Pinealectomy in Young Non-Human Primates Does Not Result In Scoliosis Development: A Long Term Follow-Up Study

• a - Research Grants Council of Hong Kong

Introduction: Pinealectomy in newborn chickens consistently resulted in scoliosis development, while no scoliosis developed after pinealectomy in quadripedal rats and hamster. Yet pinealectomised bipedal rats develop scoliosis. Work so far would suggest that the surgical removal of the pineal, loss of melatonin secretion and a bipedal posture are important elements in the development of scoliosis in these lower animal models. However, controversy exists as to how applicable these lower animal models are to human idiopathic scoliosis. The present study aims to examine the effect of loss of melatonin production by pinealectomy in a bipedal nonhuman primate model.

Methods: With institutional approval, 18 rhesus monkeys between 8 to 11 months of age (mean 10 months) underwent open craniotomy and pineal excision using microsurgical techniques. All the monkeys were kept in a 12 hour light:dark cycle from one week before surgery. Radiographs were taken before surgery and at monthly intervals after surgery. Completeness of pineal excision was assessed by measurement of a major metabolite of melatonin in the urine, 6-sulphatoxymelatonin using an ELISA assay.

Results: The surgery was carried out between 1999 and 2001, thus the longest follow-up was for 41 months, with a mean of 28 months and a minimum of 10 months. Seven monkeys died prematurely from chest infection or diarrhea, resulting in a shortened duration of follow-up. However, at the time of death or the latest follow-up, none of the monkeys have developed scoliosis. Urinary 6-sulphatoxymelatonin measurements revealed 3 patterns. Group 1 consisted of 12 monkeys which showed definite evidence of complete pineal excision, with loss of melatonin circadian rhythm and a low night-time level. Group 2 consisted of 3 monkeys that had incomplete pineal excision or ectopic melatonin production, with persistently high melatonin levels similar to before surgery. Group 3 consisted of an uncertain group of 4 monkeys in which the circadian rhythm was lost, but both the day and night time melatonin levels remained high.

Discussion: This is the first report of pinealectomy in non-human primates, an animal model much closer to humans. Despite some doubtful and unsuccessful cases, 12 of the 18 monkeys had loss of melatonin secretion for a mean of 30 months after surgery and were skeletally mature at the latest follow-up. As none developed scoliosis, this study strongly suggests that the possible etiological factors producing idiopathic scoliosis in lower animals are different from primates, and findings in lower animals cannot necessarily be extrapolated to human beings.

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