Periventricular anteroventral third ventricle lesions diminish the pressor response produced by systemic injection of the N-methyl-D-aspartate receptor antagonist MK-801

Angiotensin and NMDA receptors in the median preoptic nucleus mediate hemodynamic response patterns to stress

The brain renin-angiotensin system plays an important role in the regulation of arterial pressure in response to stress, in part due to activation of AT1 receptors in the hypothalamic median preoptic nucleus (MnPO) by endogenous angiotensin II (ANG II). N-methyl-d-aspartate (NMDA) receptors are also involved in the angiotensinergic signaling pathway through the MnPO. We investigated whether AT1 and NMDA receptors in the MnPO are responsible for variable hemodynamic response patterns to stress. Cocaine or startle with cold water evoked a pressor response in Sprague-Dawley rats due, in some rats [vascular responders (VR)], to a large increase in systemic vascular resistance (SVR) and, in other rats [mixed responders (MR)], to small increases in SVR and cardiac output (CO). Microinjection of the GABAA agonist muscimol into the MnPO to block synaptic transmission attenuated the cocaine- or stress-induced increase in SVR and the decrease in CO seen in VR without altering either response in MR. Likewise, administration of either an AT1 receptor antagonist, losartan, or an NMDA receptor antagonist, MK-801, attenuated the increase in SVR and the decrease in CO in VR in response to either cocaine (losartan and MK-801) or startle with cold water (losartan) without altering either response in MR. We propose that the MnPO is responsible for greater SVR responses in VR and that AT1 and NMDA receptors play an important role in greater SVR responses in VR. These data provide additional support for the critical role of the MnPO in cardiovascular responses to stress.

Effects of chronic lesions of the anteroventral region of the third ventricle on cardiac beta-adrenoceptor function in conscious rats

This study examined whether cardiac beta-adrenoceptor (beta-AR) function was altered in conscious rats with lesions surrounding the anteroventral third ventricle (AV3V). The findings were: (1) beta(1,2)-AR-mediated tachycardia was similar in sham and AV3V-lesion rats, (2) beta(3)- and/or atypical beta-AR-mediated tachycardia elicited by isoproterenol (10 microg/kg, i.v.; ISO) was diminished in AV3V-lesion rats treated with beta(1,2)-AR antagonists, but was not in similarly-treated sham-lesion rats, and (3) the tachycardia elicited by the membrane permeable cAMP-analogue, 8-(4-chlorophenylthiol)-cAMP (10 micromol/kg, i.v.), was similar in AV3V- and sham-lesion rats. The possibility that increased plasma sodium/osmolality in AV3V-lesion rats down-regulated cardiac beta(3)- and/or atypical beta-ARs, but not beta(1,2)-ARs or intracellular cAMP signaling is discussed.