Gk. Bhat et al., LOCALIZATION OF THE N-METHYL-D-ASPARTATE R(1) RECEPTOR SUBUNIT IN SPECIFIC ANTERIOR-PITUITARY HORMONE CELL-TYPES OF THE FEMALE RAT, Neuroendocrinology, 62(2), 1995, pp. 178-186
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.