Cross-talk between luteinizing hormone-releasing hormone (LHRH) neurons and astroglial cells: Developing glia release factors that accelerate neuronal differentiation and stimulate LHRH release from GT(1-1) neuronal cell line and LHRH neurons induce astroglia proliferation

Recent evidences indicate that the bidirectional flow of informations governing neuron-astrocyte interactions plays a crucial role during the development and in the adult brain. In the present study, we have used the immortalized hypothalamic luteinizing hormone-releasing hormone (LHRH) neuronal cell line (GT(1-1) subclone) to investigate LHRH-astroglial cell interactions, and addressed the following questions: (a) does the astroglial cell compartment influence GT(1-1) neuron morphology, LHRH secretion and/or proliferation?; (b) does the bidirectional flow of informational molecules released during neuron-astroglia interactions influence one or both cell compartments? (c) are receptor-mediated cell-cell interactions between neurons and astroglia involved in such crosstalk? In this experimental design, GT(1-1) neuronal cells were grown either: (1) in Dulbecco's modified eagle's medium (DMEM); (2) in the presence of conditioned medium from astroglial cell (ACM) cultures at different stages of glia differentiation and maturation in vitro; (3) in the presence of astroglial cells, in co-cultures or mixed-cultures; and (4) in the absence or the presence of antibodies (Abs) for neural cell adhesion molecule (N-CAM) receptor. This work shows that during its maturation and differentiation in vitro (8-40 days, DIV), astroglial cells in primary culture release factors able to markedly influence GT(1-1) cell morphology and accelerate LHRH cell secretory potential, with a potency depending on both the 'age' of astroglia and the degree of GT(1-1) neuron differentiation in vitro. Regional differences in glial-derived factors that promote LHRH neuronal differentiation and secretion were observed, with hypothalamic astroglia being the most potent neurotrophic stimulus. Such effects were specific for astroglia conditioned medium (CM), since oligodendrocyte CM was without effect. Boiling of the ACM for 10 min completely abolished stimulatory activity on neuronal cells. When immature astroglial cells (12 DIV) were co-cultured with GT(1-1) neurons, LHRH release increased by about 2- to 3-fold over basal levels and GT(1-1) neuron proliferation was doubled. Astroglial cells responded to GT(1-1) neuronal signals with an almost doubling of the [H-3]-thymidine incorporation and DNA synthesis. Extensive neurite outgrowth and establishment of cell-cell contacts between the two cell compartments were observed in the mixed culture preparation, accompanied by a marked stimulatory effect on both cell proliferation and LHRH secretion. Addition of N-CAM-Ab in the GT(1-1)-astroglial cell mixed cultures resulted in a dramatic disruption of GT(1-1)-astroglia morphology and a 95% suppression of the stimulatory effect on both cell proliferation and LHRH release, suggesting the local adhesive mechanisms are importantly involved in the crosstalk between GT(1-1) neurons and astroglial cells in vitro. This work shows for the first time the presence of a bidirectional interaction between the LHRH neurons and astroglial cells and suggest a potential interplay between the two compartments in the regulation of LHRH neuronal physiology.