The dorsal periaqueductal and basolateral amygdala are necessary for the expression of conditioned place avoidance induced by semicarbazide stimulation of the dorsal periaqueductal region.

The amygdala is critically involved in the regulation of unconditioned and conditioned reactions to threatening stimuli. It has been suggested that a neural circuit responsible for the production of defensive behavior elicited by the dorsal periaqueductal gray (dPAG) stimulation may project through ascending fibers to forebrain structures such as the basolateral complex of the amygdala (BLA). The present study evaluates the involvement of the dPAG and BLA in the mediation of unconditioned and conditioned responses organized in the dPAG using the open field and the conditioned place aversion (CPA) tests. In both tests, the intra-dPAG injections of semicarbazide (SEM), an inhibitor of the GABA synthesizing enzyme, was used as unconditioned stimulus (US). Using the open field test, we examine the effects of BLA inactivation with the GABA-(A) receptor agonist muscimol (MUS) on the unconditioned fear. We also investigated, through the CPA test, the effects of BLA and/or dPAG inactivation with MUS on the acquisition and the expression of the fear conditioned response. Our results showed that intra-BLA injections of MUS did not change the unconditioned fear elicited by dPAG injections of SEM. As for the CPA test, intra-BLA and intra-dPAG injections of MUS impaired the expression of CPA behavior induced by SEM injections into the dPAG. However, this inactivation of BLA did not impair the acquisition of the CPA behavior induced by injections of SEM into the dPAG. Altogether, these findings suggest that BLA does not participate in the mediation of unconditioned fear induced by dPAG chemical stimulation or in the acquisition of CPA in which aversive stimulation of the dPAG was used as US. In contrast, our results indicate that the activation of the dPAG and BLA is essential to the expression of the conditioned aversive response.