Expression of glutamate receptor subunits in the hypothalamus of the female rat during the afternoon of the proestrous luteinizing hormone surge and effects of antiprogestin treatment and aging.
The excitatory transmitter, glutamate has been implicated in the control of reproduction, hormone secretion and neuroendocrine regulation. The present study examined whether the hypothalamic expression of three key ionotropic glutamate receptor subunits (NMDAR1, GluR1 and GluR6) fluctuates significantly on proestrus in the rat, and whether treatment with the antiprogestin, RU486 affected glutamate receptor subunit expression. The studies revealed that NMDAR1, GluR1 and GluR6 mRNA levels in the mediobasal hypothalamus (MBH) and preoptic area (POA) fluctuate little throughout the day of proestrus. However, treatment with the antiprogestin, RU486 induced a significant elevation of GluR6 mRNA levels at 14.00 and 16.00 h on proestrus in the MBH, suggesting that endogenous progesterone (P4) may act to inhibit hypothalamic GluR6 levels. In support of this suggestion, exogenous P4 treatment to estrogen (E2)-primed ovariectomized (ovx) rats significantly suppressed GluR6 mRNA levels in the afternoon (12.00-16.00 h) in the MBH, and at 12.00 h in the POA, which preceded LH surge induction. Likewise, temporal examination of hypothalamic GluR6 protein levels in E2 + P4-treated young and middle-aged ovx rats revealed an early elevation from 12.00 to 14.00 h, which was followed by a fall from 16.00 to 20.00 h. The early elevation of GluR6 protein levels was most pronounced in the POA of the young rat, and this elevation was markedly attenuated in the middle-aged rat. As a whole, the studies suggest that glutamate receptor expression fluctuates little on proestrus in the hypothalamus, but that expression of the kainate GluR6 receptor subunit may be modulated by progesterone and aging.
Brann
Darrell W
DW
Institute of Molecular Medicine and Genetics, Department of Neurology, Program in Developmental Neurobiology, School of Medicine, Medical College of Georgia, Augusta, Georgia, USA. dbrann@mail.mcg.edu
Zamorano
Pedro L
PL
De Sevilla
Liesl
L
Mahesh
Virendra B
VB
D000375:Aging / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D015152:Blotting, Northern / Q000379:methods; D015153:Blotting, Western / Q000379:methods; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D007031:Hypothalamus / Q000187:drug effects / Q000502:physiology*; D007986:Luteinizing Hormone / Q000235:genetics / Q000378:metabolism*; D015735:Mifepristone / Q000494:pharmacology; D010052:Ovariectomy / Q000379:methods; D011359:Proestrus / Q000187:drug effects / Q000378:metabolism*; D011374:Progesterone / Q000494:pharmacology; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011863:Radioimmunoassay / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D017470:Receptors, Glutamate / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013997:Time Factors
D004791:Enzyme Inhibitors; D004967:Estrogens; D021122:Protein Subunits; D012333:RNA, Messenger; D017470:Receptors, Glutamate; D015735:Mifepristone; D011374:Progesterone; D007986:Luteinizing Hormone