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 stellat e, and expressed glial fibrillary acidic protein (GFAP) and vimentin i n cell bodies and processes as revealed by immunohistochemistry. Follo wing bromocriptine and quinpirole treatments, the number of cell bodie s and processes expressing vimentin did not change, whereas those expr essing GFAP increased, although never to exceed the number of vimentin containing structures, The percent of cells and processes coexpressin g GFAP and vimentin also increased. The GFAP response was reversible b y haloperidol treatment following the agonist treatment, Haloperidol t reatment alone did not change GFAP expression. Thus, following D-2 rec eptor agonist treatment, GFAP was induced in pre-existing vimentin-pos itive glial cells, Dopamine D-2 receptor mRNA and protein were detecte d in melanotropes, but not in cells expressing GFAP or vimentin. Altho ugh glial-like cells may express dopamine D-2 receptor mRNA and protei n below the detection levels of our methods, the possibility of an ind irect effect via dopamine D-2 receptor agonists acting on melanotropes needs to be considered.