Organization and Properties of GABAergic Neurons in Solitary Tract Nucleus (NTS)

Abstract

. 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 ϩ ). Finely graded electrical shocks to ST recruit STsynchronized 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 (ϳ70%) GAD ϩ neurons received ST-evoked excitatory postsynaptic currents (EPSCs) that had minimally variant latencies (jitter, SD of latency Ͻ200 s) and waveforms consistent with single, direct ST connections (i.e., monosynaptic). Increasing stimulus intensity evoked additional ST-synchronized synaptic responses with jitters Ͼ200 s including inhibitory postsynaptic currents (IPSCs), indicating indirect connections (polysynaptic). Shocks of suprathreshold intensity delivered adjacent (50 -300 m) to the ST failed to excite non-ST inputs to second-order neurons, suggesting a paucity of axons passing near to ST that connected to these neurons. Despite expectations, we found similar ST synaptic patterns in GAD ϩ and unlabeled neurons. Generally, ST information that arrived indirectly had small amplitudes (EPSCs and IPSCs) and frequency-dependent failures that reached Ͼ50% for IPSCs to bursts of stimuli. This ST afferent pathway organization is strongly use-dependent-a property that may tune signal propagation within and beyond NTS.

The μ-opioid receptor agonist DAMGO presynaptically suppresses solitary tract-evoked input to neurons in the rostral solitary nucleus

“…2). These results are similar to those from the cNST, where 50 -70% of GABAergic neurons have been shown to be monosynaptically innervated by the ST (Bailey et al 2008;Glatzer et al 2007). However, our report of a high proportion of rNST GAD67ϩ neurons with monosynaptic input appears at odds with a recent anatomical report (Wang et al 2012) that showed that only a small fraction of identified CT afferent fibers make synaptic contact with GABAergic neurons in the adult rat.…”

Inhibitory control of ascending glutamatergic projections to the lamprey respiratory rhythm generator

“…This interpretation is consistent with the functional organization of inhibitory modulation of NTS neurons in mammals (e.g. Miyazaki et al, 1999;Ezure and Tanaka, 2004;Kubin et al, 2006;Bailey et al, 2008). The OLA consists of three primary octavolateralis nuclei arranged dorsoventrally which receive multiple sensory inputs.…”

“…Accordingly, both the caudal ventral respiratory group and the caudal NTS neurons have been shown to be subject to a potent inhibitory control (see e.g. Miyazaki et al, 1999;Tonkovic-Capin et al, 2001Ezure and Tanaka, 2004;Kubin et al, 2006;Bailey et al, 2008).…”

GABA signaling in the nucleus tractus solitarius sets the level of activity in dorsal motor nucleus of the vagus cholinergic neurons in the vagovagal circuit

“…These EGFP-GABA neurons are identified in the NTS and recorded in the whole-cell, voltage-clamp configuration. Whole cell recordings made during electrical stimulation of the solitary tract exhibited constant-latency responses in the majority of neurons (3,15), indicative of a monosynaptic connection. However, when EGFP-GABA neurons in the NTS were retrogradely labeled by pseudorabies virus (PRV) injected in the corpus of the stomach, none of the double-labeled neurons exhibited a constant-latency response.…”