Dissociation between epileptic seizures induced by convulsant drugs and alteration in the concentrations of pyridoxal phosphate in rat brain regions

The status of vitamin B6 metabolism in brains of genetically epilepsy-prone rats

The status of vitamin B6 in brains of genetically epilepsy-prone and epilepsy-resistant rats was ascertained by measuring the concentrations of pyridoxal phosphate and the activities of pyridoxal kinase in the hippocampus, basal ganglia, cerebellum, and cerebral cortex, as well as in the entire brain. The concentrations of pyridoxal phosphate in whole brain of control rats and seizure-prone rats did not vary significantly from each other and were 1.2 +/- 0.02 and 1.2 +/- 0.03 microgram/g, respectively. Similarly, the activities of pyridoxal kinase in brains of the two groups were uniform and had values of 3.6 +/- 0.1 and 3.5 +/- 0.06 microgram pyridoxal phosphate formed/mg protein/15 min, respectively. Unlike in the whole brain, the concentration of pyridoxal phosphate in the cerebral cortex of seizure-prone rats was lower (1.24 +/- 0.026 microgram/g) than that of seizure-resistant rats (1.47 +/- 0.23 microgram/g). The opposite was noted in the cerebellum. The concentrations of pyridoxal phosphate in the hippocampus and in the basal ganglion of seizure-prone and seizure-resistant rats were identical. The activities of pyridoxal kinase in the basal ganglion (3.84 +/- 0.23 vs. 4.99 +/- 0.11 microgram pyridoxal phosphate/mg protein/15 min) and in the cerebral cortex (3.40 +/- 0.06 vs. 3.70 +/- 0.04 microgram pyridoxal phosphate/mg protein/15 min) were lower in seizure-prone rats than in seizure-resistant rats. The reverse took place in the hippocampus and in the cerebellum. No uniform associations among the concentration of pyridoxal phosphate, the activity of pyridoxal kinase, and the susceptibility or lack of susceptibility to seizure could be demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Pyridoxal phosphate-unrelated inhibition of hippocampal glutamic acid decarboxylase by convulsant pyridoxal sulphate

Previous studies from this laboratory have shown that pyridoxal-5'-sulphate, the synthetic analogue of pyridoxal phosphate, causes epileptic seizures including tonic-clonic convulsions. These seizure activities are prevented or reversed by GABA or muscimol. In an attempt to delineate the biochemical basis of these seizure processes further, we have studied and shown that pyridoxal sulphate is a competitive inhibitor of glutamic acid decarboxylase. In addition, the chronic administration of pyridoxal sulphate was shown to reduce the concentration of pyridoxal phosphate in the cerebellum, the cerebrum, and basal ganglion, but not in the hippocampus. The activity of hippocampal glutamic acid decarboxylase was reduced after 1, 3, and 5 days of chronic application of pyridoxal sulphate. The inhibition was demonstrated, whether glutamic acid decarboxylase was assayed in the presence or absence of its coenzyme pyridoxal phosphate. Unlike findings in the hippocampus, the activity of glutamic acid decarboxylase in other brain regions was unaffected following chronic application of pyridoxal sulphate. The selective toxic effects of pyridoxal sulfate to the hippocampus, a brain area well known for its high susceptibility to seizure discharges, deserve additional indepth investigation.