Paraventricular and supraoptic nuclei of the hypothalamus mediate cardiovascular responses evoked by the microinjection of noradrenaline into the medial amygdaloid nucleus of the rat brain.

The medial amygdaloid nucleus (MeA) is a part of the limbic system and is involved in cardiovascular modulation. We previously reported that microinjection of noradrenaline (NA) into the MeA of unanesthetized rats caused pressor and bradycardiac responses, which were mediated by acute vasopressin release into the systemic circulation. In the present study, we tested the possible involvement of magnocellular neurons of the paraventricular (PVN) and/or supraoptic (SON) of the hypothalamus that synthesize vasopressin in the cardiovascular pathway activated by the microinjection of NA into the MeA. Pressor and bradycardiac responses to the microinjection of NA (27 nmol/100 nL) into the MeA were blocked by pretreatment of either the PVN or the SON with cobalt chloride (CoCl(2), 1 mM/100 nL), thus indicating that both hypothalamic nuclei mediate the cardiovascular responses evoked by microinjection of NA into the MeA. Our results suggest that the pressor and bradycardiac response caused by the microinjection of NA into the MeA is mediated by magnocellular neurons in both the PVN and SON.