A direct projection from the central nucleus of the amygdala to the acoustic startle pathway: anterograde and retrograde tracing studies.

Previous work has shown that lesions of the central nucleus of the amygdala block fear-potentiated acoustic startle and that electrical simulation of the central nucleus enhances acoustic startle in rats. In the present study, the anterograde tracer Phaseolus vulgaris-leucoagglutinin was used to identify and delineate the course of a direct projection from the central nucleus of the amygdala to the nucleus reticularis pontis caudalis, a nucleus in the acoustic startle circuit. Experiments using the retrograde tracer Fluoro-Gold confirmed this and indicated that the rostral part of the medial subdivision of the central nucleus of the amygdala contains the cells that project to the startle circuit. With this information, lesion studies (see companion article Hitchcock & Davis, 1991) may be used to determine whether this projection plays a role in fear-potentiated startle.