نبذة مختصرة : In mammals, the central extended amygdala is critical for the regulation of the stressresponse. This regulation is extremely complex, involving multiple subpopulations of GABAergic neurons and complex networks of internal and external connections. Twoneuron subpopulations expressing corticotropin-releasing factor (CRF), located in the central amygdala and the lateral bed nucleus of the stria terminalis (BSTL), play a keyrole in the long-term component of fear learning and in sustained fear responses akin toanxiety. Very little is known about the regulation of stress by the amygdala in nonmammals,hindering efforts for trying to improve animal welfare. In birds, one of the majorproblems relates to the high evolutionary divergence of the telencephalon, where theamygdala is located. In the present study, we aimed to investigate the presence of CRFneurons of the central extended amygdala in chicken and the local connections withinthis region. We found two major subpopulations of CRF cells in BSTL and the medialcapsular central amygdala of chicken.Based on multiple labeling of CRF mRNA with different developmental transcription factors, all CRF neurons seem to originate withinthe telencephalon since they express Foxg1, and there are two subtypes with differentembryonic origins that express Islet1 or Pax6. In addition, we demonstrated direct projectionsfrom Pax6 cells of the capsular central amygdala to BSTL and the oval centralamygdala.We also found projections from Islet1 cells of the oval central amygdala toBSTL,which may constitute an indirect pathway for the regulation of BSTL output cells.Part of these projections may bemediated by CRF cells, in agreement with the expressionof CRF receptors in both Ceov and BSTL. Our results show a complex organization of the central extended amygdala in chicken and open new venues for studying howdifferent cells and circuits regulate stress in these animals.
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