Dendrite growth increased by visual activity requires NMDA receptor and Rho GTPases

Abstract

Previous studies suggest that neuronal activity may guide the development of synaptic connections in the central nervous system through mechanisms involving glutamate receptors and GTPase-dependent modulation of the actin cytoskeleton. Here we demonstrate by in vivo time-lapse imaging of optic tectal cells in Xenopus laevis tadpoles that enhanced visual activity driven by a light stimulus promotes dendritic arbor growth. The stimulus-induced dendritic arbor growth requires glutamate-receptor-mediated synaptic transmission, decreased RhoA activity and increased Rac and Cdc42 activity. The results delineate a role for Rho GTPases in the structural plasticity driven by visual stimulation in vivo.

“Let There be Light!” pigeon eggs are regularly exposed to light during breeding

“…However light can effect neuronal morphology faster since an increase in dendritic arbor growth within the optic tectum of tadpoles becomes already obvious during the first hour of visual stimulation (Sin et al, 2002). Moreover, the enhanced growth rates are maintained during a subsequent dark rearing period (Sin et al, 2002). Hence, light pulses to which the pigeon embryos of the present study were regularly exposed during relieves very likely continued to have an effect even after the parental bird covered the eggs again.…”

“…These activity-dependent signalling pathways induce neural gene transcription by modulating the function of transcriptional activators and repressors which finally lead to structural changes of the nerve cells (West and Grace, 2002). Accordingly, 2-4 h of light stimulation are sufficient to increase dendritic growth rates (Sin et al, 2002), or to enhance translation of the neurotrophic factor BDNF (Tropea et al, 2001) while blocking synaptic activity for 1 h enhances tectal cell death (Galliresta et al, 1993) and reduces growth of tectal dendrites or promotes arborisation of retinal ganglion cell axons (O'Rourke et al, 1994;Rajan et al, 1999;Cohen-Cory, 1999). Increased axonal arbor dynamics are also achieved within 2 h by tectal BDNF application (Cohen-Cory and Fraser, 1995; Alsina et al, 2001).…”

“…Increased axonal arbor dynamics are also achieved within 2 h by tectal BDNF application (Cohen-Cory and Fraser, 1995; Alsina et al, 2001). However light can effect neuronal morphology faster since an increase in dendritic arbor growth within the optic tectum of tadpoles becomes already obvious during the first hour of visual stimulation (Sin et al, 2002). Moreover, the enhanced growth rates are maintained during a subsequent dark rearing period (Sin et al, 2002).…”

“…Trophic light effects are not infinite since the growth promoting effects onto tectal dendrites cannot be further enhanced by longer stimulation than 4 h (Sin et al, 2002). Consequently, there is possibly an optimal amount of light stimulation that reflects a balance between the necessity of retinal activation for visual development and the protection of the clutch that is achieved by the parental bird sitting on the eggs.…”

Two-photon imaging of synaptic plasticity and pathology in the living mouse brain

“…In particular, the advent of Green Flourescent Protein (GFP) and its spectral variants and the ability to generate transgenic mice or viral vectors to drive the expression of such proteins in specific cell types in the nervous system [17][18][19] are allowing for long-term imaging of individual synaptic structures at high resolution in living animals. 18,[20][21][22][23] The other major technical advance relates to better instrumentation for optical imaging of living tissues. Specifically, two-photon microscopy (TPM) has dra-matically enhanced the ability of deep tissue imaging.…”