Spinal cord morphology and PKD2L1+ cells distribution: effects of age, sex, and spinal segment in mice.

Introduction: Morphometrical studies of the mouse spinal cord are often limited to one age or sex, restricting our understanding of anatomical variability. This study provides a detailed analysis of the spinal cord in mice, examining the effects of age, sex, and spinal region, along with the distribution of PKD2L1-positive (PKD2L1+) cells along the rostro-caudal axis. Methods: Using 811 transverse sections from a total of 18 3- and 8-week-old mice, DAPI immunofluorescence and confocal imaging, 14 dimensions of gray matter (GM), white matter (WM), and the central canal (CC) were assessed using landmarks positioning and segmentation methods. Results: Age was the most influential factor: between 3- and 8- weeks-old, the spinal cord showed reduced rostro-caudal length (p = 2.49e-04), smaller ventral GM horns (p < 0.005), deeper ventral commissures (p = 5.58e-13), and an increase in CC area (from 1925.58 ± 630.16 μm2 to 2199.50 ± 569.44 μm2). Looking at sex-related differences, females showed higher variability across several parameters, with subtle differences in GM organization (p < 0.05) and CC morphology (mean area = 2146.39 ± 632.91 μm2 in females vs. 1998.36 ± 589.85 μm2 in males). Along the rostro-caudal axis, WM size, as well as GM dorsal and ventral horn dimensions, differed significantly across spinal segments (p < 0.005). CC position also shifted dorsally in cervical and lumbar regions depending on age and sex (p < 0.005). PKD2L1+ cells were mainly clustered near the CC, with over 46% located proximally. The highest densities (>300 cells/segment) were found in lumbar and lower thoracic regions. Discussion: These results indicate progressive structural changes during development, including reorganization of cells and CC architecture stabilization. The distribution of PKD2L1+ cells is consistent with their proposed role as cerebrospinal fluid-contacting neurons potentially involved in sensing fluid composition and modulating locomotor control. Their increased presence in caudal segments suggests functional specialization in different spinal regions. Conclusion: This work provides detailed, segment-specific anatomical data crucial for developing accurate and physiological numerical models. Adding age and sex differences emphasizes the need to reflect biological variability in simulations. Additionally, the mapping of PKD2L1+ neurons offers valuable insight into their spatial organization and potential involvement in sensory processing, locomotor function, and neurological or developmental disorders.