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 promo te 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 kinas e plus one of two structurally related GPI-linked receptors, GFR alpha-1 an d GFR alpha-2. To ascertain how the expression of these receptors is regula ted during development, we cultured embryonic neurons under different exper imental conditions and used competitive RT/PCR to measure the levels of the mRNAs encoding these receptors. We found that depolarisiug levels of KCl c aused a marked increase in GFR alpha-1 mRNA and a marked decrease in GFR al pha-2 mRNA in sympathetic, parasympathetic and sensory neurons. These chang es were accompanied by increased responsiveness to GDNF and decreased respo nsiveness to neurturin, and were inhibited by L-type Ca2+ channel antagonis ts, suggesting that they were due to elevated intracellular free-Ca2+. Ther e was no consistent effect of depolarising levels of KCI on ret mRNA expres sion, and neither GDNF nor neurturin significantly affected receptor expres sion. These results show that depolarisation has marked and opposing action s on the expression of GFR alpha-1 and GFR alpha-2, which are translated in to corresponding changes in neuronal responsiveness to GDNF and neurturin. This provides evidence for a mechanism of regulating the neurotrophic facto r responses of neurons by neural activity that has important implications f or structural and functional plasticity in the developing nervous system.