RESUMEN
The hypothalamic neuropeptide melanin-concentrating hormone (MCH) plays important roles in energy homeostasis, anxiety, and sleep regulation. Since the MCH receptor-1 (MCH-R1), the only functional receptor that mediates MCH functions in rodents, facilitates behavioral performance in hippocampus-dependent learning tasks, we investigated whether glutamatergic transmission in CA1 pyramidal cells could be modulated in mice lacking the MCH-R1 gene (MCH-R1(-/-)). We found that both α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartate (NMDA) receptor-mediated transmissions were diminished in the mutant mice compared with their controls. This deficit was explained, at least in part, by a postsynaptic down-regulation of these receptors since the amplitude of miniature excitatory postsynaptic currents and the NMDA/AMPA ratio were decreased. Long-term synaptic potentiation (LTP) was also impaired in MCH-R1(-/-) mice. This was due to an altered induction, rather than an impaired, expression because repeating the induction stimulus restored LTP to a normal magnitude. In addition, long-term synaptic depression was strongly diminished in MCH-R1(-/-) mice. These results suggest that MCH exerts a facilitatory effect on CA1 glutamatergic synaptic transmission and long-term synaptic plasticity. Recently, it has been shown that MCH neurons fire exclusively during sleep and mainly during rapid eye movement sleep. Thus these findings provide a mechanism by which sleep might facilitate memory consolidation.
Asunto(s)
Ácido Glutámico/fisiología , Hipocampo/fisiología , Plasticidad Neuronal/fisiología , Receptores de Somatostatina/fisiología , Sinapsis/fisiología , Transmisión Sináptica/fisiología , Animales , Potenciales Postsinápticos Excitadores/fisiología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Receptores de Somatostatina/deficiencia , Factores de TiempoRESUMEN
STUDY OBJECTIVES: It has been shown that wake (W) and slow wave sleep (SWS) modulate synaptic transmission in neocortical projections. However the impact of paradoxical sleep (PS) quantities on synaptic transmission remains unknown. We examined whether PS modulated the excitatory transmission and expression of glutamate receptor subtypes and phosphorylated extracellular signal-regulated kinases (p-ERK1/2). DESIGN: PS deprivation (PSD) was carried out with the multiple platforms method on adult male Sprague-Dawley rats. LTP, late-LTP, and synaptic transmission were studied in the dorsal and ventral hippocampus of controls, 75-h PSD and 150-min PS rebound (PSR). GluR1 and NR1 protein and mRNA expression were evaluated by western blot and real-time PCR. p-ERK1/2 level was quantified by western blot and immunohistochemistry. MEASUREMENT AND RESULTS: PSD decreased synaptic transmission and LTP selectively in dorsal CA1 and PSR rescued these deficits. PSD-induced synaptic modifications in CA1 were associated with a decrease in GluR1, NR1, and p-ERK1/2 levels in dorsal CA1 without change in GluR1 and NR1 mRNA expression. Regression analysis shows that LTP is positively correlated with both PS quantities and SWS episodes duration, whereas synaptic transmission and late-LTP are positively correlated with PS quantities and negatively correlated with SWS quantities. CONCLUSIONS: These findings unveil previously unrecognized roles of PSD on synaptic transmission and LTP in the dorsal, but not in the ventral, hippocampus. The fact that the decrease in protein expression of GluR1 and NR1 was not associated with a change in mRNA expression of these receptors suggests that a sleep-induced modulation of translational mechanisms occurs in dorsal CA1.
Asunto(s)
Hipocampo/patología , Potenciación a Largo Plazo/genética , Receptores AMPA/genética , Receptores de N-Metil-D-Aspartato/genética , Privación de Sueño/genética , Transmisión Sináptica/genética , Animales , Activación Enzimática/genética , Hipocampo/fisiopatología , Potenciación a Largo Plazo/fisiología , Masculino , Proteína Quinasa 1 Activada por Mitógenos/genética , Proteína Quinasa 3 Activada por Mitógenos/genética , Biosíntesis de Proteínas/genética , ARN Mensajero/genética , Ratas , Ratas Sprague-Dawley , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Privación de Sueño/patología , Privación de Sueño/fisiopatología , Sueño REM/genética , Sueño REM/fisiología , Transmisión Sináptica/fisiologíaRESUMEN
BACKGROUND: Recent data suggest that cytoskeletal defects may play a role in schizophrenia. We previously imitated features of schizophrenia in an animal model by disrupting gene coding for a microtubule-associated protein called STOP. STOP-null mice display synaptic defects in glutamatergic neurons, hyper-dopaminergy, and severe behavioral disorders. Synaptic and behavioral deficits are amended by neuroleptic treatment in STOP-null mice, providing an attractive model to test new antipsychotic agents. We examined the effects of a taxol-related microtubule stabilizer, epothilone D. METHODS: Mice were treated either with vehicle alone or with epothilone D. Treatment effects on synaptic function were assessed using electron-microscopy quantification of synaptic vesicle pools and electrophysiology in the CA1 region of the hippocampus. Dopamine transmission was investigated using electrochemical assays. Behavior was principally assessed using tests of maternal skills. RESULTS: In STOP-null mice, treatment with epothilone D increased synaptic vesicle pools, ameliorated both short- and long-term forms of synaptic plasticity in glutamatergic neurons, and had a dramatic beneficial effect on mouse behavior. CONCLUSIONS: A microtubule stabilizer can have a beneficial effect on synaptic function and behavior, suggesting new possibilities for treatment of schizophrenia.