Diazepam binding inhibitor (DBI) gene expression in the brains of sociallyisolated and group-housed mice

Diazepam binding inhibitor (DBI), a putative endogenous polypeptide ligand for benzodiazepine (BZD) receptors, has been shown to act as an inverse BZD receptor agonist in the brain. We previously suggested that the social iso lation stress-induced decrease in pentobarbital sleeping time in mice was p artly due to an increase in the activity of endogenous substances with an i nverse BZD receptor agonist-like property such as DBI. In this study, we ex amined whether the DBI gene expression is affected by socially isolated str ess. Consistent with the previous findings, the in situ hybridization resul t showed very strong signals of DBI mRNA around the regions of the third ve ntricle, especially the lining cells, the arcuate nucleus of the hypothalam us and the cerebellum, in both socially isolated and group-housed animals. Unexpectedly, however, semi-quantitative experiments with reverse transcrip tion-polymerase chain reaction technique revealed that socially isolated mi ce had significantly less expression of DBI mRNA in the hypothalamus than g roup-housed animals, and no difference in the expression in the other brain areas was observed between two animal groups. We discuss the relationship between the decrease of DBI mRNA expression in the hypothalamus and the dec rease of GABA(A) receptor function following long-term social isolation in mice. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.