CYTOLOGICAL CHANGES IN THE MOUSE ANTERIOR PITUITARY AFTER NEONATAL THYMECTOMY: A LIGHT AND ELECTRON MICROSCOPICAL STUDY

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Abstract
SUMMARY A detailed light and electron microscope examination of the anterior pituitary gland of mice at different times after neonatal thymectomy was performed. Neonatal removal of the thymus resulted in a progressive increase in the number of somatotrophic hormone-producing cells showing characteristic changes represented by extremely distended cisternae of the endoplasmic reticulum and reduction in the number of hormone granules. These modifications were not observed in sham-operated controls or in neonatally splenectomized mice. The functional significance of these changes in relation to thymectomy and the significance of somatotrophic hormone for the development of the thymus and for immunological maturation is discussed. It is suggested that somatotrophic hormone and possibly other hormones determine certain specific steps of differentiation of precursor cells to immunocompetent cells and that the thymus is an endocrine target gland of somatotrophic hormone.