Anxiolytic-like Effect Induced by Chronic Stress Is Reversed by Naloxone Pretreatment

L. M. CANCELA, 1C. BREGONZIO AND V. A. MOLINA

BRAIN RESEARCH BULLETIN

PERGAMON-ELSEVIER SCIENCE LTD

Año: 1995 vol. 36 p. 209 - 213

0361-9230

ABSTRACT: The present study assesses the influence of different restraint schedules on behavioral parameters determined by a conflict test, namely the light-dark transitions (LDT) as well as the opiate modulation on the behavioral consequences induced by chronic restraint. Finally, another group of animals that received naloxone (NAL) and/or chronic stress was either exposed to a single foot shock session or administered a single dose of the,B-carboline FG 7142 (N'-methyl-,6-carboline-3-carboxamide) immediately prior to the LDT test. We observed that a single restraint session (2 h) induced a decrease of LDT and time spent in the lit box, while chronic restraint (2 h per day for up to 7 days) induced a significant increase in both parameters. However, this increasing effect was blocked by a NAL administration (2 mg/kg IP) prior to each of the seven restraint events. A single foot shock or FG administration produced a clear anxiogenic response, an effect that was absent in animals previously submitted to chronic stress. In addil~on, NAL pretreatment abolished the chronic stbress-induced attenuating effect on the behavioral suppression induced after either foot shock or FG administration. Therefore, these findings demonstrate that a previous history of chronic stress, leading to adaptation, induced an anxiolytic-like effect, and attenuated the behavioral supression produced by acute stressors. There seems to he an endogenous opiate mechanism involved in the behavioral influence induced by chronic stress.