Terman, D. H. | bioRxiv Science

bioRxiv2021

GABA and IA Independently Regulate rNST Responses to Afferent Input

Taste responses in the rostral nucleus of the solitary tract (rNST) influence motivated ingestive behavior via ascending pathways, and consummatory reflex behavior via local, brainstem connections. Modifications to the afferent signal within the rNST include changes in gain (the overall rate of neuron activity) and changes in gustatory tuning (the degree to which individual neurons respond to divergent gustatory qualities). These alterations of the sensory signal derive from both synaptic interactions within the nucleus and the constitutive cellular membrane properties of rNST neurons. GABA neurons are well represented within the rNST, as is expression of KV4.3, a channel for a rapidly inactivating outward K+ current (IA). GABAergic synapses suppress rNST responses to afferent input and previous studies showed that this suppression is greater in cells expressing IA, suggesting a possible interaction. Here, we examine the potential interaction between GABAergic inhibition and IA channels in a series of patch clamp experiments. Optogenetic release of GABA suppressed rNST responses to afferent (electrical) stimulation and this effect was greater in cells with IA, confirming an earlier report. We further observed that the composite inhibitory postsynaptic potential was larger in IA positive cells, suggesting one mechanism for the greater afferent suppression. Blocking IA with the channel blocker AmmTX3, enhanced the response to afferent stimulation, suggesting a suppressive role for this channel in regulating afferent input at rest. However, pharmacologic blockade of IA did not suppress GABAergic inhibition, indicating that IA and GABA independently regulate excitatory afferent input.

neuroscience↗

bioRxiv2018

A Mechanism of Real-Time Noise Modulation in Neurons

Uncertainties pose an ongoing challenge for information processing in the nervous system. It is not entirely clear how neurons maintain dynamic stability of information, encoded in the temporal features of spike trains, notwithstanding stochastic influences. Here we examined the contribution of subclasses of membrane sodium currents in real-time noise modulation in sensory neurons. Fast sodium (Na+) currents are essential for spike generation, and a persistent Na+ current can entrain preferred input frequencies via membrane resonance. Using mathematical modeling, theory and experiments, we show that a resurgent Na+ current can stabilize the temporal features of burst discharge and confer noise tolerance. These novel insights reckon the role of biophysical properties of Na+ currents beyond mere spike generation. Instead, these mechanisms might be how neurons perform real-time signal processing to maintain order and entropy in neural discharge. Our model analysis further predicts a negative feedback loop in the molecular machinery of an underlying Nav1.6-type Na+ channel gating considered in this study.

neuroscience↗