Developmental Dynamics of Telocytes and Microglia in the Spinal Cord of Japanese Quail Embryos: A Histological and Immunohistochemical Study

This study was conducted on 27 normal Japanese quail embryos from the second to the 17th embryonic day (ED). The present work aimed to investigate the histological changes in the spinal cord during development and identify the immunohistochemical distribution of telocytes (TCs) and microglia. Our study revealed in the early stages (2-3 ED): development of tubular neuroepithelium and onset of neurogenesis through radial cell migration. Mid stages (5-7 ED): significant cellular remodeling and differentiation of the ventral canal. By 9-11 ED: notable structural development with expansion of gray and white matter and increased glial cell density. Advanced stages (13-15 ED): complete formation of the meninges (pia, arachnoid, dura matter). Immunohistochemically, CD34-positive TCs were detected in the pia matter (PM), white matter, and gray matter of the spinal cord, with a highly significant increase in their number in the PM at 7ED and redistribution toward white matter by 9-13ED. CD45-positive microglia were found among ependymal cells of the ventral canal and within the gray, white matter and arachnoid matter of the spinal cord. Their numbers increased significantly on 9 and 13 ED compared with 7 ED, peaking at 9 ED. These findings provide a comprehensive timeline of structural differentiation and reveal, for the first time, the distribution and developmental dynamics of TCs and microglia in the avian spinal cord.