The Depolarizing Action of GABA Controls Early Network Activity in the Developing Hippocampus (original) (raw)
Related papers
Journal of Neuroscience, 2010
GABA, the main inhibitory transmitter in adulthood, early in postnatal development exerts a depolarizing and excitatory action. This effect, which results from a high intracellular chloride concentration ([Cl Ϫ ] i), promotes neuronal growth and synaptogenesis. During the second postnatal week, the developmental regulated expression of the cation-chloride cotransporter KCC2 accounts for the shift of GABA from the depolarizing to the hyperpolarizing direction. Changes in chloride homeostasis associated with high [Cl Ϫ ] i have been found in several neurological disorders, including temporal lobe epilepsy. Here, we report that, in adult transgenic mice engineered to express recombinant neutralizing anti-nerve growth factor antibodies (AD11 mice), GABA became depolarizing and excitatory. AD11 mice exhibit a severe deficit of the cholinergic function associated with an age-dependent progressive neurodegenerative pathology resembling that observed in Alzheimer patients. Thus, in hippocampal slices obtained from 6-month-old AD11 (but not wild-type) mice, the GABA A agonist isoguvacine significantly increased the firing of CA1 principal cells and, at the network level, the frequency of multiunit activity recorded with extracellular electrodes. In addition, in AD11 mice, the reversal of GABA A-mediated postsynaptic currents and of GABA-evoked single-channel currents were positive with respect to the resting membrane potential as estimated in perforated patch and cell attached recordings, respectively. Real-time quantitative reverse transcription-PCR and immunocytochemical experiments revealed a reduced expression of mRNA encoding for Kcc2 and of the respective protein. This novel mechanism may represent a homeostatic response that counterbalances within the hippocampal network the Alzheimer-like neurodegenerative pathology found in AD11 mice.
Journal of Neuroscience, 2009
A high intracellular chloride concentration in immature neurons leads to a depolarizing action of GABA that is thought to shape the developing neuronal network. We show that GABA-triggered depolarization and Ca 2ϩ transients were attenuated in mice deficient for the Na-K-2Cl cotransporter NKCC1. Correlated Ca 2ϩ transients and giant depolarizing potentials (GDPs) were drastically reduced and the maturation of the glutamatergic and GABAergic transmission in CA1 delayed. Brain morphology, synaptic density, and expression levels of certain developmental marker genes were unchanged. The expression of lynx1, a protein known to dampen network activity, was decreased. In mice deficient for the neuronal Cl Ϫ /HCO 3 Ϫ exchanger AE3, GDPs were also diminished. These data show that NKCC1mediated Cl Ϫ accumulation contributes to GABAergic excitation and network activity during early postnatal development and thus facilitates the maturation of excitatory and inhibitory synapses.
Delaying the GABA shift indirectly affects membrane properties in the developing hippocampus
During the first two postnatal weeks intraneuronal chloride concentrations in rodents gradually decrease, causing a shift from depolarizing to hyperpolarizing γ-aminobutyric acid (GABA) responses. The postnatal GABA shift is delayed in rodent models for neurodevelopmental disorders and in human patients, but the impact of a delayed GABA shift on the developing brain remain obscure. Here we examine the direct and indirect consequences of a delayed postnatal GABA shift on network development in organotypic hippocampal cultures made from 6 to 7-day old mice by treating the cultures for one week with VU0463271, a specific inhibitor of the chloride exporter KCC2. We verified that VU treatment delayed the GABA shift and kept GABA signaling depolarizing until day in vitro (DIV) 9. We found that the structural and functional development of excitatory and inhibitory synapses at DIV9 was not affected after VU treatment. In line with previous studies, we observed that GABA signaling was alread...
