiological and neurochemical data concerning the effects of L-DOPA on 5-HT cell function. This review will argue that L-DOPA disrupts the link between the electrical activity of 5-HT neurons and 5-HT release as well as that between 5-HT release and extracellular 5-HT levels. These effects are caused by the actions of L-DOPA and DA in 5-HT neurons, which affect 5-HT neurotransmission from the biosynthesis of 5-HT to the impairment of the 5-HT transporter. The interaction between L-DOPA and 5-HT transmission is especially relevant in those Parkinson's disease (PD) patients that suffer dyskinesia, comorbid anxiety or depression, since the efficacy of antidepressants or 5-HT compounds may be affected.
RESUMO
The serotonergic tone of the dorsal raphe (DR) is regulated by 5-HT1A receptors, which negatively control serotonergic activity via the activation of G protein-coupled inwardly rectifying K+ (GIRK) channels. In addition, DR activity is modulated by local GABAergic transmission, which is believed to play a key role in the development of mood-related disorders. Here, we sought to characterize the role of GIRK2 subunit-containing channels on the basal electrophysiological properties of DR neurons and to investigate whether the presynaptic and postsynaptic activities of 5-HT1A, GABAB, and GABAA receptors are affected by Girk2 gene deletion. Whole-cell patch-clamp recordings in brain slices from GIRK2 knockout mice revealed that the GIRK2 subunit contributes to maintenance of the resting membrane potential and to the membrane input resistance of DR neurons. 5-HT1A and GABAB receptor-mediated postsynaptic currents were almost absent in the mutant mice. Spontaneous and evoked GABAA receptor-mediated transmissions were markedly reduced in GIRK2 KO mice, as the frequency and amplitude of spontaneous IPSCs were reduced, the paired-pulse ratio was increased and GABA-induced whole-cell currents were decreased. Similarly, the pharmacological blockade of GIRK channels with tertiapin-Q prevented the 5-HT1A and GABAB receptor-mediated postsynaptic currents and increased the paired-pulse ratio. Finally, deletion of the Girk2 gene also limited the presynaptic inhibition of GABA release exerted by 5-HT1A and GABAB receptors. These results indicate that the properties and inhibitory activity of DR neurons are highly regulated by GIRK2 subunit-containing channels, introducing GIRK channels as potential candidates for studying the pathophysiology and treatment of affective disorders.
Assuntos
Núcleo Dorsal da Rafe/fisiologia , Canais de Potássio Corretores do Fluxo de Internalização Acoplados a Proteínas G/fisiologia , Potenciais Pós-Sinápticos Inibidores , Neurônios/fisiologia , Sinapses/fisiologia , Potenciais de Ação , Animais , Camundongos , Camundongos Knockout , Subunidades Proteicas , Receptor 5-HT1A de Serotonina/fisiologia , Receptores de GABA-A/fisiologia , Receptores de GABA-B/fisiologia , Ácido gama-Aminobutírico/metabolismoRESUMO
Background: There is increasing evidence suggesting that the Locus Coeruleus plays a role in pain-related anxiety. Indeed, we previously found that prolonged arthritis produces anxiety-like behavior in rats, along with enhanced expression of phosphorylated extracellular signal-regulated kinase 1/2 (a marker of plasticity) in the Locus Coeruleus. However, it is unknown how this effect correlates with the electrophysiological activity of Locus Coeruleus neurons or pain-related anxiety. Methods: Using the complete Freund's adjuvant model of monoarthritis in male Sprague-Dawley rats, we studied the behavioral attributes of pain and anxiety as well as Locus Coeruleus electrophysiology in vivo 1 (MA1W) and 4 weeks (MA4W) after disease induction. Results: The manifestation of anxiety in MA4W was accompanied by dampened tonic Locus Coeruleus activity, which was coupled to an exacerbated evoked Locus Coeruleus response to noxious stimulation of the inflamed and healthy paw. When a mitogen-activating extracellular kinase inhibitor was administered to the contralateral Locus Coeruleus of MA4W, the phosphorylated extracellular signal-regulated kinase 1/2 levels in the Locus Coeruleus were restored and the exaggerated evoked response was blocked, reversing the anxiogenic-like behavior while pain hypersensitivity remained unaltered. Conclusion: As phosphorylated extracellular signal-regulated kinase 1/2 blockade in the Locus Coeruleus relieved anxiety and counteracted altered LC function, we propose that phosphorylated extracellular signal-regulated kinase 1/2 activation in the Locus Coeruleus plays a crucial role in pain-related anxiety.
