Organization and properties of GABAergic neurons in solitary tract nucleus (NTS)

Cranial visceral afferents enter the brain at the solitary tract nucleus (NTS). GABAergic neurons are scattered throughout the NTS, but their relation to solitary tract (ST) afferent pathways is imprecisely known. We hypothesized that most GABAergic NTS neurons would be connected only indirectly to the ST. We identified GABAergic neurons in brain stem horizontal slices using transgenic mice in which enhanced green fluorescent protein (EGFP) expression was linked to glutamic acid decarboxylase expression (GAD+). Finely graded electrical shocks to ST recruit ST-synchronized synaptic events with all-or-none thresholds and individual waveforms did not change with greater suprathreshold intensities—evidence consistent with initiation by single afferent axons. Most (∼70%) GAD+ neurons received ST-evoked excitatory postsynaptic currents (EPSCs) that had minimally variant latencies (jitter, SD of latency <200 μs) and waveforms consistent with single, direct ST connections (i.e., monosynaptic). Increasing stimulus...