Activation of ionotropic glutamate receptors reduces the production of transforming growth factor-β2 by developing neurons

Neuronal cultures derived from developing rat cerebral cortex were used to investigate the influence of glutamate receptors on the neuronal production of transforming growth factor-B2 (TGFB2), a multifunctional cytokine that modulates neuronal and glial growth. Long-term exposure (48 h) of cortical neurons to selective antagonists of N-methyl-D-aspartate (NMDA) and alpha -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors markedly increased TGFB2 levels in the culture medium. Conversely, treatment with NMDA or kainate reduced TGFB2 to levels below those in untreated cultures. The effect of kainate did not require NMDA receptor activity. Neuronal depolarization with K+ also reduced TGFB2 levels by opening voltage-gated L-type Ca2+ channels. Semi-quantitative RT-PCR measurements of neuronal TGFB2 mRNA showed that NMDA or AMPA/kainate receptor stimulation reduced TGFB2 mRNA levels. These results demonstrate that tonic activation of glutamate-gated cation channels downregulates neuronal expression of the TGFB2 gene and provide evidence for a novel mechanism whereby excitatory amino acids could influence the development of glial and neuronal lineages.