Met-enkephalin, age and anatomy: a microiontophoretic study in the hippocampus

Met-enkephalin, administered microiontophoretically, produced a greater increase in firing in cells in area CA 3-4 in the hippocampus of both young and aged Fisher 344 rats than it did in the CA 1 area. Furthermore, the effect of met-enkephalin on neuronal firing rates was not as great in old rats as it was in young rats. Finally, 20-40 nA of met-enkephalin produced an increase in firing in old rats that was equivalent to the difference (2.5 spikes/sec) in baseline firing between old (2.6 spikes/sec) and young rats (5.1 spikes/sec).