Involvement of the paraventricular nucleus of the hypothalamus in the presser response to chemoreflex activation in awake rats

Chemoreflex activation with potassium cyanide (KCN. i.v.) produces presser and bradycardic responses in awake rats in addition to the tachypneic respo nse. In the present study we evaluated the role of the paraventricular nucl eus of the hypothalamus (PVN) in the cardiovascular responses to chemorefle x activation in awake rats. Bilateral electrolytic lesion of the PVN was pe rformed 1 day before chemoreRex activation and the results were compared to those obtained with sham-lesioned rats. Bilateral electrolytic lesion of t he PVN (n=6) produced a significant reduction ill both the magnitude (+51 /-5 vs. +22 +/-2 mmHg) and duration (+26 +/-5 vs, +6 +/-2 s) of the presser response to chemoreflex activation when compared to sham-lesioned rats (n= 10). The bradycardic response to chemoreflex activation in rats with bilate ral lesion of the PVN was not significantly different from the response of sham-lesioned rats (-229 +/- 20 vs. -88 +/- 76 bpm). Unilateral or partial bilateral lesion of the PVN (n=10) produced no significant changes in the p resser response ( +51 +/-5 vs. +49 +/-3 mmHg). in the duration of the respo nse (+26 +/-5 vs. +18 +/-3 s) or in the bradycardic response (-129 +/- 20 v s. -230 +/- 27 bpm) compared to sham-lesioned rats. The data show that effe ctive bilateral lesion of the PVN produced a significant reduction in the m agnitude and duration of the presser response, indicating that the PVN play s a key role in the processing of the sympathoexcitatory component of the c hemoreRex. (C) 2001 Elsevier Science B.V. All rights reserved.