Cuneiform neurons activated during cholinergically induced active sleep inthe cat

In the present study, we report that the cuneiform (Cun) nucleus, a brainst em structure that before now has not been implicated in sleep processes, ex hibits a large number of neurons that express c-fos during carbachol-induce d active sleep (AS-carbachol). Compared with control (awake) cats, during A S-carbachol, there was a 671% increase in the number of neurons that expres sed c-fos in this structure. Within the Cun nucleus, three immunocytochemic ally distinct populations of neurons were observed. One group consisted of GABAergic neurons, which predominantly did not express c-fos during AS-carb achol. Two other different populations expressed c-fos during this state. O ne of the Fos-positive (Fos(+)) populations consisted of a distinct group o f nitric oxide synthase (NOS)-NADPH-diaphorase (NADPH-d)-containing neurons ; the neurotransmitter of the other Fos(+) population remains unknown. The Cun nucleus did not contain cholinergic, catecholaminergic, serotonergic, o r glycinergic neurons. On the basis of neuronal activation during AS-carbac hol, as indicated by c-fos expression, we suggest that the Cun nucleus is i nvolved, in an as yet unknown manner, in the physiological expression of ac tive sleep. The finding of a population of NOS-NADPH-d containing neurons, which were activated during AS-carbachol, suggests that nitrergic modulatio n of their target cell groups is likely to play a role in active sleep-rela ted physiological processes.