Chronic stress attenuation of alpha 2-adrenoceptor reactivity is reversed by naltrexone.
Low doses of clonidine (50-100 micrograms/kg IP) evoke a clear dose-dependent hypoactivity response. Seven daily immobilization sessions prevented the motor activity decrease induced by clonidine. On the contrary, a single stress failed to modify clonidine response. Pretreatment with naltrexone (2 mg/kg IP) fully antagonized the attenuating effect induced by chronic stress on clonidine sedative action. These evidences suggest that chronic but not acute stress reduces the reactivity of alpha 2-adrenoceptors involved in clonidine-induced sedation. In addition, a regulatory mechanism of endogenous opioids seems to participate on alpha 2-adrenoceptors adaptative changes.
Cancela
L M
LM
Departamento de Farmacología, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
Volosin
M
M
Molina
V A
VA
D000818:Animals; D003000:Clonidine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008297:Male; D009043:Motor Activity / Q000187:drug effects*; D009271:Naltrexone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000502:physiology; D013312:Stress, Physiological
D011942:Receptors, Adrenergic, alpha; D009271:Naltrexone; D003000:Clonidine