Neuronal Gonadotrophin‐Releasing Hormone (GnRH) and Astrocytic Gonadotrophin Inhibitory Hormone (GnIH) Immunoreactivity in the Adult Rat Hippocampus |
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| Authors: | J. K. Ferris M. T. Tse D. K. Hamson M. D. Taves C. Ma N. McGuire L. Arckens G. E. Bentley L. A. M. Galea S. B. Floresco K. K. Soma |
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| Affiliation: | 1. Department of Psychology, University of British Columbia, Vancouver, BC, Canada;2. Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, BC, Canada;3. Graduate Program in Neuroscience, University of British Columbia, Vancouver, BC, Canada;4. Department of Zoology, University of British Columbia, Vancouver, BC, Canada;5. Department of Integrative Biology, University of California‐Berkeley, Berkeley, CA, USA;6. Laboratory of Neuroplasticity and Neuroproteomics, University of Leuven, Leuven, Belgium |
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| Abstract: | Gonadotrophin‐releasing hormone (GnRH) and gonadotrophin inhibitory hormone (GnIH) are neuropeptides secreted by the hypothalamus that regulate reproduction. GnRH receptors are not only present in the anterior pituitary, but also are abundantly expressed in the hippocampus of rats, suggesting that GnRH regulates hippocampal function. GnIH inhibits pituitary gonadotrophin secretion and is also expressed in the hippocampus of a songbird; its role outside of the reproductive axis is not well established. In the present study, we employed immunohistochemistry to examine three forms of GnRH [mammalian GnRH‐I (mGnRH‐I), chicken GnRH‐II (cGnRH‐II) and lamprey GnRH‐III (lGnRH‐III)] and GnIH in the adult rat hippocampus. No mGnRH‐I and cGnRH‐II+ cell bodies were present in the hippocampus. Sparse mGnRH‐I and cGnRH‐II+ fibres were present within the CA1 and CA3 fields of the hippocampus, along the hippocampal fissure, and within the hilus of the dentate gyrus. No lGnRH‐III was present in the rodent hippocampus. GnIH‐immunoreactivity was present in the hippocampus in cell bodies that resembled astrocytes. Males had more GnIH+ cells in the hilus of the dentate gyrus than females. To confirm the GnIH+ cell body phenotype, we performed double‐label immunofluorescence against GnIH, glial fibrillary acidic protein (GFAP) and NeuN. Immunofluorescence revealed that all GnIH+ cell bodies in the hippocampus also contained GFAP, a marker of astrocytes. Taken together, these data suggest that GnRH does not reach GnRH receptors in the rat hippocampus primarily via synaptic release. By contrast, GnIH might be synthesised locally in the rat hippocampus by astrocytes. These data shed light on the sites of action and possible functions of GnRH and GnIH outside of the hypothalamic‐pituitary‐gonadal axis. |
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| Keywords: | astrocyte oestradiol
LHRH
neurosteroid progesterone RFRP‐3 sex difference testosterone |
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