Hyperpolarizing Inhibition Develops without Trophic support by GABA in Cultured Rat Midbrain Neurons

Abstract

During a limited period of early neuronal development, GABA is depolarizing and elevates [Ca2+]i, which mediates the trophic action of GABA in neuronal maturation. We tested the attractive hypothesis that GABA itself promotes the developmental change of its response from depolarizing to hyperpolarizing (Ganguly et al. 2001). In cultured midbrain neurons we found that the GABA response changed from depolarizing to hyperpolarizing, although GABAA receptors had been blocked throughout development. In immature neurons prolonged exposure of the cells to nanomolar concentrations of GABA or brief repetitive applications of GABA strongly diminished the elevation of [Ca2+]i by GABA. As revealed by gramicidin perforated‐patch recording, reduced [Ca2+]i responses were due to a diminished driving force for Cl−. This suggests that immature neurons do not have an efficient inward transport that can compensate the loss of cytosolic Cl− resulting from sustained GABAA receptor activation by ambient GABA. Transient increases in external K+, which can induce voltage‐dependent Cl− entry, restored GABA‐induced [Ca2+]i elevations. In mature neurons, GABA reduced [Ca2+]i provided that background [Ca2+]i was elevated by the application of an L‐type Ca2+ channel agonist. This was probably due to a hyperpolarization of the membrane by Cl− currents. K+‐Cl− cotransport maintained the gradient for hyperpolarizing Cl− currents. We conclude that in immature midbrain neurons an inward Cl− transport is not effective although the GABA response is depolarizing. Further, GABA itself is not required for the developmental switch of GABAergic responses from depolarizing to hyperpolarizing in cultured midbrain neurons.

Non–cell-autonomous factor induces the transition from excitatory to inhibitory GABA signaling in retina independent of activity

“…In turtle retina, prolonged blockade of GABA A signaling prevented the maturation of adult levels of the chloride transporter KCC2 (15). The finding in turtle retina that signaling through GABA A Rs is linked to maturation of GABA signaling via regulation of KCC2 levels is consistent with findings in dissociated hippocampal neurons (8, 37), but not other findings (19,20). Our results indicate that even if KCC2 levels are regulated by activity in mouse RGCs, this is not sufficient to change the timing of the GABA switch.…”

“…12-14). However, whether the timing of the GABA switch is modulated by local circuit activity (8,(15)(16)(17)(18) or occurs independent of activity (19,20) and is therefore intrinsic to developmental program of the cell remains controversial.Retinal ganglion cells (RGCs) undergo a switch in their response to GABA during the first two postnatal weeks of development (21-23). In vivo recordings in zebrafish demonstrate that the timing of the GABA switch is critical for the timing of the development of light responses (24) and therefore might be linked to the onset of visual experience.…”

“…12-14). However, whether the timing of the GABA switch is modulated by local circuit activity (8,(15)(16)(17)(18) or occurs independent of activity (19,20) and is therefore intrinsic to developmental program of the cell remains controversial.…”

NKCC1-Dependent GABAergic Excitation Drives Synaptic Network Maturation during Early Hippocampal Development

“…S1 J, S7D, available at www.jneurosci.org as supplemental material). Together with previous work (Ludwig et al, 2003;Titz et al, 2003;Wojcik et al, 2006), our results do not support a role of depolarizing GABA in inducing KCC2 expression, an effect previously reported in cultured neurons (Ganguly et al, 2001). , and Olig1 (found in independent screen) at different ages during development (normalized to WT Ϯ SEM; n Ͼ 3 animals per genotype and age).…”

Compensatory Enhancement of Intrinsic Spiking upon NKCC1 Disruption in Neonatal Hippocampus

“…Furthermore, this synergistic action is implicated in the functional activation of "AMPA-silent" synapses in immature neurons (Ben-Ari et al, 1997). Depolarizing GABAergic transmission has also been suggested to play an obligatory role in the developmental negative shift in the reversal potential of GABA A -mediated responses (E GABA ) (Ganguly et al, 2001) (but see Ludwig et al, 2003;Titz et al, 2003).…”