Adrenergic and serotonergic receptors in aged monkey neocortex

Autoradiography was employed to compare the distribution and density of adrenergic (α1, α2, and β) and serotonergic (5-HT 1) and 5-HT 2) receptors in the neocortex of young adult (3 to 10 years of age) and aged (>20 years of age) rhesus monkeys. The age-related changes in the density of adrenergic and serotonergic sites were area and layer specific. A decrease in the density of α1 receptors occurred only in the superficial layers of the somatosensory cortex, whereas the density of α2 receptors declined in layer 1 of the prefrontal cortex and in most layers of the motor and somatosensory regions. The increase in β receptors was largely confined to the deep layers of the motor and somatosensory areas. The density of 5-HT 1 sites decreased in most layers of the somatosensory cortex, while 5-HT 2 receptors declined in the deep layers of the motor cortex and middle strata of the visual cortex. Overall, adrenergic and serotonergic receptors were least affected in the prefrontal cortex and most compromised in the motor and somatosensory cortex of aged primates.