The
gonadotropin-releasing hormone (
GnRH) neurosecretory system undergoes marked structural and functional changes during the ovarian cycle. The aim of this study was to examine the neuroanatomical relationship between
GnRH neurons and a polysialylated form of
neural cell adhesion molecule (
PSA-NCAM), a known marker of neuronal plasticity. Using immunohistofluorescent dual labeling, we determined that axon terminals of
GnRH in the median arcuate nucleus (ME-
ARC) region of the hypothalamus in the proestrous phase of the estrous cycle were intimately associated with
PSA-NCAM. To further examine whether
PSA-NCAM expression associated with
GnRH neuron terminals varies in conjugation with cyclic changes in ovarian
steroid hormone levels, we examined
GnRH and
PSA-NCAM dual expression in ovariectomized (OVX) and
estrogen-
progesterone-primed OVX (EBP-OVX) rats. The expression of
PSA-NCAM immunoreactivity associated with the
GnRH neurons in the proestrous phase and EBP-OVX rats was significantly higher than during the diestrous phase and in OVX rats where
GnRH secretion declines. We further examined whether the structural changes in
GnRH axon terminals in the ME-
ARC region are also associated with glial plasticity. By extension and retraction of the glial processes, the
GnRH neuron terminals in the ME-
ARC region could undergo dynamic
plastic changes that control
GnRH release during the proestrous phase.
PSA-NCAM expression was also seen on glial cells in the ME-
ARC region. The close association between
PSA-NCAM on
GnRH and glial cells in the ME-
ARC region of the hypothalamus in the rat showed dynamic structural changes in
GnRH neuron terminals during the estrous cycle. These observations suggested that
PSA-NCAM may act as a molecular substrate to promote neuroplastic changes in the
GnRH neurosecretory system.