Tonic current through GABA_A receptors and hyperpolarization‐activated cyclic nucleotide‐gated channels modulate resonance properties of rat subicular pyramidal neurons

Abstract

The subiculum, considered to be the output structure of the hippocampus, modulates information flow from the hippocampus to various cortical and sub-cortical areas such as the nucleus accumbens, lateral septal region, thalamus, nucleus gelatinosus, medial nucleus and mammillary nuclei. Tonic inhibitory current plays an important role in neuronal physiology and pathophysiology by modulating the electrophysiological properties of neurons. While the alterations of various electrical properties due to tonic inhibition have been studied in neurons from different regions, its influence on intrinsic subthreshold resonance in pyramidal excitatory neurons expressing hyperpolarization-activated cyclic nucleotide-gated (HCN) channels is not known. Using pharmacological agents, we show the involvement of α5βγ GABAA receptors in the picrotoxin-sensitive tonic current in subicular pyramidal neurons. We further investigated the contribution of tonic conductance in regulating subthreshold electrophysiological properties using current clamp and dynamic clamp experiments. We demonstrate that tonic GABAergic inhibition can actively modulate subthreshold properties, including resonance due to HCN channels, which can potentially alter the response dynamics of subicular pyramidal neurons in an oscillating neuronal network.

Running reorganizes the circuitry of one-week-old adult-born hippocampal neurons

“…Membrane time constant was estimated by fitting a single exponential to the initial 100 ms of membrane potential deflection and capacitance was calculated as the ratio of membrane time constant and input resistance. GABA/NMDA receptor currents from each cell were converted to conductance values using the equation: where g is conductance, I is the peak current amplitude, V is the holding potential (+50 mV) and V rev is the reversal potential (GABA: −75 mV and NMDA: 0 mV) 72 .…”

Cholinergic receptor–independent modulation of intrinsic resonance in the rat subiculum neurons through inhibition of hyperpolarization‐activated cyclic nucleotide‐gated channels

“…55 With decreased ACh concentration, I h is expected to suppress IPSPs through other passive membrane properties and conductances. 56 A picrotoxin-sensitive tonic inhibition by GABA has also been shown in subicular neurons, 57 which changes the resonance strength with a minor change in the resonance frequency. With low ACh, the adaptive filtering of synaptic inputs can be different that can alter the response dynamics of subicular neurons in an oscillating network.…”