Research report The long-term effects of nefiracetam on learning in older rabbits Diana S. Woodruff-Pak a,b, *, John T. Green b , Jonathan T. Pak b , Tadashi Shiotani c , Shigeo Watabe c , Makoto Tanaka c a Research and Technology Development, Albert Einstein Healthcare Network, Korman Suite 100, 5501 Old York Road, Philadelphia, PA 19141, USA b Temple University, Philadelphia, PA, USA c Daiichi Pharmaceutical Co., Ltd., Tokyo, Japan Received 28 January 2002; received in revised form 3 June 2002; accepted 3 June 2002 Abstract Classical conditioning of the nictitating membrane (NM)/eyeblink response has proven utility in the study of age-related memory disorders. The 750 ms delay eyeblink conditioning procedure was used to investigate the magnitude and duration of the nootropic drug nefiracetam’s effect on retention and relearning. After administering daily injections of 0 (vehicle), 5, 10, or 15 mg/kg nefiracetam to 34 retired breeder rabbits during 15 days of acquisition, we tested retention and relearning 1, 5, and 12 weeks post- training. Rabbits received no drug after the initial 15 daily injections. Significant relearning was observed in the 10 mg/kg nefiracetam group 1 and 5 weeks after initial acquisition. Differences in tone-alone retention did not achieve statistical significance, although responses were numerically greater in the 10 mg/kg nefiracetam group. The effect of nefiracetam upon the ability of older rabbits to relearn a previously learned task is apparent up to 5 weeks after drug administration. Under normal conditions, a drug is administered continuously. In this experiment, nefiracetam had a significant effect long after drug administration had ceased. Prolonged administration of nefiracetam may have ameliorating effects greater than those observed in only 15 days of drug administration. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Cognition-enhancing drug; Relearning; Retention; Alzheimer’s disease; Eyeblink classical conditioning; Nicotinic acetylcholine receptors; Aging; Hippocampus 1. Introduction Eyeblink classical conditioning reveals natural age- related deficits in several non-human mammals, and the similarities between age differences in eyeblink condi- tioning displayed in normal aging by these animal species and humans are strikingly similar. Brain imaging studies using positron emission topography [10] and functional magnetic resonance imaging [9] of normal young adults as well as studies with human patient populations with lesions in various brain structures, suggest that the neural circuitry for eyeblink condition- ing in humans is similar to the circuitry demonstrated in mice, rats, cats, and rabbits [5,32]. Moreover, delay eyeblink classical conditioning is a task in which patients diagnosed with probable Alzheimer’s disease (AD) are profoundly impaired, making it a useful model system for preclinical trials of cognition-enhancing drugs [31]. In addition to its parallels with human behavior and neurobiology, the model system of eyeblink classical conditioning in non-human mammals possesses a con- siderable advantage over the behavioral models com- monly used in preclinical trials: the neural circuitry is almost completely understood [27,28]. 1.1. Eyeblink classical conditioning paradigm The standard format for the presentation of stimuli in eyeblink classical conditioning is called the delay para- digm. The subject is presented with a neutral stimulus such as a tone or light, called the conditioned stimulus (CS), for a short duration  /usually less than 1 s. Before the CS expires, the unconditioned stimulus (US) is presented concurrently, and the briefly coinciding CS * Corresponding author. Tel.:  /1-215-456-6351; fax:  /1-215-456- 8122 E-mail address: woodrufd@einstein.edu (D.S. Woodruff-Pak). Behavioural Brain Research 136 (2002) 299 /308 www.elsevier.com/locate/bbr 0166-4328/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0166-4328(02)00186-9