PSYCHOLOGICAL STRESS REPEATEDLY BLOCKS HIPPOCAMPAL PRIMED BURST POTENTIATION IN BEHAVING RATS

Primed burst (PB) potentiation is a long-term increase in CA1 populati on spike amplitude produced by brief physiologically patterned electri cal stimulation of the hippocampal commissure. Exposure of rats to a n ovel environment resulted in a blockade of short-term (Post-tetanic po tentiation, PTP) and long-term (PB potentiation) plasticity in all cas es (n = 6). When the animals had extensive exposure to the environment (14 consecutive days), PTP and PB potentiation occurred. With placeme nt of the rats in a second novel environment, once again, neither PTP nor PB potentiation was observed. Placement of rats in each of the two novel environments produced a significant increase in serum corticost erone levels, while placement in the familiar environment produced no increase in response. These findings support the hypothesis that hippo campal plasticity is repeatedly susceptible to modulation by the stres s of forced exposure to a novel environment.