Characteristic localization of non-NMDA type glutamate receptor subunits in the rat pituitary gland

While the involvement of the glutamate receptors in the hypothalamo-hypophyseal system has been clarified at the hypothalamic level, the existence of glutamate receptors in the pituitary gland has remained obscure. We investigated the localization of the glutamate receptors, the non-NMDA type receptor subunits (GluR1-4) in particular, by immunocytochemistry using specific antibodies. The antibodies specific to GluR1, GluR2/3 and GluR4 exhibited the characteristic localization of the receptor molecules in each lobe of the pituitary gland. GluR1- and GluR2/3-positive cells were identified in the anterior and intermediate lobe, and intense terminals of GluR4 and weak terminals of GluR2/3 were observed in the posterior lobe. Such immunoreactivity appeared to be at the axonal terminal of the neurosecretory magnocellular cells. This was confirmed by in situ hybridization histochemistry using specific oligodeoxynucleotide probes and by immunocytochemistry in the neurosecretory magnocellular neurons. The GluR4 mRNA-positive signal and GluR4 immunoreactivity were abundantly observed in magnocells of paraventricular and supraoptic nuclei. In addition to the positive fibers, some pituicytes in the posterior lobe exhibited GluR2/3 immunoreactivity. This suggests that pituicytes have non-NMDA type glutamate receptors. Thus, present study suggests that some anterior pituitary cells and pituicytes in the neural lobe are regulated by the glutamate.