Cardiovascular and respiratory responses to microinjection of L-glutamate into the caudal pressor area in conscious and anesthetized rats

ABSTRACT

The role of the caudal pressor area (CPA) in the maintenance of vasomotor tonus in anesthetized and decerebrate animals has been clearly established. In conscious animals, however, the participation of CPA in the cardiovascular control remains to be fully elucidated. In the present study, unilateral L-glutamate (L-Glu) (10 and/or 20 nmol/70 nl) microinjection into CPA, in conscious male Wistar rats (250-280 g) caused a significant increase in mean arterial blood pressure (MAP; control 112 + or - 1.9 mmHg; after 20 nmol L-Glu 139 + or - 4.5 mmHg, N = 12, P<0.05) and respiratory rate (control 81 + or - 3.5 breaths/min; after 10 nmol L-Glu 92 + or - 3 breaths/min, P<0.05; after 20 nmol L-Glu 104 + or - 5 breaths/min, N = 6, P<0.05). The subsequent anesthesia with urethane caused a significant increase in basal respiratory frequency (conscious 81 + or - 3.5 breaths/min; under urethane 107 + or - 1.3 breaths/min, N = 6, P<0.05). Anesthesia also significantly attenuated L-Glu-evoked pressor (conscious deltaMAP = +27 mmHg; anesthetized deltaMAP = +18 mmHg, P<0.05) and respiratory responses. These results suggest that glutamatergic receptors in the CPA are involved in cardiovascular and respiratory modulation in conscious rats