Efeito do lítio sobre a hiperatividade locomotora induzida pela lesão eletrolítica da região do núcleo mediano da rafe em ratos

A lesão do núcleo mediano da rafe (NMR) produz sintomas que sugerem validade de face ao episódio maníaco. Esta pesquisa avaliou o efeito do lítio sobre a hiperatividade locomotora induzida por esta lesão. Vinte e um ratos Wistar machos foram submetidos à lesão eletrolítica da região do NMR (LR) e 17 foram submetidos à lesão fictícia (LF). Após recuperação, a atividade locomotora foi avaliada na caixa de atividade (Med Associates/ENV-515). Parte dos animais destes grupos recebeu tratamentos com lítio (47,5 mg/kg/2x dia i.p.) por 10 dias, enquanto o restante foi tratado com salina no mesmo esquema. A reavaliação ao final dos tratamentos demonstrou que o lítio reduziu significantemente a atividade locomotora em relação à avaliação inicial no grupo LR (ANOVA/Bonferroni p < 0,05), tornando-a equivalente aos baixos níveis dos grupos LF. Estes dados sustentam a hipótese de que as manifestações induzidas pela lesão do NMR podem constituir um modelo animal de mania.

Facilitation of 5-HT(2A/2C)-mediated neurotransmission in the ventromedial hypothalamic nucleus decreases anxiety in the elevated T-maze

Previous evidence has shown that facilitation of GABA/benzodiazepine-mediated neurotransmission in the ventromedial hypothalamus (VMH) inhibits both escape and inhibitory avoidance responses generated in the elevated T-maze test of anxiety (ETM). These defensive behaviors have been associated with panic and generalized anxiety, respectively. Aside from GABA/benzodiazepine receptors, the VMH also contains a significant number of serotonin (5-HT) receptors, including 1A, 2A and 2C subtypes. The purpose of the present study was to investigate the effect of the activation of 5-HT(1A) and 5-HT(2A/2C) receptors in the VMH on defensive behavioral responses in rats submitted to the ETM. For that, male Wistar rats were treated intra-VMH with the 5-HT(1A) agonist 8-OH-DPAT, with the 5-HT(2A/2C) agonist DOI, with the 5-HT(2C) selective agonist MK-212, or with the 5-HT(2A/2C) antagonist ketanserin and 10 min after were submitted to the ETM. Results showed that both DOI and MK-212 significantly decreased avoidance measurements, an anxiolytic-like effect, without altering escape. 8-OH-DPAT and ketanserin were without effect, although the last drug attenuated the effects of DOI. None of the drugs altered locomotor activity in an open field. These results suggest that 5-HT(2A/2C) receptors of the VMH are involved in the regulation of inhibitory avoidance and might be of relevance to the physiopathology of generalized anxiety. (C) 2010 Elsevier B.V. All rights reserved.

Raphe magnus nucleus is involved in ventilatory but not hypothermic response to CO2

There is evidence that serotonin [ 5- hydroxytryptamine ( 5- HT)] is involved in the physiological responses to hypercapnia. Serotonergic neurons represent the major cell type ( comprising 15 - 20% of the neurons) in raphe magnus nucleus ( RMg), which is a medullary raphe nucleus. In the present study, we tested the hypothesis 1) that RMg plays a role in the ventilatory and thermal responses to hypercapnia, and 2) that RMg serotonergic neurons are involved in these responses. To this end, we microinjected 1) ibotenic acid to promote nonspecific lesioning of neurons in the RMg, or 2) anti- SERT- SAP ( an immunotoxin that utilizes a monoclonal antibody to the third extracellular domain of the serotonin reuptake transporter) to specifically kill the serotonergic neurons in the RMg. Hypercapnia caused hyperventilation and hypothermia in all groups. RMg nonspecific lesions elicited a significant reduction of the ventilatory response to hypercapnia due to lower tidal volume ( V-T) and respiratory frequency. Rats submitted to specific killing of RMg serotonergic neurons showed no consistent difference in ventilation during air breathing but had a decreased ventilatory response to CO2 due to lower VT. The hypercapnia- induced hypothermia was not affected by specific or nonspecific lesions of RMg serotonergic neurons. These data suggest that RMg serotonergic neurons do not participate in the tonic maintenance of ventilation during air breathing but contribute to the ventilatory response to CO2. Ultimately, this nucleus may not be involved in the thermal responses CO2.

