Studies conducted in this laboratory over the last ten years have clearly demonstrated that exposure to the widely used anxiolytic drug diazepam (DZ) during late gestation in the rat induces neural and behavioral changes that (1) are apparent long after the drug can be detected and (2) often are not expressed until after the onset of puberty. The induced effects include altered arousal and stress-related functions. Research is now proposed to test the hypothesis that early developmental exposure to DZ interferes with the organization and development of neural systems mediating behavioral and physiologic responses to challenge; specifically, that: (1) Functional characteristics at the benzodiazepine (BZD)/GABA receptor complex that are altered by prenatal DZ exposure can be attributed to changes in permeability of the GABA-associated chloride (Cl-) channel. Information will be contained on Cl- channel function in adult animals using specific binding assays. The density of low affinity GABA(A) receptors and challenge-induced changes in the Cl-channel will be measured. (2) The expression of behavioral and neural consequences of prenatal DZ exposure is under the influence of pubertal-related changes in gonadal hormones. The time of expression during postnatal development of the changes in functional indices of the BZD/GABA complex and how this expression is influenced by early castration will be evaluated. In addition, how manipulation of the hormonal environment in male rats influences the expression of the effects of early DZ exposure on noradrenergic projections to the hypothalamus will be determined. (3) Prenatal exposure tb DZ affects specific hypothalamic neuropeptide-containing cells. Specific hypothalamic peptides involved in adaption to stressors (corticotrophin releasing hormone, thyrotropic releasing hormone, and vasopressin) will be visualized using immunocytochemical procedures and the effect of early DZ exposure in adult and developing rats will be evaluated. (4) Prenatal DZ-induced alterations at the BZD/GABA receptor complex and in hypothalamic peptides can be attributed to a direct action of BZD compounds during neural development. Dispersed fetal brain cultures prepared from the cortex and hypothalamus will be exposed to DZ (10(-6) or 10(-5) M) and the effects on BZD/GABA receptor function and peptide immunoreactivity will be determined. Cultures will also be exposed to other drugs that act at the same complex. (5) Prenatal exposure to DZ influences the postnatal development of brain corticosteroid (CS) receptors. Cytosolic CS receptors will be measured in adult and developing prenatally exposed animals. The effect of exposure of cultures on the expression of mRNAs for specific CS receptors will also be determined. These studies will provide information on the developmental organization of neural systems mediating responses to stressors and indicate whether early developmental exposure to specific drugs may contribute to the expression of behavioral disorders in late adolescence.
