1. Figure 5 Coordinated glial–endothelial–neuronal interactions
that regulate the neurosecretion of gonadotropin-releasing hormone (GnRH)
Figure 5 | Coordinated glial–endothelial–neuronal interactions that regulate the neurosecretion of gonadotropin-releasing hormone (GnRH). In the external zone of the median eminence GnRH terminals access to pericapillary space is regulated in two separate ways. a | In dioestrus, high levels of progesterone in a context of low circulating levels of oestrogens promotes the secretion of SEMA7A by tanycytes in the median eminence192. SEMA7A activates integrin β1, which is expressed by tanycytes, via a paracrine and/or autocrine action. Integrin β1 activation promotes the growth of tanycytic endfeet (thick black arrows), which engulf GnRH neuroendocrine terminals and form a diffusion barrier impeding GnRH release into the pericapillary space and fenestrated capillaries192. In parallel, tanycytic SEMA7A acts on the receptor PlexinC1, which is expressed by GnRH neuroendocrine terminals, to induce the retraction of GnRH terminals from the pericapillary space (thin black arrow)192. b | In pro-oestrus, high circulating levels of oestrogens promote the release of nitric oxide (NO) and SEMA3A from the fenestrated endothelial cells of the median eminence. The release of NO promotes the retraction of tanycytic endfeet from the parenchymatous basal lamina (thick black arrows)164,182, whereas SEMA3A acts on neuropilin 1 (NRP1) to promote the outgrowth of GnRH neuroendocrine axons guided by a scaffold of tanycytic processes towards the pericapillary space (thin black arrow) thus facilitating the release of GnRH into the pericapillary space and fenestrated capillaries191.
Clasadonte, J. & Prevot, V. (2017) The special relationship: glia–neuron interactions in the neuroendocrine hypothalamus
Nat. Rev. Endocrinol. doi: /nrendo