RESUMO
The diurnal variations in spontaneous and diazepam-induced anxiolysis and exploratory behavior were examined in Syrian hamsters in a plus-maze paradigm. The administration of diazepam or flunitrazepam augmented the percentage of time spent in the open arms, the percentage of entries to the open arms, and the number of crosses to both arms, whereas ethyl-beta-carboline injection decreased them. These three behavioral parameters showed significant daily variations, with the maxima being found at night (2400-0400 h). Flumazenil (5 mg/kg) injected at 0400 h decreased significantly the percentage of time spent in open arms and of entries to the open arms, without affecting significantly the total number of entries to both arms. Day-night differences in anxiety-related behavior persisted in hamsters kept under constant darkness for 3 days. Diazepam (0.5 mg/kg) increased the time spent in the open arms at 1600 and 2000 h only, and augmented the percent of entries to the open arms at 2000 h only. The total number of entries to both arms was augmented significantly by diazepam at all time intervals tested, except for 0400 h. The results indicate that Syrian hamsters exhibited significant diurnal changes in anxiolysis-related behavior in the plus-maze paradigm.
Assuntos
Ansiolíticos/farmacologia , Comportamento Animal/fisiologia , Ritmo Circadiano/fisiologia , Diazepam/farmacologia , Aprendizagem em Labirinto/efeitos dos fármacos , Animais , Cricetinae , MasculinoRESUMO
The existence of diurnal changes in postsynaptic expression of gamma-aminobutyric acid (GABA) type A receptors was assessed in cerebral cortex of Syrian hamsters by measuring [3H]GABA binding and the influx of 36Cl- in synaptoneurosomes. A diurnal variation in dissociation constant of [3H]GABA binding to cerebral cortex membranes, and the absence of diurnal differences in maximal number of sites, were found. When the nycthemeral changes in muscimol-stimulated 36Cl- uptake by cortical synaptoneurosomes were assessed, a maximum occurred late at night (i.e. 0400 h). At 1600 h, micromolar concentrations of flunitrazepam potentiated significantly the influx of chloride induced by muscimol, while at 0400 h flunitrazepam did not exert any significant effect on 36Cl- uptake. The results indicate that postsynaptic type A GABAergic activity peaked at nocturnal hours in the cerebral cortex of Syrian hamsters.
Assuntos
Córtex Cerebral/fisiologia , Ritmo Circadiano/fisiologia , Receptores de GABA-A/fisiologia , Animais , Córtex Cerebral/metabolismo , Canais de Cloreto/efeitos dos fármacos , Canais de Cloreto/metabolismo , Cricetinae , Flunitrazepam/farmacologia , Agonistas GABAérgicos/farmacologia , Moduladores GABAérgicos/farmacologia , Cinética , Masculino , Mesocricetus , Muscimol/farmacologia , Ácido gama-Aminobutírico/metabolismoRESUMO
The objective of this study was to assess whether rat pineal melatonin content could be modified in a classical conditioning paradigm. In rats kept under light (200 lux) from 06.00 to 18.00 h daily, the time of lights off was selected as the unconditioned stimulus (US). Restricted water availability (from 10 min before to 10 min after light-dark, LD, transition) was the conditioned stimulus (CS). The conditioned and unconditioned responses were measured as the changes in pineal melatonin levels 4 h after LD transition. In animals under regular lighting conditions, lights out at 18.00 h (the US) caused a 4.4-7.8-fold increase of pineal melatonin concentration 4 h after later, when compared to animals maintained under light for the 4 h-period. After a training period of 7 days of restricted water availability (the CS), significantly augmented pineal melatonin levels were found in rats that were exposed to water but were maintained under light for the 4 h period after expected LD transition. The control animals for this experiment, i.e., rats which had undergone the training period, were kept for 4 h under light after expected LD transition, and did not receive water at LD transition, exhibited very low pineal melatonin levels. The conditioned increase of pineal melatonin content attained lower values than those in rats exposed to normal lighting conditions. It also fulfilled the contingency criterion, that is, it caused at trial a significant elevation of pineal melatonin content only when water availability was applied from 10 min previously to LD transition during training, and not 20 min after LD transition. After a training period of 7 days, restricted water availability applied 4 h before lights off (at 14.00 h), caused an enhanced production of melatonin 4 h later, regardless of the animals being exposed either to a dark or to a light environment. The results indicate that pineal melatonin production can be manipulated in a classical conditioning paradigm, when an appropriate CS stimulus is used.
