Effects of prolonged exposure to context following contextual fear conditioning on synaptic properties in rat hippocampal slices.

Acute stressful events enhance plasma corticosterone release and profoundly affect synaptic functions, which are involved in the development of stress-related cognitive and mental disorders. However, how exposure to stressful context immediately after stress further modulates the physiological responses is not fully understood. Here, we found that acute stress inhibited paired-pulse facilitation in hippocampal slices of Wistar rats which were subjected to contextual fear conditioning. But such inhibition was reversed by subsequent prolonged exposure to foot-shock context or returning to home cage for 1 h. Interestingly, foot-shock stress-facilitated LTD induced by low frequency stimulation (LFS, 900 pulses at 1 Hz) was maintained by subsequent exposure to foot-shock context but was reversed by returning to home cage environment. Moreover, plasma corticosterone level was still kept higher in rats exposed to foot-shock context but not to home cage. Findings suggest that remaining in stressful environment immediately after stress maintains acute stress-facilitated LTD and higher level of neuroendocrine response. Our results also contribute to further understanding the critical role of timely intervention in mediating stress-related aversive changes in human.