THE EFFECTS OF TYPE-I AND TYPE-II CORTICOSTEROID RECEPTOR AGONISTS ONEXPLORATORY-BEHAVIOR AND SPATIAL MEMORY IN THE Y-MAZE

We investigated the effects of two adrenal steroid agonists on adrenal ectomized (ADX) rats' performance on the Y-maze. The Y-maze was chosen because memory can be. assessed quickly and because it is sensitive t o various parameters of exploratory behavior and spatial memory perfor mance. Four days after surgery, ADS rats were injected with aldosteron e (ALDO, a selective Type I receptor agonist), RU362 (a selective Type II receptor agonist) or sesame vehicle sit three different time point s (120 min prior to Trial 1, immediately after Trial 1 or 120 min afte r Trial 1). SHAM-operated rats injected with vehicle were also tested. The results indicate that vehicle-treated ADX rats were impaired on s patial recognition memory compared to SHAM rats. Treatment with ALDO r estored spatial recognition memory performance of ADX rats to a level comparable to SHAM-treated rats by acting on acquisition and consolida tion, whereas treatment with RU362 did not change the poor spatial rec ognition memory performance of ADX rats. Discrimination memory was imp roved only when either agonist was injected prior to the first trial, strongly suggesting a non-selective effect of corticosteroids on discr imination memory such as increasing arousal. A detailed analysis of ex ploratory behavior showed that both the ALDO- and RU362-treated rats e xplored the Y-maze more than the ADS and SHAM groups at all periods of the experiment. These results show that the non-specific increase in exploratory behavior induced by replacing corticosteroids targeted at Type I and Type II receptors was used differentially with the ALDO-tre ated rats learning and consolidating spatial information better than t he RU362-treated rats. These data are discussed along with other evide nce to suggest that Type II receptors may require the simultaneous occ upancy of Type I receptors to affect learning and memory processes.