RESUMO
In the present work we study the contribution of the chloride channel of the Cystic Fibrosis Transmembrane Regulator (CFTR) in the postsynaptic inhibition of somatic motoneurons during rapid-eye-movement (REM) sleep atonia. Postsynaptic inhibition of motoneurons is partially responsible for the atonia that occurs during REM sleep. Disfacilitation is an additional mechanism that lowers motoneuron excitability in this state. Postsynaptic inhibition is mediated by the release of glycine from synaptic terminals on motoneurons, and by GABA that plays a complementary role to that of glycine. In this work we look in brain stem motoneurons of neonatal rats at a mechanism unrelated to the actions of glycine, GABA or to disfacilitation which depends on the chloride channel of the CFTR. We studied the presence of CFTR by immunocytochemistry. In electrophysiological experiments utilizing whole cell recordings in in vitro slices we examined the consequences of blocking this chloride channel. The effects on motoneurons of the application of glycine, of the application of glibenclamide (a CFTR blocker) and again of glycine during the effects of glibenclamide were studied. Glycine produced an hyperpolarization, a decrease in motoneuron excitability and a decrease in input resistance, all characteristic changes of the postsynaptic inhibition produced by this neurotransmitter. Glibenclamide produced an increase in input resistance and in motoneurons' repetitive discharge as well as a shift in the equilibrium potential for chloride ions as indicated by the displacement of the reversal potential for glycinergic actions. In motoneurons treated with glibenclamide, glycine produced postsynaptic inhibition but this effect was smaller when compared to that elicited by glycine in control conditions. The fact that blocking of the CFTR-chloride channel in brain stem motoneurons influences glycinergic inhibition suggests that this channel may play a complementary role in the glycinergic inhibition that occurs during REM sleep.
Assuntos
Regulador de Condutância Transmembrana em Fibrose Cística/fisiologia , Glicina/fisiologia , Neurônios Motores/fisiologia , Inibição Neural/fisiologia , Ponte/fisiologia , Núcleos do Trigêmeo/fisiologia , Animais , Animais Recém-Nascidos , Neurônios Motores/citologia , Técnicas de Cultura de Órgãos , Ponte/citologia , Ratos , Ratos Wistar , Sono REM/fisiologia , Transmissão Sináptica/fisiologia , Núcleos do Trigêmeo/citologiaRESUMO
The ventrolateral subdivision of the periaqueductal gray (vlPAG) and the adjacent dorsal mesencephalic reticular formation (dMRF) are involved in the modulation of active (rapid eye movement) sleep (AS). In order to determine the effects on AS of the suppression of neuronal activity in these regions, muscimol, a GABA receptor A (GABA(A)) receptor agonist, and bicuculline, a GABA(A) receptor antagonist, were microinjected bilaterally in guinea pigs and the states of sleep and wakefulness were examined. The main effect of muscimol was an increase in AS; this increase occurred in conjunction with a reduction in the time spent in wakefulness. The powerful effect of muscimol was striking especially when considering the small amount of naturally-occurring AS that is present in this species. Additional observable effects that were induced by muscimol were: 1) long lasting episodes of hypotonia/atonia during wakefulness and quiet sleep that included a lack of extensor tone in the hind limbs, and 2) frequently occurring cortical spindles, similar to those observed during naturally-occurring quiet sleep (sleep spindles), that were present during wakefulness. Conversely, bilateral microinjections of bicuculline induced a prolonged state of wakefulness and blocked the effect of subsequent injections of muscimol. These data suggest that endogenous GABA acts on GABA(A) receptors within the vlPAG and dMRF to promote AS in the guinea pig.
