Discharge rate profiles of paratrigeminal nucleus neurons throughout a pressor event in non-anaesthetized rats

Located in the lower brainstem, the paratrigeminal nucleus (Pa5) is related to cardiorespiratory autonomic reflex functions. To characterize the structures' role in blood pressure regulation and the cardiovascular reflex responses Pa5 unit activity was evaluated during a phenylephrine-produced pressor response in non-anaesthetized rats by means of simultaneous many-unit recording. Ninety five percent of the identified Pa5 responded to baroreceptor stimulation, 77% increasing and 23% decreasing firing rates. Cross-correlation analysis of neuron electrical behavior referenced to the heart beat event revealed that 65% of the featured cardiac cycle-locked rhythmic activity. The identification of neurons that change firing rates in response to increases of arterial pressure with cardiac cycle-locked rhythmic activity, further supports for a role for the nucleus in moment to moment control of blood pressure. The largest changes in firing rate occurred in the units with low resting firing rates in response to the ascending phase of the pressor event. Thus, the group displaying both cardiac cycle-locked and other rhythmic activities within the ranges of cardiac and respiratory rates or arterial pressure low frequencies, is probably the most influential regarding homoeostatic reflex responses. The findings advance the notion that the dynamic control of blood pressure involves lower brainstem integration of cardiac and respiratory reflexes.