Differences in the density of barosensitive neurons in the medulla of spontaneously hypertensive and Wistar-Kyoto rats

1. The density of barosensitive neurons in the medulla was examined in spontaneously hypertensive rats (SHR) and in normotensive Wistar-Kyoto (WKY) rats, In control experiments, rats were sham-operated, while in test experiments arterial baroreceptors were stimulated by presser responses to i,v, administration of phenylephrine and the density of c-Fos-labelled neurons was inmunocytologically examined, 2. In both control and test experiments, c-Fos-labelled neurons were distributed in cardiovascular control sites: the nucleus tractus solitarii (NTS) and the caudal and rostral ventrolateral medullas (CVLM/RVLM). 3. In both WKY rats and in SHR, the total density of labelled neurons in test experiments was significantly higher than in control experiments, 4. In control experiments, no significant difference was found in the distribution and density of labelled neurons in the NTS and in the CVLM/RVLM between WKY rats and SHR. 5. In test experiments, no significant difference was found in the distribution and density of labelled neurons in the NTS between WKY rats and SHR, 6. In test experiments in SHR, the density of labelled neurons in the CVLM just caudal to the obex level was significantly higher than that in WKY rats, whereas the density of labelled neurons in WKY rats in the RVLM just rostral to the obex level was significantly higher than that in SHR, 7. These results indicate that stimulation of the arterial baroreceptor induces strain-specific differences in the density of barosensitive neurons in the CVLM/RVLM near the obex level.