OBJECTIVE: Spinal bifida aperta (SBA) can lead to different degrees of bladder dysfunction, the mechanism is unclear. This paper determined the expression of choline acetyl transferase (CHAT), dopamine-β-hydroxylase (DBH) and calcitonin gene related peptide (CGRP) in the urinary bladder in rat embryos with SBA. The goal was to study the role of these genetic expressions in the development of bladder dysfunction. METHODS: Rat embryos with SBA were generated by an administration of retinoic acid (RA) to pregnant rats. Normal rat embryos (Control group, n=20) and rat embryos with SPA (Study group, n=20) on day 20 of gestation were taken out. The specimens from the bladder were stained with hematoxylin-eosin and immunohistochemistry for the detection of CHAT, DBH and CGRP expression. RESULTS: In the Control group, the bladder was composed of mucosa, submucosa, muscle and adventitia, and the immunoreactive nerve fibers of all markers were abundant in various layers of the bladder. In the Study group, the bladder muscle layer of the rat embryos was thin and less abundant. The expressions of CHAT (156±9), DBH (32±6) and CGRP (121±11) in the Study group were significantly lower than those in the Control group (398±13, 378±14 and 412±25, respectively) (P<0.01). CONCLUSIONS: The bladder muscles were poorly developed and the expression of CGRP, CHAT and DBH were decreased in the rat embryos with SPA. These changes might contribute to the bladder dysfunction caused by SPA.