RESUMEN
Micropipette recording with juxtacellular Neurobiotin ejection, linked micropipette-microwire recording, and antidromic and orthodromic activation from the ventral tegmental area and locus coeruleus were used to identify hypocretin (Hcrt) cells in anesthetized rats and develop criteria for identification of these cells in unanesthetized, unrestrained animals. We found that Hcrt cells have broad action potentials with elongated later positive deflections that distinguish them from adjacent antidromically identified cells. They are relatively inactive in quiet waking but are transiently activated during sensory stimulation. Hcrt cells are silent in slow wave sleep and tonic periods of REM sleep, with occasional burst discharge in phasic REM. Hcrt cells discharge in active waking and have moderate and approximately equal levels of activity during grooming and eating and maximal activity during exploratory behavior. Our findings suggest that these cells are activated during emotional and sensorimotor conditions similar to those that trigger cataplexy in narcoleptic animals.
Asunto(s)
Potenciales de Acción/fisiología , Conducta Exploratoria/fisiología , Péptidos y Proteínas de Señalización Intracelular/fisiología , Neuronas/fisiología , Neuropéptidos/fisiología , Animales , Estimulación Eléctrica/métodos , Locus Coeruleus/citología , Locus Coeruleus/fisiología , Masculino , Orexinas , Ratas , Ratas Wistar , Área Tegmental Ventral/citología , Área Tegmental Ventral/fisiologíaRESUMEN
The pontine oral reticular nucleus, gigantocellular reticular nucleus (Gi) and dorsal paragigantocellular nucleus (DPGi) of the medulla are key elements of a brainstem-reticulospinal inhibitory system that participates in rapid eye movement (REM) sleep atonia. Our recent study has shown that excitation of these brainstem nuclei in decerebrate rats inhibits locus coeruleus cells and the midbrain locomotor region neurons related to muscle tone facilitation. In the present study we have examined the influences of electrical and chemical stimulation of Gi and DPGi inhibitory sites on the activity of neurons located in the magnocellular part of the red nucleus (RMC), a cell group that participates in both the tonic and phasic regulation of motor output. A total of 192 RMC neurons were recorded in precollicular-premammillary decerebrate rats with muscle rigidity and induced locomotion. Thirty-three RMC neurons were identified antidromically as rubrospinal (RMC-spinal) cells by stimulation of the contralateral dorsolateral funiculus at the L2 level. A total of 141 RMC neurons (88.7 %) and all RMC-spinal neurons were inhibited during electrical stimulation of Gi and DPGi inhibitory sites. This cessation of activity was correlated with bilateral muscle atonia or blockage of locomotion. Six RMC cells (3.8 %) were excited (224 +/- 50 %, n = 6, minimum = 98, maximum = 410, P < 0.05) and 11 cells (7 %) gave no response to Gi and DPGi stimulation. Microinjections of kainic acid (100 microM, 0.2 microl) into Gi and DPGi inhibitory sites, previously identified by electrical stimulation, produced a short-latency (35 +/- 3.5 s, n = 11) decrease of rigid hindlimb muscle tone and inhibition of all tested RMC (n = 7) and RMC-spinal (n = 5) neurons. These results, combined with our recent published data, suggest that inhibition of motor function during activation of the brainstem inhibitory system is related to both the descending inhibition of spinal motoneurons and suppression of activity in supraspinal motor facilitatory systems. These two mechanisms acting synergistically may cause generalized motor inhibition during REM sleep and cataplexy.
