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The Journal of Neuroscience, January 23, 2008, 28(4):850-861; doi:10.1523/JNEUROSCI.5078-07.2008

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Development/Plasticity/Repair
Roles of NR2A and NR2B in the Development of Dendritic Arbor Morphology In Vivo

Rebecca C. Ewald, Kendall R. Van Keuren-Jensen, Carlos D. Aizenman, and Hollis T. Cline

Watson School of Biological Sciences and Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724

Correspondence should be addressed to Dr. Hollis T. Cline, Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724. Email: cline{at}cshl.edu

NMDA receptors (NMDARs) are important for neuronal development and circuit formation. The NMDAR subunits NR2A and NR2B are biophysically distinct and differentially expressed during development but their individual contribution to structural plasticity is unknown. Here we test whether NR2A and NR2B subunits have specific functions in the morphological development of tectal neurons in living Xenopus tadpoles. We use exogenous subunit expression and endogenous subunit knockdown to shift synaptic NMDAR composition toward NR2A or NR2B, as shown electrophysiologically. We analyzed the dendritic arbor structure and found evidence for both overlapping and distinct functions of NR2A and NR2B in dendritic development. Control neurons develop regions of high local branch density in their dendritic arbor, which may be important for processing topographically organized inputs. Exogenous expression of either NR2A or NR2B decreases local branch clusters, indicating a requirement for both subunits in dendritic arbor development. Knockdown of endogenous NR2A reduces local branch clusters, whereas knockdown of NR2B has no effect on branch clustering. Analysis of the underlying branch dynamics shows that exogenous NR2B-expressing neurons are more dynamic than control or exogenous NR2A-expressing neurons, demonstrating subunit-specific regulation of branch dynamics. Visual experience-dependent increases in dendritic arbor growth rate seen in control neurons are blocked in both exogenous NR2A- and NR2B-expressing neurons. These experiments indicate that NR2A and NR2B have subunit-specific properties in dendritic arbor development, but also overlapping functions, indicating a requirement for both subunits in neuronal development.

Key words: structural plasticity; branch dynamics; in vivo imaging; visual system; activity dependent; glutamatergic transmission

Received July 27, 2007; accepted Dec. 13, 2007.

Correspondence should be addressed to Dr. Hollis T. Cline, Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724. Email: cline{at}cshl.edu






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