Pinealectomy in the chicken: a good model of scoliosis?

Abstract

The phenomenon of spinal deformity in the pinealectomized chicken has led researchers to postulate a disturbance of melatonin activity as a potential cause of adolescent idiopathic scoliosis (AIS). More recently, structural differences between curves seen in this model and those seen in scoliosis have been highlighted suggesting the deformities observed are not as similar as first thought. We examined melatonin levels, and the radiological and histological characteristics of scoliosis after pinealectomy in chickens. They underwent pinealectomy (P) at 2 days of age, sham surgery (S) or served as controls (C). Mean melatonin levels were 32.9 pmol/L (P), 175 pmol/L (S) and 227.3 pmol/L (C). Scoliosis developed in 75% of chickens after pinealectomy and 38% after a sham procedure. Nineteen percent of unoperated controls also developed scoliosis. A lower melatonin level was associated with the development of scoliosis (p B 0.001), but exceptions were seen with levels up to 265 pmol/L observed in one case. Most of the curves occurring spontaneously and after sham surgery and almost half after pinealectomy were short angular curves: distinct from those resembling idiopathic scoliosis. These occur over one or two segments and are characterized by marked apical wedging, frequently associated with subluxation or dislocation. The intervertebral joint in the chicken is more like a synovial joint histologically than an intervertebral disc. This study highlights important differences between the chicken and the human, and between their respective spinal deformities. Caution is advised when drawing conclusions regarding the pathogenesis of AIS from this model.

Animal models of scoliosis

“…The scoliosis produced in these animals can be prevented by melatonin therapy or re‐implantation of the pineal gland into a skeletal muscle pouch. Grossly, the curvatures evident in these animals appeared very similar to those seen in IS, characterized by similar distributions of single and double curves, location of curves, degree of rotation, and degree of stability …”

“…The most common model of bipedal scoliosis involves inducing a state of melatonin deficiency in test animals, often by removal of the pineal gland. The progression to scoliosis following pinealectomy was first observed in chickens by Thillard in 1959. Animals were subjected to pinealectomy upon hatching and were observed to develop a high incidence of spinal deformity of between 52% and 100%.…”

ptk7 mutant zebrafish models of congenital and idiopathic scoliosis implicate dysregulated Wnt signalling in disease

“…Bipedalism has made induced chick models popular; however, in chick, anatomical restraints on spinal mobility are likely protective and prevent the full range of spinal curvatures that can develop in humans. 22 …”

The Effects of Melatonin on the Physical Properties of Bones and Egg Shells in the Laying Hen

“…Data suggest that melatonin may also be necessary for bone growth during early development. Pinealectomy in developing chicks, which abolishes circulating melatonin, induces a high incidence of scoliosis [14]. The incidence of this developmental bone disease is attenuated by melatonin administration [15], suggesting that lack of pineal melatonin is, in part, responsible for this deformity [15].…”