Single-unit recordings at dorsal raphe nucleus in the awake-anesthetized rat: spontaneous activity and responses to cutaneous innocuous and noxious stimulations

Publisher Website
Google Scholar
Abstract
Num-iridium wire as the recording electrode. In both the awake and anesthetized conditions, and in agreement with most of the studies performed at the DRN level, we found that a vast majority of the units, displaying small amplitude and long-duration action potentials, possessed a low level of spontaneous activity (0.2–4 Hz). Among these units, found in greater number under pentobarbital, it was possible to establish that this activity was regular or irregular, in accordance with the literature reports. However, as opposed to these studies, we determined that the ‘regularity’ was relative, only noticeable in more or less prolonged phases of activity. In particular, we never recorded the so-called ‘clock-like’ activity, largely reported as an unambiguous criterion for selecting the serotoninergic neurons. In both the awake and anesthetized conditions, the responses of the DRN neurons to peripheral mechanical innocuous and noxious stimulations were observed in only one-half of the units recorded and were weak in comparison to other results that we obtained at the nucleus raphe magnus level in previous studies. When present, these responses were excitation or inhibition, occurring during or after the stimulus application. These results question the direct involvement of the DRN in acute nociception. ∗Corresponding author: J.-L. Oliveras, Unité de Recherches de Physiopharmacologie du Système Nerveux de l'INSERM (U 161), 2 rue d'Alésia, 75014 Paris, France. FAX: (45) 88-13-04. (Received 11 January 1994; revision received 30 March 1994; accepted 8 June 1994.) © Lippincott-Raven Publishers....