Adult male Brown Norway rats were long-term intracerebroventricularly (i.c.v.) infused with antisense oligodeoxynucleotides (18-mer, double endcapped phosphorothioate protected) targeting either mineralocorticoid or glucocorticoid receptor mRNA, or received the respective mixed bases sequence or vehicle. Mineralocorticoid receptor-mixed bases and glucocorticoid receptor-mixed bases oligodeoxynucleotide infusion (1 microg/0.5 microl/h) over a time period of seven days did not alter hippocampal mineralocorticoid receptor and glucocorticoid receptor binding when compared to vehicle treatment. In contrast, i.c.v. administration of mineralocorticoid receptor, as well as glucocorticoid receptor-antisense over the same time period resulted in a significantly reduced binding of mineralocorticoid receptor and glucocorticoid receptor in the hippocampus [mineralocorticoid receptor-antisense group approx. 72% of mineralocorticoid receptor-mixed bases and vehicle groups (100%); glucocorticoid receptor antisense group approx. 77% of glucocorticoid receptor-mixed bases and vehicle]. The specificity of these antisense effects is indicated by the finding that rats treated with mineralocorticoid receptor-antisense did not show any changes in glucocorticoid receptor and vice versa. Animals treated according to this infusion protocol and tested in the Morris water maze for their spatial navigation abilities failed to show significant differences among the groups. These data indicate that a reduction of hippocampal mineralocorticoid receptor or glucocorticoid receptor binding capacity by 20-30% does not interfere with spatial navigation.