Assuntos
Muscimol/farmacologia , Sono REM , Tegmento Mesencefálico/fisiologia , Ácido gama-Aminobutírico/fisiologia , Animais , Monitoramento Ambiental , Cobaias , Receptores de GABA-A/efeitos dos fármacos , Receptores de GABA-A/fisiologia , Sono REM/efeitos dos fármacos , Tegmento Mesencefálico/efeitos dos fármacos , VigíliaRESUMO
It is currently thought that the hypothalamus influences motor output through connections with premotor structures which in turn project to motor nuclei. However, hypocretinergic/orexinergic projections to different motor pools have recently been demonstrated. The present study was undertaken to examine whether hypocretinergic/orexinergic neurons are the only source of projections from the hypothalamus to the trigeminal motor nucleus in the guinea-pig. Cholera toxin subunit b was injected into the trigeminal motor nucleus in order to retrogradely label premotor neurons. Two anatomically separated populations of labeled neurons were observed in the hypothalamus: one group was distributed along the dorsal zone of the lateral hypothalamic area, the lateral portion of the dorsomedial hypothalamic nucleus and the perifornical nucleus; the other was located within the periventricular portion of the dorsomedial hypothalamic nucleus. Numerous cholera toxin subunit b+ neurons in both populations displayed glutamate-like immunoreactivity. In addition, premotor neurons containing hypocretin/orexin were distributed throughout the lateral dorsomedial hypothalamic nucleus, perifornical nucleus and lateral hypothalamic area. Other premotor neurons were immunostained for melanin concentrating hormone; these cells, which were located within the lateral hypothalamic area and the perifornical nucleus, were intermingled with glutamatergic and hypocretinergic/orexinergic neurons. Nitrergic premotor neurons were located only in the periventricular zone of the dorsomedial hypothalamic nucleus. None of the hypothalamic premotor neurons were GABAergic, cholinergic or monoaminergic. The existence of diverse neurotransmitter systems projecting from the hypothalamus to the trigeminal motor pool indicates that this diencephalic structure may influence the numerous functions that are subserved by the trigeminal motor system.
Assuntos
Vias Aferentes/anatomia & histologia , Hipotálamo/citologia , Neurônios/metabolismo , Núcleos do Trigêmeo/anatomia & histologia , Acetilcolinesterase/metabolismo , Vias Aferentes/metabolismo , Albuminas/metabolismo , Animais , Contagem de Células/métodos , Toxina da Cólera/administração & dosagem , Toxina da Cólera/metabolismo , Lateralidade Funcional/fisiologia , Glutamato Descarboxilase/metabolismo , Cobaias , Hormônios Hipotalâmicos/metabolismo , Hipotálamo/metabolismo , Imuno-Histoquímica/métodos , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Masculino , Melaninas/metabolismo , NADP/metabolismo , Neurônios/classificação , Neuropeptídeos/metabolismo , Óxido Nítrico/metabolismo , Óxido Nítrico Sintase Tipo I/metabolismo , Orexinas , Hormônios Hipofisários/metabolismo , Fatores de Tempo , Núcleos do Trigêmeo/metabolismoRESUMO
In the present study, we report that the cuneiform (Cun) nucleus, a brainstem structure that before now has not been implicated in sleep processes, exhibits a large number of neurons that express c-fos during carbachol-induced active sleep (AS-carbachol). Compared with control (awake) cats, during AS-carbachol, there was a 671% increase in the number of neurons that expressed c-fos in this structure. Within the Cun nucleus, three immunocytochemically distinct populations of neurons were observed. One group consisted of GABAergic neurons, which predominantly did not express c-fos during AS-carbachol. Two other different populations expressed c-fos during this state. One of the Fos-positive (Fos(+)) populations consisted of a distinct group of nitric oxide synthase (NOS)-NADPH-diaphorase (NADPH-d)-containing neurons; the neurotransmitter of the other Fos(+) population remains unknown. The Cun nucleus did not contain cholinergic, catecholaminergic, serotonergic, or glycinergic neurons. On the basis of neuronal activation during AS-carbachol, as indicated by c-fos expression, we suggest that the Cun nucleus is involved, in an as yet unknown manner, in the physiological expression of active sleep. The finding of a population of NOS-NADPH-d containing neurons, which were activated during AS-carbachol, suggests that nitrergic modulation of their target cell groups is likely to play a role in active sleep-related physiological processes.
