Activity of mesencephalic dopamine and non-dopamine neurons across stages of sleep and walking in the rat

Single unit activity of dopamine and non-dopamine neurons in the substantia nigra and ventral tegmental area was recorded across stages of sleep and waking in the rat. These stages consisted of slow wave sleep (SWS), rapid eye movement (REM) sleep, awake-quiet (AQ) and awake-moving (AM). The dopamine neurons showed no change in mean firing rate across the stages of sleep or waking. During REM sleep, however, the dopamine cells fired with a more variable interspike interval than during SWS. In contrast, non-dopamine neurons in the substantia nigra and ventral tegmental area showed large increases in firing rate in REM compared to SWS, and in AM compared to AQ, without showing changes in interspike interval variability. In conclusion, whereas other monoaminergic neurons and various cortical and subcortical neurons exhibit marked changes in firing rate across the stages of sleep and waking, the dopamine neurons are unique in their lack of change in firing rate across stages.