Benzodiazepine-induced amnesia in rats: reinstatement of conditioned performance by noxious stimulation on test.

A benzodiazepine (midazolam), injected either systemically or directly into the basolateral amygdala (BLA), differentially affected the acquisition of fear responses to a shocked context: Administration of the drug before conditioning impaired subsequent freezing to the context but spared analgesic responses in rats tested there for sensitivity to formalin pain. Moreover, the pain test not only revealed evidence for analgesic responses but also served to reinstate conditioned freezing that was otherwise absent in rats conditioned under midazolam. The results were interpreted as showing that the presence of noxious stimulation on test serves either (a) to assist in retrieval of the context-shock association whose storage had been modified by midazolam's action in the BLA, or (b) to enable performance of the context-shock association whose affective properties had been blocked by midazolam's action in the BLA.