VASOACTIVE INTESTINAL POLYPEPTIDE MICROINJECTIONS INTO THE ORAL PONTINE TEGMENTUM ENHANCE RAPID EYE MOVEMENT SLEEP IN THE RAT P. BOURGIN,*‡ C. LEBRAND,* P. ESCOURROU,† C. GAULTIER,† B. FRANC,* M. HAMON* and J. ADRIEN* *INSERM U288, Neurobiologie cellulaire et fonctionnelle, CHU Pitie ´-Salpe ˆtriere, Paris, France †De ´partement de Physiologie, CHU Kremlin Bice ˆtre, Kremlin Bice ˆtre, France Abstract––Rapid eye movement sleep can be elicited in the rat by microinjection of the cholinergic agonist carbachol into the oral pontine reticular nucleus. Intracerebroventricular administration, during the light period, of vasoactive intestinal peptide enhances rapid eye movement sleep in several species. Since this peptide is co-localized with acetylcholine in many neurons in the central nervous system, it was assumed that the oral pontine tegmentum could also be one target for vasoactive intestinal peptide to induce rapid eye movement sleep. This hypothesis was tested by recording the sleep-wakefulness cycle in freely-moving rats injected with vasoactive intestinal peptide or its fragments (1–12 and 10–28) directly into the oral pontine reticular nucleus. When administered into the posterior part of this nucleus, vasoactive intestinal peptide at 1 and 10 ng (in 0.1 μl of saline), but not its fragments, induced a 2-fold enhancement of rapid eye movement sleep during 4 h, at the expense of wakefulness. At the dose of 10 ng, a significant increase in rapid eye movement sleep persisted for up to 8 h. Moreover, when the peptide was injected into the centre of the positive zone, rapid eye movement sleep was enhanced during three to eight consecutive days. These data provide the first evidence that rapid eye movement sleep can be elicited at both short- and long-term by a single intracerebral microinjection of vasoactive intestinal peptide. Peptidergic mecha- nisms, possibly in association with cholinergic mechanisms, within the caudal part of the oral pontine reticular nucleus may play a critical role in the long-term regulation of rapid eye movement sleep in rats.  1997 IBRO. Published by Elsevier Science Ltd. Key words: sleep-wakefulness cycle, nucleus reticularis pontis oralis, vasoactive intestinal peptide, long-term induction. Vasoactive intestinal peptide (VIP) is an amidated 28 amino acid peptide which was originally isolated from porcine duodenum. 64 It is widely distributed in the organism including the brain 40 and belongs to a family of regulatory peptides including secretin, glucagon and growth hormone-releasing hormone. Among endogenous molecules possibly involved in the control of sleep-wakefulness cycle, VIP has been the subject of particular interest because convergent studies showed that i.c.v. administration of this pep- tide enhances rapid eye movement sleep (REMS) in the cat 15,60 and the rabbit. 54 In the rat, VIP injected i.c.v. during the light period enhances REMS whereas it increases both slow wave sleep (SWS) and REMS following its injection during the dark period. 36,55,62 In addition, VIP restores REMS to control levels in rats rendered partially insomniac by p-chlorophenylalanine or chloramphenicol. 62 Con- versely, i.c.v. administration of VIP antiserum 62 or of a competitive VIP antagonist 50 causes a selective decrease in REMS. Finally, it was shown in cats that the cerebrospinal fluid (CSF) obtained from sleep- deprived animals contained VIP, 28 and could restore REMS when injected i.c.v. in recipient cats pre- treated with chloramphenicol, except if the CSF had been immunoneutralized with anti-VIP antibodies prior to the transfer. 16 Although the involvement of VIP in the regulation of sleep is generally acknowledged, its mechanisms of action are as yet unknown. One group 21 suggested a possible role of VIP through the inhibition of the serotoninergic system. Indeed, in rats microinjection of VIP into the nucleus raphe dorsalis (nRD), where serotoninergic neurons which project to the forebrain are located, 12 has been reported to induce an increase in SWS at the dose of 10 ng, and an increase in REMS at the dose of 100 ng. However, since the latter dose was rather large, it can be argued that the ‡To whom correspondence should be addressed. Abbreviations: CSF, cerebrospinal fluid; EEG, electro- encephalogram; EMG, electromyogram; EOG, electro- oculogram; LDT, laterodorsal tegmentum; LTP, long-term potentiation; mPRF, medial pontine reticular formation; NGF, nerve growth factor; nRD, nucleus raphe dorsalis; PnC, caudal pontine reticular nucleus; PnO, oral pontine reticular nucleus; PPT, pediculopontine tegmentum; PRF, pontine reticular formation; PRL, prolactin; REMS, rapid eye movement sleep; SWS, slow wave sleep; VIP, vasoactive intestinal peptide; W, wakefulness. Pergamon Neuroscience Vol. 77, No. 2, pp. 351–360, 1997 Copyright  1997 IBRO. Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved 0306–4522/97 $17.00+0.00 PII: S0306-4522(96)00455-1 351