Differential effects of i.c.v. microinfusion of agmatine on spatial working and reference memory in the rat

Recent evidence suggests that agmatine, the metabolite of arginine by arginine decarboxylase, exists in the mammalian brain and is a novel neurotransmitter. Exogenous agmatine can modulate behaviour function, including learning and memory. The present study investigated the effects of repeated i.c.v. microinfusion of agmatine (once daily) on the reference and working memory versions of the water maze task, as well as the elevated plus maze and open field. Rats with high (100 microg), but not low (10 microg), dose of agmatine displayed reduced exploratory and locomotor activity in the open field relative to the saline controls on day 1 (received three infusions), but not day 12 (received 14 infusions). The three groups performed similarly on both days in the elevated plus maze tested prior to the open field. In the reference memory version of the water maze task, rats with agmatine treatment at both doses performed as well as the saline controls in the cued navigation (day 2), place navigation (days 3-7) and probe test (day 7). In the working memory version of the water maze task (days 8-11), the two agmatine groups generated markedly shorter path length and took significantly less time to reach the platform at the 180 s, but not 30 s, delay as compared to the saline group. These results demonstrate that repeated agmatine treatment produces transient impairments in exploratory and locomotor activity in the open field in a dose-dependent manner. Agmatine significantly facilitates spatial working memory at a longer delay, but not reference memory, suggesting its differential influence on the two types of spatial learning and memory. The underlying mechanisms need to be explored in the future.