Localization of Gonadotropin Releasing Hormone (GnRH) Within the Bovine Hypothalamus11

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Abstract
The distribution of immunoreactive gonadotropin releasing hormone (GnRH) was determined within regions of the bovine hypothalamus. Fresh, frozen bovine hypothalami were cut in serial sections (500 .mu.) in the horizontal, frontal or sagittal planes. All sections were individual extracted with 2N acetic acid and the 10,000 .times. g supernatant lyophilized. Extracts were reconstituted in water and radioimmunoassayed for GnRH. In the frontal plane, GnRH concentration was localized in a peak centered at the midpoint of the pituitary stalk and extending 5 mm anterior and posterior. A small (18% of major peak) but significant (P < 0.05) peak of GnRH was localized 8-10 mm anterior to the midpoint of the pituitary stalk. In the sagittal plane, GnRH was localized in a symmetrical peak centered at the midpoint of the stalk and extending 3.5 mm from the midline. In the horizontal plane, peak GnRH concentration was found in the pituitary stalk and a smaller quantity (5% of major peak) was found 3.5 mm dorsal to the ventral surface of the median eminence. Luteinizing hormone releasing activity of these extracts was estimated by evaluating their ability to release LH [luteinizing hormone] from bovine anterior pituitary cells in primary culture. Areas of greatest bioactivity corresponded to areas of greatest immunoreactive GnRH concentration. GnRH in the bovine hypothalamus may be confined to the pituitary stalk and a rostral hypothalamic region. Areas of LH releasing activity and immunologically detectable GnRH concentrations coincide.