BRAIN RESEARCH ELSEVIER Brain Research 686 (1995) 150-159 Research report Sleep permissive components within the dorsal raphe nucleus in the rat B. E1 Karl *, L. Leger, S. Seguin, M. Jouvet, R. Cespuglio Department of Experimental Medicine, 1NSERM U 52, CNRS-URA 1195, Claude Bernard University, 69373 Lyon Cedex 08, France Accepted 14 March 1995 Abstract Two peptides known for their hypnogenic properties, CLIP (corticotropin-like intermediate lobe peptide or ACTH 18-39) or VIP (vasoactive intestinal polypeptide), were injected locally into the nucleus raphe dorsalis (nRD) of rats pretreated with p-chlorophenyl- alanine (PCPA). During the dark period, the PCPA insomnia was primarily associated with a reduction in paradoxical sleep (PS), whereas both slow wave sleep (SWS) and PS were decreased during the light period. Immunohistochemistry of serotonin in PCPA-pretreated animals indicated a clear disappearance of 5-HT fibers in the basal hypothalamus and the nRD as compared to control animals. Local injections of CLIP or VIP in the nRD restored PS and SWS. The positive injection sites corresponded to the anatomical distribution of either CLIP or VIP fibers, i.e., the entire nRD for VIP and the antero-dorsal part of this nucleus for CLIP. The sleep effects obtained in PCPA-pretreated rats involve a non-5-HT sleep permissive component within the nRD upon which these injected peptides act. Keywords: Rat; Sleep; Wake; Nucleus raphe dorsalis; Local injection; Corticotropin-like intermediate lobe peptide; Vasoactive intestinal polypeptide; p-Chlorophenylalanine 1. Introduction That certain neuropeptides play a role in sleep regula- tory processes is now generally accepted since they are sleep inducing when administered by intraperitoneal (i.p.), intravenous (i.v.) or intracerebroventricular (i.c.v.) routes. Among these peptides, it is reported that i.c.v, administra- tion of vasoactive intestinal polypeptide (VIP) at a 10 ng dose produces an increase in slow wave sleep (SWS), whereas at 100 ng paradoxical sleep (PS) is also enhanced [16,39]. The administration of corticotropin-like intermedi- ate lobe peptide (CLIP or ACTH18-39) during either the dark [11] or light periods [47] also induces a PS increase. Despite the common sleep inducing property of both of the above peptides, their anatomical distribution within the brain is very different. With respect to VIP, it is now known that 4 major neuronal VIP systems are present in brain whose perikarya are contained within the cortex, the limbic system, the hypothalamus (suprachiasmatic nucleus) and the rhombencephalic area (central grey, raphe nuclei, medulla). From these different groups of perikarya, the axonal processes produce a VIP innervation of almost the * Corresponding author. Fax: (33) 7877-7172. 0006-8993/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0006-8993(95)00390-8 entire brain. It must be emphasized that the nucleus raphe dorsalis (nRD), an area of interest for the present report, contains VIP perikarya in its medio-dorsal part and widespread VIP axonal processes throughout the entire nucleus. These anatomical aspects have been demonstrated either by immunochemistry [18,42] or by VIP radio-im- muno-assay [17]. The anatomical distribution of the proopiomelanocortin (POMC) perikarya is more limited. These perikarya are mainly located in the basal hypothalamus (within and around the arcuate nuleus). Only one additional small group has been described in the rat within the nucleus of the solitary tract [28]. In contrast to VIP, the CLIP axonal processes emerging from both of these groups of perikarya are less numerous and do not reach the cortex. Instead, they remain limited to the hypothalamus, thalamus, limbic system, mesenchephalon and rhombencephalon [25,35]. The anterior and dorsal part of the nRD receives a strong POMC innervation arising exclusively from the basal hy- pothalamic group of perikarya [48]. Some of the axonal POMC nerve endings have been demonstrated to be in contact with nRD neurons [27]. Taking into account the above anatomical data and that the nRD is thought to be a sleep permissive structure gating phasic sleep events through its serotoninergic com- ponent [23] and tonic sleep phenomena through a non