Single unit activity of locus coeruleus neurons in the freely moving cat. I. During naturalistic behaviors and in response to simple and complex stimuli.

The single unit activity of presumed noradrenergic (NE) neurons in the area of the locus coeruleus (LC) was recorded in freely moving cats. Consistent with previous reports, the activity of LC neurons was found to be state dependent: active waking greater than quiet waking greater than slow wave sleep greater than REM sleep (virtually silent). The activity of these neurons showed no relationship to movement per se. In response to simple sensory stimulation, LC units showed a short latency, short duration excitatory response. In response to a variety of non-noxious naturalistic stimuli, e.g. rats, food and a conspecific, LC unit activity did not increase above an active waking baseline. However, in response to noxious stimuli, e.g. pinches, visual threats, emesis, and forced treadmill running, LC unit activity increased above that during active waking and reached its highest levels. These data, in conjunction with those in the following report, are consistent with a general role for NE-LC neurons in the organism's adaptive response to environmental and physiological challenges.