Extracellular serotonin level in the basolateral nucleus of the amygdala and dorsal periaqueductal gray under unconditioned and conditioned fear states: An in vivo microdialysis study

Serotonin (5-HT) plays a key role in the neural circuitry mediating unconditioned and conditioned fear responses related to panic and generalized anxiety disorders. The basolateral nucleus of the amygdala (BLA) and the dorsal periaqueductal gray (dPAG) appear to be mainly involved in these conditions. The aim of this study was to measure the extracellular level of 5-HT and its metabolite 5-hydroxyindolacetic acid (5-HIAA) in the BLA and dPAG during unconditioned and conditioned fear states using in vivo microdialysis procedure. Thus, for the unconditioned fear test, animals were chemically stimulated in the dPAG with semicarbazide, an inhibitor of the gamma-aminobutyric acid-synthesizing enzyme glutamic acid decarboxylase. For the conditioned fear test, animals were subjected to a contextual conditioned fear paradigm using electrical footshock as the unconditioned stimulus. The results show that the 5-HT and 5-HIAA level in the BLA and dPAG did not change during unconditioned fear, whereas 5-HT concentration, but not 5-HIAA concentration, increased in these brain areas during conditioned fear. The present study showed that the 5-HT system was activated during conditioned fear, whereas it remained unchanged during unconditioned fear, supporting the hypothesis that 5-HT has distinct roles in conditioned and unconditioned fear (dual role of 5-HT in anxiety disorders). (C) 2009 Elsevier B.V. All rights reserved.

Stimulation-Produced Analgesia From the Occipital or Retrosplenial Cortex of Rats Involves Serotonergic and Opioid Mechanisms in the Anterior Pretectal Nucleus

The electrical stimulation of the occipital (OC) or retrosplenial (RSC) cortex produces antinociception in the rat tail-flick test. These cortices send inputs to the anterior pretectal nucleus (APtN) which is implicated in antinociception and nociception. At least muscarinic cholinergic, opioid, and serotonergic mechanisms in the APtN are involved in stimulation-produced antinociception (SPA) from the nucleus. In this study, the injection of 2% lidocaine (.25 mu L) or methysergide (40 and 80 ng/.25 mu L) into the APtN reduced the duration but did not change the intensity of SPA from the OC, whereas both duration and intensity of SPA from the RSC were significantly reduced in rats treated with lidocaine or naloxone (10 and 50 ng/.25 mu L), injected into the ANN. Naloxone or methysegide injected into the APtN was ineffective against SPA from the OC or RSC, respectively. Atropine (100 ng/.25 mu L) injected into the ANN was ineffective against SPA from either the OC or RSC. We conclude that the APtN acts as an intermediary for separate descending pain inhibitory pathways activated from the OC and RSC, utilizing at least serotonin and endogenous opioid as mediators in the nucleus. Perspective: Stimulation-induced antinociception from the retrosplenial or occipital cortex in the rat tail-flick test depends on the activation of separate descending pain inhibitory pathways that utilize the APtN as a relay station. (C) 2011 by the American Pain Society

Substance P, récepteurs NK1 et neurones à sérotonine : relations anatomiques et fonctionnelles dans le noyau raphe dorsalis

