Much evidence shows that glia regulates the cation and anion content of brain interstitial space. In rats the pH and bicarbonate (HCO3-) concentration of neurons and glia were derived from carbon 14-labeled HCO3- and dimethyloxazolidinedione uptake into brain and cerebrospinal fluid. Acetazolamide increases the total CO2 concentration in neurons and decreases the pH and HCO3- concentration in glia. Inhibition of glial carbonic anhydrase (CA) reduces conversion of neuronally derived CO2 to HCO3-, glial pH is lowered, and neuronal CO2 accumulates. CA therefore has an essential role in regulating pH in neurons, glia, and interstitial fluid. In audiogenic seizure mice, glial CA activity is increased and glial anion transport is reduced. As the mice age, seizure susceptibility, the increased CA activity, and the defect in anion transport disappear concurrently. The enhanced CA activity in the glial cells of these mice is an adaptive mechanism to overcome the defect in anion transport that results from a deficiency of HCO3- -dependent and Na+- and K+ -dependent adenosine triphosphatase. Pentylenetetrazol stimulates neurons in neonatal rats, but after 10 days of age, when glia is present, it too is stimulated and the seizures are attenuated. Cobalt implantation in the cortex of rats also induces a glial response that ameliorates the focal seizures produced by this procedure.

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The effect of pharmacological doses of phenytoin (DPH) administered for a maximum of 28 days was studied in pregnant and nonpregnant rats as well as in 14- and 21-day fetuses. The following parameters were monitored in the adult rats: maximal electroshock seizures, serum DPH and folate, liver microsomal P-450, and 14C-DPH tissue distribution. 14C-DPH distribution was also evaluated in fetal tissues. Pregnant animals demonstrated an increase in anticonvulsant activity as well as increased serum concentrations of DPH throughout pregnancy and on the 7th post-partum day. Brain concentrations of DPH increased during pregnancy but had returned to the values in the nonpregnant group at the 7th post-partum day. Liver microsomal P-450 was decreased in pregnant animals receiving DPH at days 7 and 14 of pregnancy. Serum folate also decreased at day 14 of pregnancy in animals receiving DPH. Fetal tissue binding of DPH appeared to be related to serum concentrations of the drug at day 14. Teratogenic effects of DPH could be related to the increased serum and tissue concentrations of the drug observed during pregnancy as well as its effect on serum folate at day 14 of gestation.