Proceedings of The Physiological Society

Puerto de la Cruz, Tenerife (2003) J Physiol 548P, P137

Poster Communications

5-HT1A receptor antagonist 8-OH-DPAT attenuates passive avoidance in the elevated T-maze induced by acute stress

J.A. Aguirre*, J. Rioja*, L.J. Santín†, A. Doña*, M. García*, L. De Pablo† and S. González-Barón*

*Depto Fisiología, Facultad de Medicina, Universidad de Málaga and †Depto Psicobiología y Metodología de las CC, Facultad de Psicología, Universidad de Malaga, Spain

Acute stress exposure induces long-lasting effects on animal behaviour and neuronal plasticity. Previous stressful experiences can modify the animal's responses to new aversive stimuli. Furthermore the reduction of serotoninergic activity provokes anxiolytic effects, counteracting the behavioural consequences induced by stress. This work studies the behavioural long-term consequences of acute stress in rats and the effects of 5-HT1A receptor activation on the behavioural consequences of the acute immobilization (IMMO).

Following acclimation, the rats (Sprague-Dawley, 200-250 g) were randomly divided into four experimental groups (n = 10 in each group): (1) control group (with identical pre-experimental treatment without either agonist/antagonist administration or IMMO), (2) group submitted to IMMO (3 h in Plexiglas tubes), (3) group submitted to IMMO with 8-OH-DPAT pre-treatment (0.3 mg kg-1, S.C.) 30 min before acute IMMO and (4) group submitted to IMMO (3 h) after administration of the specific 5-HT1A antagonist WAY-100635 (0.3 mg kg-1 S.C., 15 min before 8-OH-DPAT pretreatment. Neuroendocrine effects (corticosterone serum levels) of IMMO with and without 8-OH-DPAT pre-treatment were also studied in different groups following the same protocol. The rats submitted to 3 h IMMO were, 24 h later, assessed for their performance in both conditioned (passive avoidance) and unconditioned (escape behaviour) anxiety tests in the elevated T maze. One-way ANOVA was applied for statistical significance between groups using SPSS for Windows. The experiments were performed following the European Communities Council directive (86/609/EEC) for animal care and experimental procedure and the experiments were approved by the Ethical Community for Animal Research of the University of Malaga.

Our results show that pre-exposure to acute IMMO induces long-term behavioural changes in contrast to control rats. These behavioural alterations include a great increase of anxiogenic responses such as exploratory behaviour and passive avoidance response. These responses were counteracted by 8-OH-DPAT pre-treatment and were reversed by WAY-100635 was administered prior to 8-OH-DPAT. Serum corticosterone levels increased during the first hour of acute stress and after 8-OH-DPAT administration.

Our results clearly support the hypothesis that involvement of acute stress is crucial in the formation of anxiety disorders and aversive memories. Moreover, the 5-HT1A receptor stimulation is able to counteract this long-term effects induced by acute IMMO. In this way, it is suggested that there are molecular interactions between 8-OH-DPAT and glucocorticoid receptors in the brain regions underlying these behaviours.

This work has been supported by a grant of the Spanish DGYCIT (PM99-0159).

Where applicable, experiments conform with Society ethical requirements