Response of dopaminergic neurons in cat to auditory stimuli presented across the sleep-waking cycle

The response of dopaminergic neurons of the substantia nigra pars compacta to auditory clicks continuously presented across the sleep-wake cycle was studied in cats. The initial excitatory followed by inhibitory response to the click which occurred during quiet waking diminished as the cat progressed into slow-wave sleep and was absent during REM sleep. Upon awakening from REM sleep, dopamine neurons once again displayed an excitatory/inhibitory response to the clicks, implying that the decrease across the sleep-wake cycle was not attributable to long-term habituation.