LOCALIZATION OF THE N-METHYL-D-ASPARTATE R(1) RECEPTOR SUBUNIT IN SPECIFIC ANTERIOR-PITUITARY HORMONE CELL-TYPES OF THE FEMALE RAT

N-methyl-D-aspartate (NMDA), a specific agonist of the NMDA-type gluta mate receptor, has been shown to stimulate the release of several ante rior pituitary hormones when administered in vivo. The primary site of action of NMDA has been suggested to be at the level of the hypothala mus via the control of hypothalamic releasing factors. However, recent studies have demonstrated that NMDA can exert stimulatory effects dir ectly upon anterior pituitary cells perifused in vitro, suggesting tha t the anterior pituitary may also be a site of action for glutamate. H ence, the purpose of the present study was to determine whether the NM DA R(1) receptor subunit is co-localized in specific hormone-secreting cells of the anterior pituitary. To achieve this aim, immunohistochem ical studies were performed using an antibody specific for the NMDA R( 1) receptor subunit to stain sections from the pituitaries of steroid- treated ovariectomized immature rats. Double-immunohistochemistry was employed to demonstrate co-localization, The results of the studies re vealed that moderate immunoreactive NMDA R(1) receptor staining was ob served in the anterior and intermediate lobe of the pituitary with lit tle staining observed in the posterior lobe. Double-immunohistochemist ry using antibodies for the NMDA R(1) receptor subunit and specific an terior pituitary hormones revealed that the NMDA R(1) receptor subunit is co-localized in many cell types of the anterior pituitary includin g LH (11.2%), FSH (9%), GH (4.6%), TSH (5.7%) and PRL cells (8%). Only one ACTH cell was found to co-localize the NMDA R(1) receptor subunit . Finally, Northern blot analysis revealed that the anterior pituitary of the adult female rat, like the immature rat, possesses NMDA R(1) r eceptor subunit mRNA. Taken as a whole, the present study provides fur ther evidence that, in addition to the hypothalamus, the anterior pitu itary could be an important site of action for the neuroendocrine effe cts of excitatory amino acids.