Rapid reduction in somatostatin mRNA expression by hypothalamic neurons induced by dexamethasone

We have previously reported that peripherally administered dexamethasone in duces a rapid increase in hypothalamic somatostatin release. Here we invest igated whether somatostatin synthesis could also be affected by this treatm ent and the potential involvement of glutamate in this effect. Male rats re ceived a saline or a dexamethasone injection (300 mu g/100 g body weight) a nd were killed 30 min later. Thirty minutes prior to dexamethasone treatmen t, another group received an i.p. injection of MK-801, a NMDA receptor anta gonist. Cells expressing somatostatin mRNA in the periventricular nucleus w ere analyzed by in situ hybridization using digoxigenin-labeled somatostati n oligonucleotide probe. Dexamethasone decreased the number of digoxigenin- labeled cells expressing somatostatin mRNA in the periventricular nucleus a s compared to the same histological sections from control rats. The dexamet hasone effect was reversed by pretreatment with MK-801, which alone also de creased the number of cells expressing somatostatin mRNA. In summary, dexam ethasone administration induces a significant rapid decrease in periventric ular cells expressing somatostatin mRNA and this effect is partly abolished by MK-801. NeuroReport 11:3163-3167 (C) 2000 Lippincott Williams & Wilkins .