Asunto(s)
Bulbo Raquídeo/fisiología , Neuronas/fisiología , Núcleo Rojo/fisiología , Animales , Estado de Descerebración , Estimulación Eléctrica , Electrofisiología , Ácido Kaínico/administración & dosificación , Microinyecciones , Actividad Motora/fisiología , Tono Muscular/fisiología , Inhibición Neural/fisiología , Neuronas/efectos de los fármacos , Ratas , Núcleo Rojo/efectos de los fármacos , Médula Espinal/efectos de los fármacos , Médula Espinal/fisiologíaRESUMEN
Hypocretin (Hcrt or orexin) somas are located in the hypothalamus and project widely to forebrain and brainstem regions, densely innervating monoaminergic and cholinergic cells. Loss of Hcrt function results in the sleep disorder narcolepsy. However, the normal pattern of Hcrt release across the sleep-wake cycle is unknown. We monitored Hcrt-1 release in the basal forebrain, perifornical hypothalamus, and locus ceruleus (LC) across the sleep-wake cycle using microdialysis in freely moving cats and a sensitive solid phase radioimmunoassay. We found that the peptide concentration in dialysates from the hypothalamus was significantly higher during active waking (AW) than during slow-wave sleep (SWS). Moreover, Hcrt-1 release was significantly higher during rapid eye movement (REM) sleep than during SWS in the hypothalamus and basal forebrain. We did not detect a significant difference in release across sleep-waking states in the LC, perhaps because recovered levels of the peptide were lower at this site. Because there was a trend toward higher levels of Hcrt-1 release during AW compared with quiet waking (QW) in our 10 min dialysis samples, we compared Hcrt-1 levels in CSF in 2 hr AW and QW periods. Hcrt-1 release into CSF was 67% higher during AW than during QW. Elevated levels of Hcrt during REM sleep and AW are consistent with a role for Hcrt in the central programming of motor activity.
Asunto(s)
Encéfalo/metabolismo , Proteínas Portadoras/metabolismo , Péptidos y Proteínas de Señalización Intracelular , Neuropéptidos/metabolismo , Sueño , Vigilia , Animales , Proteínas Portadoras/líquido cefalorraquídeo , Proteínas Portadoras/inmunología , Gatos , Femenino , Hipotálamo/metabolismo , Cinética , Locus Coeruleus/metabolismo , Masculino , Neuropéptidos/líquido cefalorraquídeo , Neuropéptidos/inmunología , Orexinas , Periodicidad , Prosencéfalo/metabolismo , RadioinmunoensayoRESUMEN
Orexins/hypocretins are synthesized in neurons of the perifornical, dorsomedial, lateral, and posterior hypothalamus. A loss of hypocretin neurons has been found in human narcolepsy, which is characterized by sudden loss of muscle tone, called cataplexy, and sleepiness. The normal functional role of these neurons, however, is unclear. The medioventral medullary region, including gigantocellular reticular nucleus, alpha (GiA) and ventral (GiV) parts, participates in the induction of locomotion and muscle tone facilitation in decerebrate animals and receives moderate orexinergic innervation. In the present study, we have examined the role of orexin-A (OX-A) in muscle tone control using microinjections (50 microM, 0.3 microl) into the GiA and GiV sites in decerebrate rats. OX-A microinjections into GiA sites, previously identified by electrical stimulation as facilitating hindlimb muscle tone bilaterally, produced a bilateral increase of muscle tone in the same muscles. Bilateral lidocaine microinjections (4%, 0.3 microl) into the dorsolateral mesopontine reticular formation decreased muscle rigidity and blocked muscle tone facilitation produced by OX-A microinjections into the GiA sites. The activity of cells related to muscle rigidity, located in the pedunculopontine tegmental nucleus and adjacent reticular formation, was correlated positively with the extent of hindlimb muscle tone facilitation after medullary OX-A microinjections. OX-A microinjections into GiV sites were less effective in muscle tone facilitation, although these sites produced a muscle tone increase during electrical stimulation. In contrast, OX-A microinjections into the gigantocellular nucleus (Gi) sites and dorsal paragigantocellular nucleus (DPGi) sites, previously identified by electrical stimulation as inhibitory points, produced bilateral hindlimb muscle atonia. We propose that the medioventral medullary region is one of the brain stem target for OX-A modulation of muscle tone. Facilitation of muscle tone after OX-A microinjections into this region is linked to activation of intrinsic reticular cells, causing excitation of midbrain and pontine neurons participating in muscle tone facilitation through an ascending pathway. Moreover, our results suggest that OX-A may also regulate the activity of medullary neurons participating in muscle tone suppression. Loss of OX function may, therefore, disturb both muscle tone facilitatory and inhibitory processes at the medullary level.