Cardiovascular changes following acute and chronic chemical lesions of thedorsal periaqueductal gray in conscious rats

This study was carried out to investigate the effects of chemical lesions o f dorsal periaqueductal gray (DPAG) on resting arterial pressure (AP) and h eart rate (HR) as well as on cardiac baroreflex of conscious normotensive r ats. Lesions were performed by bilateral microinjections of 150 mM NMDA int o the DPAG (DPAG-lesion group). Controls were similarly injected with 165 m M NaCl (DPAG-sham group). Animals with chronic lesions confined only to the superior colliculus (SC-lesion group) were also used as controls of DPAG-l esion. Cardiovascular parameters were recorded 1 or 7 days after the microi njections of NMDA in acute and chronic groups, respectively. Cardiac barore flex was assessed by measuring the HR responses to the intravenous injectio n of phenylephrine or sodium nitroprusside. Baroreflex was estimated by sig moidal curve fitting of HR responses. An increased baroreflex gain was obse rved in chronic DPAG-lesion rats compared to both DPAG-sham(p < 0.01) and S C-lesion(p < 0.05) chronic groups. The chronic DPAG-lesion group showed als o an elevation of both the tachycardia (p < 0.05) and bradycardia (p < 0.01 ) plateaus compared to chronic DPAG-sham rats, while the SC-lesion group sh owed an elevation of the bradycardia plateau only (p < 0.01). Similar resul ts on baroreflex function were observed following acute lesion of the DPAG, i.e. an increase in baroreflex gain (p < 0.01) and the elevation of both t achycardia (p < 0.05) and bradycardia plateaus (p < 0.01) compared to the a cute DPAG-sham group. Resting AP and HR did not differ among the chronic gr oups. In contrast, the acute lesion of the DPAG produced a reduction in AP (p < 0.01) accompanied by an increase in HR (p < 0.01). The present data su ggest that the DPAG is involved in the tonic and reflex control of AP and H R in conscious rats. In addition, the SC seems to contribute to the baroref lex cardioinhibition. (C) 1999 Elsevier Science B.V. All rights reserved.