Discharge of neurons in the parabrachial pons related to the cardiac cycle: Changes during different sleep-waking states

Neuronal activity in the nucleus parabrachialis medialis (NPBM) was examined in unanesthetized, unrestrained cats during each sleep-waking state. Discharge related to the cardiac cycle was assessed by calculating cross-correlation functions between neuronal and cardiac events (using the peak of the EKG 'R' wave as a reference). Of the 60 NPBM neurons examined, the activity of 20 cells showed discharge relationships to the cardiac cycle. Firing of NPBM neurons in phase with the cardiac cycle was observed during each sleep-waking state, but was most apparent during awake (AW) and rapid eye movement (REM) sleep states. State-related changes in the correlation of NPBM neuronal discharge to the cardiac cycle included variations in the extent of rhythmic modulation of activity, and shifts in the phase relationship to the cardiac reference. The predominant phase relationship of NPBM neuronal activity to the cardiac cycle was an increased probability of discharge during a period ranging from 50 msec preceding to 50 msec following the peak of the EKG 'R' wave.