Introduction: No appropriate animal model for studying adolescent idiopathic scoliosis (AIS) exists and this hampers research. In recent years, we have been examining a model in which scoliosis consistently develops in young chickens following pinealectomy and which has been shown to have many characteristics similar to those seen in AIS. Not all of the pinealectomised chickens develop scoliosis following the pinealectomy and so we have the opportunity to examine differences between the two groups. The obvious candidate for study of the mechanism underlying this phenomenon is melatonin which is the principal product of the pineal gland. In this study we have measured the serum melatonin levels of pinealectomised chickens that have developed scoliosis and compared these with similar measurements taken from chickens that have developed scoliosis.

Methods and results: Newly-hatched chickens were obtained from a local hatchery and kept in a single pen with standard heating and lighting. A 12:12 light dark cycle was introduced immediately and the two-thirds of the chickens were pinealectomised three days later. The remainder acted as controls. At weekly intervals following surgery, the chickens were radiographed in a supine position while anaesthetised and the presence of scoliosis was determined from the radiographs. Three weeks after surgery the chickens were euthanised and blood samples were collected and analysed using radioimmunological techniques to determine levels of serum melatonin. The samples were collected in the presence of red light in the middle of the dark cycle when melatonin levels have been shown to be at their highest.

Approximately 55% of the pinealectomised chickens developed scoliosis within the three weeks following surgery whereas none of the control chickens developed scoliosis. The results showed that the serum melatonin levels of pinealectomised chickens were significantly lower than the normal controls and were in fact all close to zero. However, there was no significant difference in serum melatonin levels between those chickens that developed scoliosis and those that did not.

Conclusion: The results of this study have shown that pinealectomy significantly reduces serum melatonin levels close to zero in all chickens. The results also show that there is no significant difference in serum melatonin levels between those pinealectomised chickens that develop scoliosis and those that do not. Unless there is a subtle threshold level that is unable to be detected using our methodology or that melatonin levels in the days immediately after surgery are of critical importance, these results suggest that other causes for this phenomenon need to be examined. An understanding of the underlying cause would be of great importance and might represent a significant breakthrough in the study of AIS.