Biochemical characterization and interaction of neuronal and glial cells in culture

Block of glutamate-glutamine cycle between astrocytes and neurons inhibits epileptiform activity in hippocampus

Recurrent epileptiform activity occurs spontaneously in cultured CNS neurons and in brain slices in which GABA inhibition has been blocked. We demonstrate here that pharmacological treatments resulting in either the block of glutamine production by astrocytes or the inhibition of glutamine uptake by neurons suppress or markedly decrease the frequency of spontaneous epileptiform discharges both in primary hippocampal cultures and in disinhibited hippocampal slices. These data point to an important role for the neuron-astrocyte metabolic interaction in sustaining episodes of intense rhythmic activity in the CNS, and thereby reveal a new potential target for antiepileptic treatments.

Regulation of in vivo glutamine synthetase activity by glucocorticoids in the developing rat brain

Induction of glutamine synthetase in vivo by glucocorticoids was studied in different brain regions of the rat during development. Corticosterone treatment resulted in an age-dependent increase in glutamine synthetase activity. In 11-day-old rats, in comparison with controls, the increase was about 80% in the cerebellum, 50% in the olfactory bulbs and 20% in the forebrain. During development the effect diminished markedly and at day 20 a marked increase was detectable only in the cerebellum, suggesting that the elevation of glutamine synthetase was dependent on the maturational state of the region at the time of hormone treatment. The increase in enzyme activity was dose-dependent, and was also observed after treatment with dexamethasone but not with testosterone, estradiol or progesterone. Pre-treatment with the protein synthesis inhibitor anisomycin blocked the hormonal response. Also, immunochemical detection of glutamine synthetase in brain homogenates fractionated by SDS-polyacrylamide gel electrophoresis and transferred to diazobenzyloxymethyl paper showed that the increase in enzyme activity was due to induction of protein synthesis. This may be the first report showing a regulation by glucocorticoids of mammalian brain glutamine synthetase in vivo, and it is in good agreement with previous findings with chick retina in vivo and various avian and mammalian cells in vitro.