Nous avons étudié les relations anatomiques entre les systèmes de neurotransmission à substance P (SP) et à sérotonine (5-hydroxytryptamine, 5-HT) dans le noyau du raphé dorsal (NRD) du rongeur, afin de mieux comprendre les interactions entre ces systèmes durant la régulation de l’humeur. Le NRD reçoit une innervation SP provenant de l’habenula, et le blocage pharmacologique des récepteurs neurokinine-1 (rNK1) de la SP aurait des effets antidépresseurs. Chez le rongeur, le traitement par les antagonistes des rNK1 s’accompagne d’une désensibilisation des autorécepteurs 5-HT1A de la 5-HT et d’une hausse de l’activité des neurones 5-HT dans le NRD, suggérant des interactions locales entre ces deux systèmes. Dans un premier temps, nous avons démontré par doubles marquages immunocytochimiques en microscopies optique, confocale et électronique, la présence du rNK1 dans une sous-population de neurones 5-HT du NRD caudal. Lors de l’analyse en microscopie électronique, nous avons pu constater que les rNK1 étaient principalement cytoplasmiques dans les neurones 5-HT et membranaires sur les neurones non 5-HT du noyau. Grâce à d’autres doubles marquages, nous avons aussi pu identifier les neurones non-5-HT porteurs de rNK1 comme étant GABAergiques. Nous avons ensuite combiné l’immunomarquage de la SP avec celui du rNK1, dans le but d’examiner les relations entre les terminaisons (varicosités *) axonales SP et les neurones 5-HT (pourvus de rNK1 cytoplasmiques du NRD caudal. En simple marquage de la SP, nous avons pu estimer à 41% la fréquence avec laquelle les terminaisons SP font synapse. Dans le matériel doublement marqué pour la SP et son récepteur, les terminaisons SP ont été fréquemment retrouvées en contact direct ou à proximité des dendrites munies de rNK1 cytoplasmiques, mais toujours éloignées des dendrites à rNK1 membranaires. Pour tester l’hypothèse d’une internalisation soutenue des rNK1 par la SP dans les neurones 5-HT, nous avons ensuite examiné la localisation subcellulaire du récepteur chez le rat traité avec un antagoniste du rNK1, le RP67580. La densité du marquage des rNK1 a été mesurée dans le cytoplasme et sur la membrane des deux types de dendrites (5-HT: rNK1 cytoplasmiques; non 5-HT: rNK1 membranaires). Une heure après une injection unique de l’antagoniste, la distribution du rNK1 est apparue inchangée dans les deux types de neurones (5-HT et non 5-HT). Par contre, après un traitement quotidien de 7 ou 21 jours avec l’antagoniste, nous avons mesuré une augmentation significative des densités cytoplasmique et membranaire du rNK1 dans les neurones 5-HT, sans aucun changement dans les neurones non 5-HT. Ces traitements ont aussi augmenté l’expression du gène rNK1 dans le NRD. Enfin, nous avons mesuré une hausse de la densité membranaire du rNK1 dans les neurones 5-HT, sans hausse de densité cytoplasmique, par suite d’une lésion bilatérale de l’habenula. Ces résultats confortent l’hypothèse d’une activation et d’une internalisation soutenues des rNK1 par la SP dans les neurones 5-HT du NRD caudal. Ils suggèrent aussi que le trafic des rNK1 dans les neurones 5-HT du NRD représente un mécanisme cellulaire en contrôle de l’activation du système 5-HT par les afférences SP en provenance de l’habenula.

Immunocytochemical characterization of the pregeniculate nucleus and distribution of retinal and neuropeptide Y terminals in the suprachiasmatic nucleus of the Cebus monkey

