Age-related reduction in responses of rat hippocampal neurons to locally applied monoamines.

Age-related changes in the responsiveness of hippocampal pyramidal neurons to norepinephrine (NE) and serotonin (5HT) were investigated using electrophysiological techniques. Local application of each monamine via pressure micro-ejection was employed to establish the dose which elicited a 50% change in spontaneous discharge rate of single pyramidal neurons; these data were used to construct dose response curves for the population of neurons tested in 3-6, 11-13, 18-20, and 27-30 month old rats. The percentage of cells responding in rats 18-20 and 27-30 months old decreased for both NE and 5HT. There was also a progressive increase with age in the population ED50 for 5HT starting at 18-20 months. For neurons which demonstrated a response to NE, no decrease in the population ED50 was observed. Taken together these data indicate that there is a progressive age-related decline in the postsynaptic response to NE and 5HT in the rodent hippocampus.