The Effects of Melatonin Therapy on the Development of Scoliosis After Pinealectomy in the Chicken*

Abstract

The mechanism underlying the development of scoliosis after pinealectomy in young chickens is unknown. However, since the main product of the pineal gland is melatonin, melatonin remains an obvious focus in studies designed to discover this mechanism. One confounding factor is that serum melatonin levels are close to zero after pinealectomy but scoliosis does not develop in all chickens that have had this procedure. Therefore, the role of melatonin in the development of scoliosis in chickens after pinealectomy remains controversial. In the current investigation, two pilot studies demonstrated that a physiological therapeutic dose of melatonin (2.5 milligrams per kilogram of body weight) restored the circadian rhythm of melatonin, as measured by serum assay. In the main study, this dose was administered daily starting either immediately after the pinealectomy or two weeks after it, when scoliosis had developed. Scoliosis was assessed on weekly radiographs, and the Cobb angle was determined for all chickens in which scoliosis developed. Overall, scoliosis developed in only 56 percent (fifty) of the eighty-nine chickens that had had a pinealectomy; this rate was consistent throughout all experimental groups. Scoliosis did not develop in any of the control chickens, which did not have a pinealectomy. On the basis of the average Cobb angles in the chickens in which scoliosis had developed, it was determined that neither the prevalence nor the pattern of the scoliosis was affected by the therapy in any of the experimental groups. It was thus concluded that melatonin therapy after pinealectomy in young chickens has no effect on the development or progression of scoliosis. These results raise doubts regarding the role of melatonin in the development of scoliosis after pinealectomy in the young chicken.