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Distribution of chicken‐II gonadotropin‐releasing hormone in mammalian brain
Author(s) -
Rissman Emilie F.,
Alones Vinessa E.,
CraigVeit Chris B.,
Millam James R.
Publication year - 1995
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.903570404
Subject(s) - biology , median eminence , endocrinology , hypothalamus , suncus , midbrain , medicine , forebrain , habenula , preoptic area , hormone , immunocytochemistry , central nervous system
Brains of nonmammalian vertebrates typically contain multiple forms of gonadotropinreleasing hormone (GnRH). Until recently, only the mammalian form of GnRH (mGnRH) had been isolated in placental mammals. Biochemical and histological data show that both mGnRH and chicken‐II GnRH (cGnRH‐II) are present in a primitive placental mammal, the musk shrew ( Suncus murinus ). Similar to the case in nonmammalian species, in the musk shrew, neurons that express cGnRH‐Il are located in a discrete cluster in the midbrain. We have used a combination of radioimmunoassay and immunocytochemistry, analyzed at the light level and with electron microscopy, to describe the distribution of cGnRH‐II cell bodies and fibers in the musk shrew brain. All cGnRH‐II‐immunoreactive (ir) neurons reside in the midbrain, and this area contains the greatest concentration of cGnRH‐II peptide in the brain, At the light and electron micrographic levels, we have identified synaptic terminals containing dense core vesicles that are immunoreactive for cGnRH‐II in the medhd habenula. Radioimmunoassay reveals that this region contains the second greatest concentration of cGnRH‐II in the brain. Widely scattered cGnRH‐II‐ir fibers are present throughout the forebrain, particularly in the medial septum, hypothalamus, and midbrain central gray. Scant cGnRH‐II fibers are present in the median eminence, arcuate nucleus, and infundibular stem, and only low concentrations of the peptide are detected in these areas. Finally, intravenous administration of mGnRH is ten times more effective than cGnRH‐II in promoting ovulation. Taken together, the results suggest that cGnRH‐II is likely to act as a neuromodulator or neurotransmitter in mammals and that the medial habenula is the major site of cGnRH‐II action in mammalian brain. © 1995 Wiley‐Liss, Inc.