Assuntos
Ansiedade/enzimologia , Artrite Experimental/enzimologia , Artrite Experimental/psicologia , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Locus Cerúleo/enzimologia , Dor/enzimologia , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Aminoacetonitrila/análogos & derivados , Aminoacetonitrila/farmacologia , Animais , Ansiedade/tratamento farmacológico , Ansiedade/etiologia , Ansiedade/patologia , Artrite Experimental/tratamento farmacológico , Artrite Experimental/patologia , Estudos de Coortes , MAP Quinases Reguladas por Sinal Extracelular/antagonistas & inibidores , Adjuvante de Freund , Locus Cerúleo/efeitos dos fármacos , Locus Cerúleo/patologia , Masculino , Neurônios/enzimologia , Neurônios/patologia , Nociceptividade/efeitos dos fármacos , Nociceptividade/fisiologia , Dor/complicações , Dor/tratamento farmacológico , Dor/patologia , Fosforilação/efeitos dos fármacos , Inibidores de Proteases/farmacologia , Ratos Sprague-Dawley , Tirosina 3-Mono-Oxigenase/metabolismoRESUMO
Selective serotonin reuptake inhibitors (SSRIs) regulate brain noradrenergic neurotransmission both at somatodendritic and nerve terminal areas. Previous studies have demonstrated that noradrenaline (NA) reuptake inhibitors are able to desensitize α2-adrenoceptor-mediated responses. The present study was undertaken to elucidate the effects of repeated treatment with the SSRI citalopram on the α2-adrenoceptor sensitivity in locus coeruleus (LC) and prefrontal cortex (PFC), by using in vivo microdialysis and electrophysiological techniques, and in vitro stimulation of [35S]GTPγS binding autoradiography. Repeated, but not acute, treatment with citalopram (5 mg/kg, i.p., 14 days) increased extracellular NA concentration selectively in PFC. The α2-adrenoceptor agonist clonidine (0.3 mg/kg, i.p.), administered to saline-treated animals (1 ml/kg i.p., 14 days) induced NA decrease in LC (Emax = -44 ± 4%; p < 0.001) and in PFC (Emax = -61 ± 5%, p < 0.001). In citalopram chronically-treated rats, clonidine administration exerted a lower decrease of NA (Emax = -25 ± 7%; p < 0.001) in PFC whereas the effect in LC was not different to controls (Emax = -36 ± 4%). Clonidine administration (0.625-20 µg/kg, i.v.) evoked a dose-dependent decrease of the firing activity of LC noradrenergic neurons in both citalopram- (ED50 = 3.2 ± 0.4 µg/kg) and saline-treated groups (ED50 = 2.6 ± 0.5 µg/kg). No significant differences between groups were found in ED50 values. The α2-adrenoceptor agonist UK14304 stimulated specific [35S]GTPγS binding in brain sections containing LC (144 ± 14%) and PFC (194 ± 32%) of saline-treated animals. In citalopram-treated animals, this increase did not differ from controls in LC (146 ± 22%) but was lower in PFC (141 ± 8%; p < 0.05). Taken together, long-term citalopram treatment induces a desensitization of α2-adrenoceptors acting as axon terminal autoreceptors in PFC without changes in somatodendritic α2-adrenoceptor sensitivity.
Assuntos
Citalopram/administração & dosagem , Locus Cerúleo/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Córtex Pré-Frontal/efeitos dos fármacos , Receptores Adrenérgicos alfa 2/fisiologia , Inibidores Seletivos de Recaptação de Serotonina/administração & dosagem , Neurônios Adrenérgicos/efeitos dos fármacos , Neurônios Adrenérgicos/fisiologia , Agonistas de Receptores Adrenérgicos alfa 2/administração & dosagem , Animais , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Tartarato de Brimonidina/administração & dosagem , Citalopram/farmacocinética , Locus Cerúleo/metabolismo , Locus Cerúleo/fisiologia , Masculino , Neurônios/fisiologia , Norepinefrina/metabolismo , Córtex Pré-Frontal/metabolismo , Córtex Pré-Frontal/fisiologia , Ratos , Ratos Sprague-Dawley , Inibidores Seletivos de Recaptação de Serotonina/farmacocinéticaRESUMO
The cystine/glutamate antiporter is a membrane transport system responsible for the uptake of extracellular cystine and release of intracellular glutamate. It is the major source of cystine in most cells, and a key regulator of extrasynaptic glutamate in the CNS. Because cystine is the limiting factor in the biosynthesis of glutathione, and glutamate is the most abundant neurotransmitter, the cystine/glutamate antiporter is a central player both in antioxidant defense and glutamatergic signaling, two events critical to brain function. However, distribution of cystine/glutamate antiporter in CNS has not been well characterized. Here, we analyzed expression of the catalytic subunit of the cystine/glutamate antiporter, xCT, by immunohistochemistry in histological sections of the forebrain and spinal cord. We detected labeling in neurons, oligodendrocytes, microglia, and oligodendrocyte precursor cells, but not in GFAP(+) astrocytes. In addition, we examined xCT expression and function by qPCR and cystine uptake in primary rat cultures of CNS, detecting higher levels of antiporter expression in neurons and oligodendrocytes. Chronic inhibition of cystine/glutamate antiporter caused high toxicity to cultured oligodendrocytes. In accordance, chronic blockage of cystine/glutamate antiporter as well as glutathione depletion caused myelin disruption in organotypic cerebellar slices. Finally, mice chronically treated with sulfasalazine, a cystine/glutamate antiporter inhibitor, showed a reduction in the levels of myelin and an increase in the myelinated fiber g-ratio. Together, these results reveal that cystine/glutamate antiporter is expressed in oligodendrocytes, where it is a key factor to the maintenance of cell homeostasis. GLIA 2016. GLIA 2016;64:1381-1395.