Neurotoxic lesion of the rostral perirhinal cortex blocks stress-induced exploratory behavioral changes in male rats

Exposure to stress leads to adaptive responses including both behavioral and physiological changes. This process is induced by the activation of multiple brain regions. The present study examined the role of the rostral perirhinal cortex (rPRh) in behavioral changes following electrical foot shock-induced stress. The rPRh of rats was lesioned bilaterally by local microinjections of 10g N-methyl-d-aspartic acid (NMDA) before foot shocks (0.7mA, 1s). The effects of these lesions on foot shock-induced changes in exploratory behaviors were tested in the open field (4h, 48h, 72h, and 14days after foot shocks) and the light-dark box (7days after foot shocks). Foot-shocked and sham-lesioned rats showed several well known behavioral changes in the open field (e.g., immobility, reduction of exploratory activity) most marked at 48h after foot shocks, and the light-dark box (e.g., reduction of time spent and activity in the lit compartment). All these stress-induced behavioral changes were blocked by neurotoxic lesions of the rPRh. Furthermore, rPRh lesions did not affect behavior in the open field and the light-dark box in unstressed rats. Taken together, these data indicate that the rPRh is involved in neurophysiological mechanisms that mediate changes induced by foot-shock stress in exploratory behaviors which indicate unconditioned fear or anxiety.