Developmental delay in islet-1-positive motor neurons in chick spina bifida.

Spina bifida aperta (SBA) is a congenital malformation of the spinal cord with complications such as spinal ataxia and bowel and bladder dysfunction. We have developed a chick model with surgery-induced SBA that shows spinal ataxia after hatching. In the present study, motor neurons in the early stages in chicks with and without SBA were observed by immunohistochemical staining with a monoclonal antibody against Islet-1, a motor neuron marker. Delay in migration and maturation of motor neurons was observed in SBA. Although the final numbers of Islet-1-positive neurons in these two groups were not different, a defect in the production and elimination of excess motor neurons in the early developmental stages in the SBA group may be involved in the pathological mechanism of the motor complications of this disease.

Sensory tract abnormality in the chick model of spina bifida.

Spina bifida aperta (SBA) is an open neural tube defect that occurs during the embryonic period. We created SBA chicks by incising the roof plate of the neural tube in the embryo. The area of the dorsal funiculus was smaller in the SBA chicks than in the normal controls. Additionally, the SBA group had fewer nerve fibres in the dorsal funiculus than the normal controls. The pathway of the ascending sensory nerves was revealed by tracing the degenerated nerve fibres using osmification. We cut the sciatic nerve (L5) of the control and SBA chicks at the central end of the dorsal root ganglion 1 day after hatching and fixed the tissue 3 days later. Degenerated sensory nerve fibres were observed in the ipsilateral dorsal funiculus in the control chicks. In contrast, degenerated sensory nerve fibres were observed in the ipsilateral and contralateral dorsal, ventral and lateral funiculi of the spinal cord in the SBA chicks. Consequently, fewer sensory nerve fibres ascended to the thoracic dorsal funiculus in the SBA chicks than in the normal controls. This is the first report of abnormal changes in the ascending sensory nerve fibres in SBA.

Leg dysfunctions in a hatched chick model of spina bifida aperta.

We created chicks with spina bifida aperta (SBA) by incising the roof plate of the neural tube of embryos at Hamburger and Hamilton stage 18 or 19. Incision over the length of three somites caused spina bifida occulta (SBO)-like malformation in 47% of the hatchlings. Incision over the length of five and seven somites caused SBA-like malformation in 100% of the hatchlings. The SBO chicks exhibited no symptoms, whereas the SBA chicks exhibited paralysis of a leg muscle and imbalance between an agonist and an antagonist leg muscles. Lesions in these SBA chicks were located in the spinal segments that give rise to motor neurons that innervated the dysfunctional muscles. Histological analysis revealed that there were fewer small spinal neurons (interneurons) at the site of the lesion in SBA chicks than in the normal chicks and that there was no such difference in the number of the large spinal neurons (motor neurons). Leg dysfunctions in this model of SBA may be attributable to the smaller number of interneurons in the spinal segments that contain motor neurons that innervate the dysfunctional muscle. This model may facilitate studies of the pathological mechanisms that lead to leg dysfunctions in SBA chicks.