Role of pyridoxine in GABA synthesis and degradation in the hippocampus

Pyridoxa1-5'-phosphate, the active form of vitamin B-6, is associated with activities of several enzymes and the treatment of various neurological disorders. Here, we investigated the effects of pyridoxine on the immunoreactivity and protein levels of gamma-aminobutyric acid (GABA)-synthesizing and degradation enzymes such as glutamic acid decarboxylase (GAD), GABA transaminase (GABA-T), and succinic semialdehyde dehydrogenase (SSADH), in the hippocampus of mice. The mice intraperitonially received physiological saline and 350 mg/kg pyridoxine, twice a day for 21 days, and were euthanized 2 h after the final dose. In the vehicle-treated group, we observed GAD67 immunoreactivity in the stratum pyramidale of the CA1 and CA3 region, Schaffer collateral, polymorphic layer, and outer granule cell layer of the dentate gyrus. Pyridoxine administration significantly increased GAD67 immunoreactivity, while significantly decreasing GABA-T immunoreactivity in pyridoxine-treated mouse hippocampi (CA1 region and dentate gyrus). In the stratum lacunosum-moleculare of CA1 region, GABA-T immunoreactivity was significantly increased in the pyridoxine-treated group compared to that in the vehicle-treated group, although GAD67 immunoreactivity was similarly observed in these groups. Alternatively, there were no significant differences in SSADH immunoreactivity in any regions of the hippocampus between the vehicle- and pyridoxine-treated groups. Western blot analysis showed significant increases in GAD67 and GABA-T protein levels in the pyridoxine-treated group compared with those in the vehicle-treated group. Therefore, pyridoxine administration facilitates GABA turnover in mouse hippocampus by modulating the GABA-synthesizing and degradation enzymes.