Circadian rhythms generated by the suprachiasmatic nucleus (SCN) are modulated by photic and non-photic stimuli. In rodents, direct photic stimuli reach the SCN mainly through the retinohypothalamic tract (RHT), whereas indirect photic stimuli are mainly conveyed by the geniculohypothalamic tract (GHT). In rodents, retinal cells form a pathway that reaches the intergeniculate leaflet (IGL) where they establish synapses with neurons that express neuropeptide Y (NPY), hence forming the GHT projecting to the SCN. In contrast to the RHT, which has been well described in primates, data regarding the presence or absence of the IGL and GHT in primates are contradictory. Some studies have suggested that an area of the pregeniculate nucleus (PGN) of primates might be homologous to the IGL of rodents, but additional anatomical and functional studies on primate species are necessary to confirm this hypothesis. Therefore, this study investigated the main histochemical characteristics of the PGN and the possible existence of the GHT in the SCN of the primate Cebus, comparing the distribution of NPY immunoreactivity, serotonin (5-HT) immunoreactivity and retinal terminal fibers in these two structures. The results show that a collection of cell bodies containing NPY and serotonergic immunoreactivity and retinal innervations are present within a zone that might be homologous to the IGL of rodents. The SCN also receives dense retinal innervations and we observed an atypical distribution of NPY- and 5-HT-immunoreactive fibers without regionalization in the ventral part of the nucleus as described for other species. These data may reflect morphological differences in the structures involved in the regulation of circadian rhythms among species and support the hypothesis that the GHT is present in some higher primates (diurnal animals). (C) 2009 Elsevier B.V. All rights reserved.

5-HT(1B) receptor in the suprachiasmatic nucleus of the common marmoset (Callithrix jacchus)

Serotonin (5-HT) is involved in the fine adjustments at several brain centers including the core of the mammal circadian timing system (CTS) and the hypothalamic suprachiasmatic nucleus (SCN). The SCN receives massive serotonergic projections from the midbrain raphe nuclei, whose inputs are described in rats as ramifying at its ventral portion overlapping the retinohypothalamic and geniculohypothalamic fibers. In the SCN, the 5-HT actions are reported as being primarily mediated by the 5-HT1 type receptor with noted emphasis for 5-HT(1B) subtype, supposedly modulating the retinal input in a presynaptic way. In this study in a New World primate species, the common marmoset (Callithrix jacchus), we showed the 5-HT(1B) receptor distribution at the dorsal SCN concurrent with a distinctive location of 5-HT-immunoreactive fibers. This finding addresses to a new discussion on the regulation and synchronization of the circadian rhythms in recent primates. (C) 2010 Elsevier Ireland Ltd. All rights reserved.

Mapping brain Fos immunoreactivity in response to water deprivation and partial rehydration: influence of sodium intake

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Reorganization of CA3 area of the mouse hippocampus after pilocarpine induced temporal lobe epilepsy with special reference to the CA3-septum pathway

We showed that when CA3 pyramidal neurons in the caudal 80% of the dorsal hippocampus had almost disappeared completely, the efferent pathway of CA3 was rarely detectable. We used the mouse pilocarpine model of temporal lobe epilepsy (TLE), and injected iontophoretically the anterograde tracer phaseolus vulgaris leucoagglutinin (PHA-L) into gliotic CA3, medial septum and the nucleus of diagonal band of Broca, median raphe, and lateral supramammillary nuclei, or the retrograde tracer cholera toxin B subunit (CTB) into gliotic CA3 area of hippocampus. In the afferent pathway, the number of neurons projecting to CA3 from medial septum and the nucleus of diagonal band of Broca, median raphe, and lateral supramammillary nuclei increased significantly. In the hippocampus, where CA3 pyramidal neurons were partially lost, calbindin, calretinin, parvalbumin immunopositive back-projection neurons from CA1-CA3 area were observed. Sprouting of Schaffer collaterals with increased number of large boutons in both sides of CA1 area, particularly in the stratum pyramidale, was found. When CA3 pyramidal neurons in caudal 80% of the dorsal hippocampus have almost disappeared completely, surviving CA3 neurons in the rostral 20% of the dorsal hippocampus may play an important role in transmitting hyperactivity of granule cells to surviving CA1 neurons or to dorsal part of the lateral septum. We concluded that reorganization of CA3 area with its downstream or upstream nuclei may be involved in the occurrence of epilepsy.

