Neural activity-dependent regulation of radial glial filopodial motility is mediated by glial cGMP-dependent protein kinase 1 and contributes to synapse maturation in the developing visual system

Abstract

Radial glia in the developing optic tectum extend highly dynamic filopodial protrusions within the tectal neuropil, the motility of which has previously been shown to be sensitive to neural activity and nitric oxide (NO) release. Using in vivo two-photon microscopy, we performed time-lapse imaging of radial glial cells and measured filopodial motility in the intact albino Xenopus laevis tadpole. Application of MK801 to block neuronal NMDA receptor (NMDAR) currents confirmed a significant reduction in radial glial filopodial motility. This reduction did not occur in glial cells expressing a dominant-negative form of cGMP-dependent protein kinase 1 (PKG1), and was prevented by elevation ofcGMPlevels with the phosphodiesterase type 5 inhibitor sildenafil. These results suggest that neuronalNMDAR activation results in the release of NO, which in turn modulates PKG1 activation in glial cells to control filopodial motility. We further showed that interfering with the function of the small GTPases Rac1 or RhoA, known to be regulated byPKG1phosphorylation, decreased motility or eliminated filopodial processes respectively. These manipulations led to profound defects in excitatory synaptic development and maturation of neighboring neurons.