IMMORTALIZED HYPOTHALAMIC LUTEINIZING-HORMONE-RELEASING HORMONE (LHRH) NEURONS - A NEW TOOL FOR DISSECTING THE MOLECULAR AND CELLULAR BASISOF LHRH PHYSIOLOGY

Authors
Citation
Wc. Wetsel, IMMORTALIZED HYPOTHALAMIC LUTEINIZING-HORMONE-RELEASING HORMONE (LHRH) NEURONS - A NEW TOOL FOR DISSECTING THE MOLECULAR AND CELLULAR BASISOF LHRH PHYSIOLOGY, Cellular and molecular neurobiology, 15(1), 1995, pp. 43-78
Citations number
175
Categorie Soggetti
Neurosciences,"Cell Biology",Biology
ISSN journal
02724340
Volume
15
Issue
1
Year of publication
1995
Pages
43 - 78
Database
ISI
SICI code
0272-4340(1995)15:1<43:IHLH(>2.0.ZU;2-H
Abstract
1. Two LHRH neuronal cell lines were developed by targeted tumorigenes is of LHRH neurons in vivo. These cell lines (GN and GT-1 cells) repre sent a homogeneous population of neurons. GT-1 cells have been further subcloned to produce the GT1-1, GT1-3, and GT1-7 cell lines. While co nsiderable information is accumulating about GT-1 cells, very little i s currently known about the characteristics and responses of GN cells. 2. By both morphological and biochemical criteria, GT-1 cells are cle arly neurons. All GT-1 cells immunostain for LHRH and the levels of pr ohormone, peptide intermediates, and LHRH in the cells and medium are relatively high. 3. GT-1 cells biosynthesize, process, and secrete LHR H. Processing of pro-LHRH appears to be very similar to that reported for LHRH neurons in vivo. At least four enzymes may be involved in pro cessing the prohormone to LHRH. 4. LHRH neurons are unique among the n eurons of the central nervous system because they arise from the olfac tory placode and grow back into the preoptic-anterior hypothalamic reg ion of the brain. Once these neurons reach this location, they send th eir axons to the median eminence. With respect to the immortalized neu rons, GN cells were arrested during their transit to the brain. In con trast, GT-1 cells were able to migrate to the preoptic-anterior hypoth alamic region but were unable correctly to target their axons to the m edian eminence. These problems in migration and targeting appear to be due to expression of the simian virus T-antigen. 5. While GT-1 cells are a homogeneous population of neurons, they are amenable to cocultur e with other types of cells. Coculture experiments currently under way should help not only to reveal some of the molecular and cellular cue s that are important for neuronal migration and axonal targeting, but they should also highlight the nature of the cellular interactions whi ch normally occur in situ. 6. GT-1 cells spontaneously secrete LHRH in a pulsatile manner. The interpulse interval for LHRH from these cells is almost identical to that reported for release of LH and LHRH in vi vo. GT-1 cells are interconnected by both gap junctions and synapses. The coordination and synchronization of secretion from these cells cou ld occur through these interconnections. by feedback from LHRH itself, and/or by several different compounds that are secreted by these cell s. One such compound is nitric oxide. 7. GT-1 cells have Na+, K+, Ca2, and Cl- channels. Polymerase chain reaction experiments coupled with Southern blotting and electrophysiological recordings reveal that GT- 1 cells contain at least five types of Ca2+ channels. R-type Ca2+ chan nels appear to be the most common type of channel and this channel is activated by phorbol esters in the GT-1 cells. 8. LHRH is secreted fro m GT-1 cells in response to norepinephrine, dopamine, histamine, GABA (GABA-A agonists), glutamate, nitric oxide, neuropeptide Y, endothelin , prostaglandin E(2), and activin A. Phorbol esters are very potent st imulators of LHRH secretion. Inhibition of LHRH release occurs in resp onse to LHRH, GABA (GABA-B agonists), prolactin, and glucocorticoids. 9. Compared to secretion studies, far fewer agents have been tested fo r their effects on gene expression. All of the agents which have been tested so far have been found either to repress LHRH gene expression o r to have no effect. The agents which have been reported to repress LH RH steady-state mRNA levels include LHRH, prolactin, glucocorticoids, nitric oxide, and phorbol esters. While forskolin stimulates LHRH secr etion, it does not appear to have any effect on LHRH mRNA levels.