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Immortalized gonadotropin‐releasing hormone neurons secrete γ‐aminobutyric acid – evidence for an autocrine regulation
Author(s) -
AhnertHilger G.,
John M.,
Kistner U.,
Wiedenmann B.,
Jarry H.
Publication year - 1998
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.1460-9568.1998.00129.x
Subject(s) - exocytosis , synaptotagmin 1 , biology , population , synaptic vesicle , secretion , microbiology and biotechnology , gonadotropin releasing hormone , gabaergic , medicine , endocrinology , biochemistry , hormone , inhibitory postsynaptic potential , vesicle , luteinizing hormone , sociology , demography , membrane
The immortalized hypothalamic neuronal cell lines GT1‐1 and GT1‐7 represent unique model systems to investigate the physiological control of gonadotropin‐releasing hormone (GnRH) secretion. Using immunofluorescence microscopy, key proteins of regulated exocytosis, e.g. synaptotagmin, synaptobrevin and SNAP‐25 (synaptosomal associated protein of 25 kDa) were found in GT1 neurons. In addition, GT1 neurons contained synaptophysin, a marker protein for small synaptic vesicles (SSVs) which are responsible for the storage of neurotransmitters such as γ‐aminobutyric acid (GABA). Upon subcellular fractionation, a lighter vesicle population characterized by synaptophysin separated from a denser vesicle population containing GnRH. Both vesicle populations contained synaptobrevin and synaptotagmin. Besides GnRH, GT1 neurons expressed glutamic acid decarboxylase at the mRNA‐level and synthesized GABA. More importantly, GT1 neurons took up and stored 3 H‐GABA. The stored GABA was released after stimulation with increasing K + concentrations and by α‐latrotoxin. Reducing the extracellular Ca 2+ ‐concentration abolished stimulated secretion, indicating that GABA was released by regulated exocytosis. Hormone secretion from GT1 neurons is controlled by GABA via GABA A and GABA B receptors reflecting the situation in vivo . Our data provide the first evidence that GT1 neurons possess a second regulated secretory pathway sustained by SSVs storing and releasing GABA. The released GABA influences GnRH secretion by an auto‐ or paracrine loop.