Altered modulatory actions of serotonin on dentate granule cells of aged rats

The effects of serotonin (5-HT) on dentate granule (DG) neurons in hippocampal slices taken from young mature (6-8 months) and old (25-29 months) rats were compared. Intracellular measurements of membrane potential, cell input resistance and slow postspike afterhyperpolarization did not differ significantly between young and old neurons. Neurons recorded in slices taken from old animals responded with less hyperpolarization to increasing doses of the drug, and their responses were significantly reduced after repeated applications of 5-HT. Serotonin-mediated reduction of the slow afterhyperpolarization in young DG neurons was less prominent or totally absent in the old cells. It is concluded that serotonergic postsynaptic actions are impaired in old age.