RESUMEN
Leptin, an adipocytokine encoded by an obesity gene and expressed in adipose tissue, affects feeding behavior, thermogenesis, and neuroendocrine status via leptin receptors distributed in the brain, especially in the hypothalamus. Leptin may also modulate the synaptic plasticity and behavioral performance related to learning and memory since: leptin receptors are found in the hippocampus, and both leptin and its receptor share structural and functional similarities with the interleukin-6 family of cytokines that modulate long-term potentiation (LTP) in the hippocampus. We therefore examined the effect of leptin on (1) behavioral performance in emotional and spatial learning tasks, (2) LTP at Schaffer collateral-CA1 synapses, (3) presynaptic and postsynaptic activities in hippocampal CA1 neurons, (4) the intracellular Ca(2+) concentration ([Ca(2+)](i)) in CA1 neurons, and (5) the activity of Ca(2+)/calmodulin protein kinase II (CaMK II) in the hippocampal CA1 tissue that exhibits LTP. Intravenous injection of 5 and/or 50mug/kg, but not of 500mug/kg leptin, facilitated behavioral performance in passive avoidance and Morris water-maze tasks. Bath application of 10(-12)M leptin in slice experiments enhanced LTP and increased the presynaptic transmitter release, whereas 10(-10)M leptin suppressed LTP and reduced the postsynaptic receptor sensitivity to N-methyl-d-aspartic acid. The increase in the [Ca(2+)](i) induced by 10(-10)M leptin was two times greater than that induced by 10(-12)M leptin. In addition, the facilitation (10(-12)M) and suppression (10(-10)M) of LTP by leptin was closely associated with an increase and decrease in Ca(2+)-independent activity of CaMK II. Our results show that leptin not only affects hypothalamic functions (such as feeding, thermogenesis, and neuroendocrine status), but also modulates higher nervous functions, such as the behavioral performance related to learning and memory and hippocampal synaptic plasticity.
Asunto(s)
Proteínas Quinasas Dependientes de Calcio-Calmodulina/metabolismo , Hipocampo/fisiología , Leptina/farmacología , Potenciación a Largo Plazo/fisiología , Aprendizaje por Laberinto/efectos de los fármacos , Memoria/efectos de los fármacos , Animales , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina , Proteínas Quinasas Dependientes de Calcio-Calmodulina/efectos de los fármacos , Hipocampo/efectos de los fármacos , Leptina/fisiología , Potenciación a Largo Plazo/efectos de los fármacos , Masculino , Neuronas/efectos de los fármacos , Neuronas/fisiología , Fosforilación/efectos de los fármacos , Ratas , Ratas WistarRESUMEN
Mesolimbic dopamine neurons in the ventral tegmental area (VTA), which project to the nucleus accumbens and prefrontal cortex, play an important role in the regulation of emotion, rewarding, and cognition. The dopamine neurons in the VTA have also been implicated in schizophrenia and drug abuse. Methamphetamine (METH) can induce a schizophrenia-like psychosis. Thus, the VTA is a likely effector site for the action of METH. However, effects of METH on the mesolimbic dopamine neurons are largely unknown. We treated adult SD rats with METH (5 mg/kg/day) or saline for 7 days, isolated single VTA neurons from these treated rats, and monitored the neuronal activities by measuring cytosolic Ca2+ concentration ([Ca2+]i), which was followed by immunocytochemical identification of dopamine neurons. Acute administration of METH under superfusion conditions concentration-dependently increased [Ca2+]i in VTA dopamine neurons isolated from METH- and saline-treated rats. Furthermore, acutely administered METH induced oscillations of [Ca2+]i only in the dopamine neurons of the METH-treated group. The METH-induced [Ca2+]i oscillations were inhibited by Ca2+-free conditions and by Ca2+ channel blockers. In conclusion, subchronic METH treatment sensitizes VTA dopamine neurons to this drug, resulting in induction of [Ca2+]i oscillations. This sensitization of VTA dopamine neurons may account, at least in part, for the psycho-stimulant effects of METH, such as the dependence on and sensitization to METH.