PLoS ONE, 2011
Two recent reports propose that the depolarizing action of GABA in the immature brain is an artifact of in vitro preparations in which glucose is the only energy source. The authors argue that this does not mimic the physiological environment because the suckling rats use ketone bodies and pyruvate as major sources of metabolic energy. Here, we show that availability of physiologically relevant levels of ketone bodies has no impact on the excitatory action of GABA in immature cultured hippocampal neurons. Addition of b-hydroxybutyrate (BHB), the primary ketone body in the neonate rat, affected neither intracellular calcium elevation nor membrane depolarizations induced by the GABA-A receptor agonist muscimol, when assessed with calcium imaging or perforated patch-clamp recording, respectively. These results confirm that the addition of ketone bodies to the extracellular environment to mimic conditions in the neonatal brain does not reverse the chloride gradient and therefore render GABA hyperpolarizing. Our data are consistent with the existence of a genuine ''developmental switch'' mechanism in which GABA goes from having a predominantly excitatory role in immature cells to a predominantly inhibitory one in adults.
The Journal of physiology, 2004
GABA is the principal inhibitory neurotransmitter in the mature brain, but during early postnatal development the elevated [Cl(-)](i) in immature neocortical neurones causes GABA(A) receptor activation to be depolarizing. The molecular mechanisms underlying this intracellular Cl(-) accumulation remain controversial. Therefore, the GABA reversal potential (E(GABA)) or [Cl(-)](i) in early postnatal rat neocortical neurones was measured by the gramicidin-perforated patch-clamp method, and the relative expression levels of the cation-Cl(-) cotransporter mRNAs (in the same cells) were examined by semiquantitative single-cell multiplex RT-PCR to look for statistical correlations with [Cl(-)](i). The mRNA expression levels were positively (the Cl(-) accumulating Na(+),K(+)-2Cl(-) cotransporter NKCC1) or negatively (the Cl(-) extruding K(+)-Cl(-) cotransporter KCC2) correlated with [Cl(-)](i). NKCC1 mRNA expression was high in early postnatal days, but decreased during postnatal development...
The GABA Excitatory/Inhibitory Shift in Brain Maturation and Neurological Disorders
The Neuroscientist, 2012
Ionic currents and the network-driven patterns they generate differ in immature and adult neurons: The developing brain is not a “small adult brain.” One of the most investigated examples is the developmentally regulated shift of actions of the transmitter GABA that inhibit adult neurons but excite immature ones because of an initially higher intracellular chloride concentration [Cl−]i, leading to depolarizing and often excitatory actions of GABA instead of hyperpolarizing and inhibitory actions. The levels of [Cl−]i are also highly labile, being readily altered transiently or persistently by enhanced episodes of activity in relation to synaptic plasticity or a variety of pathological conditions, including seizures and brain insults. Among the plethora of channels, transporters, and other devices involved in controlling [Cl−]i, two have emerged as playing a particularly important role: the chloride importer NKCC1 and the chloride exporter KCC2. Here, the authors stress the importanc...
Early expression of KCC2 in rat hippocampal cultures augments expression of functional GABA synapses
The Journal of Physiology, 2005
The development of GABAergic synapses is associated with an excitatory to inhibitory shift of the actions of GABA because of a reduction of [Cl − ] i. This is due to a delayed postnatal expression of the K +-Cl − cotransporter KCC2, which has low levels at birth and peaks during the first few postnatal weeks. Whether the expression of the cotransporter and the excitatory to inhibitory shift have other consequences on the operation of GABA A receptors and synapses is not yet known. We have now expressed KCC2 in immature neurones at an early developmental stage and determined the consequences on the formation of GABA and glutamate synapses. We report that early expression of the cotransporter selectively enhances GABAergic synapses: there is a significant increase of the density of GABA A receptors and synapses and an increase of the frequency of GABAergic miniature postsynaptic currents. The density of glutamate synapses and frequency of AMPA miniature postsynaptic currents are not affected. We conclude that the expression of KCC2 and the reduction of [Cl − ] i play a critical role in the construction of GABAergic networks that extends beyond the excitatory to inhibitory shift of the actions of GABA.
