PARTICIPATION OF HYPOTHALAMIC PARAVENTRICULAR NUCLEUS IN LOCUS CERULEUS-INDUCED BAROREFLEX SUPPRESSION IN RATS

We evaluated the potential rob of the paraventricular nucleus (PVN) of the hypothalamus in the suppression of baroreceptor reflex (BRR) resp onse by locus ceruleus (LC), using adult male Sprague-Dawley rats anes thetized with pentobarbital sodium. Electrical stimulation of histolog ically verified sites in the LC elicited significant reduction in the BRR response. This suppressive effect of LC on BRR response was apprec iably antagonized by bilateral electrolytic lesions of the PVN and rev ersibly blocked by bilateral microinjection of 2% Lidocaine into simil ar hypothalamic loci. Local administration of the alpha(1)-adrenocepto r antagonist, prazosin (50 pmol), or an antiserum directed against neu ropeptide Y (NPY) (1:20) into the bilateral PVN also significantly att enuated the suppression elicited by LC on BRR response. In contrast, t reatments with the alpha(2)-adrenoceptor blocker, yohimbine (50 pmol), heatinactivated NPY antiserum (1:20), artificial cerebrospinal fluid, or normal rabbit serum (1:20) produced no discernible effect. These r esults suggest that the PVN may constitute part of the efferent pathwa ys through which LC elicits its inhibition on the BRR response. Furthe rmore, LC may activate this pathway via alpha(1)-adrenoceptors and NPY receptors in the PVN.