CHLORDIAZEPOXIDE MICROINJECTED INTO THE REGION OF THE DORSAL RAPHE NUCLEUS ELIMINATES THE INTERFERENCE WITH ESCAPE RESPONDING PRODUCED BY INESCAPABLE SHOCK WHETHER ADMINISTERED BEFORE INESCAPABLE SHOCK OR ESCAPE TESTING

Systemic administration of benzodiazepines before exposure to inescapa ble shock (IS) blocks the enhanced fear conditioning and escape learni ng deficits that follow exposure to IS, whereas administration before the subsequent behavioral testing eliminates the enhanced fear but not the interference with escape. The failure of benzodiazepines to reduc e the IS-produced escape learning deficit when given before testing is inconsistent with a recent proposal that interference with escape is mediated by an IS-induced sensitization of dorsal raphe nucleus (DRN) activity. The present experiments demonstrate that chlordiazepoxide wi ll block both the enhancement of fear and interference with escape res ponding when given before either IS or testing if microinjected in the region of the DRN. This suggests that systemic benzodiazepines fail t o block escape deficits when given before testing because action at a site distant from the DRN counters the effect of the drug at the DRN.