Neuroendocrine Control of Gonadotropin Secretion

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Neuroendocrine Control of Gonadotropin Secretion

• What is timing mechanism for cycles?
• Rat sexual differentiation of the hypothalamus
  (see notes)
• Arcuate Nucleus/VMN releases GnRH at a constant
  rate in males and females
• POA induces cyclic secretion of LH FSH (from
  ARC/VMN) in females
• POA acts as timing mechanism

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Neuroendocrine Control of Gonadotropin Secretion

• Primate (monkey probably human)
• Arcuate Nucleus (ARC) releases GnRH at a constant
  1 pulse/hour
• ARC appears to be the only hypothalamic area
  involved (higher CNS regions can modulate GnRH
  secretion from ARC)
• Evidence Halasz knife radiofreq lesion expts.
• Conclusion ovary is timing mechanism

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Cycling Monkey
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Halasz Knife Experiment
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RadiofrequencyLesion in ARC
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Pulsatile and Continuous GnRH in ARC lesioned
Monkey
Serum LH and FSH concentrations in an OVX monkey
with a lesion in the arcuate region. Pulsatile
administration (given for six minutes every hour)
of gonadotropin-releasing hormone (GnRH)
maintains serum FSH and LH concentrations. In
comparison, a continuous infusion of GnRH (middle
panel) leads to rapid and reversible suppression
of both LH and FSH release. Data from Belchetz,
PE, Plant, TM, Nakai, Y, et al, Science 1978
202631
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Effect of GnRH in ARC lesioned Monkey
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Hypothalamic Nuclei
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Hypothalamic GnRH Generators