RESUMO
BACKGROUND: Peptidergic neurons containing the melanin-concentrating hormone (MCH) and the hypocretins (or orexins) are intermingled in the zona incerta, perifornical nucleus and lateral hypothalamic area. Both types of neurons have been implicated in the integrated regulation of energy homeostasis and body weight. Hypocretin neurons have also been involved in sleep-wake regulation and narcolepsy. We therefore sought to determine whether hypocretin and MCH neurons express Fos in association with enhanced paradoxical sleep (PS or REM sleep) during the rebound following PS deprivation. Next, we compared the effect of MCH and NaCl intracerebroventricular (ICV) administrations on sleep stage quantities to further determine whether MCH neurons play an active role in PS regulation. RESULTS: Here we show that the MCH but not the hypocretin neurons are strongly active during PS, evidenced through combined hypocretin, MCH, and Fos immunostainings in three groups of rats (PS Control, PS Deprived and PS Recovery rats). Further, we show that ICV administration of MCH induces a dose-dependent increase in PS (up to 200%) and slow wave sleep (up to 70%) quantities. CONCLUSION: These results indicate that MCH is a powerful hypnogenic factor. MCH neurons might play a key role in the state of PS via their widespread projections in the central nervous system.
Assuntos
Sistema Nervoso Central/fisiologia , Hormônios Hipotalâmicos/biossíntese , Peptídeos e Proteínas de Sinalização Intracelular , Melaninas/biossíntese , Neurônios/fisiologia , Hormônios Hipofisários/biossíntese , Sono REM/fisiologia , Animais , Proteínas de Transporte/biossíntese , Contagem de Células , Sistema Nervoso Central/citologia , Sistema Nervoso Central/efeitos dos fármacos , Ritmo Circadiano/efeitos dos fármacos , Ritmo Circadiano/fisiologia , Relação Dose-Resposta a Droga , Eletroencefalografia , Eletromiografia , Hormônios Hipotalâmicos/farmacologia , Hipotálamo/citologia , Hipotálamo/metabolismo , Injeções Intraventriculares , Masculino , Melaninas/farmacologia , Neurônios/metabolismo , Neuropeptídeos/biossíntese , Orexinas , Hormônios Hipofisários/farmacologia , Proteínas Proto-Oncogênicas c-fos/biossíntese , Ratos , Ratos Sprague-Dawley , Sono/efeitos dos fármacos , Sono/fisiologia , Fases do Sono/efeitos dos fármacos , Fases do Sono/fisiologia , Sono REM/efeitos dos fármacosRESUMO
We recently determined in rats that iontophoretic application of bicuculline or gabazine [two GABAa antagonists] and kainic acid (a glutamate agonist) in the sublaterodorsal nucleus (SLD) induces with a very short latency a paradoxical sleep-like state. From these results, we proposed that GABAergic and glutamatergic inputs to the SLD paradoxical sleep (PS)-executive neurons gate the onset of PS [R. Boissard et al. (2002) Eur. J. Neurosci., 16, 1959-1973]. We therefore decided to determine the origin of the GABAergic and non-GABAergic inputs to the SLD combining ejection of a retrograde tracer [cholera-toxin B subunit (CTb)] with glutamate decarboxylase (GAD) immunohistochemistry. The presence of GAD-immunoreactive neurons in the SLD was confirmed. Then, following CTb ejections centred on the SLD, combined with GAD and CTb immunohistochemistry, double-labelled cells were observed in the mesencephalic and pontine reticular nuclei and to a lesser extent the parvicellular reticular nucleus. A large number of GAD-negative retrogradely labelled cells was also seen in these structures as well as in the primary motor area of the frontal cortex, the central nucleus of the amygdala, the ventral and lateral bed nucleus of the stria terminalis, the lateral hypothalamic area, the lateral and ventrolateral periaqueductal grey and the lateral paragigantocellular reticular nucleus. From these results, we propose that the activation of PS-executive neurons from the SLD is due to the removal of a tonic inhibition from GABAergic neurons localized in the SLD, and the mesencephalic and pontine reticular nuclei. Strong non-GABAergic inputs to the SLD could be excitatory and responsible for the tonic glutamatergic input on the PS-on neurons we have previously described. They could also terminate on SLD GABAergic interneurons and be indirectly responsible for the inhibition of the PS-on neurons during waking and slow-wave sleep.
Assuntos
Glutamato Descarboxilase/metabolismo , Bulbo/metabolismo , Vias Neurais/anatomia & histologia , Neurônios/metabolismo , Sono REM/fisiologia , Animais , Toxina da Cólera/metabolismo , Eletroencefalografia , Eletromiografia , Imuno-Histoquímica , Iontoforese , Masculino , Bulbo/anatomia & histologia , Bulbo/fisiologia , Vias Neurais/metabolismo , Neurônios/classificação , Fito-Hemaglutininas/farmacocinética , Ratos , Ratos Sprague-Dawley , Sono REM/efeitos dos fármacos , Ácido gama-Aminobutírico/metabolismoRESUMO
The neuronal network responsible for paradoxical sleep (PS) onset and maintenance has not previously been identified in the rat, unlike the cat. To fill this gap, this study has developed a new technique involving the recording of sleep-wake states in unanaesthetized head-restrained rats whilst locally administering pharmacological agents by microiontophoresis from glass multibarrel micropipettes, into the dorsal pontine tegmentum and combining this with functional neuroanatomy. Pharmacological agents used for iontophoretic administration included carbachol, kainic acid, bicuculline and gabazine. The injection sites and their efferents were then identified by injections of anterograde (phaseolus vulgaris leucoagglutinin) or retrograde (cholera toxin B subunit) tracers through an adjacent barrel of the micropipette assembly and by C-Fos immunostaining. Bicuculline, gabazine and kainic acid ejections specifically into the pontine sublaterodorsal nucleus (SLD) induced within a few minutes a PS-like state characterized by a continuous muscle atonia, low voltage EEG and a lack of reaction to stimuli. In contrast, carbachol ejections into the SLD induced wakefulness. In PHA-L, glycine and C-Fos multiple double-labelling experiments, anterogradely labelled fibres originating from the SLD were seen apposed on glycine and C-Fos positive neurons (labelled after 90 min of pharmacologically induced PS-like state) from the ventral gigantocellular and parvicellular reticular nuclei. Altogether, these data indicate that the SLD nuclei contain a population of neurons playing a crucial role in PS onset and maintenance. Furthermore, they suggest that GABAergic disinhibition and glutamate excitation of these neurons might also play a crucial role in the onset of PS.