0138 DIFFERENTIAL C-FOS EXPRESSION IN GABAERGIC NEURONS OF THE NUCLEUS PONTIS ORALIS DURING WAKEFULNESS AND CARBACHOL-INDUCED ACTIVE SLEEP

Abstract

Previous studies have demonstrated that GABAergic processes in the nucleus pontis oralis (NPO) play an important role in the generation and maintenance of active sleep and wakefulness. However, the location of cell bodies and neural activity of this pontine GABAergic system during wakefulness and active sleep are unknown. Accordingly, the present study was undertaken to determine the distribution of activated GABAergic neurons within the NPO during wakefulness and carbachol-induced active sleep (active sleep-carbachol) using c-Fos immunocytochemistry as a functional marker of neuronal activity. Adult cats that were prepared for monitoring behavioral states were used in this experiment. In the awake group, animals were kept awake for 2 hours following the microinjection of saline into the NPO before being euthanized. In the active sleep-carbachol group, animals were euthanized after prolonged episodes of active sleep that was induced by the microinjection of carbachol into the NPO. Subsequently, brainstem sections were immunostained with a GABA antiserum in addition to a Fos polyclonal antiserum in order to double-label neurons that were both GABAergic and Fos immunoreactive. In awake cats, there was a large number of GABAedrgic neurons that expressed c-Fos in the NPO. These GABA+/c-Fos+ neurons were small to medium-sized and were located mainly within the lateral part of the NPO. In contrast, in active sleep-carbachol cats, the numbers of c-Fos expressing GABAergic neurons were decreased in the NPO. Specifically, there were only few GABAergic neurons in the lateral part of the NPO that expressed c-Fos during active sleep-carbachol. The present results demonstrate that there exists a discrete group of GABAergic neurons in the NPO that are activated during wakefulness and inactivated during active sleep. We therefore suggest that these local GABAergic cells may be the neurons that comprise the pontine GABAergic system which functions to promote wakefulness and suppress active sleep by inhibiting active sleep-generator neurons in the NPO during wakefulness and disinhibiting them during active sleep. NS092383.