Time-dependent inhibition of hindlimb somatic afferent inputs to nucleus tractus solitarius.

1. In the present investigation, experiments were performed in anesthetized, paralyzed rats (n = 40) to 1) identify and characterize responses of nucleus tractus solitarius (NTS) neurons to hindlimb somatic afferent inputs; 2) determine if hindlimb somatic inputs to NTS undergo time-dependent inhibition similar to that observed among visceral afferent inputs; and 3) determine if somatic afferent-evoked NTS unit discharge is altered by activation of baroreceptor afferent inputs. 2. Extracellular discharge was recorded from single NTS units following electrical stimulation (approximately 500 microA) of the contralateral tibial nerve (TN) (skeletal muscle afferents), sural nerve (SN) (cutaneous afferents), and the ipsilateral aortic nerve (AN) (baroreceptor afferents). To identify possible time-dependent interactions, a paired pulse or conditioning-test stimulation procedure was employed. The activity of NTS neurons was recorded in response to test stimuli delivered to either TN or SN first in the absence and then in the presence of conditioning stimuli delivered to TN, SN, or AN 50, 150, and 250 ms before the test stimuli. 3. The results indicate that among 31 NTS cells activated by somatic nerve stimulation, 14 (approximately 50%) received convergent inputs from both the TN and SN, 9 responded to TN stimulation only and 2 were activated by SN stimulation only. These cells were not spontaneously active but showed two distinct patterns of evoked discharge. Some had only a short latency, unimodal response that averaged 25.5 +/- 2.0 (SE) ms for TN inputs (n = 21) and 27.9 +/- 2.8 ms for SN inputs (n = 8).(ABSTRACT TRUNCATED AT 250 WORDS)