BEHAVIORAL AND NEURAL BIOLOGY 57, 233--243 (1992) Chlordiazepoxide-lnducedWorking Memory Impairments:Site Specificity and Reversal by Flumazenil (RO15-1788) ROBERT W. STACKMAN AND THOMAS J. WALSH 1 Department of Psychology, Rutgers University, New Brunswick, New Jersey 08903 The following studies examined the dose and time de- pendence, site specificity, and reversibility of chlordiaz- epoxide (CDP)-induced working memory impairments in adult male Sprague-Dawley rats. The rats were tested in a delayed non-match-to-sample radial-arm maze task in which a 1-h delay was imposed between the first four (predelay) and all subsequent (postdelay) arm choices. Intraperitoneal (ip) injection of 2.5 or 5.0 but not 1.25 mg/kg CDP immediately following the predelay session impaired performance in the task. CDP increased the number of errors and decreased the number of correct choices during the postdelay session. The observed work- ing memory impairments also appeared to be site specific since injection of CDP into the medial septum, but not into the anterior amygdala nuclei, immediately following the predelay session also impaired working memory in a dose-related manner. Furthermore, there was a time win- dow for CDP-induced working memory impairments since intraseptal injection of the drug immediately but not 15 rain following the predelay session disrupted memory. This observation suggests that the performance deficits reflect disrupted working memory and not proactive ef- fects on performance or the induction of state-dependent learning. In the final experiment, rats were injected ip with either saline or an amnestic dose of CDP (5.0 mg/kg) following the predelay session and then were immediately infused with 10 nmol flumazenil (RO15-1788), a benzo- diazepine receptor antagonist or vehicle, into either the medial septum or anterior nuclei of the amygdala. Intra- septal injection of flumazenil prevented the working mem- ory impairments produced by ip injection of CDP. In con- trast, intra-amygdala injection of flumazenil did not attenuate, enhance, or modify the CDP-induced working memory impairment. These observations suggest that CDP disrupts working memory by interacting with ben- zodiazepine receptors in the medial septum. ~ 1~2 Academic Press, Inc. 1 This research was supported in part by NSF Grant BNS- 9109163 to T.J.W. Please address correspondence and reprint requests to Dr. Thomas J. Walsh, Department of Psychology, Rutgers University, Busch Campus, New Brunswick, NJ 08903. INTRODUCTION Benzodiazepines (BDZ) are widely used as anx- iolytics, anticonvulsants, sedative hypnotics, and muscle relaxants (File & Pellow, 1987). In addition to these broad therapeutic actions they can also pro- duce such undesirable side effects as amnesia (Lister, 1985; Thiebot, 1985). While the neurophar- macological mechanisms of action and sites respon- sible for their therapeutic effects are becoming in- creasingly understood (see Walsh & Stackman, 1992), there is little understanding of how these compounds produce amnesia. BDZs interact with specific receptors which con- stitute part of the macromolecular GABA-A recep- tor complex and act to increase the affinity of the receptor for GABA (Duman, Sweetnam, Gallom- bardo, & Tallman, 1987). BDZ receptors are widely distributed in the forebrain and limbic system sug- gesting a variety of potential sites for their diverse pharmacological actions (Young & Kuhar, 1980; Mohler, Wu, & Richards, 1981). Several sources of evidence indicate that the amygdala contributes to the anxiolytic effects of BDZs. Intra-amygdala injection of BDZs produces an anxiolytic action that is comparable in magni- tude to that produced by systemic injection (Nagy, Zambo, & Decsi, 1979; Scheel-Kruger & Peterson, 1982; Hodges, Green, & Glenn, 1987). Furthermore, the anxiolytic efficacy of various BDZs is positively correlated with their affinity for BDZ receptors in the amygdala (Thomas, Lewis, & Iversen, 1985). These data point to the amygdala as a primary site mediating the anxiolytic actions of BDZs. There is also evidence that a GABA/BDZergic mechanism in this region plays a modulatory role in memory (Brioni, Nagahara, & McGaugh, 1989; Izquierdo, Da Cunha, Huang, Wolfman, & Medina, 1990a). How- ever, other brain systems, known to be involved in 233 0163-1047/92 $5.00 Copyright © 1992 by Academic Press, Inc. All rights of reproduction in any form reserved