REGION-SPECIFIC REGULATION OF GLUTAMIC-ACID DECARBOXYLASE (GAD) MESSENGER-RNA EXPRESSION IN CENTRAL STRESS CIRCUITS

Neurocircuit inhibition of hypothalamic paraventricular nucleus (PVN) neurons controlling hypothalamo-pituitary-adreno-cortical (HPA) activi ty prominently involves GABAergic cell groups of the hypothalamus and basal forebrain. In the present study, stress responsiveness of GABAer gic regions implicated in HPA inhibition was assessed by in situ hybri dization, using probes recognizing the GABA-synthesizing enzyme glutam ic acid decarboxylase (GAD65 and GAD67 isoforms). Acute restraint pref erentially increased GAD67 mRNA expression in several stress-relevant brain regions, including the arcuate nucleus, dorsomedial hypothalamic nucleus, medial preoptic area, bed nucleus of the stria terminalis (B ST) and hippocampus (CA1 and dentate gyrus). In all cases GAD67 mRNA p eaked at 1 hr after stress and returned to unstimulated levels by 2 hr . GAD65 mRNA upregulation was only observed in the BST and dentate gyr us. In contrast, chronic intermittent stress increased GAD65 mRNA in t he anterior hypothalamic area, dorsomedial nucleus, medial preoptic ar ea, suprachiasmatic nucleus, anterior BST, perifornical nucleus, and p eriparaventricular nucleus region. GAD67 mRNA increases were only obse rved in the medial preoptic area, anterior BST, and hippocampus. Acute and chronic stress did not affect GAD65 or GAD67 mRNA expression in t he caudate nucleus, reticular thalamus, or parietal cortex. Overall, t he results indicate preferential upregulation of GAD in central circui try responsible for direct (hypothalamus, BST) or multisynaptic (hippo campus) control of HPA activity. The distinct patterns of GAD65 and GA D67 by acute versus chronic stress suggest stimulus duration-dependent control of GAD biosynthesis. Chronic stress-induced increases in GAD6 5 mRNA expression predict enhanced availability of GAD65 apoenzyme aft er prolonged stimulation, whereas acute stress-specific GAD67 upregula tion is consistent with de novo synthesis of active enzyme by discrete stressful stimuli.