Pilocarpine improves olfactory discrimination and social recognition memory deficits in 24 month-old rats

Muscarinic receptor agonists have been suggested as potential drugs to counteract age-related cognitive decline since critical changes in cholinergic system occur with aging. Recently, we demonstrated that single administration of the non-selective muscarinic receptor agonist pilocarpine prevents age-related spatial learning impairments in rats. In addition, increasing evidence suggests that areas in the central nervous system processing olfactory information are affected at the early stages of age-related diseases, such as Alzheimer's disease, and that specific olfactory testing may represent an important tool in the diagnosis of these diseases. In the present study, olfactory discrimination and short-term social memory of 3 and 24 month-old rats were assessed with the olfactory discrimination and social recognition memory tasks, respectively. The actions of the repeated treatment with pilocarpine (30 mg/kg, i.p.; once per day for 21 days) in relation to age-related effects on olfactory and cognitive functions were also studied. The 24 month-old rats exhibited significantly impaired performance in both models, demonstrating deficits in their odour discrimination and in their ability to recognize a juvenile rat after a short period of time. The treatment with pilocarpine improved in a specific manner these age-related deficits in 24 month-old rats without altering their motor performance. The present results extend the notion of the participation of muscarinic receptors in control of olfactory functions and reinforce the potential of muscarinic receptor agonists for the treatment of age-related cognitive decline.