GFAP expression induced by dopamine D(2) receptor agonists in the rat pituitary intermediate lobe.

This study was conducted to determine if intermediate lobe glial-like cells are affected by compounds that regulate melanotrope biosynthetic activity via the dopamine D(2) receptor. Glial-like cells were stellate, and expressed glial fibrillary acidic protein (GFAP) and vimentin in cell bodies and processes as revealed by immunohistochemistry. Following bromocriptine and quinpirole treatments, the number of cell bodies and processes expressing vimentin did not change, whereas those expressing GFAP increased, although never to exceed the number of vimentin containing structures. The percent of cells and processes coexpressing GFAP and vimentin also increased. The GFAP response was reversible by haloperidol treatment following the agonist treatment. Haloperidol treatment alone did not change GFAP expression. Thus, following D(2) receptor agonist treatment, GFAP was induced in pre-existing vimentin-positive glial cells. Dopamine D(2) receptor mRNA and protein were detected in melanotropes, but not in cells expressing GFAP or vimentin. Although glial-like cells may express dopamine D(2) receptor mRNA and protein below the detection levels of our methods, the possibility of an indirect effect via dopamine D(2) receptor agonists acting on melanotropes needs to be considered.