Activated pathway from the parabrachial nucleus to rostal ventrolateral medulla during stimulation of cardiac sympathetic afferents (686.8)

Our previous studies have shown that stimulation of cardiac sympathetic afferents activates pontine nuclei like the parabrachial nucleus (PBN) and locus coeruleus (LC) as well as rostral ventrolateral medulla (rVLM), a critical area that controls cardiac sympathoexcitatory responses. However, there is no information on direct influence of pontine nuclei on the rVLM during stimulation of cardiac sympathetic afferents. Thus, the present study evaluated neuronal activation of the pontine nuclei in response to stimulation of cardiac sympathetic afferents, with regard to their projections to the rVLM. Seven to ten days after unilateral microinjection of rodamine‐conjugated microspheres retrograde tracer (100 nl) into the rVLM, rats with bilateral cervical vagotomy were subjected to epicardial application of α, β‐meATP (1.1 to 6.5 mM, in 40 µl) or 0.9% normal saline for six times over 90 min. Repetitive increases in blood pressure were observed in the rats following repeated stimulation of the heart with α, β‐meATP, but not with normal saline. Perikarya containing the microsphere tracer were found in the PBN and, but not in the LC of both groups. Compared to three controls, c‐Fos immunoreactivity and neurons double‐labeled with c‐Fos, an immediate early gene and the tracer were more frequently found in the PBN, but not LC of rats with cardiac stimulation (n=5), particularly in the lateral PBN and Kölliker‐Fuse nucleus. These results suggest that PBN neurons responsive to cardiac sympathetic afferent stimulation frequently project directly to the rVLM, which is known to participate in processing of excitatory cardiovascular responses during stimulation of cardiac sympathetic afferents. Grant Funding Source : NIH grant HL‐66217