Prolactin Stimulates MS Remission

Researchers working with a mouse model of multiple sclerosis (MS) have found that the disease went into remission when the mice became pregnant and that the hormone prolactin could mimic this condition in non-pregnant animals.

MS is a chronic autoimmune disease of the central nervous system in which gradual destruction of myelin occurs in patches throughout the brain or spinal cord or both, interfering with the nerve pathways and causing muscular weakness, loss of coordination, and speech and visual disturbances. Investigators at the University of Calgary (Alberta, Canada) were looking for an explanation at the molecular level as to why MS, a disease that affects about 2.5 million people worldwide, often goes into remission during pregnancy.

They reported in the February 21, 2007, issue of the Journal of Neuroscience that pregnant mice showed an increase in the generation of myelin-forming oligodendrocytes and in the number of myelinated axons in the central nervous system. The pregnant mice had twice as many oligodendrocytes and continued to generate new ones during pregnancy. After giving birth, these mice also had 50% more myelin coating their nerve cells. A significant additional finding was that the hormone prolactin could stimulate remyelination in non-pregnant animals.

"It was thought that during pregnancy, their immune systems no longer destroyed the myelin,” said senior author Dr. Samuel Weiss, professor of neurosciences at the University of Calgary. "But no previous study has tested whether pregnancy actually results in the production of new myelin, which may explain improvement of symptoms.”
Prolactin is a single chain polypeptide of 199 amino acids with a molecular weight of about 24,000 Dda. Its structure is similar to that of growth hormone and placental lactogen. The molecule is folded due to the activity of three disulfide bonds. Prolactin is synthesized and secreted by lactotrope cells in the anterior pituitary gland. It is also produced in other tissues including the breast and the decidua. Pituitary prolactin secretion is regulated by neuroendocrine neurons in the hypothalamus, most importantly by neurosecretory dopamine neurons of the arcuate nucleus, which inhibit prolactin secretion.


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