Plasticity in the stress-regulating circuit: Decreased input from the bed nucleus of the stria terminalis to the hypothalamic paraventricular nucleus in Wistar rats following adrenalectomy

The bed nucleus of the stria terminalis is involved in the stress-regulating circuit by funnelling limbic information to the hypothalamic paraventricular nucleus. Since adrenalectomy influences both limbic structures (by inducing cell death in the hippocampus) and the hypothalamic paraventricular nucleus (by increased corticotrophin-releasing hormone synthesis), we investigated whether the bed nucleus of the stria terminalis is also influenced by adrenalectomy. For this purpose, we analysed and compared the projections from the bed nucleus of the stria terminalis to the hypothalamic paraventricular nucleus in normal and adrenalectomized rats by anterograde tracer injections in the bed nucleus of the stria terminalis. Quantitative analysis of the fibre pattern in the hypothalamic paraventricular nucleus of normal rats revealed a homogeneous distribution of fibres of the bed nucleus of the stria terminalis over the different subdivisions of the hypothalamic paraventricular nucleus. In adrenalectomized rats, the absolute fibre density was significantly lower in the whole hypothalamic paraventricular nucleus (1.17 +/- 0.27 10(-3) mu m/mu m(3) in adrenalectomized rats versus 2.59 +/- 0.24 10(-3) mu m/mu m(3) in normal rats; P < 0.01) and all its subdivisions. The largest decrease of fibre density was found in the corticotrophin-releasing hormone-rich part of the hypothalamic paraventricular nucleus (relative fibre density; adrenalectomized rats: 0.602 +/- 0.106, versus 1.095 +/- 0.019 in normal rats, P < 0.01). These results show a loss of input from the bed nucleus of the stria terminalis to the hypothalamic paraventricular nucleus, and particularly to the corticotrophin-releasing hormone neurons, following adrenalectomy. The data suggest that this pathway within the stress-regulating circuit is functionally affected by corticosteroids in adult rats and may imply that human disorders associated with corticosteroid imbalance are allied to a changed circuitry in the brain.