EFFECTS OF BENZODIAZEPINE MICROINJECTION INTO THE AMYGDALA OR PERIAQUEDUCTAL GRAY ON THE EXPRESSION OF CONDITIONED FEAR AND HYPOALGESIA IN RATS

Four experiments studied the effects of an intracranial microinjection of a benzodiazepine (midazolam) on the expression of conditioned fear (measured as passive avoidance) and conditioned hypoalgesia in rats. Unilateral microinjection of midazolam into the basolateral amygdala r educed both hypoalgesic and avoidance responses, whereas unilateral mi croinjection of midazolam into the ventrolateral region of the periaqu eductal gray (vlPAG) reduced the hypoalgesic response but not the avoi dance response. The results are discussed in terms of gamma-aminobutyr ic acid-ergic inhibition of antinociceptive mechanisms in the vlPAG an d of the activation of these mechanisms by amygdala-based fear process es.