Brain Sciences
GABA, the main inhibitory neurotransmitter in the adult brain, depolarizes and excites immature neurons because of an initially higher intracellular chloride concentration [Cl−]i due to the delayed expression of the chloride exporter KCC2 at birth. Depolarization-induced calcium rise via NMDA receptors and voltage-dependent calcium channels is instrumental in shaping neuronal circuits and in controlling the excitatory (E)/inhibitory (I) balance in selective brain areas. An E/I imbalance accounts for cognitive impairment observed in several neuropsychiatric disorders. The aim of this review is to summarize recent data on the mechanisms by which alterations of GABAergic signaling alter the E/I balance in cortical and hippocampal neurons in Alzheimer’s disease (AD) and the role of cation-chloride co-transporters in this process. In particular, we discuss the NGF and AD relationship and how mice engineered to express recombinant neutralizing anti-NGF antibodies (AD11 mice), which develo...
Neuroscience Research, 2008
The regulation of intracellular chloride homeostasis plays a crucial role in the maturation of neuronal circuits. Levels of intracellular Cl À concentration ([Cl À ] i) are relatively high in immature neurons and decrease with development, mainly as a result of the alterations of two electrically neutral cation/chloride co-transporters, the Na +-K +-Cl À cotransporter (NKCC1) and the K +-Cl À cotransporter (KCC2) (Ben-Ari, 2002; Payne et al., 2003). Early in development, neurons accumulate Cl À carried by NKCC1 and maintain a high level of [Cl À ] i , which renders GABA/glycinergic transmission depolarizing and excitatory (Kakazu et al., 1999; Yamada et al., 2004). A developmental up-regulation of KCC2, a neuron specific isoform of KCC, leads to a negative shift in the reversal potential for Cl À (E Cl), resulting in a switch of GABA/ glycine action from excitatory to inhibitory (Kakazu et al., 1999; Rivera et al., 1999). KCC2 is particularly interesting in the adult animal, because KCC2 function contributes to the determination of the [Cl À ] i (Ueno et al., 2002) and is modulated by many physiologically relevant conditions. For example, KCC2 expression levels are reduced by BDNF (Rivera et al., 2002), axotomy (Nabekura et al., 2002) and oxidative stress (Wake et al., 2007). Neuronal circuit activity has been reported to modulate GABAergic responses by controlling KCC2 function and/or expression (see Fiumelli and Woodin, 2007). Rivera et al. (2004) reported
2010
Fukuda, Atsuo, Kanji Muramatsu, Akihito Okabe, Yasunobu mann 1992; Rosen and Morris 1993). A loss of the normal Shimano, Hideki Hida, Ichiro Fujimoto, and Hitoo Nishino. Cl 0 gradient during hypoxia was suggested as a mechanism Changes in intracellular Ca 2/ induced by GABA A receptor activathat might underlie the reduction and/or reversal of the tion and reduction in Cl 0 gradient in neonatal rat neocortex. J. GABAergic IPSP/Cs (Katchman et al. 1994; Khazipov et Neurophysiol. 79: 439-446, 1998. We have studied the effects of . Such a withdrawal and/or g-aminobutyric acid (GABA) and of reducing the Cl 0 gradient reversal of GABAergic inhibition could aggravate the on the [Ca 2/ ] i in pyramidal neurons of rat somatosensory cortex. cell deterioration caused by ischemia/hypoxia, because The Cl 0 gradient was reduced either with furosemide or by oxygen-GABA, as well as glutamate, increases in the extracellular glucose deprivation. Immature slices taken at postnatal day (P) space during ischemia (Matsumoto et al. 1996; O'Regan et 7-14 were labeled with fura-2, and [Ca 2/ ] i was monitored in al. 1995). In a previous study, we revealed that bicuculline identified pyramidal cells in layer II/III as the ratio of fluorescence intensities (R F340 / F380 ). The magnitude of the [Ca 2/ ] i increases reduces the magnitude of the [Ca 2/ ] i increases induced by induced by oxygen-glucose deprivation was significantly reduced oxygen-glucose deprivation in neocortical neurons (Fukuda (by 44%) by bicuculline (10 mM), a GABA A receptor antagonist. et al. 1998). This result indicates that GABA may act to Under normal conditions, GABA generally did not raise [Ca 2/ ] i , increase [Ca 2/ ] i during ischemia, indicating a collapse or although in some neurons a small and transient [Ca 2/ ] i increase reversal of the GABAergic inhibitory system. was observed. These transient [Ca 2/ ] i increases were blocked by 439 0022-3077/98 $5.00