HISTOCHEMICAL LOCALIZATION OF BRAIN SUCCINIC SEMIALDEHYDE DEHYDROGENASE-A γ-AMINOBUTYRIC ACID DEGRADATIVE ENZYME

Succinic semialdehyde dehydrogenase is the final enzyme in the degradative pathway of γ-aminobutyric acid, a postulated inhibitory synaptic transmitter. This study reports a specific, sensitive technique for the localization of succinic semialdehyde dehydrogenase in rat brain. The technique utilizes the direct reduction of nitroblue tetrazolium by reduced pyridine nucleotide at an alkaline pH, a mechanism of formazan production substantiated by biochemical studies. The succinic semialdehyde dehydrogenase histochemical reaction is completely inhibited by p-hydroxybenzaldehyde and m-hydroxybenzaldehyde, compounds which have no effect on succinic acid dehydrogenase and reduced diphosphopyridine nucleotide diaphorase. Conversely, succinic acid dehydrogenase and reduced diphosphopyridine nucleotide diaphorase are inhibited by malonate and nordihydroguaiaretic acid, respectively, substances which have no effect on succinic semialdehyde dehydrogenase. The distribution and intensity of staining for succinic semialdehyde dehydrogenase are different from that seen following the succinic acid dehydrogenase and reduced diphosphopyridine nucleotide diaphorase reactions and can be localized to groups of neurons and their cell processes, e.g., the Purkinje cell dendritic tree, and in specific regions of neuropil.