Assuntos
Tronco Encefálico/metabolismo , Neurônios/metabolismo , Proteínas Proto-Oncogênicas c-fos/metabolismo , Sono REM/fisiologia , Animais , Tronco Encefálico/efeitos dos fármacos , Carbacol/farmacologia , Gatos , Agonistas Colinérgicos/farmacologia , NADP/metabolismo , Neurônios/efeitos dos fármacos , Óxido Nítrico Sintase/metabolismo , Proteínas Proto-Oncogênicas c-fos/efeitos dos fármacos , Sono REM/efeitos dos fármacos , Ácido gama-Aminobutírico/metabolismoRESUMO
Weakly electric fish generate meaningful electromotor behaviors by specific modulations of the discharge of their medullary pacemaker nucleus from which the rhythmic command for each electric organ discharge (EOD) arises. Certain electromotor behaviors seem to involve the activation of specific neurotransmitter receptors on particular target cells within the nucleus, i.e., on pacemaker or on relay cells. This paper deals with the neural basis of the electromotor behavior elicited by activation of Mauthner cells in Gymnotus carapo. This behavior consists of an abrupt and prolonged increase in the rate of the EOD. The effects of specific glutamate agonists and antagonists on basal EOD frequency and on EOD accelerations induced by Mauthner cell activation were assessed. Injections of both ionotropic (AMPA, kainate, and NMDA) and metabotropic (trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid) glutamate agonists induced increases in EOD rate that were maximal when performed close to the soma of pacemaker cells. In contrast, injections in the proximity of relay cells were ineffective. Therefore, pacemaker neurons are probably endowed with diverse glutamate receptor subtypes, whereas relay cells are probably not. The Mauthner cell-evoked electromotor behavior was suppressed by injections of AP-5 and (+/-)-amino-4-carboxy-methyl-phenylacetic acid, NMDA receptor and metabotropic glutamate receptor antagonists, respectively. Thus, this electromotor behavior relies on the activation of the NMDA and metabotropic glutamate receptor subtypes of pacemaker cells. Our study gives evidence for the synergistic effects of NMDA and metabotropic receptor activation and shows how a simple circuit can produce specific electromotor outputs.
Assuntos
Relógios Biológicos/fisiologia , Peixe Elétrico/fisiologia , Bulbo/fisiologia , Atividade Motora/fisiologia , Neurônios/fisiologia , Receptores de Glutamato Metabotrópico/fisiologia , Receptores de N-Metil-D-Aspartato/fisiologia , 2-Amino-5-fosfonovalerato/farmacologia , 6-Ciano-7-nitroquinoxalina-2,3-diona/farmacologia , Animais , Órgão Elétrico/efeitos dos fármacos , Órgão Elétrico/fisiologia , Eletrofisiologia , Agonistas de Aminoácidos Excitatórios/farmacologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Ácido Glutâmico/farmacologia , Bulbo/citologiaRESUMO
In the present report, we provide evidence that mesencephalic trigeminal (Mes-V) sensory neurons, a peculiar type of primary afferent cell with its cell body located within the CNS, may operate in different functional modes depending on the degree of their membrane polarization. Using intracellular recording techniques in the slice preparation of the adult rat brain stem, we demonstrate that when these neurons are depolarized, they exhibit sustained, high-frequency, amplitude-modulated membrane potential oscillations. Under these conditions, the cells discharge high-frequency trains of spikes. Oscillations occur at membrane potential levels more depolarized than -53 +/- 2.3 mV (mean +/- SD). The amplitude of these oscillations increases with increasing levels of membrane depolarization. The peak-to-peak amplitude of these waves is approximately 3 mV when the cells are depolarized to levels near threshold for repetitive firing. The frequency of oscillations is similar in different neurons (108.9 +/- 15.5 Hz) and was not modified, in any individual neuron, by changes in the membrane potential level. These oscillations are abolished by hyperpolarization and by TTX, whereas blockers of voltage-dependent K+ currents slow the frequency of oscillations but do not abolish the activity. These data indicate that the oscillations are generated by the activation of inward Na+ current/s and shaped by voltage-dependent K+ outward currents. The oscillatory activity is not modified by perfusion with low-calcium, high-magnesium, or cobalt-containing solutions nor is it modified in the presence of cadmium or Apamin. These results indicate that a calcium-dependent K+ current does not play a significant role in this activity. We postulate that the membrane oscillatory activity in Mes-V neurons is synchronized in adjoining electrotonically coupled cells and that this activity may be modulated in the behaving animal by synaptic influences.
