Cardiovascular and baroreceptor functions of the paratrigeminal nucleus for pressor effects 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 baroreflex response, both resting cardiovascular parameters and reflex responses were evaluated during phenylephrine-produced pressor responses in non-anaesthetized rats with or without bilateral chemical Pa5 ablation. The Pa5-ablated animals, in contrast to the Pa5-intact control animals, presented increased resting arterial pressure (115+/-4 vs. 100+/-3 mm Hg), decreased heart (293+/-10 vs. 315+/-7 bpm) and increase of the respiratory (104+/-3 vs. 94+/-5 rpm) rates, larger pressor responses and reduced baroreflex index (1.6+/-0.2 vs. 2.8+/-0.2, p<0.05). The cardiovascular changes, compatible to those produced by nucleus of the solitary tract (NTS) lesions in non-anaesthetized rats, indicate a reduction of both the sympathetic and cardiac components of the baroreflex response. Further analyses showed the Pa5 mediates reflex responses to smaller blood pressure increases, while the NTS would be predominantly active in surges over 40 mm Hg. Thus, the integrity of the Pa5 is important for resting blood pressure maintenance as for a full baroreceptor response.