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

Chemoreflex activation with potassium cyanide (KCN, i.v.) produces pressor and bradycardic responses in awake rats in addition to the tachypneic response. In the present study we evaluated the role of the paraventricular nucleus of the hypothalamus (PVN) in the cardiovascular responses to chemoreflex activation in awake rats. Bilateral electrolytic lesion of the PVN was performed 1 day before chemoreflex activation and the results were compared to those obtained with sham-lesioned rats. Bilateral electrolytic lesion of the PVN (n=6) produced a significant reduction in both the magnitude (+51+/-5 vs. +22+/-2 mmHg) and duration (+26+/-5 vs. +6+/-2 s) of the pressor response to chemoreflex activation when compared to sham-lesioned rats (n=10). The bradycardic response to chemoreflex activation in rats with bilateral 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 pressor response (+51+/-5 vs. +49+/-3 mmHg), in the duration of the response (+26+/-5 vs. +18+/-3 s) or in the bradycardic response (-229+/-20 vs. -230+/-27 bpm) compared to sham-lesioned rats. The data show that effective bilateral lesion of the PVN produced a significant reduction in the magnitude and duration of the pressor response, indicating that the PVN plays a key role in the processing of the sympathoexcitatory component of the chemoreflex.