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Neuronal Gonadotrophin‐Releasing Hormone (GnRH) and Astrocytic Gonadotrophin Inhibitory Hormone (GnIH) Immunoreactivity in the Adult Rat Hippocampus
Author(s) -
Ferris J. K.,
Tse M. T.,
Hamson D. K.,
Taves M. D.,
Ma C.,
McGuire N.,
Arckens L.,
Bentley G. E.,
Galea L. A. M.,
Floresco S. B.,
Soma K. K.
Publication year - 2015
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/jne.12307
Subject(s) - medicine , endocrinology , hippocampus , hippocampal formation , dentate gyrus , biology , hypothalamus , gonadotropin releasing hormone , astrocyte , glial fibrillary acidic protein , hormone , luteinizing hormone , immunohistochemistry , central nervous system
Gonadotrophin‐releasing hormone (Gn RH ) and gonadotrophin inhibitory hormone (Gn IH ) are neuropeptides secreted by the hypothalamus that regulate reproduction. Gn RH receptors are not only present in the anterior pituitary, but also are abundantly expressed in the hippocampus of rats, suggesting that Gn RH regulates hippocampal function. Gn IH 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 Gn RH [mammalian Gn RH ‐I ( mGnRH ‐I), chicken Gn RH ‐ II ( cGnRH ‐ II ) and lamprey Gn RH ‐ III ( lGnRH ‐ III )] and Gn IH 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 CA 1 and CA 3 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. Gn IH ‐immunoreactivity was present in the hippocampus in cell bodies that resembled astrocytes. Males had more Gn IH + cells in the hilus of the dentate gyrus than females. To confirm the Gn IH + cell body phenotype, we performed double‐label immunofluorescence against Gn IH , glial fibrillary acidic protein (GFAP) and NeuN. Immunofluorescence revealed that all Gn IH + cell bodies in the hippocampus also contained GFAP , a marker of astrocytes. Taken together, these data suggest that Gn RH does not reach Gn RH receptors in the rat hippocampus primarily via synaptic release. By contrast, Gn IH might be synthesised locally in the rat hippocampus by astrocytes. These data shed light on the sites of action and possible functions of Gn RH and GnIH outside of the hypothalamic‐pituitary‐gonadal axis.