Assuntos
Mesencéfalo/fisiologia , Neurônios Aferentes/fisiologia , Potenciais de Ação/fisiologia , Animais , Cálcio/fisiologia , Potenciais da Membrana/fisiologia , Mesencéfalo/citologia , Neurônios Aferentes/metabolismo , Oscilometria , Bloqueadores dos Canais de Potássio , Ratos , Ratos Wistar , Tetrodotoxina/farmacologiaRESUMO
Trigeminal motoneurons of the guinea pig brain stem slice preparation were studied using intracellular recording techniques. The voltage response to a 100-ms constant-current pulse was studied and a population of cells was found which did not exhibit sag or overshoot of their voltage response to a pulse of hyperpolarizing current of < 1 nA but did exhibit both phenomena when a current pulse of > 1 nA was used. The sag and overshoot observed with large-current pulses were reduced or blocked when 4 mM CsCl was added to the bathing solution. This observation supports the hypothesis that these phenomena were due to the voltage- and time-dependent activation of the Q-current. The method of peeling exponentials was then used to correct raw voltage data from cells in which the Q-current was present. The mean membrane time constant was within 1% and the mean input resistance was within 2% of the means for these parameters when measured in these same cells under conditions in which the Q-current was absent. We conclude from these experiments that the method of peeling exponentials is valid for obtaining estimates of the membrane time constant and input resistance from cells that exhibit sag and overshoot due to voltage- and time-dependent changes in the magnitude of the Q-current.
Assuntos
Neurônios Motores/fisiologia , Potenciais de Ação/fisiologia , Animais , Membrana Celular/fisiologia , Impedância Elétrica , Eletrofisiologia , Cobaias , Potenciais da Membrana/fisiologia , Técnicas de Patch-Clamp , Nervo Trigêmeo/citologia , Nervo Trigêmeo/fisiologiaRESUMO
Brainstem and spinal cord motoneurons that innervate somatic musculature serving antigravity functions are postsynaptically inhibited during active sleep. However, it has been reported that hypoglossal motoneurons (which do not innervate antigravity muscles) are not postsynaptically inhibited during active sleep, but are disfacilitated. In the present report we describe changes, during active sleep, in the excitability and membrane potential of digastric and synergistic motoneurons of the trigeminal motor pool; these neurons do not perform antigravity functions. The experiments described in the present report were performed in chronic cats that were prepared for intracellular recording. The motoneurons hyperpolarized an average of 11 mV (S.D. +/- 1.29, n = 8, P < 0.005) during active sleep compared to quiet sleep. Hyperpolarization was accompanied by a reduction in the excitability of the somadendritic regions of the neurons, as indicated by an increase in the delay of propagation of antidromic spikes from the initial segment to the somadendritic portion of the cell. High gain membrane potential recordings from these motoneurons revealed the occurrence of a remarkably large number of hyperpolarizing potentials during active sleep. When K-chloride-filled microelectrodes were utilized and chloride ions were injected intracellularly, the polarity of these potentials was reversed. During phasic episodes of active sleep, there was a clear increase in hyperpolarizing potential activity, a blockade of somadendritic spikes and phasic reductions in the amplitude of the initial segment spikes. Hyperpolarizing potentials occurred in conjunction with ponto-geniculo-occipital waves.(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Arcada Osseodentária/inervação , Arcada Osseodentária/fisiologia , Neurônios Motores/fisiologia , Movimento , Fases do Sono/fisiologia , Potenciais de Ação , Animais , Gatos , Potenciais Evocados , Músculos da Mastigação/inervação , Potenciais da Membrana , Tempo de Reação , Núcleo Espinal do Trigêmeo/citologia , Núcleo Espinal do Trigêmeo/fisiologiaRESUMO
Stimulation of a region within the parvocellular medullary reticular formation (PcRF) that contains somas of premotor interneurons produces short latency inhibitory synaptic potentials (IPSPs) in cat trigeminal motoneurons. The present study was undertaken to determine whether glycinergic synapses are responsible for these IPSPs. The intravenous administration of strychnine, an established glycine antagonist, abolished these PcRF-IPSPs. This effect appears to be specific for glycinergic inhibitory synapses because the short lasting component of the IPSP produced by inferior alveolar nerve (IAN) stimulation was also abolished, whereas, in contrast, the long lasting non-glycinergic component of this IPSP was not suppressed. These results indicate that a glycinergic system in the reticular formation is responsible for the non-reciprocal postsynaptic inhibition of trigeminal motoneurons.