Asunto(s)
Señalización del Calcio/efectos de los fármacos , Estimulantes del Sistema Nervioso Central/administración & dosificación , Dopamina/metabolismo , Metanfetamina/administración & dosificación , Neuronas/efectos de los fármacos , Área Tegmental Ventral/citología , Animales , Calcio/metabolismo , Bloqueadores de los Canales de Calcio/farmacología , Quelantes/farmacología , Relación Dosis-Respuesta a Droga , Ácido Egtácico/farmacología , Inyecciones Subcutáneas/métodos , Masculino , Inhibición Neural/efectos de los fármacos , Neuronas/metabolismo , Ratas , Ratas Sprague-Dawley , omega-Conotoxinas/farmacologíaRESUMEN
The orexin-orexin receptor system has been implicated in the regulation of wakefulness/sleep states. Behavioral and psycho-stimulant effects of orexins have also been shown. Mesolimbic dopamine neurons in the ventral tegmental area (VTA) are implicated in the regulation of reward and wakefulness/sleep, In the present study, we examined the effect of orexin-A on cytosolic [Ca2+]i concentration ([Ca2+]) in the isolated rat VTA dopamine neurons. Orexin-A (10-12-10-8 M) concentration dependently increased [Ca2+]i in dopamine-containing neurons. The [Ca2+]i responses to orexin-A were inhibited under Ca2+-free conditions and by blockers of voltage-gated L- and N-type [Ca2+]i channels, nitrendipine and omega-conotoxin, respectively. The [Ca2+]i responses were also abolished by a phosphatidylcholine-specific phospholipase C inhibitor, D609, and a protein kinase C (PKC) inhibitor, calphostin C. A PKC activator, TPA, mimicked orexin-A in increasing [Ca2+]i. These results indicate that orexin-A increases [Ca2+]i in VTA dopamine neurons via phosphatidylcholine-specific PLC- and PKC-mediated activation of L- and N-type Ca2+ channels. This effect may serve as the mechanism by which orexin regulates wakefulness/sleep states and exerts its behavioral and psychostimulant effects.
Asunto(s)
Señalización del Calcio/efectos de los fármacos , Proteínas Portadoras/farmacología , Dopamina/metabolismo , Péptidos y Proteínas de Señalización Intracelular , Neuronas/efectos de los fármacos , Neuropéptidos/farmacología , Proteína Quinasa C/efectos de los fármacos , Fosfolipasas de Tipo C/efectos de los fármacos , Área Tegmental Ventral/efectos de los fármacos , Animales , Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio Tipo L/efectos de los fármacos , Canales de Calcio Tipo L/metabolismo , Canales de Calcio Tipo N/efectos de los fármacos , Canales de Calcio Tipo N/metabolismo , Señalización del Calcio/fisiología , Proteínas Portadoras/metabolismo , Células Cultivadas/citología , Células Cultivadas/efectos de los fármacos , Células Cultivadas/metabolismo , Citosol/efectos de los fármacos , Citosol/metabolismo , Relación Dosis-Respuesta a Droga , Inhibidores Enzimáticos/farmacología , Inmunohistoquímica , Masculino , Vías Nerviosas/citología , Vías Nerviosas/efectos de los fármacos , Vías Nerviosas/enzimología , Neuronas/citología , Neuronas/enzimología , Neuropéptidos/metabolismo , Orexinas , Proteína Quinasa C/metabolismo , Ratas , Ratas Sprague-Dawley , Sueño/efectos de los fármacos , Sueño/fisiología , Fosfolipasas de Tipo C/metabolismo , Área Tegmental Ventral/citología , Área Tegmental Ventral/enzimología , Vigilia/efectos de los fármacos , Vigilia/fisiologíaRESUMEN
Methamphetamine (METH) induces a schizophrenia-like psychosis. The dopamine neurons in the ventral tegmental area (VTA) have been implicated in schizophrenia and drug abuse. The present study investigated direct effects of METH on VTA dopamine neurons. We treated adult SD rats with METH (5 mg/kg/day) or saline for 7 days, isolated single VTA neurons, and monitored neuronal activities by measuring cytosolic Ca2+ concentration ([Ca2+]i) in immunocytochemically identified dopamine neurons. Acutely administered METH increased [Ca2+]i in dopamine neurons from METH- and saline-treated rats and induced oscillations of [Ca2+]i in dopamine neurons only from METH-treated rats. The METH-induced [Ca2+]i oscillations were inhibited by Ca(2+)-free conditions and Ca2+ channel blockers. The results indicate that acute METH increases [Ca2+]i in VTA dopamine neurons and that subchronic METH treatment sensitizes them to this drug, resulting in induction of [Ca2+]i oscillations. The activation of VTA dopamine neurons may be related to psycho-stimulant effects of METH.
