| The central nucleus of the amygdala (CeA) is critical for threat association and defensive behavior. Distinct populations of neurons in the CeA are known to express an array of neuropeptides, but the role of these different neurons and their cognate neuropeptides in the modulation of fear is only beginning to be discerned. The neuropeptide corticotropin-releasing factor (CRF) is robustly produced in the CeA, yet whether CRF neurons represent a subset of neurons that modulate threat association is unknown. In the present study, we used a combination of molecular, physiological, and behavioral strategies to determine how CRF neurons contribute to adaptive fear processes.;Using immunohistochemistry and gene expression analyses, we found that CRF neurons represent a population of neurons distinct from other previously characterized cell types. Electrophysiological experiments demonstrate CRF neurons, like other defined populations in the CeA, undergo synaptic plasticity in a fear-dependent manner. In vivo fiber optic imaging of calcium activity revealed stimulus-specific responses of CRF neurons following cued fear conditioning. We further showed, using a number of behavioral assays coupled with cell-selective silencing and conditional gene inactivation, that CRF neuronal activity is required for the acquisition of cued fear to sub-generalization threat levels and that the CRF peptide produced by the CeA is the principal mediator during this process.;CRF neurons in the CeA engage in complex local and long range circuitry, and may thus regulate different aspects of fear through distinct pathways. Determining the function of downstream neurons is critical for understanding how CRF-dependent fear learning is processed. We therefore generated a novel mouse line expressing Cre-recombinase under the endogenous promoter of the gene expressing the primary receptor for CRF, CRFR1 (Crhr1 IRES-Cre). This targeted knock-in mutation allows for cell-selective manipulation and labeling of neurons directly downstream of CRF neurons. We found that a significant portion of Sst neurons express Crhr1, likely representing the primary target of locally projecting CRF neurons.;The results describing CRF neuronal function in cued fear behaviors, together with the Crhr1IRES-Cre mouse line, have provided a detailed report of the intricate circuitry underlying specific fear behaviors. Furthermore, the work presented here highlights how complex emotional states can be regulated at multiple levels, with distinct biochemical signaling and anatomical arrangements. |