Assuntos
Neurônios Motores/efeitos dos fármacos , Formação Reticular/fisiologia , Estricnina/farmacologia , Nervo Trigêmeo/citologia , Animais , Gatos , Estimulação Elétrica , Eletrodos Implantados , Potenciais Evocados/efeitos dos fármacos , Glicina/fisiologia , Interneurônios/efeitos dos fármacos , Interneurônios/fisiologia , Arcada Osseodentária/inervação , Músculos/inervação , Formação Reticular/efeitos dos fármacos , Sinapses/efeitos dos fármacos , Sinapses/fisiologia , Nervo Trigêmeo/efeitos dos fármacosRESUMO
The present report describes the effects on trigeminal motoneurons of stimulation of a circumscribed site within the parvocellular region of the medullary reticular formation. This medullary site was selected because anatomical studies have shown that premotor interneurons project from this site to the trigeminal motorpool. Electrical stimulation of this site induced IPSPs (PcRF-IPSPs) in jaw-closer motoneurons. A population of these IPSPs, recorded contralateral to the site of stimulation, exhibited latencies shorter than 1.5 ms (mean 1.16 +/- 0.08 SD). Their mean amplitude was 1.72 mV +/- 1.13 SD and their mean duration was 3.52 ms +/- 2.15 SD. We believe that these PcRF-IPSPs arose as the result of activation of a monosynaptic pathway. A comparable inhibitory input from this site to ipsilateral jaw-closer motoneurons and to both contra and ipsilateral digastric motoneurons was also observed. We therefore conclude that this medullary PcRF site contains premotor interneurons that are capable of postsynaptically inhibiting motoneurons that innervate antagonistic jaw muscles.
Assuntos
Bulbo/fisiologia , Neurônios Motores/fisiologia , Nervo Trigêmeo/fisiologia , Animais , Gatos , Estimulação Elétrica , Eletrodos , Potenciais Evocados/fisiologia , Microeletrodos , Formação Reticular/citologia , Formação Reticular/fisiologia , Sinapses/fisiologia , Nervo Trigêmeo/citologiaRESUMO
This study was undertaken to explore the effects, on digastric motoneurons, of electrical stimulation of a site within the parvocellular medullary reticular formation (PcRF). This site is located lateral to the hypoglossal nucleus and ventral to the dorsal motor nucleus of the vagus nerve. Within this site are somas of premotor interneurons that project to trigeminal motor nuclei. Stimulation of this site resulted in the generation of IPSPs in digastric motoneurons. We postulate that these IPSPs were due to the activation of a monosynaptic path from the PcRF to digastric motoneurons. The present results, in conjunction with those previously reported which indicate that the PcRF also induces monosynaptic IPSPs in masseter motoneurons, demonstrate that this is a site of origin for the postsynaptic inhibitory control of motoneurons that innervate both jaw opening and closing muscles.