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Keywords:

  • estrogen receptor-α;
  • Fos;
  • Fluoro-Gold;
  • arcuate nucleus

Abstract

Gonadotropin-releasing hormone (GnRH) secretion is controlled by various factors, including the excitatory neurotransmitter glutamate. Estrogen (E) regulates GnRH secretion by means of E-responsive cells in the brain that relay the feedback effects to the preoptic area (POA). We used an antibody to vesicular glutamate transporter 2 (VGluT2) to label glutamatergic neurons in the areas of the ewe brain that control GnRH secretion. VGluT2-immunoreactive cells were observed in the arcuate nucleus (ARC)/ventromedial hypothalamic nucleus (VMH) complex, POA, bed nucleus of stria terminalis (BnST), and A1 and A2 cell groups in the brainstem. In three ewes, E receptor-α was detected in 52–61% of glutamatergic neurons in ARC/VMH, 37–52% of neurons in the POA, and 37–58% of neurons in the BnST. E injection (i.m. or i.v.) increased the percentage of glutamatergic cells that expressed Fos protein in the ARC (P < 0.01 and P < 0.001, respectively). In six ewes, injection of the retrograde tracer Fluoro-Gold into the POA labeled cells in the ARC and 6–29% of these were also VGluT2-immunoreactive. Double-labeling of varicosities in the POA showed colocalization of VGluT2 in 12.5 ± 3% of dopamine β-hydroxylase–immunoreactive terminals, indicating that a subset of glutamatergic inputs could arise from brainstem noradrenergic neurons cells. In the POA, 60% of GnRH neurons had close appositions that were VGluT2-immunoreactive. We conclude that E-responsive glutamatergic neurons arising from the brainstem, the BnST, and ARC/VMH provide input to the POA and may be involved in the regulation of GnRH secretion. J. Comp. Neurol. 465:136–144, 2003. © 2003 Wiley-Liss, Inc.