A conditioned stressful environment causes short-term metaplastic-like changes in the rat nucleus accumbens.

Stress-related alterations to the induction of hippocampal synaptic plasticity have been implicated in certain forms of psychiatric disorders. However, relatively little is known about such changes in other psychiatric disorders-related structures. We tested this possibility in one of such structures, the nucleus accumbens, during re-exposure of rats to a conditioned stressful environment, in which they had previously received shock. In both control rats (no shock) and shocked rats previously submitted to an extensive pre-exposure to the to-be-conditioned contextual cues (latent inhibition), high- and low-frequency stimulation of fimbria-accumbens pathway induced, in the nucleus accumbens, similar pattern of increases and decreases in synaptic efficacy, respectively. However, in non-pre-exposed shocked rats, re-exposure to the conditioned contextual cues evoked high levels of freezing, which was accompanied by a blockade of the induction of enhancement, but a facilitation of the depression, of synaptic efficacy. In addition, contextual conditioning did not alter the baseline transmission whatever the stimulus intensity and was ineffective on the induction of fimbria-accumbens synaptic plasticity following complete extinction of freezing response to the conditioned contextual cues. These data support the idea according to which stress may be involved in certain forms of psychiatric disorders via induction of metaplastic changes in circuits including the hippocampus and hippocampal limbic target structures such as the nucleus accumbens.