Is there a central nervous system component to acute baroreflex resetting in rats?

This study was designed to evaluate a possible central nervous system (CNS) component to acute baroreflex resetting. In nine arterial baroreceptor- denervated, chloralose-urethan-anesthetized rats, a control (C) aortic nerve stimulation curve (3-5 V, 1 ms, 0-64 Hz) was obtained. Next, a constant 'baroreceptor' input was delivered to the CNS (left aortic nerve stimulation, 10 min, 10.2 ± 1.5 Hz). Within the first 13 s of aortic nerve stimulation, maximum inhibition of lumbar sympathetic nerve activity (LSNA) was 60 ± 7.8% of baseline and at 1 min it increased to 68 ± 5.6% of baseline. At the end of the 10-min aortic nerve stimulation, LSNA was not different from the response at 1 min (68 ± 5.6% = 74 ± 4.1%). Immediately after the constant stimulation (within 30 s), a test or reset (RS) curve was obtained (0-64 Hz). A recovery (RC) curve was obtained 10-20 min later. The slope of the linear portion of the curve and the stimulation frequency that produced 50% maximum inhibition (ES₅₀) were compared among the three baroreflex curves (C, RS, RC,) and no significant differences were found. Thus, although a CNS component to baroreflex adaptation was evident during the first minute of aortic nerve stimulation, a longer term acute resetting of the baroreflex curve did not occur.