Abstract
Corticotrophin-releasing factor (CRF) is expressed in the central nucleus of the amygdala (CeA), where the CRF receptor (CRFr) plays an important role in anxiety- and stress-related behaviors. To determine the subcellular sites of CRFr activation in this region, we examined the electron microscopic immunolabeling of antisera recognizing CRF or CRFr. The ultrastructural analysis was principally conducted in the lateral subdivision of the rat CeA, with comparisons being made in mice so as to optimally utilize mutant mice in control experiments. The CRFr labeling was seen in many small dendrites and dendritic spines as well as in a few somata, large dendrites, axons, and axon terminals or more rarely in glial processes. Approximately 35% of the CRFr-labeled dendrites contained CRF immunoreactivity, which was distributed diffusely throughout the cytoplasm, or specifically affiliated with either endomembranes or large dense-core vesicles. The CRF-immunoreactive vesicles also were present in somata and axon terminals with or without CRFr labeling. The CRF immunoreactivity was usually absent from both terminals and dendrites joined by asymmetric, excitatory-type synapses, where a postsynaptic location of the CRFr was commonly observed. Numerous terminals containing both CRF and CRFr were seen, however, within the neuropil and sometimes apposing the excitatory synapses. These results provide ultrastructural evidence for a primary involvement of CRF receptors in modulation of the postsynaptic excitability of CeA neurons, an effect that may be limited by the availability of CRF. The findings have important implications for understanding CRF mediation of rapid responses to stress.