FAILURE OF THE NMDA RECEPTOR ANTAGONIST KETAMINE TO IMPAIR MEMORY WHEN ADMINISTERED AFTER STIMULUS-PRESENTATION

Glutamatergic dysfunction has been hypothesized to underlie memory def icits in patients suffering from Alzheimer's and schizophrenia. NMDA r eceptor antagonists (e.g., PCP, ketamine) impair memory by blocking lo ng-term potentiation in the hippocampus. Limited research in humans ha s taken place and studies typically administer the antagonists before the learning experience, perhaps resulting in inattention induced by t he psychotomimetic effects of these drugs and/or alterations in sensor y processing. Bolus injections of ketamine (.01, .03, and 0.5 mg/kg) o r placebo were given to 11 normal controls. Immediately prior to injec tion a verbal memory test and a digit supraspan procedure were adminis tered. Unlike previous studies in which the drug is administered befor e stimulus presentation, postinjection (30-45 min) scores revealed no differences between the drug and placebo conditions for either task.