Sleep-related increase in activity of mesopontine neurons in old rats.

Relationships between age-related changes in sleep patterns and neuronal activity have received scant attention. In the present study, reticularis pontis oralis (RPO) and ventral tegmental nucleus of Gudden (VTN) neurons were recorded in unanesthetized restrained young (3 months) and old (23 months) Sprague-Dawley rats during wakefulness (W), slow wave sleep (SWS) and rapid eye movement (REM) sleep. All RPO neurons displayed a tonic activity. Firing rates were similar during W in young and old rats. In contrast, firing rates were higher during SWS in old rats (P < 0.001). In both young and old rats, firing rates increased significantly during REM sleep as compared to W and SWS but this increase was markedly greater in old rats. Neurons recorded from VTN displayed bursting activity at theta frequencies during W and REM sleep. The frequency of VTN bursting neurons was higher during REM sleep as compared to W in both groups of age. This difference was significantly more pronounced in old as compared to young rats (P < 0.001). Sleep-related hyperactivity of pontine neurons is discussed in terms of a possible deficit in inhibitory processes in old rats.