Parallel nature of hippocampal synaptic plasticity.

This study demonstrates that the mechanisms involved in the production of long-term potentiation (LTP) in the hippocampus appear to be independent of those which generate shorter-lasting plasticity, but that both processes are activated concurrently following an LTP-inducing stimulus. Adult male Sprague-Dawley rats were anesthetized using either pentobarbital or secobarbital to record extracellular field potentials from the hippocampal CA1 pyramidal cell layer in response to stimulation of commissural afferents. Plasticity was generated by the delivery of a five-pulse patterned stimulus train, consisting of one priming pulse followed 170 milliseconds later by a burst of four pulses at 200 Hz. While similar LTP was observed in both groups, short-term plasticity was absent in the secobarbital-anesthetized animals. This result suggests that different plasticity mechanisms in the hippocampus are activated in parallel by the triggering stimulus.