Effects of Hypothalamic Deafferentation on the Pulsatile Rhythm in Plasma Concentrations of Luteinizing Hormone in Ovariectomized Rats¹

Pulsatile Luteinizing Hormone Secretion in the Castrate Male Bovine: Effects of Testosterone or Estradiol Replacement Therapy1

“…The rhythmic pulsatile pattern of LH release observed in castrates is believed to result from a LHRH pulse generator located in the medial basal hypothalamus (Blake and Sawyer, 1974;Levine and Ramirez, 1980). In support of this theory, low-dose, pulsatile administration of exogenous LHRH is capable of reproducing the pulstatile pattern of LH secretion in rams (Lincoln, 1979) and bulls Furthermore, neutralization of endogenous LHRH by passive (Lincoln and Frazer, 1979) or active immunization against LHRH results in cessation of pulsatile LH release and failure of animals to respond to exogenous LHRH.…”

Generation and synchronization of gonadotropin-releasing hormone (GnRH) pulses: intrinsic properties of the GT1-1 GnRH neuronal cell line.

“…Synchronization could be mediated by synaptic mechanisms or possibly electrotonic coupling via gap junctions. Evidence that both the pulse generator and the mechanism for synchronization reside within the medial basal hypothalamus comes from the observations that deafferentation of the medial basal hypothalamus does not inhibit pulsatile release of luteinizing hormone (7,8) and that release of GnRH from the hypothalamus in vitro is pulsatile (10 (2,22). The duration of the pulses observed with superfused GT1-1 cells is considerably longer and the relative amplitude smaller than those characteristics observed for GnRH pulses in the portal blood of the ovariectomized sheep (22).…”

“…A synchronous and intermittent discharge of multiple GnRH neurons (6) is required for episodic increases in the concentration of GnRH in hypophyseal portal blood. This intermittent secretion is the result ofan oscillator, the so-called GnRH pulse generator, localized in the mediobasal hypothalamic-anterior hypothalamic-preoptic area (7)(8)(9). In both the rat (7) and monkey (8) surgical deafferentation of the mediobasal hypothalamus does not interfere with GnRH pulses.…”

“…This intermittent secretion is the result ofan oscillator, the so-called GnRH pulse generator, localized in the mediobasal hypothalamic-anterior hypothalamic-preoptic area (7)(8)(9). In both the rat (7) and monkey (8) surgical deafferentation of the mediobasal hypothalamus does not interfere with GnRH pulses. Lesions of the arcuate nuclei in primates, which destroy many of the GnRH neurons, abolish the ultradian pattern of release, and neural activity within this region has been correlated with the pulses (6,9).…”

Is Aromatization of Testosterone to Estradiol Required for Inhibition of Luteinizing Hormone Secretion in Men?

“…Interpretation of the significance of these observations requires an understanding of the physiologic mechanisms which initiate LH pulses and modulate pulse amplitude. A large number of studies sin rodents and primates suggest that spontaneous LU pulses reflect the periodic secretion of LU-RU from the hypothalamus in response to firing of a-adrenergically mediated CNS neurons (14,(28)(29)(30)(31). If this consideration 15 correct, LU pulse amplitude could be modulated either by (a) the amount of endogenous LU-RU released to initiate each spontaneous LU pulse or (b) by the responsiveness of the pituitary to a given quantity of LU-RU.…”