Immunohistochemical demonstration of dopamine receptor D2R in the primary cilia of the mouse pituitary gland.

Dopamine regulates the synthesis and secretion of prolactin and α-MSH/β-endorphin in lactotrophs and melanotrophs, respectively. While a predominant dopamine receptor, D2R, is known to be expressed in both the anterior and intermediate lobes of the pituitary gland, no previous immunohistochemical studies have shown the existence of D2R in the plasma membrane of pituitary endocrine cells. The present study clearly demonstrated a selective localization of the D2R immunoreactivity in primary cilia of lactotrophs and melanotrophs in the mouse adenohypophysis. Another immunoreactivity of D2R was found along the plasma membrane of melanotrophs. The intensity of immunoreactivity for D2R in the primary cilia of lactrotrophs changed during the estrous cycle and with genital conditions in contrast to a consistent immunolabeling in the melanotrophs. Since there is accumulating evidence that the primary cilium functions as a sensory device at a cellular level, the D2R-expressing primary cilia in the pituitary gland may be involved in the sensation of dopamine and dopaminergic compounds-though their involvement differs between the anterior and intermediate lobes.