NTS NEURONAL RESPONSES TO ARTERIAL-PRESSURE AND PRESSURE CHANGES IN THE RAT

Central representation of arterial pressure by baroreceptor target neu rons in the nucleus of the solitary tract (NTS) has not been studied. The present experiments sought to characterize response patterns of NT S baroreceptive cells in anesthetized, paralyzed, and artificially ven tilated rats to both resting pressures and induced blood pressure chal lenges. Single-unit extracellular recordings were made from 83 barorec eptive NTS cells that received a synaptic input after electrical stimu lation of the aortic nerve [latency, 2.46 +/- 0.78 (+/- SD) ms] and we re located at an anatomically defined region known to receive barorece ptor afferents. Seventy-one neurons were presumed second order, since they received a short (< 5 ms) and invariant (<+/- 0.5 ms) synaptic in put from the ipsilateral aortic nerve. Thirty-five of these neurons we re silent at resting blood pressures and produced few (1-4) spikes whe n presented with induced pressor responses. The remainder (n = 36) had ongoing activity that was not pulse rhythmic and that varied in rate nonuniformly with arterial blood pressure during an induced challenge. Ongoing activity was analyzed for active neurons, revealing both R wa ve-related and lung inflation-related phasic activity. The present dat a suggest that baroreceptive NTS neurons may be sensitive to many char acteristics of the input signal, such as dP/dt, mean pressure, and car diac frequency, as well as pulmonary afferent drive.