NTS neuronal responses to arterial pressure and pressure changes in the rat

Central representation of arterial pressure by baroreceptor target neurons in the nucleus of the solitary tract (NTS) has not been studied. The present experiments sought to characterize response patterns of NTS baroreceptive cells in anesthetized, paralyzed, and artificially ventilated rats to both resting pressures and induced blood pressure challenges. Single-unit extracellular recordings were made from 83 baroreceptive NTS cells that received a synaptic input after electrical stimulation of the aortic nerve [latency, 2.46 +/- 0.78 (+/- SD) ms] and were located at an anatomically defined region known to receive baroreceptor afferents. Seventy-one neurons were presumed second order, since they received a short (< 5 ms) and invariant (< +/- 0.5 ms) synaptic input from the ipsilateral aortic nerve. Thirty-five of these neurons were silent at resting blood pressures and produced few (1-4) spikes when 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 wave-related and lung inflation-related phasic activity. The present data suggest that baroreceptive NTS neurons may be sensitive to many characteristics of the input signal, such as dP/dt, mean pressure, and cardiac frequency, as well as pulmonary afferent drive.