1. Discharge pattern has been characterized by autocorrelation analysis of stationary portions of extracellularly recorded discharge trains of cat pontine brain stem neurons during spontaneously occurring desynchronized sleep episodes. 2. Neurons localized to the area implicated in control of the desynchronized phase of sleep, the gigantocellular tegmental field (FTG), show the most phasic or clustered discharge pattern, as evinced by initial peaks in the autocorrelations. At the peak, the FTG population average discharge probability is 3 times that expected had the discharges been evenly distributed over time. The initial peak extends beyond a lag of 3 s, indicating runs of clustered discharge extending beyond this duration. Neurons in other reticular tegmental fields, the tegmental reticular nucleus and pontine gray, show a more sustained or tonic discharge pattern. 3. Discharge patterns of a given cell are consistent from one desynchronized sleep episode to the next; units with phasic discharge patterns remain phasic, and tonic patterns remain tonic. 4. There is a three-way correlation among FTG units recorded at sites with many giant cells, units with high discharge rate increases on transition to desynchronized sleep, and units with a markedly phasic discharge pattern. This implicates the giant cells as the source of both the distinctive discharge rate and pattern changes of neurons during desynchronized sleep. 5. Stereotyped, regular discharge patterns are not characteristic of FTG or other units, suggesting they are not pacemakers and that endogenous activation of pacemaker cells is unlikely to be a mechanism for generation of the marked discharge rate increases on transition to desynchronized sleep that are found in FTG units. The irregular, clustered discharge pattern of FTG is more compatible with generation of discharge rate increases through interaction with other cells. The markedly phasic discharge of FTG units is also consistent with a driving role in generation of the phasic electrophysiologic events of desynchronized sleep.
Single-cell activity recorded from the brain stem dorsal raphe nucleus (DRN) of cats showed a regular firing pattern during wakefulness (2-3 spikes/s), decreased activity during slow-wave or synchronized sleep (1 spike/s), and cessation of regular discharge during desynchronized sleep (0.05 spikes/s). DRN discharge was negatively correlated with the onset and maintenance of the polycyclic desynchronized sleep rhythm. These findings were derived from analyses of DRN firing rate sampled during different behavioral states. The present time-course analyses of DRN discharge described for the first time the period, amplitude, and phase characteristics of DRN activity relative to the timing of behavioral states that comprise the complete sleep cycle. The time course of both DRN discharge and the occurrence of wakefulness, slow-wave (S) sleep, transition, and desynchronized (D) sleep were behaviorally manipulated. Forced locomotor activity imposed by a treadmill task shortened the period length of the sleep cycle and the duration of the DRN discharge cycle. The magnitude and direction of these shifts in period length were consistent across multiple sleep cycles, and there was a high degree of coherence between the period length of the sleep cycle and the DRN discharge profiles. The DRN discharge rate also displayed phase dependence within S and D sleep. These results support the hypothesis that the DRN has a physiological role in regulating the timing of the ultradian sleep cycle.
1. Reticulospinal neurons were identified by antidromic invasion from spinal cord electrodes chronically implanted at C4 in cats. 2. Most of the neuronal population studied lay within the medial portion of the giant cell field from the anterior pontine and to the anterior medullary reticular formation (FTG). A few cells were found in the tegmental reticular nucleus (TRC) which has not previously been known to project to the spinal cord. 3. Extracellular action potentials from the neuronal somata of the identified neurons were recorded continuously throughout naturally occurring sleep-waking cycles. 4. The identified reticulospinal neurons shared three properties, suggesting a generator function in desynchronized sleep (D) (with previously recorded but unidentified FTG neurons): selectivity (or concentration of discharge in D); tonic latency (or firing rate increases beginning several minutes prior to D); and phasic latency (or firing rate increases occurring prior to eye movements within D). 5. The location, discharge properties, and spinal projections of FTG neurons are, thus, all consistent with the hypothesis that they may directly mediate some of the descending excitatory and inhibitory influences on spinal reflex pathways in desynchronized sleep.
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