Rapid dendritic remodeling in the developing retina: Dependence on neurotransmission and reciprocal regulation by Rac and Rho

We demonstrate that within the intact and spontaneously active retina, dend ritic processes of ganglion cells exhibit rapid and extensive movements dur ing the period of synaptogenesis. Marked restructuring occurs in seconds, b ut structural changes are relatively balanced across the dendritic arbor, m aintaining overall arbor size and complexity over hours. Dendritic motility is regulated by spontaneous glutamatergic transmission. Both the rate and extent of the movements are decreased by antagonists to NMDA and non-NMDA g lutamate receptors but are unaffected by tetrodotoxin, a sodium channel blo cker. The dendritic movements are actin dependent and are controlled by the Rho family of small GTPases. Transfection of dominant-negative and constit utively active mutants into ganglion cells showed that Rac and Rho exert re ciprocal effects on motility. We suggest that the Rho family of small GTPas es could integrate activity-dependent and -independent signals from afferen ts, thereby adjusting target motility and maximizing the chance for initial contact and subsequent synaptogenesis.