Assuntos
Condicionamento Clássico/fisiologia , Melatonina/metabolismo , Glândula Pineal/metabolismo , Privação de Água/fisiologia , Animais , Masculino , Fotoperíodo , Ratos , Ratos WistarRESUMO
Circadian rhythms of GABA turnover rate in cerebral cortex, preoptic area-medial basal hypothalamus (PMBH), cerebellum, and pineal gland were examined in Syrian hamsters kept for 3 months under either long (14 h of light/day) or short days (10 h of light/day). In vivo GABA turnover rate was measured by the increase of GABA levels following inhibition of GABA-transaminase by gamma-acetylenic GABA. Under long photoperiods, a significant rhythm of GABA turnover was detected in the four areas studied (cerebral cortex, PMBH, cerebellum, and pineal gland), with maxima at night. A Cosinor analysis indicated acrophases which varied from 2300 to 0400 h (3rd to 8th h of darkness). Under short photoperiods, there were no significant circadian variations in GABA turnover in the cerebral cortex, and the synchronization in turnover rate among the remaining regions was lost, with acrophases being detectable either during the light phase of daily photoperiod (PMBH) or at night (cerebellum, pineal gland). Steady state levels of GABA also changed periodically in the same brain regions under both lighting environments, although phase relationships of circadian rhythms in GABA content and turnover rate varied significantly among tissues, as well as on photoperiodic conditions.
Assuntos
Encéfalo/metabolismo , Ritmo Circadiano/fisiologia , Mesocricetus/fisiologia , Glândula Pineal/metabolismo , Ácido gama-Aminobutírico/metabolismo , Animais , Cricetinae , Masculino , Mesocricetus/metabolismoRESUMO
The presence of gamma-aminobutyric acid (GABA) and peripheral and central benzodiazepine receptors in the mammalian pineal gland prompted the examination of GABAergic transmission in dispersed bovine pineal cells. The effect of GABA on 3H-serotonin (5HT) release was examined in bovine pineal cells. GABA, by acting through GABA B receptor subtype, decreased 5HT release and by acting through GABA B, and presumably through GABA A receptor subtypes, inhibited depolarization-induced 45Ca2+ uptake in bovine pinealocytes. GABA, by acting on GABA B as well as on GABA A receptors, prevented the 5HT2- or 5HT1C-mediated stimulatory effect of serotonergic agonists on calcium uptake in pineal cells. GABA augmented 36Cl- uptake by bovine pineal cells. These results are interpreted to indicate that, by regulating the release of 5HT, GABA may modulate the synthesis and action of melatonin.
Assuntos
Cálcio/metabolismo , Cloretos/metabolismo , Glândula Pineal/metabolismo , Serotonina/metabolismo , Ácido gama-Aminobutírico/metabolismo , Análise de Variância , Animais , Bovinos , Antagonistas GABAérgicos , Técnicas In Vitro , Cinética , Glândula Pineal/citologiaRESUMO
The activity of 0.01-1 microM of melatonin on depolarization-induced 45Ca2+ influx by hypothalamic synaptosomes of rats killed at late evening (2000 h) depended on melatonin preincubation time, exhibiting an early (10 min) stimulation of uptake and an inhibition after 30 min of incubation. Both stimulatory and inhibitory effects were maximal at 2000 h and tended to a minimum at 2400 h, exhibiting intermediate values at 400 h. At 1000 h, only inhibitory effects of melatonin (1 microM) on Ca2+ uptake were found.