Effect of age on burst firing characteristics of rat hippocampal pyramidalcells

During behavior, hippocampal pyramidal cells emit high frequency bursts, mo dulated by the animal's location and the 7 Hz theta rhythm. During rest, CA I EEG exhibits large irregular activity (LIA), containing sharp-wave/ripple complexes, during which pyramidal cells exhibit burst discharge. Aging res ults in altered intracellular calcium homeostasis, increased electrical cou pling and reduced cholinergic modulation within CAI, all of which might aff ect burst discharge characteristics. During LIA, old rats exhibited more sh ort (3-7 ms) inter-spike intervals, with no change in mean firing rate. Dur ing behavior induced theta rhythm, however, interval distributions were not affected by age. Thus, different mechanisms must underlie burst discharge in theta and LIA states. Moreover, age related changes in the cholinergic s ystem appear not to play a major role in shaping the temporal discharge cha racteristics of CAI pyramidal cells. The mechanism and significance of the higher frequency bursting in old rats during LIA remains to be determined. NeuroReport 11:33865-3871 (C) 2000 Lippincott Williams & Wilkins.