FOS AND SEROTONIN IMMUNOREACTIVITY IN THE RAPHE NUCLEI OF THE CAT DURING CARBACHOL-INDUCED ACTIVE SLEEP - A DOUBLE-LABELING STUDY

The microinjection of carbachol into the nucleus pontis oralis produce s a state which is polygraphically and behaviorally similar to active sleep (rapid eye movement sleep). In the present study, using double-l abeling techniques for serotonin and the protein product of c-fos (Fos ), we sought to examine whether immunocytochemically identified seroto nergic neurons of the raphe nuclei of the cat were activated, as indic ated by their expression of c-fos, during this pharmacologically-induc ed behavioral state (active sleep-carbachol). Compared with control ca ts, which were injected with saline, active sleep-carbachol cats exhib ited a significantly greater number of c-fos-expressing neurons in the raphe dorsalis, magnus and pallidus. Whereas most of the c-fos-expres sing neurons in the raphe dorsalis were small, those in the raphe magn us were medium-sized and in the raphe pallidus they were small and med ium-sized. The mean number of serotonergic neurons that expressed c-fo s (i.e. double-labeled cells) was similar in control and active sleep- carbachol cats. These data indicate that there is an increased number of non-serotonergic, c-fos-expressing neurons in the raphe dorsalis, m agnus and pallidus during the carbachol-induced state. It is suggested that during both active sleep-carbachol and naturally-occurring activ e sleep (i) the small-sized, non-serotonergic, c-fos-expressing neuron s in the raphe dorsalis and in the raphe pallidus may function as loca l inhibitory interneurons, (ii) the medium-sized, non-serotonergic, c- fos-expressing neurons in the raphe magnus may participate in the modu lation of sensory input, and (iii) the medium-sized, non-serotonergic, c-fos-expressing neurons in the raphe pallidus may participate in the modulation of motor and autonomic functions.