Role of the basolateral nucleus of the amygdala in the formation of a phobia.

Specific phobia is an anxiety disorder that does not respond to benzodiazepines. The elevated plus-maze test of anxiety is sensitive to benzodiazepines on trial 1, but during the first 5-min trial the nature of the anxiety generated changes to a specific fear of heights, and, as a result, on trial 2 the rats no longer respond to benzodiazepines. However, rats that received reversible bilateral lesions of the basolateral amygdala (by lidocaine injection) immediately after trial 1 responded with an anxiolytic response to chlordiazepoxide when tested 48 h later on trial 2. Those that received vehicle injections after trial 1 showed the usual lack of response to chlordiazepoxide on trial 2. Thus, the basolateral amygdala plays a crucial role in the consolidation of information that leads to the formation of a specific phobia and subsequent insensitivity to benzodiazepines.