Aged Stone mazeimpaired rats exhibit reduced striatal muscarinic receptor densities

MUSCARINIC receptor densities, measured by saturation radioligand binding using the muscarinic antagonist [3H]QNB, were compared in the striatum, frontal cortex and hippocampus between two populations of young (3 month) and aged (12–20 month) Hooded Lister rats which had previously been tested in a complex maze task. Aged rats were impaired in their performance of a Stone (14-unit T-maze) task and were less spontaneously active than young rats. Muscarinic receptor numbers were significantly decreased in the striatum of aged rats, whilst numbers in the hippocampus and frontal cortex and receptor affinities in all three areas were unaltered. These results indicate that the age-associated depletion of striatal muscarinic receptors may contribute to deficits in cognitive processing and/or motor behaviour which underlie impairments in the performance of complex spatial tasks.