Sleep in the cat: raphe dorsalis and vasotocin

To determine the relationship between the raphe nuclei and the sleep-inducing pineal peptide arginine vasotocin (AVT), we investigated the hypnogenic effects of intraventricularly administered AVT in adult cats with electrolytic lesions performed either in the raphe dorsalis nucleus (RDN) or the raphe pontis nucleus (RPN). The following results were observed: (a) RDN lesions produced a quantitative decrease in NREM sleep and a transitory increase in REM sleep and narcoleptic-like alterations of REM sleep in the first 2-5 postoperative days. On the eighth postoperative day, normal (prelesion) sleep parameters were restored. (b) RDN lesions prevented AVT from inducing its hypnogenic effects during the first 5 postoperative days, but the AVT hypnogenic effects reappeared when sleep parameters reached prelesion levels. (c) Although the RPN lesions produced a slight but statistically significant REM sleep decrease, this did not prevent AVT from inducing its hypnogenic effects. We conclude that (a) the anatomic site of AVT action within the brain may be related to RDN; (b) at least some of the sleep disturbances observed after RDN lesions (narcolepsy) may be due to damage of the AVT site of action or to modifications of AVT synthesis or release; (c) RDN belongs to a large neural circuit that includes the pineal gland and habenula, a circuit that may play an important role in the sleep-wake cycle by "fine-tuning" sleep mechanisms. We hypothesize that AVT could be the specific inhibitory neuromodulator of this neural circuit.