Neuropharmacology 43 (2002) 348–356 www.elsevier.com/locate/neuropharm NAALADase (GCP II) inhibition prevents cocaine-kindled seizures  Jeffrey M. Witkin * , Maciej Gasior a,1 , Christina Schad c , Agustin Zapata b , Toni Shippenberg b , Theresa Hartman c , Barbara S. Slusher c a Drug Development Group, Addiction Research Center, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, USA b Integrative Neurosciences Section, Addiction Research Center, National Institute on Drug Abuse, National Institutes of Health Baltimore, MD, USA c Guilford Pharmaceuticals Inc., Baltimore, MD, USA Received 12 October 2001; received in revised form 10 May 2002; accepted 26 June 2002 Abstract The prediction that inhibition of NAALADase, an enzyme catalyzing the cleavage of glutamate from N-acetyl-aspartyl-glutamate, would produce antiepileptogenic effects against cocaine was tested. Cocaine kindled seizures were developed in male, Swiss– Webster mice by daily administration of 60 mg/kg cocaine for 5 days. The NAALADase inhibitor 2-(phosphonomethyl)pentanedioic acid (2-PMPA) produced dose-dependent protection (10–100 mg/kg) against both the development of seizure kindling and the occurrence of seizures during the kindling process without observable behavioral side-effects. It is not likely that 2-PMPA produced protection against cocaine kindling by altering the potency of the convulsant stimulus as daily administration of 2-PMPA did not alter the convulsant thresholds for cocaine. Lower daily doses of cocaine (40 mg/kg) did not increase the incidence of seizures but produced kindling, as evidenced by the increase in seizure susceptibility when mice were probed with a higher dose of cocaine. 2-PMPA was also effective in preventing the development of sensitization to this covert kindling process. In contrast to its efficacy against cocaine kindled seizures, 2-PMPA failed to attenuate the convulsions engendered by acute challenges with pentylenetetrazole, bicuculline, N-methyl-d-aspartate, maximal electroshock or cocaine. Similarly, acutely-administered 2-PMPA did not block cocaine seizures in fully-kindled mice. NAALADase inhibition thus provides a novel means of attenuating the development of cocaine seizure kindling.  2002 Elsevier Science Ltd. All rights reserved. Keywords: NAALADase inhibition; NAAG; Cocaine; Seizure kindling; Mice 1. Introduction Cocaine dependence has been linked to high rates of morbidity and mortality in humans (Benowitz, 1993; * Corresponding author. tel.: +1-317-277-4470; fax: +1-317-276- 7600. E-mail address: jwitkin@lilly.com (J.M. Witkin).  The facilities in which the animals were maintained are fully accredited by the American Association for the Accredidation of Lab- oratory Animal Care (AAALAC), and the studies described herein were conducted in accordance with the Guide for Care and Use of Laboratory Animals provided by the NIH and adopted by NIDA. 1 Maciej Gasior was a visiting fellow in the National Institutes of Health granted from Fogarty International Center, Bethesda, MD. His current address is Department of Psychiatry, McLean Hospital, Harv- ard Medical School, 115 Mill Street Belmont, MA 02178-2417. Neuro- science Discovery Research, Lilly Research Laboratories, Indianapolis, IN 46285-0510, 0028-3908/02/$ - see front matter  2002 Elsevier Science Ltd. All rights reserved. PII:S0028-3908(02)00124-7 SAMHSA, 1997). Status epilepticus following cocaine poisoning is often resistant to standard therapy and can be fatal (Dhuna et al., 1991). In addition to acute over- dose toxicity, repeated exposure to non-convulsant doses of cocaine increases the probability of seizures in animal models (Miller et al., 2000; Tatum and Seevers, 1929). The increased sensitivity to the convulsant effects of cocaine, following repeated exposure to this drug, has been termed seizure kindling in which repetitive sub- convulsant stimulation (chemical, electric, spontaneous) eventually result in overt convulsions (e.g., Goddard et al., 1969). In humans, cocaine kindling may not only increase seizure probability (Dhuna et al., 1991), but is associated with psychiatric symptoms, violent behaviors, panic disorders and ischemic brain infarct (Davis, 1996; Louie et al., 1989; Richards et al., 1998; Ruttenberger et al., 1997; Tuchman et al., 1992). Given that cocaine-