Depolarisation causes reciprocal changes in GFR alpha-1 and GFR alpha-2 receptor expression and shifts responsiveness to GDNF and neurturin in developing neurons

GDNF and neurturin are structurally related neurotrophic factors that promote the survival of many different kinds of neurons and influence axonal and dendritic growth and synaptic function. These diverse effects are mediated via multicomponent receptors consisting of the Ret receptor tyrosine kinase plus one of two structurally related GPI-linked receptors, GFR alpha-1 and GFR alpha-2. To ascertain how the expression of these receptors is regulated during development, we cultured embryonic neurons under different experimental conditions and used competitive RT/PCR to measure the levels of the mRNAs encoding these receptors. We found that depolarisiug levels of KCl caused a marked increase in GFR alpha-1 mRNA and a marked decrease in GFR alpha-2 mRNA in sympathetic, parasympathetic and sensory neurons. These changes were accompanied by increased responsiveness to GDNF and decreased responsiveness to neurturin, and were inhibited by L-type Ca2+ channel antagonists, suggesting that they were due to elevated intracellular free-Ca2+. There was no consistent effect of depolarising levels of KCI on ret mRNA expression, and neither GDNF nor neurturin significantly affected receptor expression. These results show that depolarisation has marked and opposing actions on the expression of GFR alpha-1 and GFR alpha-2, which are translated into corresponding changes in neuronal responsiveness to GDNF and neurturin. This provides evidence for a mechanism of regulating the neurotrophic factor responses of neurons by neural activity that has important implications for structural and functional plasticity in the developing nervous system.