Asunto(s)
Señalización del Calcio/efectos de los fármacos , Señalización del Calcio/fisiología , Citosol/efectos de los fármacos , Citosol/metabolismo , Inhibidores de Captación de Dopamina/farmacología , Dopamina/metabolismo , Metanfetamina/farmacología , Neuronas/efectos de los fármacos , Neuronas/metabolismo , Área Tegmental Ventral/efectos de los fármacos , Área Tegmental Ventral/metabolismo , Trastornos Relacionados con Anfetaminas/patología , Trastornos Relacionados con Anfetaminas/fisiopatología , Animales , Recuento de Células , Células Cultivadas , Esquema de Medicación , Masculino , Ratas , Ratas Sprague-Dawley , Factores de Tiempo , Área Tegmental Ventral/citologíaRESUMEN
We demonstrated involvement of the ventral tegmental area (VTA) dopaminergic system in orexin-induced hyperlocomotion and stereotypy in rats. In double-label immunohistochemical study of rat brain, we found that tyrosine hydroxylase (TH)-immunoreactive cells in the VTA received innervation from orexin immunoreactive-fibers. Orexin-A induced an increase in [Ca(2+)](i) in isolated A10 dopamine neurons in a dose-dependent manner. In behavioral studies, we found that orexin-A induced hyperlocomotion, stereotypy and grooming behavior when administered centrally in rats, and these effects were abolished by dopamine D(2) (haloperidol and sulpiride) or D(1) (SCH23390) antagonists. These results suggest that the orexin-induced hyperlocomotion, stereotypy and grooming behavior are mediated by the dopaminergic system and this pathway might be involved in orexin-induced emotional responses.
Asunto(s)
Conducta Animal/efectos de los fármacos , Proteínas Portadoras/farmacología , Dopamina/fisiología , Péptidos y Proteínas de Señalización Intracelular , Actividad Motora/efectos de los fármacos , Actividad Motora/fisiología , Neuropéptidos/farmacología , Conducta Estereotipada/fisiología , Animales , Axones/fisiología , Conducta Animal/fisiología , Benzazepinas/farmacología , Proteínas Portadoras/farmacocinética , Antagonistas de Dopamina/farmacología , Haloperidol/farmacología , Masculino , Terminaciones Nerviosas/fisiología , Neuronas/efectos de los fármacos , Neuronas/fisiología , Neuropéptidos/farmacocinética , Orexinas , Ratas , Ratas Wistar , Conducta Estereotipada/efectos de los fármacos , Sulpirida/farmacología , Tegmento Mesencefálico/citología , Tegmento Mesencefálico/fisiología , Tirosina 3-Monooxigenasa/metabolismoRESUMEN
Cholecystokinin-8 (CCK-8) dose-dependently increased the cytosolic Ca2+ concentration ([Ca]i) in ventromedial hypothalamic neurons acutely dissociated from the immature rat brain. The CCK-8 response was mimicked by caerulein, but not by CCK(B) agonists, and was often inhibited by CCK(A) receptor antagonists, but rarely by CCK(B) receptor antagonists. The response was dependent on external Ca2+ and Na+, and was inhibited by voltage-dependent Ca2+ channel blockers. The results suggest that CCK-8-induced depolarization via CCK(A) receptors increased Ca2+ influx through a voltage-dependent Ca2+ channel, which in turn increased [Ca]i.
Asunto(s)
Regulación del Apetito/fisiología , Canales de Calcio/metabolismo , Neuronas/metabolismo , Receptores de Colecistoquinina/metabolismo , Sincalida/agonistas , Sincalida/antagonistas & inhibidores , Núcleo Hipotalámico Ventromedial/metabolismo , Factores de Edad , Animales , Regulación del Apetito/efectos de los fármacos , Calcio/metabolismo , Canales de Calcio/efectos de los fármacos , Señalización del Calcio/efectos de los fármacos , Señalización del Calcio/fisiología , Células Cultivadas/efectos de los fármacos , Células Cultivadas/metabolismo , Citosol/efectos de los fármacos , Citosol/metabolismo , Relación Dosis-Respuesta a Droga , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Neuronas/efectos de los fármacos , Ratas , Ratas Wistar , Receptor de Colecistoquinina A , Receptor de Colecistoquinina B , Receptores de Colecistoquinina/agonistas , Receptores de Colecistoquinina/antagonistas & inhibidores , Sincalida/metabolismo , Núcleo Hipotalámico Ventromedial/efectos de los fármacos , Núcleo Hipotalámico Ventromedial/crecimiento & desarrolloRESUMEN
Orexin neurons are specifically localized in and around the lateral hypothalamus (LH), a feeding center. Intracerebroventricular administration of orexin-A and -B stimulates feeding as well as arousal. However, little is known regarding the regulators of the orexin neuron activity. The neurons that are activated under low glucose conditions, glucose-sensitive neurons, are located in the LH and have been implicated in the control of feeding. The present study investigated the effect of glucose on the single orexin neurons isolated from the rat LH, by measuring cytosolic Ca(2+) concentration ([Ca(2+)](i)) by fura-2 microfluorometry followed by immunocytochemical staining with anti-orexin antiserum. A shift of glucose concentration form 8.3 to 2.8 mM in the superfusion solution increased [Ca(2+)](i) in 13 out of 32 orexin-immunoreactive LH neurons. The results demonstrate that glucose-sensitive orexin neurons are present in the LH and that these neurons may play a role in linking the metabolic state in the body to the orexigenic, and could also, awakening signaling in the brain.