Exposure to a Novel environment interferes with the induction of hippocampal primed burst potentiation in behaving rats

Examined primed burst (PB) potentiation induced by electrical stimulation that mimics hippocampal physiology. Stimulation of the hippocampal commissural afferents by a single priming pulse, followed 170 msec later by 4 pulses at 200 Hz, induced PB potentiation of the CA1 population spike. 59 recording sessions in 29 rats served as the database. PB potentiation occurred in only 15% of the 1st recording sessions. Incidence increased with continued stimulations: 30% with the 2nd, 75% with the 3rd, and 92% with the 4th–6th sessions. In additional studies of 21 rats, acclimation to the environment, rather than a kindling-like phenomenon, was identified as a precondition. Findings suggest that exposure of a rat to a novel environment results in a profound, but temporary, inhibition of hippocampal plasticity