The effects of central injections of calcitonin gene-related peptide on fear-related behavior.

Calcitonin gene-related peptide (CGRP) has been localized in several regions of the rat brain that are known to be important for the expression of fear responses. Some evidence suggests that CGRP may act as a neurotransmitter at synapses that are believed to be important for aversive learning. In the present study, male rats were prepared with intracerebroventricular cannulae and injected with CGRP during different phases of training and testing when a distinctive environment was paired with foot shock. When injected prior to training, CGRP directly evoked fear-related behavior and postshock freezing. When pretreated with CGRP and exposed to the shock-associated environment 24 h after training rats again showed an enhanced fear response. These results support the idea that this peptide functions as a neurotransmitter at central synapses which are important for the expression of fear.