Age-related declines in delayed non-match-to-sample performance (DNMS) are reversed by the novel 5HT6 receptor...

Alterations in synaptic plasticity and neurocognitive function with age have been well documented in the literature. These changes are accompanied by modifications of neurotransmitter systems in the central nervous system (CNS). The serotonergic system in particular plays an important role in attention, alertness and cognition. Disturbances in serotonergic function have been implicated in differing neurological and neuropsychiatric disorders including depression, psychosis aggression and dementia. The serotonin receptor subtype 5HT6 is distributed within CNS regions relevant to learning and memory, including the striatum, cortex and hippocampus. We examined here the effects of acute and chronic administration of the 5HT6 receptor antagonist SB742457 on performance in a delayed non-matching-to-sample task (DNMS), which was used to identify neurocognitive differences between middle-aged (MA, 13 months) and young adult (YG, 3 months) rats. We found that MA rats have significantly lower performance in the DNMS task compared to YG rats. Acute administration of SB742457 (3 mg/kg/po) significantly improved performance of the MA rats. Chronic administration of SB742457 (3 mg/kg) reversed the age-related deficit of the MA to match their performance to that of YG rats. Furthermore, these improvements were observed for 1 week post-SB742457 treatment cessation. The acute and chronic effects of this treatment suggest that there is both an immediate effect on neurotransmitter action and potentially a longer-term modification of synaptic plasticity. Together these data indicate a role for modulation of the serotonergic system in the development of cognition-enhancing agents.