Enhanced evoked responses after early adversity and repeated platform exposure: the neurobiology of vulnerability?

Background There is a long-standing clinical awareness of the significance of adverse early experiences and subsequent stress in the evolution of psychiatric disorder. Methods We investigated the impact of a single episode of preweaning maternal separation on in vivo electrophysiologic responses in the hippocampus of the mature rat after repeated exposure to an open elevated platform. Results Only rats that had experienced both maternal separation followed by stressful platform exposure when mature had significantly increased granule cell response to perforant path stimulation, compared with control rats. Rats exposed to either maternal separation or the elevated platform in adulthood alone did not differ significantly from control rats. Conclusions Adverse early experience seems to induce functional changes in the hippocampus that remain latent until activated by stress in adulthood. Such electrophysiologic changes might represent a neural substrate for vulnerability to stress-associated psychopathology.