Integration of aortic nerve inputs in hypertensive rats

The integration of arterial baroreceptor afferent inputs was studied in ren al wrap hypertensive (HT) and normotensive (NT) rats. In anesthetized and p aralyzed rats, aortic nerve (AN)-evoked depressor responses were reduced in HT compared with NT rats (P<0.05). We tested the hypothesis that the atten uated baroreflex was associated with altered integration of baroreceptor in puts within the nucleus of the solitary tract. Based on onset latency and t he ability of monosynaptic neurons (MSNs) to respond to each of 2 AN stimul i separated by 5 ms, cells in PIT and NT rats were divided into 3 groups: s hort-latency MSNs (SLMSNs), long-latency MSNs (LLMSNs), and polysynaptic ne urons (PSNs). A higher percentage of PSNs (73% versus 61%) and a lower perc entage of SLMSNs (20% versus 27%) or LLMSNs (7% versus 12%) were found in H T rats (P<0.05). In addition, in HT compared with NT rats, the AN onset lat ency was greater in PSNs (29.9+/-1.1 versus 26.7+/-0.8 ms) but not in SLMSN s (5.0+/-0.5 versus 5.0+/-0.3 ms) or LLMSNs (22.9+/-1.2 versus 24.1+/-0.7 m s) (P<0.05). Finally, in HT compared with NT rats, the number of PSNs respo nding to a single AN stimulus with multiple action potentials was increased (40% versus 19%) (P<0.05). This was not observed in SLMSNs (26% versus 13% ) or LLMSNs (12% versus 18%). The results indicate that renal wrap hyperten sion is associated with reduced AN-evoked depressor responses. There also w ere alterations in the integration of AN afferent inputs within the nucleus of the solitary tract, and these alterations were most marked in the PSN p opulation.