EVIDENCE FOR TERMINAL REGULATION OF GNRH RELEASE BY EXCITATORY AMINO-ACIDS IN THE MEDIAN-EMINENCE IN FEMALE RATS - A DUAL IMMUNOELECTRON MICROSCOPIC STUDY

The present study was designed to determine whether excitatory amino a cids directly act on the gonadotropin-releasing hormone (GnRH) nerve t erminals to release the peptide. The median eminence taken from ovarie ctomized rats was dual immunostained with GnRH and ionotropic glutamat e receptor subtypes (NR1, GluR1, GluR2/3, GluR6/7 and KA2), and their colocalization was examined under electron microscopy. The connection of fibers immunopositive for GnRH and glutamate was also examined. Of the glutamate receptor subtypes, NR1- and KA2-immunoreactivities were colocalized with GnRH-immunoreactivity in nerve terminals of the media n eminence. In addition, some glutamate-immunopositive nerve terminals were shown to abut the many GnRH-immunopositive nerve terminals. No s ynaptic contacts were observed on these immunopositive nerve terminals . These results suggest that GnRH release is regulated at the GnRH ner ve terminals by excitatory amino acids in a non-synaptic manner in the median eminence.