Immunocytochemical localization of thyroid hormone nuclear receptors in cultured hypothalamic dopaminergic neurons.

By means of a monoclonal antibody against the rat liver L-triiodothyronine nuclear receptor and a polyclonal anti-tyrosine hydroxylase serum, it has been possible to demonstrate thyroid hormone nuclear receptors in immunoreactive tyrosine hydroxylase cell nuclei in fetal rat hypothalamic cultures. After 8 days in vitro, the ratio of tyrosine hydroxylase cells that were immunoreactive for the thyroid hormone receptor to those not stained for this receptor (64% to 36% respectively) remains unchanged despite an increase in the number of tyrosine hydroxylase-positive cells with time (from day 8 to day 21) in culture. The presence of thyroid hormone nuclear receptor in dopaminergic neurons is correlated with a morphological effect of L-triiodothyronine in this neuronal population. Our results demonstrate, for the first time, the presence of triiodothyronine nuclear receptors in fetal rat dopaminergic neurons and the existence of a cellular heterogeneity in the distribution of the thyroid hormone receptor. The presence of these receptors in fetal hypothalamic dopaminergic neurons suggests that some effects of L-triiodothyronine on the maturation of DA neurons may result from a direct effect of this hormone through an interaction with its specific nuclear receptors.