Pre- and postsynaptic factors influencing the neural encoding of afferent baroreceptor activity in the rat

The processing of baroreceptor activity by neurons within the dorsomedial region of the nucleus of the tractus solitarius (mNTS) is essential to neural circulatory control. Here, we are investigating the dynamic characteristics of mNTS neurons in response to activation patterns that are typical of both myelinated (A-type) and unmyelinated (C-type) baroreceptor fibers. Also examined is the relative balance between pre- and postsynaptic mechanisms that may underlie the neural integration of barosensory signals. This is accomplished using a comprehensive model of this first synapse in the baroreflex pathway. In addition to reproducing a wide variety of experimental data, we investigate how such use-dependent properties as vesicular mobilization, postsynaptic receptor desensitization and the nonlinear dynamics of mNTS neurons can effect the encoding of synaptic activity in spontaneously active mNTS cells. We demonstrate that because of the intrinsic dynamics of this sensory afferent synapse, C-type baroreceptors may have a more pronounced and sustained influence upon mNTS neurons than A-type. This work is part of a continuing collaborative effort investigating the neural integration of the broad spectrum of barosensory information arriving at the mNTS.