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PubMed2001

Discharge patterns of neurons in the medial pontobulbar reticular formation during fictive mastication in the rabbit.

In this study, we describe functional characteristics of neurons forming networks generating oral ingestive motor behaviours. Neurons in medial reticular nuclei on the right side of the brainstem between the trigeminal and hypoglossal motor nuclei were recorded in anaesthetized and paralysed rabbits during two types of masticatory-like motor patterns induced by electrical stimulation of the left (contralateral) or right (ipsilateral) cortical masticatory areas. Sixty-seven neurons in nucleus reticularis pontis caudalis (nPontc), nucleus reticularis parvocellularis (nParv), and nucleus reticularis gigantocellularis (Rgc) were studied. These were classified as phasic or tonic depending on their firing pattern during the fictive jaw movement cycle. Phasic neurons located in the dorsal part of nPontc were active during the jaw opening phase, whilst those in dorsal nParv tended to fire during the closing phase. In most neurons, burst duration and firing frequency changed between the two motor patterns, but there was little change in phase of firing. Tonic units were mainly recorded in the ventral half of nPontc, and at the junction between Rgc and caudal nParv. Cortical inputs with short latency from the contralateral masticatory area were more frequent in phasic (82%) than tonic (44%) neurons, whilst inputs from the ipsilateral cortex were equal in the two subgroups (57% and 56%). Phasic neurons had significantly shorter mean contralateral than ipsilateral cortical latencies, whilst there was no difference among tonic neurons. Intra- and perioral primary afferent inputs activated both types of neurons at oligo-synaptic latencies. Our results show that subpopulations of neurons in medial reticular nuclei extending from the caudal part of the trigeminal motor nucleus to the rostral third of the hypoglossal motor nucleus are active during the fictive masticatory motor behaviour. Unlike masticatory neurons in the lateral tegmentum, the medial subpopulations are spatially organized according to discharge pattern.

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PubMed1975

Influence of increasing doses of pentobarbital on the mesencephalic reticular formation in rats. Spontaneous firing of neuronal pairs and activity evoked by polarization.

In rats immobilized by D-tubocurarine the spontaneous activity in pairs of mesencephalic reticular neurons was recorded by means of one microelectrode and differentiated by amplitude discriminators. Spontaneous activity of neuronal pairs and activity evoked by electrical polarization of cells (5-235 nA) through the recording microelectrode was evaluated in the curarized state and after cumulative doses of 15 mg/kg pentobarbital. No correlation between mean interspike interval duration in pairs of adjacent neurons was found in the unanesthetized state. After pentobarbital a slight dependence was observed between the values. Furthermore, it is probable that adjacent neurons will both cease firing at the same dose of pentobarbital. Cross-correlation of the spike trains of two adjacent neurons was found in the range of minus 10 msec to plus 10 msec (which is probably an expression of direct interaction or of a common input) in 6 of 50 pairs analyzed in the unanesthetized state. This dependence fully disappeared after 15-30 mg/kg of pentobarbital. After 15 mg/kg of pentobarbital in 17 recorded pairs (out of 50 analyzed) peaks in the cross-correlograms appeared in a range of about 100 msec and at a distance of 150-300 msec. Such a relationship was already present in 4 pairs of neurons in the unanesthetized state. The similarity of autocorrelation and cross-correlation histograms in this case favors the hypothesis that spontaneous activity of many mesencephalic reticular neurons is synchronized after pentobarbital administration. In many reticular neurons the firing may be evoked by direct cell polarization through the recording microelectrode even at cumulative doses of pentobarbital much higher than those sufficient to block spontaneous activity.

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