Subcellular interactions of neuropeptide Y and corticotropin-releasing factor in the central nucleus of the amygdala in the mouse.

Neuropeptide Y (NPY) is ubiquitously distributed throughout the central nervous system. Recognized as a mediator of stress resilience, NPY has been shown to counteract the excitatory effects of the neuropeptide corticotropin-releasing factor (CRF), that orchestrates the stress response. In the mouse, while NPY and CRF exhibit a high degree of neuroanatomical association in the central nucleus of the amygdala (CeA) indicating potential significant interactions, the synaptic organizations of these neuropeptides have not been elucidated. In the present study, we determined the anatomical interactions between NPY and CRF in the CeA. Immunofluorescence microscopy presented that NPY-immunoreactive varicose processes were distributed throughout the CeA and appeared to be closely apposed to CRF-containing neurons. Using electron microscopy, immunoperoxidase labeling for NPY and gold-silver labeling for CRF showed that NPY-labeled axon terminals (NPY-t) form synapses with CRF-labeled dendrites (CRF-d). Semi-quantitative analysis revealed that 247 of NPY-t directly target CRF-d. In addition, approximately 80% of NPY-t form symmetric synapses with CRF-d while approximately 1% form asymmetric synapses. These findings provide the first ultrastructural evidence that NPY-containing axon terminals make direct contact with CRF-containing dendrites in the CeA. This suggests that the CRF-containing neurons in the CeA may be a key site for NPY action, potentially influencing brain regions involved in stress responses and stress-related psychiatric disorders, and alcohol use disorders.