EFFECT OF CROWDING ON CORTICOSTERONE RESPONSES TO CENTRAL ADRENERGIC-STIMULATION

The social stress of crowding for 3, 7 and 14 days considerably reduce d the increase in serum corticosterone elicited by intracerebroventric ular administration of isoprenaline, a beta-adrenergic agonist, on the 3rd and 7th days of crowding. The corticosterone response to clonidin e, an alpha(2)-adrenergic agonist, was significantly diminished only a fter 3 days of crowding and this reduction was paralleled by a signifi cant decrease in hypothalamic histamine content. The stimulatory effec t of phenylephrine, an alpha(2)-adrenergic agonist, was not significan tly changed by crowding stress. Social crowding stress caused almost t otal and persistent reduction in the hypothalamic-pituitary-adrenocort ical (HPA) responsiveness to noradrenaline which stimulates the HPA ax is via both alpha- and beta-adrenergic receptors.