Intraseptal flumazenil enhances, while diazepam binding inhibitor impairs, performance in a working memory task

GABAA/benzodiazepine receptors in the medial septum modulate the activity of cholinergic neurons that innervate the hippocampus. Injection of benzodiazepine (BDZ) agonists into the medial septum impairs working memory performance and decreases high-affinity choline transport (HAChT) in the hippocampus. In contrast, intraseptal injection of the BDZ antagonist flumazenil increases HAChT and prevents the memory deficits induced by systemic BDZs. The present studies attempted to further characterize the behavioral effects of medial septal injections of flumazenil to an endogenous negative modulator of the GABAA/BDZ receptor complex, diazepam binding inhibitor (DBI). Male Sprague-Dawley rats were cannulated to study the effects of intraseptal injections of these BDZ ligands on spatial working memory, anxiety-related behaviors in the elevated plus maze, and on general locomotor activity. Intraseptal flumazenil (10 nmol/0.5 microliter) produced a delay-dependent enhancement of DNMTS performance after an 8-h, but not a 4-h, delay interval. This promnestic dose of flumazenil had no effect on locomotor activity and did not produce changes in measures of anxiety on the plus maze. Intraseptal injection of DBI had no effect (8 nmol/0.5 microliter) or slightly impaired (4 nmol/0.5 microliter) DNMTS radial maze performance following an 8-h delay, without producing changes in locomotion or plus maze behavior. These data demonstrate that flumazenil has a unique profile of activity in enhancing working memory following intraseptal injection.