VASOACTIVE INTESTINAL POLYPEPTIDE MICROINJECTIONS INTO THE ORAL PONTINE TEGMENTUM ENHANCE RAPID EYE-MOVEMENT SLEEP IN THE RAT

Rapid eye movement sleep can be elicited in the rat by microinjection of the cholinergic agonist carbachol into the oral pontine reticular n ucleus. Intracerebroventricular administration, during the light perio d, of vasoactive intestinal peptide enhances rapid eye movement sleep in several species. Since this peptide is co-localized with acetylchol ine in many neurons in the central nervous system, it was assumed that the oral pontine tegmentum could also be one target for vasoactive in testinal peptide to induce rapid eye movement sleep. This hypothesis w as tested by recording the sleep-wakefulness cycle in freely-moving ra ts injected with vasoactive intestinal peptide or its fragments (1-12 and 10-28) directly into the oral pontine reticular nucleus. When admi nistered into the posterior part of this nucleus, vasoactive intestina l peptide at 1 and 10 ng (in 0.1 mu l of saline), but not its fragment s, 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 i ncrease in rapid eye movement sleep persisted for up to Sh. Moreover, when the peptide was injected into the centre of the positive zone, ra pid eye movement sleep was enhanced during three to eight consecutive days. These data provide the first evidence that rapid eye movement sl eep can be elicited at both short- and long-term by a single intracere bral microinjection of vasoactive intestinal peptide. Peptidergic mech anisms, possibly in association with cholinergic mechanisms, within th e caudal part of the oral pontine reticular nucleus may play a critica l role in the long-term regulation of rapid eye movement sleep in rats . (C) 1997 IBRO.