Exposure to a novel environment interferes with the induction of hippocampal primed burst potentiation in the behaving rat

Abstract

Primed burst (PB) potentiation is a low threshold form of long-term potentiation that is induced by a pattern of electrical stimulation that mimics specific features of hippocampal physiology. In our paradigm, stimulation of the hippocampal commissural afferents composed of a single priming pulse, followed 170 msec later by a burst of four pulses at 200 Hz, induces PB potentiation of the CA1 population spike. We now report that the capacity for patterned stimulation to induce PB potentiation in behaving rats is affected by the animals’ experience with the recording procedures. Specifically, PB potentiation occurred in only 15% of the first recording sessions. With continued stimulations over the course of days, the incidence of PB potentiation increased: Lasting effects occurred in 30% of the second, 75% of the third, and 92% of the fourth through sixth recording sessions. In additional studies, acclimation to the environment, rather than a kindlinglike phenomenon, was identified as the critical precondition for PB potentiation to occur. Thus, our findings indicate that exposure of a rat to a novel environment results in a profound, but temporary, inhibition of hippocampal plasticity. The relationship of this work to studies of stress and hippocampal-dependent learning is discussed.