Effect of gene dosage on single-cell hippocampal electrophysiology in a murine model of SSADH deficiency (γ-hydroxybutyric aciduria)

Human and murine succinic semialdehyde dehydrogenase (SSADH; gamma-hydroxybutyric (GHB) aciduria) deficiency represents an epileptic disorder associated with hyperGABA- and hyperGHB-ergic states. Despite significant neurotransmitters alterations, well-defined single-cell electrophysiological studies, aimed to provide insight into regional neuropathology, have been lacking. In this study, we characterized the effect of residual SSADH enzyme function/increased GABA levels on single-cell hippocampal electrophysiology in SSADH+/+ (wild-type; WT), SSADH+/− (heterozygous; HET), and SSADH−/− (knock-out; KO) mice. Tonic extrasynaptic GABAA receptor (GABAAR)-mediated currents were elevated in HET and KO mice, whereas phasic synaptic GABAAR currents were unaltered in dentate gyrus granule cells. Similarly, tonic GABAAR-mediated currents were increased in dentate gyrus interneurons of KO animals, while phasic GABAergic neurotransmission was unaffected in the same cells. Our results indicate global disruption of cortical networks in SSADH KO mice, affecting both excitatory and inhibitory neurons. Our findings provide new clues concerning seizure evolution in the murine model (absence→tonic-clonic→status epilepticus), and extend pathophysiological insight into human SSADH deficiency.