Presence of nerve growth factor in the thymus of prenatal, postnatal and pregnant rats.

The presence of Nerve Growth Factor (NGF) and the expression of low- and high-affinity NGF receptor were investigated in prenatal, postnatal and pregnant rats. Using ELISA and immunohistochemistry it was found that both NGF and its receptors are present in the medulla of the thymus and are more strongly expressed in pre- and early postnatal life and nearly absent in adult and ageing rats. It was also found that during pregnancy, which is characterised by an involution of the cortex and hypertrophy of the medulla, the level of NGF in the thymus increases. The present study showed not only that NGF is produced in a specific compartment of the thymus, the medulla, but that its synthesis declines with age, following thymus involution. These results suggest that NGF may be critically involved in the proliferation and differentiation of thymic cells.