Age-related changes in rat serotonergic and adrenergic systems and in receptor responsiveness to subchronic desipramine treatment.

Noradrenergic (NA) and serotonergic (5-HT) receptor profiles were compared in the cerebral cortex of young adult (3 months old) and aged (24 months old) male Sprague Dawley rats. Beta and alpha-1 receptors were significantly decreased in 24 month old rats, whereas alpha-2 receptors remained unchanged. 5-HT-2 Postsynaptic receptors and 5-HT high affinity uptake were reduced in aged animals; on the other hand the number of 3H-imipramine (3H-IMI) recognition sites located on serotonin nerve terminals and labelled also by 3H-paroxetine (3H-PAR), were significantly higher in the cerebral cortex of old rats. The ratio 5-hydroxyindoleacetic acid (5-HIAA)/5-HT, an index of serotonin turn-over, increased in some brain areas of senescent rats. There were no age-related changes in the responsiveness of investigated binding sites to subchronic desipramine treatment; the density of beta-noradrenergic and 5-HT-2 serotonergic receptors and that of 3H-IMI binding sites was reduced both in young adult and aged rats.