Long-term potentiation in the dentate gyrus is preferentially induced at theta rhythm periodicity

In urethane-anesthetized rats, high frequency stimulation was applied to the medial perforant pathway at various time intervals (50, 100, 200, 350 and 500 ms) following stimulation of the same pathway by a single pulse of equal intensity. Recordings of dentate gyrus granule cell evoked responses were made to investigate the range of stimuli that are effective in inducing long-term potentiation (LTP). LTP was induced almost exclusively at the 200 ms interval, corresponding to the periodicity of the theta rhythm. Taken in conjunction with similar findings reported in the CA1 field of the hippocampal slice, these results suggest that the correlation between theta rhythm periodicity and LTP is a general phenomenon within the hippocampal formation and lends further support to the hypothesis that the naturally occurring theta rhythm may play a modulatory role in the induction of LTP.