Altered functional responses with preserved morphology of gonadotrophic cells in congenitally athymic mice

Neonatal thymectomy or congenital absence of the thymus induces severe repr oductive deficiencies in female mice, which are associated with reduced lev els of circulating and pituitary gonadotropins. In contrast, the reproducti ve function is well preserved in nude males. It was therefore of interest t o assess gonadotrophic cell morphology and function in congenitally athymic male mice. Circulating gonadotropins were measured under basal and stressf ul conditions, taking as a reference their haired counterparts. Adult norma l (+/+), heterozygous nude (nu/+), and homozygous (nu/nu) CD-1 mice were su bjected to l-h immobilization stress. Serum levels of luteinizing hormone ( LH) and follicle-stimulating hormone (FSH) were assessed by RIA at 0, 30, a nd 60 min poststress. Athymic animals showed significantly lower basal leve ls of serum LH and FSH than their heterozygous littermates. Immunohistochem ical assessment of LH and FSH cell populations revealed a normal morphology and cell number in the athymic animals compared to their normal littermate s. Immobilization stress induced a significant reduction in gonadotrophin l evels, particularly LH, in normal mice but had only a weak effect in athymi c animals. It is concluded that congenital athymia in the adult male mouse is associated with decreased basal levels of serum LII and FSH, in the pres ence of a normal gonadotroph number and morphology. The anomalous responses of athymic mice to stress do not appear to be due to primary hypopituitari sm but, rather, to an altered modulation of pituitary hormone secretion. (C ) 2001 Academic Press.