Study of the enteric and motor inervation, pelvic musculature, and alterations in the sacral region of rat fetuses with ethylenethiourea-induced anorectal anomaly.

Purpose: The aims of this work were to induce anorectal anomaly in rat fetuses via the planned administration of ethylenethiourea (ETU), and to study fetuses exhibiting anorectal malformation, as well as apparently normal fetuses submitted to the effect of ETU.

Methods: Time-mated pregnant Wistar rats were randomly divided into control and experimental groups. On gestational day 10, the experimental group received 10% ETU (130 mg/kg) by gavage, whereas the control rats received vehicle only. The embryos were harvested by cesarean section on gestational day 21. The fetuses exposed to ETU were divided into two groups: affected (without any clear anorectal alterations); and the malformed (with anorectal anomaly). The neuromotor plates were identified by immunohistochemistry with acetylcholinesterase, and alterations in the sacral region were evaluated by histological and morphometric studies.

Results: We used 43 control fetuses, 82 affected fetuses, and 118 malformed fetuses in this study. The most frequent associated macroscopic anomalies were spina bifida (55 fetuses), encephalocele (20), and alterations in the lower limbs (5). The sacroiliac was malformed in 45% of the affected fetuses and in 53.2 % of the malformed fetuses.

Conclusion: ETU leads to a reduced number of motor neurons in the pelvic musculature of both the malformed and the affected rats. The enteric neurons are altered in the malformed fetuses, but not in the affected ones. Both the affected and malformed rats exhibit sacral alterations that do not interfere with neurons.