The effects of the alpha 2 adrenoceptor blocker idazoxan on defeat-induced immobility and plasma corticosterone in rats is antagonized by administration of adrenocorticotrophin-antiserum.
Adult male Wistar rats were introduced into the home cage of residents accustomed to aggressive encounters. The attacks of the residents induced lasting immobility in the subjects. The alpha-2 adrenoceptor blocker idazoxan (which elicits an increase in brain norepinephrine release probably by the blockade of presynaptic autoreceptors) induced an enhancement of defeat-induced corticosterone secretion as well as a reduction in immobility. Pre-treatment with adrenocorticotrophin (ACTH) antiserum abolished both the increased adrenomedullar stress reaction and the reduction in immobility. It is concluded that norepinephrine-induced corticosterone secretion is involved in the immobility-lowering effects of alpha-2 adrenoceptor blockers. In previous experiments we have shown that the norepinephrine-induced increase in the aggressiveness of the residents depends on the ability to secrete corticosterone. Therefore it appears that the effects of norepinephrine on social conflict are at least partly mediated by corticosterone. This implies the involvement of acute corticosterone changes in fight/flight behaviours.
Haller
J
J
Institute of Experimental Medicine, Hungarian Academy of Science, Hungary.
Albert
I
I
Makara
G B
GB
D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000324:Adrenocorticotropic Hormone / Q000276:immunology*; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D003220:Conflict, Psychological; D003345:Corticosterone / Q000097:blood*; D004291:Dominance-Subordination; D019329:Idazoxan / Q000494:pharmacology*; D008297:Male; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013315:Stress, Psychological / Q000378:metabolism / Q000523:psychology
D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000906:Antibodies; D000324:Adrenocorticotropic Hormone; D003345:Corticosterone; D009638:Norepinephrine; D019329:Idazoxan