Scopolamine-induced deficits in social memory in mice: Reversal by donepezil

Deficits in social behaviour is a characteristic of numerous mental disorders including autism, schizophrenia, depression and Alzheimer's disease. For the assessment of pharmacological and genetic experimental disease models, conventional social interaction tasks bear the uncertainty that any drug-induced abnormality of the investigator may feed back to the drug-free companion modifying its reactions. A considerable technical improvement was recently reported by Moy et al. [Moy SS, Nadler JJ, Perez A, Barbaro RP, Johns JM, Magnuson T, et al. Sociability and preference for social novelty in five inbred strains: an approach to assess autistic-like behaviours in mice. Genes Brain Behav 2004;3:287-302] in which the drug free partner is confined to a small cage and social contacts of the investigator are recorded uncontaminated of any social reactions of the stranger. Using this novel behavioural paradigm, we here show in C57Bl/6 female mice that sociability (social interaction with a stranger mouse) is not impaired after administration of the anxiolytic diazepam (0.1-1 mg/kg) or the muscarinic antagonist scopolamine hydrobromide (0.1-1 mg/kg). However, social memory tested after a short time interval was impaired by both drugs in a dose-dependent manner (diazepam: ≥0.5 mg/kg; scopolamine: ≥0.3 mg/kg). The scopolamine-induced short-term memory deficit was reversed to normal by the choline esterase inhibitor donepezil (1 mg/kg). Given this dependence of social recognition on the cholinergic system, combined with the clinical observation of reduced social contacts in dementia patients, sociability may offer a novel endpoint biomarker with translational value in experimental models of cognitive dysfunction.