Fetal and perinatal expression profiles of proinflammatory cytokines in the neuroplacodes of rats with myelomeningoceles: A contribution to the understanding of secondary spinal cord injury in open spinal dysraphism

The cellular and molecular mechanisms that presumably underlie the progressive functional decline of the myelomeningocele (MMC) placode are not well understood. We previously identified key players in posttraumatic spinal cord injury cascades in human MMC tissues obtained during postnatal repair. In this study we conducted experiments to further investigate these mediators in the prenatal time course under standardized conditions in a retinoic-acid-induced MMC rat model. A retinoic acid MMC model was established using time-dated Sprague-Dawley rats, which were gavage-fed with all-trans retinoic acid (RA; 60 mg/kg) dissolved in olive oil at E10. Control animals received olive oil only. Fetuses from both groups were obtained at E16, E18, E22. The spinal cords (SCs) of both groups were formalin-fixed or snap-frozen. Tissues were screened by real-time RT-PCR for the expression of cytokines and chemokines known to play a role in the lesion cascades of the central nervous system after trauma. MMC placodes exhibited inflammatory cells and glial activation in the later gestational stages. At the mRNA level, IL-1b, TNFa, and TNF-R1 exhibited significant induction at E22. IL1-R1 mRNA was induced significantly at E16 and E22. Double labeling experiments confirmed the costaining of these cytokines and their receptors with Iba1 (i.e., inflammatory cells), Vimentin, and Nestin in different anatomical SC areas and NeuN in ventral horn neurons. CXCL12 mRNA was elevated in control and MMC animals at E16 compared to E18 and E22. CX3CL1 mRNA was lower in MMC tissues than in control tissues on E16. The presented findings contribute to the concept that pathophysiological mechanisms, such as cytokine induction in the neuroplacode, in addition to the "first hit", promote secondary spinal cord injury with functional loss in the late fetal time course. Furthermore, these mediators should be taken into consideration in the development of new therapeutic approaches for open spinal dysraphism.