A 2ND FORM OF GONADOTROPIN-RELEASING-HORMONE (GNRH) WITH CHARACTERISTICS OF CHICKEN GNRH-II IS PRESENT IN THE PRIMATE BRAIN

The primate brain was thought to contain only the GnRH known as mammal ian GnRH (mGnRH). This study investigates whether a second form of GnR H exists within the primate brain. We found that brain extracts from a dult stumptail and rhesus monkeys contained two forms of GnRH that wer e similar to mGnRH and chicken GnRH-II (cGnRH-II) based on the elution position of the peptides from HPLC and on cross-reactivity with antis era that are specific to mammalian or chicken GnRH-II in RIAs. The fet al brain of rhesus monkeys also contained mGnRH and a cGnRH-II-like pe ptide by the same criteria. Immunocytochemistry with a cGnRH-II-specif ic antiserum in adult and fetal rhesus monkeys showed immunopositive n eurons generally scattered in the periaqueductal region of the midbrai n, with a few positive cells in the posterior basal hypothalamus. Neur ons immunopositive for cGnRH-II were fewer in number and smaller in si ze, with less defined nuclei and thinner neurites compared with those for mGnRH. Administration of synthetic cGnRH-II to adult rhesus monkey s resulted in a significant increase in the plasma LH concentration du ring the luteal phase of the menstrual cycle, but not during the midfo llicular phase. We conclude that the primate brain contains mGnRH and a cGnRH-II-like molecule, although the function of the latter is unkno wn.