Experimental Scoliosis in Melatonin-Deficient C57BL/6J Mice without Pinealectomy

The etiology of idiopathic scoliosis (I.S.) is still unknown. A scoliosis with many characteristics closely resembling those seen in I.S. has been produced in young chickens and bipedal rats after pinealectomy (PNX). There are fundamental questions whether the phenomenon of scoliosis development is simply an artifact of the extensive surgery involving PNX rather than the actual removal of the pineal gland, and whether melatonin (MLT) deficiency plays primary role for the development of experimental scoliosis and also for I.S. in human. In the MLT synthesis pathway (serotonin'?N-acethylserotonin'?MLT), N-acethyltransferase (NAT) and hydroxyindol-Omethyltransferase (HIOMT) are the primary enzyme. NAT gene knocked down in the C57BL/6J strain of mice resulting in melatonin deficient mice from birth. In this study, we made experimental scoliosis in C57BL/6J mice without pinealectomy and restration of MLT levels after MLT treatment suppressed the development of scoliosis.

A total of 100 mice were divided into 4 groups. They were kept under regular light conditions (12 hr darkness/ 12 hr light) with light on at 7:00. 20 quadrupedal mice served as control. 30 mice underwent resection of two forelegs and tail at 3 weeks old (bipedal mice). The remaining 20 quadrupedal and 30 bipedal mice received intraperitoneal administration of MLT (901/4g in 10% ethanol/saline, sc) at 19:00 daily. Before sacrifice, blood samples were collected in the middle of dark cycle and MLT levels were measured by radioimmunoassay. Spine X-ray and helical 3D-CT were examined after sacrifice at 5 months old.

The bipedal mice without tail were able to walk with standing posture, whereas the quadrupedal mice could not walk with standing posture. In C57BL/6J mice, the serum MLT level was much reduced to nealy zero, however, the normal level was restored in both bipedal and quadrupedal mice after the injection of MLT. The scoliosis having rib humps developed in 29 of bipedal, 5 of quadrupedal mice. None of mice with MLT treatment developed scoliosis.

Our study suggests that bipedal mice with reduced levels of MLT appear to play crucial role for development of scoliosis. The study also provides evidence that the pinealectomy or surgical intervention was not primary cause for previously noted experimental scoliosis model. Also the restoration of MLT levels by MLT therapy prevents the development of scoliosis. The same may apply to human I.S.