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

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 +/- 1.9 mmHg; after 20 nmol L-Glu: 139 +/- 4.5 mmHg, N = 12, P<0.05) and respiratory rate (control: 81 +/- 3.5 breaths/min; after 10 nmol L-Glu: 92 +/- 3 breaths/min, P<0.05; after 20 nmol L-Glu: 104 +/- 5 breaths/min, N = 6, P<0.05). The subsequent anesthesia with urethane caused a significant increase in basal respiratory frequency (conscious: 81 +/- 3.5 breaths/min; under urethane: 107 +/- 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.