Enhanced pyridoxal 5′-phosphate synthetic enzyme immunoreactivities do not contribute to GABAergic inhibition in the rat hippocampus following pilocarpine-induced status epilepticus

To comprehend the role of pyridoxal 5′-phosphate (PLP) in epilepsy or seizure, we investigated whether the expressions of two PLP synthetic enzymes (pyridoxal kinase, PLK; pyridoxine-5′-phosphate oxidase, PNPO) are altered in the hippocampus and whether changes in paired-pulse responses in the hippocampus are associated with altered PLP synthetic enzyme expressions following status epilepticus (SE). PLK and PNPO immunoreactivities were significantly increased in the rat hippocampus accompanied by reductions in paired-pulse inhibition at 1 day and 1 week after SE. Four weeks after SE, PLK and PNPO immunoreactivities in dentate granule cells were similar to those in control animals, while their immunoreactivities were markedly reduced in Cornu Ammonis 1 (CA1) pyramidal cells due to neuronal loss. Linear regression analysis identified a direct proportional relationship between PLK/PNPO immunoreactivity and normalized population spike amplitude ratio in the dentate gyrus and the CA1 region as excluded the data obtained from 4 weeks after SE. These findings indicate that the upregulation of PLK and PNPO immunoreactivities in principal neurons may not be involved in γ-aminobutyric acid (GABA)ergic inhibition, but rather in enhanced excitability during epileptogenic periods.