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 neurochemical responses to a subsequent exposure to the elevated plus maze (EPM) was examined. Rats were submitted to either a 15-min restraint period or to a 15-min forced swimming test (FS) and one day later exposed to the EPM. Animals with early restraint exhibited a significant decrease in the percent time spent and in the number of entries on the open arms. In addition, restraint induced a reduction in the total number of entries. An identical behavior in the EPM was observed between unstressed 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 observed 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, exposed only to the EPM, or without any manipulation (controls). These findings are discussed in terms of a facilitated behavioral and neurochemical response to a fearful situation following an early and brief restraint experience.