CHRONIC CROWDING STRESS ABOLISHES THE PITUITARY-ADRENOCORTICAL RESPONSIVENESS TO CENTRAL CHOLINERGIC MUSCARINIC RECEPTOR STIMULATION

Social stress of crowding for 3, 7, 14 and 21 days persistently and al most totally abolished the increase in serum corticosterone levels ind uced by carbachol a cholinergic muscarinic receptor agonist. The respo nse to isoprenaline, a beta-adrenergic receptor agonist, was suppresse d after 3 and 7 days, whereas lesser diminution occurred after 14 and 21 days of crowding. These data suggest that social stress of crowding induces sustained and longer lasting desensitization of central musca rinic receptors than beta-adrenergic receptors involved in stimulation of the hypothalamic-pituitary-adrenal (HPA) axis.