Dorsal periaqueductal gray matter inhibits passive coping strategy elicited by forced swimming stress in rats

Neuroanatomical evidence suggests that dorsal periaqueductal gray matter (dPAG) plays a role in behavioral changes induced by uncontrollable stress. To investigate this hypothesis, male Wistar rats were stressed (forced swimming, 15 min) and 24 h later received intra-dPAG injections of glutamate (20 nmol), lidocaine (4%) or vehicle 5 min before a forced swimming test (FST). The glutamate injection increased the latency to immobility, while lidocaine treatment increased the time spent in immobility during the FST. Both treatments failed to change exploratory parameters as evaluated in the open field test. These data suggest that while dPAG stimulation inhibits passive coping, dPAG inactivation intensifies uncontrollable stress effects. Thus, it is possible that the dPAG participates in the behavioral expression in the FST, inhibiting the passive coping strategies elicited by uncontrollable stress. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.