We report that the oxytocin-mediated neuroprotective γ-aminobutyric acid (GABA) excitatory-inhibitory shift during delivery is abolished in the valproate and fragile X rodent models of autism. During delivery and subsequently, hippocampal neurons in these models have elevated intracellular chloride levels, increased excitatory GABA, enhanced glutamatergic activity, and elevated gamma oscillations. Maternal pretreatment with bumetanide restored in offspring control electrophysiological and behavioral phenotypes. Conversely, blocking oxytocin signaling in naïve mothers produced offspring having electrophysiological and behavioral autistic-like features. Our results suggest a chronic deficient chloride regulation in these rodent models of autism and stress the importance of oxytocin-mediated GABAergic inhibition during the delivery process. Our data validate the amelioration observed with bumetanide and oxytocin and point to common pathways in a drug-induced and a genetic rodent model of autism.

No abstract

Phenobarbital produces its anti-epileptic actions by increasing the inhibitory drive of γ-aminobutyric acid. However, following recurrent seizures, γ-aminobutyric acid excites neurons because of a persistent increase of chloride raising the important issue of whether phenobarbital could aggravate persistent seizures. Here we compared the actions of phenobarbital on initial and established ictal-like events in an in vitro model of mirror focus. Using the in vitro three-compartment chamber preparation with the two hippocampi and their commissural fibres placed in three different chambers, kainate was applied to one hippocampus and phenobarbital contralaterally, either after one ictal-like event or after many recurrent ictal-like events that produce an epileptogenic mirror focus. Field, perforated patch and single-channel recordings were used to determine the effects of γ-aminobutyric acid and their modulation by phenobarbital, and alterations of the chloride cotransporters were investigated using sodium-potassium-chloride cotransporter 1 and potassium chloride cotransporter 2 antagonists, potassium chloride cotransporter 2 immunocytochemistry and sodium-potassium-chloride cotransporter 1 knockouts. Phenobarbital reduced initial ictal-like events and prevented the formation of a mirror focus when applied from the start. In contrast, phenobarbital aggravated epileptiform activities when applied after many ictal-like events by enhancing the excitatory actions of γ-aminobutyric acid due to increased chloride. The accumulation of chloride and the excitatory actions of γ-aminobutyric acid in mirror foci neurons are mediated by the sodium-potassium-chloride cotransporter 1 chloride importer and by downregulation and internalization of the chloride-exporter potassium-chloride cotransporter 2. Finally, concomitant applications of the sodium-potassium-chloride cotransporter 1 antagonist bumetanide and phenobarbital decreased excitatory actions of γ-aminobutyric acid and prevented its paradoxical actions on mirror focus. Therefore, the history of seizures prior to phenobarbital applications determines its effects and rapid treatment of severe potentially epileptogenic-neonatal seizures is recommended to prevent secondary epileptogenesis associated with potassium chloride cotransporter 2 downregulation and acquisition of the excitatory γ-aminobutyric acid phenotype.