Chronic dexamethasone administration decreases noradrenaline-stimulated, but not serotonin-stimulated, phosphoinositide metabolism in the rat brain.

The present study was undertaken to investigate the effects of chronic administration of dexamethasone on the noradrenaline- and serotonin-stimulated (5-HT-stimulated) phosphoinositide metabolism in hippocampus and frontal cortex of the rat brain. For determination of phosphoinositide metabolism, slices from selected regions of the rat brain (hippocampus or frontal cortex) were loaded with myo- [3H] inositol and stimulated with the agonists (noradrenaline or 5-HT) in the presence of LiCl (7.5 mM). Administration of dexamethasone (1 mg/kg/day) every 2nd day for 14 days markedly reduced the noradrenaline-stimulated phosphoinositide metabolism in the rat hippocampus (IP1: 60% of the control value). In the rat frontal cortex, the noradrenaline-stimulated phosphoinositide metabolism was less depressed by the chronic administration of dexamethasone (IP1: 84% of the control value). However, the chronic administration of dexamethasone did not affect the 5-HT-stimulated phosphoinositide metabolism in the rat brain. The binding characteristics of alpha 1 -adrenoceptors and 5-HT2A receptors were unaffected by the chronic treatment with dexamethasone. These results indicate that chronic administration of dexamethasone induces regional and neurotransmitter-specific changes of phosphoinositide metabolism in rat brain. The results suggest that the reduction of noradrenaline-stimulated phosphoinositide metabolism is due to modification of the intracellular signal transduction system.