The dorsal periaqueductal gray modulates the increased fear-like behavior exhibited by experienced rats in the elevated plus-maze

Abstract

Elevated plus-maze (EPM) experienced rats show reduced open arms exploration in a subsequent EPM exposure, expressing the increased open arms avoidance which is characteristic of anxiety/fear-like behavior. The midbrain dorsal periaqueductal gray (dPAG) is an important integrative area of the neuroaxis able to control the motivational states of an animal. It has been shown that dPAG participates in the mediation of anxiety/fear-like behavior elicited in the EPM. The present study was outlined to evaluate the dPAG-NMDA-receptor contribution to the increased open arms avoidance found in EPM experienced rats. In addition, a possible mnemonic effect, due to the dPAG-NMDA-receptor blockade, was tested in the step-down inhibitory avoidance task (SD). Male Wistar rats received dPAG infusion of NMDA antagonists (AP5 or ifenprodil) before being submitted to the EPM test and retest sessions, or the SD training and test sessions. Both NMDA-receptor antagonists infused in the dPAG, reduced the fear-like behavior exhibited in the EPM by increasing the open arms exploration in both naïve and EPM experienced rats. In addition, the dPAG-NMDA-receptor blockade also reduced the latency to SD during the retrieval without interfering with the acquisition or the consolidation of the inhibitory avoidance. These results suggest that the NMDA-receptor dPAG activation could underlie the defensive response evoked in the EPM test and retest and also the retrieval of aversive memories involved in the SD. The results support the notion that the dPAG is a key structure in the modulation of the best behavioral strategy to cope with aversive contexts.