Degree of inhibition of ACTH release by glucocorticoids in adrenalectomized rats

Adrenocortical responses to novel stressors in acutely or repeatedly starved chickens

The effect of starvation on the corticosterone responses of immature cockerels to acute, novel stress has been determined. The marked corticosterone responses of fed birds to either horizontal treadmill exercise (0.04 km/hr) or intravenous adrenocorticotrophic hormone (ACTH) administration (P less than 0.001 in both cases) were reduced by starvation (P less than 0.01 and P less than 0.001, respectively). This reduction did not appear to be due to either feedback inhibition of corticosterone on the hypothalamus or pituitary, or to reduced adrenal responsiveness to endogenous ACTH. Starvation significantly elevated the basal level of circulating corticosterone (P less than 0.001), but the magnitude of this elevation and the level of corticosterone attained were less (P less than 0.05) in birds that were accustomed to starvation. This habituation of adrenocortical activity may be due to reduced pituitary ACTH secretion, and was specific in that the corticosterone responses to novel stressors were unaffected.

Facilitation and inhibition of plasma cortisol following electrical stimulation of the goldfish forebrain

To examine the role of forebrain structures in the control of ACTH release, electrical stimulation was performed in the brains of continuously respirated , immobilized goldfish in which endogenous ACTH release was suppressed with dexamethasone. Three active areas of the forebrain were identified. Electrical stimulation for 5 min resulted in elevations of plasma cortisol 15 min following stimulation of the nucleus preopticus (NPO) or of the nucleus tenia (NT) but a decrease in plasma cortisol following stimulation of the nucleus lateral tuberis (NLT). The results of this study demonstrate that the NPO and NT facilitate, whereas nerve fibers originating in or passing through the NLT inhibit, ACTH release in the goldfish.

The effect of adrenalectomy and dexamethasone on the antinociceptive effects of physostigmine

The tail-flick procedure was used to study the antinociceptive effects of physostigmine in adrenalectomized and sham-operated rats. At 5 days after surgery, they were tested 30 min after either 0.32 or 0.45 mg/kg IP physostigmine. Adrenalectomized animals showed significantly greater elevation of TF scores from predrug latencies than the sham controls at both doses of physostigmine. Following 3 days of dexamethasone replacement therapy on days 18, 19, and 20 post-surgery the antinociceptive effects of physostigmine were uniformly attenuated across doses or surgical groups. On the other hand, animals receiving saline injection instead of dexamethasone did not manifest any reduction of the physostigmine antinociceptive effect. The potentiation by adrenalectomy and the reduction following dexamethasone of the antinociceptive effects of physostigmine suggest that these effects may be mediated through hypothalamic-pituitary-adrenal mechanisms and are consistent with beta-endorphin-induced sensitization of opiate or cholinergic receptors.