GABA-Induced Cl⁻ Current in Cultured Embryonic Human Dorsal Root Ganglion Neurons

Abstract

gamma-Aminobutyric acid (GABA)-activated channels in embryonic (5-8 wk old) human dorsal root ganglion (DRG) neurons in dissociated culture were characterized by whole cell and single-channel techniques. All DRG neurons when held at negative holding membrane potentials displayed inward current to micromolar concentrations of GABA applied by pressure pulses from closely positioned micropipettes. The current was directly proportional to the concentration of GABA (EC50, 111 microM; Hill coefficient, 1.7). DRG neurons also responded to micromolar concentrations of pentobarbital and alphaxalone but not to cis-4-aminocrotonic acid (CACA), glycine, or taurine. Baclofen (100 microM) affected neither the holding currents nor K+ conductance (when patch pipettes were filled with 130 mM KCl) caused by depolarizing pulses. Whole cell GABA-currents were blocked by bicuculline, picrotoxin, and t-butylbicyclophosphorothionate (TBPS; all at 100 microM). The reversal potential of whole cell GABA-currents was close to the theoretical Cl- equilibrium potential, shifting with changes in intracellular Cl- concentration in a manner expected for Cl--selective channels. The whole cell I-V curve for GABA-induced currents demonstrated slight outward rectification with nearly symmetrical outside and inside Cl- concentrations. Spectral analysis of GABA-induced membrane current fluctuations showed that the kinetic components were best fitted by a triple Lorentzian function. The apparent elementary conductance for GABA-activated Cl- channels determined from the power spectra was 22.6 pS. Single-channel recordings from cell-attached patches with pipettes containing 10 microM GABA indicated that GABA-activated channels have a main and a subconductance level with values of 30 and 19 pS, respectively. Mean open and closed times of the channel were characterized by two or three exponential decay functions, suggesting two or three open channel states and two closed states. Single channels showed a lack of rectification. The actions of GABA on cultured human embryonic DRG neurons are mediated through the activation of GABAA receptors with properties corresponding to those found in the CNS of human and other mammalian species but differing from those of cultured human adult DRG neurons.

Strychnine and taurine modulation of amygdala-associated anxiety-like behavior is ‘state’ dependent

“…This dose might therefore produce an initial decrease in neuronal activity and could reduce anxiety-like behavior as is seen with GABA A receptor agonists like muscimol [9]. Although we observed such an anxiolytic effect in our studies, the lower 50pmol (6.3ng) dose produced similar effects but would be expected to produce a 0.1mM concentration equivalent near the injection site, well below that needed to activate either recombinant [15] or native [48] GABA A receptors. Thus, while we can not conclusively exclude possible contributions by GABA A receptors, it would be difficult to imagine an exclusively GABAergic mechanism to explain our taurine data given the similar effects of 50pmol (6.3ng) and 1nmol (125ng) taurine.…”

Human sensory neurons: Membrane properties and sensitization by inflammatory mediators

“…However, obtaining healthy hDRG from adult donors has been a limiting factor. Instead, sensory neurons retrieved primarily from ganglionectomized chronic pain patients or fetuses have been studied [1; 6; 7; 32; 38; 42; 50]. Consequently, little is known about membrane properties and chemo-sensitivity of adult hDRG neurons from individuals without chronic pain.…”

GABA Increases Electrical Excitability in a Subset of Human Unmyelinated Peripheral Axons

“…Adult primary afferent sensory neurons provide an interesting example in this respect. The cell bodies of dorsal root ganglion (DRG) neurones, which are devoid of synaptic contact, express functional GABA A receptors (human: [4], [5], rat: [6], [7], cat: [8], rabbit: [9], chick: [10]). Functional GABA A receptor mediated responses in the somata of DRG neurones is also evident in their unmyelinated axons (rat: [11]) where application of GABA results in depolarization (for review see [12], [13]).…”