Social interaction and elevated plus-maze tests: changes in release and uptake of 5-HT and GABA

Changes in release and uptake of [3H]5-HT and [14C]GABA were compared in slices taken from the hippocampus and frontal cortex of rats, left undisturbed in their home-cages, or exposed for 5 min to the elevated plus-maze or social interaction tests of anxiety. Exposure to the plus-maze decreased cortical GABA function (shown by decreased release) and increased hippocampal 5-HT function (shown by increased K(+)-evoked release but more markedly by decreased uptake). Compared with undisturbed home cage controls, only the high light, familiar condition of the social interaction test resulted in a significant increase in K(+)-evoked release of both [3H]5-HT and [14C]GABA from the hippocampus. All four social interaction test conditions resulted in increases in cortical uptake of [3H]5-HT and all but the high light, unfamiliar condition increased cortical uptake of [14C]GABA. Analysing the two factors manipulated in the social interaction test, unfamiliarity with the test arena resulted in increased uptake of hippocampal [3H]5-HT and decreased cortical [14C]GABA, whereas an increase in the level of light decreased the cortical uptake of [14C]GABA. The results show that changes in presynaptic function occur rapidly in response to a brief exposure to animal tests of anxiety. However, only the increased hippocampal release of 5-HT is likely to be causally linked to anxiety and the results show that this cannot be the sole explanation.