BRAIN-STEM CARBACHOL INJECTIONS IN THE URETHANE-ANESTHETIZED RAT PRODUCE HIPPOCAMPAL THETA-RHYTHM AND CORTICAL DESYNCHRONIZATION - A COMPARISON OF PEDUNCULOPONTINE TEGMENTAL VERSUS NUCLEUS PONTIS ORALIS INJECTIONS

Previous research has demonstrated that brainstem injections of acetyl choline agonists (e.g., carbachol) produced electrophysiological indic ators of rapid-eye-movement (REM) sleep in the cat. Recent reports now indicate that this phenomenon may hold true for rats as well. Relativ ely few reports, however, have examined the effect of these injections on REM indicators in the anesthetized rat, a preparation useful for e lucidating underlying neurobiological mechanisms controlling REM sleep processes. The present study compared the effect of injections of car bachol (5 mu g in 250 nl) into the pedunculopontine tegmental nucleus (PPTg) or the nucleus pontis oralis (NPO) on two tonic indicators of R EM sleep in the urethane-anesthetized rat. Namely, changes in the hipp ocampal EEG and in the cortical EEG, Carbachol injections into either site produced a change in both the hippocampal EEG and cortical EEG to a REM-like state at short latencies. The length of these changes (dur ation of effect), however, was site-dependent. Thus, PPTg carbachol in jections induced significantly longer lasting effects in both the hipp ocampal and cortical EEG than did NPO injections. The results suggest that brainstem carbachol injections in rats, as in cats, may provide a useful model for investigating tonic REM sleep processes. (C) 1998 El sevier Science B.V. All rights reserved.