Organização nuclear do sistema serotonérgico no encéfalo de morcegos Artibeus planirostris

Serotonin or 5-hydroxytryptamine (5-HT) is a substance found in many tissues of the body, including the nervous system acting as a neurotransmitter. Within the neuro-axis, the location of the majority of the 5-HT neurons is superimposed with raphe nuclei of the brain stem, in the median line or its vicinity, so that neuronal 5-HT can be considered a marker of the raphe nuclei. Serotonergic neurons are projected to almost all areas of the brain. Studies show the participation of serotonin in regulating the temperature, feeding behavior, sexual behavior, biological rhythms, sleep, locomotor function, learning, among others. The anatomy of these groups has been revised in many species, including mouse, rabbit, cat and primates, but never before in a bat species from South America. This study aimed to characterize the serotonergic clusters in the brain of the bat Artibeus planirostris through immunohistochemistry for serotonin. Seven adult bat males of Artibeus planirostris species (Microchiroptera, Mammalia) were used in this study. The animals were anesthetized, transcardially perfused and their brains were removed. Coronal sections of the frozen brain of bats were obtained in sliding microtome and subjected to immunohistochemistry for 5-HT. Delimit the caudal linear (CLi), dorsal (DR), median (MnR), paramedian (PMnR), pontine (PNR), magnus (MgR), pallidus (RPA) and obscurus (ROb) raphe nucleus, in addition to the groups B9 and rostral and caudal ventrolateral (RVL/CVL). The serotonergic groups of this kind of cheiroptera present morphology and cytoarchitecture relatively similar to that described in rodents and primates, confirming the phylogenetic stability of these cell clusters.

Facilitation of 5-HT(1A)-mediated neurotransmission in dorsal periaqueductal grey matter accounts for the panicolytic-like effect of chronic fluoxetine

Chronic administration of antidepressants such as fluoxetine and imipramine increases the responsiveness of 5-HT(1A) receptors in dorsal periaqueductal grey matter (DPAG), a midbrain area consistently implicated in the pathogenesis of panic disorder. This effect has been related to the clinically relevant anti-panic action of these drugs. In this study we determined whether long-term administration of fluoxetine also affects 5-HT efflux in DPAG. As a comparison, the effect of chronic treatment with the anxiolytic 5-HT(1A) receptor agonist buspirone on DPAG 5-HT levels was assessed. We also investigated whether the inhibitory effect of chronic fluoxetine on escape behaviour in the rat elevated T-maze, considered as a panicolytic-like effect, is counteracted by intra-DPAG injection of the 5-HT(1A) receptor antagonist WAY 100635. Male Wistar rats were treated (1 or 21 d, i.p.) with fluoxetine, buspirone or vehicle, once daily. After treatment, 5-HT in DPAG was measured by in-vivo microdialysis coupled to HPLC. In another study, rats treated (21 d, i.p.) with either fluoxetine or vehicle also received intra-DPAG injection of WAY 100635 or saline 10 min before being tested in the elevated T-maze. Chronic, but not acute, administration of fluoxetine significantly raised extracellular levels of 5-HT in DPAG. Long-term treatment with buspirone was ineffective. In the elevated T-maze, intra-DPAG injection of WAY 100635 fully blocked the anti-escape effect of chronic administration of fluoxetine. Therefore, chronic fluoxetine facilitates 5-HT(1A)-mediated neurotransmission within DPAG and this effect accounts for the panicolytic-like effect of this antidepressant in the elevated T-maze.

Antidepressant-Like Effects of Medial Prefrontal Cortex Deep Brain Stimulation in Rats

Background: Subcallosal cingulate gyrus (SCG) deep brain stimulation (DBS) is being investigated as a treatment for major depression. We report on the effects of ventromedial prefrontal cortex (vmPFC) DBS in rats, focusing on possible mechanisms involved in an antidepressant-like response in the forced swim test (FST). Methods: The outcome of vmPFC stimulation alone or combined with different types of lesions, including serotonin (5-HT) or nore-pineprhine (NE) depletion, was characterized in the FST. We also explored the effects of DBS on novelty-suppressed feeding, learned helplessness, and sucrose consumption in animals predisposed to helplessness. Results: Stimulation at parameters approximating those used in clinical practice induced a significant antidepressant-like response in the FST. Ventromedial PFC lesions or local muscimol injections did not lead to a similar outcome. However, animals treated with vmPFC ibotenic acid lesions still responded to DBS, suggesting that the modulation of fiber near the electrodes could play a role in the antidepressant-like effects of stimulation. Also important was the integrity of the serotonergic system, as the effects of DBS in the FST were completely abolished in animals bearing 5-HT, but not NE, depleting lesions. In addition, vmPFC stimulation induced a sustained increase in hippocampal 5-HT levels. Preliminary work with other models showed that DBS was also able to influence specific aspects of depressive-like states in rodents, including anxiety and anhedonia, but not helplessness. Conclusions: Our study suggests that vmPFC DES in rats maybe useful to investigate mechanisms involved in the antidepressant effects of SCG DBS.

