Reversal Potential Of GABA-induced Currents Research Articles

Commentary: GABA Depolarizes Immature Neurons and Inhibits Network Activity in the Neonatal Neocortex In vivo.

Commentary: GABA Depolarizes Immature Neurons and Inhibits Network Activity in the Neonatal Neocortex In vivo.

Development of light response and GABAergic excitation‐to‐inhibition switch in zebrafish retinal ganglion cells

The zebrafish retina has been an important model for studying morphological development of neural circuits in vivo. However, its functional development is not yet well understood. To investigate the functional development of zebrafish retina, we developed an in vivo patch-clamp whole-cell recording technique in intact zebrafish larvae. We first examined the developmental profile of light-evoked responses (LERs) in retinal ganglion cells (RGCs) from 2 to 9 days post-fertilization (dpf). Unstable LERs were first observed at 2.5 dpf. By 4 dpf, RGCs exhibited reliable light responses. As the GABAergic system is critical for retinal development, we then performed in vivo gramicidin perforated-patch whole-cell recording to characterize the developmental change of GABAergic action in RGCs. The reversal potential of GABA-induced currents (E(GABA)) in RGCs gradually shifted from depolarized to hyperpolarized levels during 2-4 dpf and the excitation-to-inhibition (E-I) switch of GABAergic action occurred at around 2.5 dpf when RGCs became light sensitive. Meanwhile, GABAergic transmission upstream to RGCs also became inhibitory by 2.5 dpf. Furthermore, down-regulation of the K(+)/Cl() co-transporter (KCC2) by the morpholino oligonucleotide-based knockdown approach, which shifted RGC E(GABA) towards a more depolarized level and thus delayed the E-I switch by one day, postponed the appearance of RGC LERs by one day. In addition, RGCs exhibited correlated giant inward current (GICs) during 2.5-3.5 dpf. The period of GICs was shifted to 3-4.5 dpf by KCC2 knockdown. Taken together, the GABAergic E-I switch occurs coincidently with the emergence of light responses and GICs in zebrafish RGCs, and may contribute to the functional development of retinal circuits.

GABA Excites and Sculpts Immature Neurons Well before Delivery: Modulation by GABA of the Development of Ventricular Progenitor Cells

Excitatory GABA Action Is Essential for Morphological Maturation of Cortical Neurons in Vivo. Cancedda L, Fiumelli H, Chen K, Poo MM. J Neurosci 2007;27(19):5224–5235. GABA exerts excitatory actions on embryonic and neonatal cortical neurons, but the in vivo function of this GABA excitation is essentially unknown. Using in utero electroporation, we eliminated the excitatory action of GABA in a subpopulation of rat ventricular progenitors and cortical neurons derived from these progenitors by premature expression of the Cl– transporter KCC2, as confirmed by the changes in the reversal potential of GABA-induced currents and the resting membrane potential after GABAA receptor blockade. We found that radial migration to layer II/III of the somatosensory cortex of neurons derived from the transfected progenitors was not significantly affected, but their morphological maturation was markedly impaired. Furthermore, reducing neuronal excitability of cortical neurons in vivo by overexpressing an inward-rectifying K+ channel, which lowered the resting membrane potential, mimicked the effect of premature KCC2 expression. Thus, membrane depolarization caused by early GABA excitation is critical for morphological maturation of neonatal cortical neurons in vivo.

Excitatory GABA Action Is Essential for Morphological Maturation of Cortical NeuronsIn Vivo

GABA exerts excitatory actions on embryonic and neonatal cortical neurons, but the in vivo function of this GABA excitation is essentially unknown. Using in utero electroporation, we eliminated the excitatory action of GABA in a subpopulation of rat ventricular progenitors and cortical neurons derived from these progenitors by premature expression of the Cl- transporter KCC2, as confirmed by the changes in the reversal potential of GABA-induced currents and the resting membrane potential after GABA(A) receptor blockade. We found that radial migration to layer II/III of the somatosensory cortex of neurons derived from the transfected progenitors was not significantly affected, but their morphological maturation was markedly impaired. Furthermore, reducing neuronal excitability of cortical neurons in vivo by overexpressing an inward-rectifying K+ channel, which lowered the resting membrane potential, mimicked the effect of premature KCC2 expression. Thus, membrane depolarization caused by early GABA excitation is critical for morphological maturation of neonatal cortical neurons in vivo.

Circadian rhythm in intracellular Cl(-) activity of acutely dissociated neurons of suprachiasmatic nucleus.

A link between the circadian rhythm and the function of Cl(-)-permeable gamma-aminobutyric acid (GABA) type A (GABA(A)) receptors on suprachiasmatic nucleus (SCN) neurons was studied by measuring intracellular activity of Cl(-) (aCl) at different times during a circadian cycle in SCN neurons acutely dissociated from rat brains. To measure aCl, the voltage-clamp mode of the gramicidin-perforated patch-clamp technique was used, and reversal potential of GABA-induced currents (E(GABA)) was converted to aCl. Measured aCl was significantly higher at around noon (20.1 +/- 1.4 mM) than at three other time zones of a circadian cycle (means ranging from 11.6 to 14.3 mM). Chord conductance of GABA-induced currents showed no circadian changes, indicating a lack of circadian changes in the number or single-channel conductance of GABA(A) receptors. These results suggest that aCl participates in modulating GABA(A) receptor functions on SCN neurons during the circadian rhythm.

GABA-mediated Ca2+ signalling in developing rat cerebellar Purkinje neurones.

1. Cellular responses to GABA(A) receptor activation were studied in developing cerebellar Purkinje neurones (PNs) in brain slices obtained from 2- to 22-day-old rats. Two-photon fluorescence imaging of fura-2-loaded cells and perforated-patch recordings were used to monitor intracellular Ca2+ transients and to estimate the reversal potential of GABA-induced currents, respectively. 2. During the 1st postnatal week, focal application of GABA or the GABA(A) receptor agonist muscimol evoked transient increases in [Ca2+]i in immature PNs. These Ca2+ transients were reversibly abolished by the GABA(A) receptor antagonist bicuculline and by Ni2+, a blocker of voltage-activated Ca2+ channels. 3. Perforated-patch recordings were used to measure the reversal potential of GABA-evoked currents (E(GABA)) at different stages of development. It was found that E(GABA) was about -44 mV at postnatal day 3 (P3), it shifted to gradually more negative values during the 1st week and finally equilibrated at -87 mV at around the end of the 2nd postnatal week. This transition was well described by a sigmoidal function. The largest change in E(GABA) was -7 mV x day(-1), which occurred at around P6. 4. The transition in GABA-mediated signalling occurs during a period in which striking changes in PN morphology and synaptic connectivity are known to take place. Since such changes were shown to be Ca2+ dependent, we propose that GABA-evoked Ca2+ signalling is one of the critical determinants for the normal development of cerebellar PNs.

Reversal potential of GABA-induced currents in rod bipolar cells of the rat retina

GABA-induced whole-cell currents were measured in rod bipolar cells dissociated from the adult rat retina. The patch-clamp electrode contained nystatin, which made the cell membrane electrically permeable without rupture, thus retarding the rate of diffusion of Cl- ions from the patch pipette to the cell interior. The reversal potential of the GABA-induced currents was around -70 mV at an extracellular Cl- concentration of 149 mM. We conclude that GABA generates hyperpolarizing responses in rod bipolar cells of the rat retina.