Task-Dependent Role for Dorsal Striatum Metabotropic Glutamate Receptors in Memory

Abstract

The effect of post-training intradorsal striatal infusion of metabotropic glutamate receptor (mGluR) drugs on memory consolidation processes in an inhibitory avoidance (IA) task and visible/hidden platform water maze tasks was examined.In the IA task, adult male Long-Evans rats received post-training intracaudate infusions of the broad spectrum mGluR antagonist ␣-methyl-4-carboxyphenylglycine (MCPG; 1.0, 2.0 mM/0.5 µL), the group I/II mGluR agonist 1-aminocyclopentane-1,3-carboxylic acid (ACPD; 0.5 or 1.0 µM/0.5 µL), or saline immediately following footshock training, and retention was tested 24 h later.In the visible-and hidden-platform water maze tasks, rats received post-training intracaudate infusions of ACPD (1.0 µM), MCPG (2.0 mM), or saline immediately following an eight-trial training session, followed by a retention test 24 h later.In the IA task, post-training infusion of ACPD (0.5 and 1.0 µM) or MCPG (1.0 and 2.0 mM) impaired retention.In the IA and visible-platform water maze tasks, post-training infusion of ACPD (1.0 µM), or MCPG (2.0 mM) impaired retention.In contrast, neither drug affected retention when administered post-training in the hidden-platform task, consistent with the hypothesized role of the dorsal striatum in stimulus-response habit formation.When intradorsal striatal injections were delayed 2 h post-training in the visible-platform water maze task, neither drug affected retention, indicating a time-dependent effect of the immediate post-training injections on memory consolidation.It is hypothesized that MCPG impaired memory via a blockade of postsynaptic dorsal striatal mGluR's, while the impairing effect of ACPD may have been caused by an influence of this agonist on presynaptic "autoreceptor" striatal mGluR populations.