Activity of serotonin-containing neurons in nucleus centralis superior of freely moving cats.

Serotonergic neurons were recorded in the nucleus centralis superior (NCS) in freely moving cats and were initially identified on-line by their slow and regular spontaneous activity (mean 2.55 +/- 0.21 spikes/s). Discharge rates of NCS serotonergic neurons were highest during active waking (AW) (mean 2.94 +/- 0.28 spikes/s), decreased during slow-wave sleep (middle of SWS: mean 1.38 +/- 0.18 spikes/s), and were lowest during REM sleep (mean 0.46 +/- 0.13 spikes/s). The activity of serotonergic NCS neurons did not significantly increase during transient elevations of the EMG during AW but did significantly decrease immediately preceding, and during the occurrence of, SWS spindles. These neurons were responsive to phasic auditory and visual stimuli, with most neurons showing excitatory responses. In response to a small dose of the serotonin-specific agonist 5-methoxy-N,N-dimethyltryptamine (50 micrograms/kg, i.m.), NCS serotonergic neurons responded with a mean decrease in unit activity of 43.9 +/- 6.1%. Among the NCS serotonergic neurons a subpopulation differed from the remaining serotonergic neurons in that they showed a much smaller decrease in unit activity across the sleep-wake cycle and responded with an inhibition of activity to phasic auditory and visual stimuli. The results of this study are compared with those previously reported for serotonergic neurons in the dorsal raphe nucleus, nucleus raphe pallidus, and nucleus raphe magnus of freely moving cats.