Stress rapidly increases alpha 1d adrenergic receptor mRNA in the rat dentate gyrus

The hippocampal formation is a highly plastic brain region that is sensitive to stress. It receives extensive noradrenergic projections, and noradrenaline is released in the hippocampus in response to stressor exposure. The hippocampus expresses particularly high levels of the α_1D adrenergic receptor (ADR) and we have previously demonstrated that α_1d ADR mRNA expression in the rat hippocampus is modulated by corticosterone. One of the defining features of a stress response is activation of the hypothalamic pituitary adrenal (HPA) axis, resulting in the release of corticosterone from the adrenal glands. However, the effect of stress on hippocampal expression of α_1d ADR mRNA has not been determined. In this study, male rats were exposed to inescapable tail shock, loud noise or restraint, and the effect on α_1d ADR mRNA expression in the hippocampus was determined by semi-quantitative in situ hybridization. All three stressors resulted in a rapid upregulation of α_1d ADR mRNA in the dentate gyrus, with expression peaking at approximately 90 min after the start of the stressor. Physical activity has previously been reported to counteract some of the effects of stress that occur within the dentate gyrus. However, 6 weeks of voluntary wheel running in rats did not prevent the restraint stress-induced increase in α_1d ADR mRNA expression in the dentate gyrus. Although the function of the α_1D ADR in the dentate gyrus is not known, these data provide further evidence for a close interaction between stress and the noradrenergic system in the hippocampus.