PRIOR EXPOSURE TO A BRIEF RESTRAINT SESSION FACILITATES THE OCCURRENCE OF FEAR IN RESPONSE TO A CONFLICT SITUATION - BEHAVIORAL AND NEUROCHEMICAL CORRELATES

The influence of two different stressors on the behavioral and neuroch emical responses to a subsequent exposure to the elevated plus maze (E PM) was examined. Rats were submitted to either a 15-min restraint per iod or to a 15-min forced swimming test (FS) and one dap later exposed to the EPM. Animals with early restraint exhibited a significant decr ease in the percent time spent and in the number of entries on the ope n arms. In addition, restraint induced a reduction in the total number of entries, An identical behavior in the EPM was observed between uns tressed rats and those exposed to a previous swimming experience. As a humoral index of stress, corticosterone (CS) secretion in response to each stressor was evaluated. A similar increase of CS release was obs erved following each aversive stimulus. Exposure to both restraint and EPM decreased the cortical chloride uptake following GABA stimulation . Similar values of chloride flux were obtained from animals submitted to either restraint but without subsequent exposure to the EPM, expos ed only to the EPM, or without any manipulation (controls). These find ings are discussed in terms of a facilitated behavioral and neurochemi cal response to a fearful situation following an early and brief restr aint experience. (C) 1997 Elsevier Science B.V.