Dissociated Gender-Specific Effects of Recurrent Seizures on GABA Signaling in CA1 Pyramidal Neurons: Role of GABA_AReceptors

Abstract

Early in development, the depolarizing GABA A ergic signaling is needed for normal neuronal differentiation. It is shown here that hyperpolarizing reversal potentials of GABA A ergic postsynaptic currents (E GABA ) appear earlier in female than in male rat CA1 pyramidal neurons because of increased potassium chloride cotransporter 2 (KCC2) expression and decreased bumetanide-sensitive chloride transport in females. Three episodes of neonatal kainic acid-induced status epilepticus (3KA-SE), each elicited at postnatal days 4 (P4)-P6, reverse the direction of GABA A ergic responses in both sexes. In males, 3KA-SE trigger a premature appearance of hyperpolarizing GABA A ergic signaling at P9, instead of P14. This is driven by an increase in KCC2 expression and decrease in bumetanide-sensitive chloride cotransport. In 3KA-SE females, E GABA transiently becomes depolarizing at P8 -P13 because of increase in the activity of a bumetanide-sensitive NKCC1 (sodium potassium chloride cotransporter 1)-like chloride cotransporter. However, females regain their hyperpolarizing GABA A ergic signaling at P14 and do not manifest spontaneous seizures in adulthood. In maternally separated stressed controls, a hyperpolarizing shift in E GABA was observed in both sexes, associated with decreased bumetanide-sensitive chloride cotransport, whereas KCC2 immunoreactivity was increased in males only. GABA A receptor blockade at the time of 3KA-SE or maternal separation reversed their effects on E GABA . These data suggest that the direction of GABA A -receptor signaling may be a determining factor for the age and sex-specific effects of prolonged seizures in the hippocampus, because they relate to normal brain development and possibly epileptogenesis. These effects differ from the consequences of severe stress.

Early Enriched Environment Promotes Neonatal GABAergic Neurotransmission and Accelerates Synapse Maturation

“…Using gramicidin-perforated whole-cell recording, we measured the reversal potential of evoked GPSCs (E Cl ) in CA1 pyramidal cells of P9 control and EE-reared mice. Consistent with previous reports (Nunez and McCarthy, 2007;Galanopoulou, 2008), we found E Cl to be more hyperpolarized in females (Ϫ52.9 Ϯ 2.9 mV) compared with males (Ϫ45.4 Ϯ 3.9 mV). Importantly, E Cl was significantly more hyperpolarized in EE-reared pups in both males (EE: Ϫ58.5 Ϯ 4.0 mV, control:…”

A Single Seizure Episode Leads to Rapid Functional Activation of KCC2 in the Neonatal Rat Hippocampus

“…A significant depolarizing contribution of NKCC1 to the native somatic E GABA has been demonstrated in CA3 neurons at P2-4 using 10 M bumetanide, a selective blocker of NKCC1 at low concentrations (Russell, 2000), in gramicidin patch-clamp recordings combined with GABA uncaging (Sipilä et al, 2006(Sipilä et al, , 2009. Using gramicidin patch-clamp recordings in combination with electrical stimulation, a similar bumetanide effect has been described for CA1 pyramidal cells at P9 -14 (Galanopoulou, 2008). In the present study, bumetanide induced only a small negative shift in the native somatic E GABA of control CA1 neurons, which remained significantly more depolarized than the postseizure E GABA (Ϫ58.8 Ϯ 4.0 mV; n ϭ 5 neurons, 3 slices, 3 animals; p ϭ 0.95 and 0.009, respectively, when compared with control and postseizure neurons).…”

“…A single kainate-induced seizure episode leads to a negative shift in E GABA A single intraperitoneal injection of kainate (2 mg/kg) in P5-7 rats resulted in behavioral seizures that were similar to those described before (Galanopoulou, 2008). One hour after seizure onset, hippocampal slices were prepared and taken for electrophysiological experiments.…”

“…In an analogous manner, depolarizing shifts in E GABA that take place during neuronal epilepsy and trauma have been associated with a decrease in the total amount of KCC2 protein (e.g., Khalilov et al, 2003;Rivera et al, 2004;Munoz et al, 2007, Huberfeld et al, 2007Glykys et al, 2009). In view of the widely recognized but poorly understood differences in neonatal and adult epilepsies (Moshe and Galanopoulou, 2002;Ben Ari and Holmes, 2006;Rennie and Boylan, 2007), it is intriguing that recurrent seizures at postnatal day (P) 4 -6 lead to a precocious hyperpolarizing E GABA shift in CA1 pyramidal neurons of male rats 3-5 d after seizure induction, paralleled by an increase in KCC2 expression (Galanopoulou, 2008). A similar effect was recently observed after enriched environment rearing (He et al, 2010).…”

Learning through Silence: Amping up Cognition after Neonatal Hypoxic Seizures through AMPA Receptor Inhibition

“…At very early developmental stages, and before AMPA receptors populate the NR-containing synapses, depolarizing GABA A receptor responses provide the depolarization needed to release Mg 2+ block and activate NMDA receptors. PN12-13 male rats are just before the age when GABA A receptors shift from depolarizing to hyperpolarizing in CA1 pyramidal neurons (13). However, it is unclear how prior neonatal hypoxic seizures may affect the direction of GABA A receptor responses, since seizures and multiple other factors may change the direction of their responses, including strain, age, sex, type and time from insult, cell type, treatments, and life experiences (13).…”