(A) The GABA metabolic pathway. GABA is synthetized from glutamate by GAD (glutamic acid decarboxylase). During GABA metabolism, GABA-T (GABA transaminase) removes an amino group from GABA, producing SSA (succinic semialdehyde). Mediated by SSADH (succinic semialdehyde dehydrogenase), SSA is converted to succinate which enters the Krebs cycle. SSA may also be converted into an alternative by-product, GHB (γ-hydroxybutyrate) catalyzed by succinic semialdehyde reductase (SSAR). SSADH deficiency leads to accumulation of GABA and GHB. GHBDH (GHB dehydrogenase). (B) Genotyping of SSADH knock-out mice. DNA was isolated from mouse tails, and PCR genotyping results were obtained for three offspring of heterozygous parents. Displayed are the results for WT, HET, and KO mice. (C) Photomicrograph of a biocytin injected granule cell and interneuron in mouse dentate gyrus.