Kn. Sampaio et al., Cardiovascular changes following acute and chronic chemical lesions of thedorsal periaqueductal gray in conscious rats, J AUTON NER, 76(2-3), 1999, pp. 99-107
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.