THE ANTERIOR CINGULATE CORTEX IS A TARGET STRUCTURE FOR THE ANXIOLYTIC-LIKE EFFECTS OF BENZODIAZEPINES ASSESSED BY REPEATED EXPOSURE TO THE ELEVATED PLUS MAZE AND FOS IMMUNOREACTIVITY

Prior experience with the elevated plus maze (EPM) increases the avoidance of rodents to the open arms and impairs the anxiolytic-like effects of benzodiazepines on the traditional behaviors evaluated upon re-exposure to the maze, a phenomenon known as one-trial tolerance. Risk assessment behaviors are also sensitive to benzodiazepines. During re-exposure to the maze, these behaviors reinstate the information-processing initiated during the first experience, and the detection of danger generates stronger open-arm avoidance. The present study investigated whether the benzodiazepine midazolam alters risk assessment behaviors and Fos protein distribution associated with test and retest sessions in the EPM. Naive or maze-experienced Wistar rats received either saline or midazolam (0.5 mg/kg i.p.) and were subjected to the EPM. Midazolam caused the usual effects on exploratory behavior, increasing exploratory activity of naive rats in the open arms and producing no effects on these conventional measures in rats re-exposed to the maze. Risk assessment behaviors, however, were sensitive to the benzodiazepine during both sessions, indicating anxiolytic-like effects of the drug in both conditions. Fos immunohistochemistry showed that midazolam injections were associated with a distinct pattern of action when administered before the test or retest session, and the anterior cingulate cortex, area 1 (Cg1), was the only structure targeted by the benzodiazepine in both situations. Bilateral infusions of midazolam into the Cg1 replicated the behavioral effects of the drug injected systemically, suggesting that this area is critically involved in the anxiolytic-like effects of benzodiazepines, although the behavioral strategy adopted by the animals appears to depend on the previous knowledge of the threatening environment. (C) 2009 IBRO. Published by Elsevier Ltd. All rights reserved.

Serotonin-1A receptors in the dorsal periaqueductal gray matter mediate the panicolytic-like effect of pindolol and paroxetine combination in the elevated T-maze

The beta-adrenergic blocker and 5-HT(1A) receptor antagonist pindolol has been combined with selective serotonin reuptake inhibitors (SSRIs) in patients with depressive and anxiety disorders to shorten the onset of the clinical action and/or increase the proportion of responders. The results of a previous study have shown that pindolol potentiates the panicolytic effect of paroxetine in rats submitted to the elevated T-maze (ETM). Since reported evidence has implicated the 5-HT(1A) receptors of the dorsal periaqueductal gray matter (DPAG) in the panicolytic effect of antidepressants, rats treated with pindolol (5.0 mg/kg, i.p.) and paroxetine (1.5 mg/kg, i.p.) received a previous intra-DPAG injection of the selective 5-HT(1A) antagonist, WAY-100635 (0.4 mu g) and were submitted to the ETM. Pretreatment with WAY-100635 reversed the increase in escape latency, a panicolytic effect, determined by the pindolol-paroxetine combination. These results implicate the 5-HT(1A) receptors of the DPAG in the panicolytic effect of the pindolol-paroxetine combination administered systemically. They also give further preclinical support for the use of this drug combination in the treatment of panic disorder. (C) 2011 Elsevier Ireland Ltd. All rights reserved.