Glutamate Uncaging

One of the first experiments uncaging glutamate on dendrites was done by Kandler on CA1 pyramidal neurons in slices. They reported the long-term depression of glutamate responses after the pairing of uncaging with depolarization of the neuron. A similar result was obtained with bursts of uncaging by Dodt; these authors used an infrared-guided laser stimulation system to uncage glutamate on the apical dendrites of layer 5 neocortical pyramidal neurons.

Uncaging Compounds

RuBi-Glutamate

- caged-glutamate compound - based on ruthenium photochemistry - excited with visible wavelengths - releases glutamate after 1-photon or 2-photon excitation. - high quantum efficiency - can be used at low concentrations, - partly avoids blockade of GABAergic transmission - 2-photon uncaging of RuBi-Glutamate has a high spatial resolution and generates excitatory responses in individual dendritic spines with physiological kinetics. - With laser beam multiplexing, two-photon RuBi-Glutamate uncaging can also be used to depolarize and fire pyramidal neurons with single-cell resolution. - RuBi-Glutamate enables the photoactivation of neuronal dendrites and circuits with visible or two-photon light sources, achieving single cell, or even single spine, precision.

ruthenium-bipyridine complexes can be used as caging compounds ruthenium is a transition metal with versatile chemistry polypyridines of ruthenium photorelease entire ligands in a heterolytic fashion, by means of a widely known mechanism in which the initial photoexcited state quickly evolves into a dissociative state, so the photorelease is therefore clean and fast.

MNI-Glutamate

2-photon uncaging of MNI-glutamate has been used successfully to functionally map synaptic receptors, activate individual spines and individual neurons.

• needs to be applied to the tissue at relatively high (mM) concentrations for effective two-photon uncaging.
• at high concentrations, MNI-glutamate, like other caged compounds, is a very effective antagonist of GABAergic transmission.

CNB-glutamate

CNB-glutamate

L-glutamic acid

L-glutamic acid α(4,5-dimethoxy-2-nitrobenzyl) ester (Callaway, Katz, 1993)

REFERENCES

• Salierno Marceca Peterka Yuste Etchenique 2010 fast ruthenium polypyridine cage complex photoreleases glutamate with visible or IR light in one and two photon regimes J Inorg Biochem

• Araya Yuste 2006 The spine neck filters membrane potentials

• Carter Sabatini 2004 State-dependent calcium signaling in dendritic spines of striatal medium spiny neurons

• Gasparini Magee 2006 State dependent dendritic computation in hippocampal CA1 pyramidal neurons

• Sobczyk Svoboda 2005 NMDA receptor subunitdependent Ca2 signaling in individual hippocampal dendritic spines

• Matsuzaki Kasai 2001 Dendritic spine geometry is critical for AMPA receptor expression in hippocampal CA1 pyramidal neurons

• Callaway Katz 1993 Photostimulation using caged glutamate reveals functional circuitry in living brain slices

• Callaway Yuste 2002 Stimulating neurons with light

• Frick Dodt 2001 Glutamate receptors form hot spots on apical dendrites of neocortical pyramidal neurons

• Pettit Augustine 1997 Chemical twophoton uncaging: a novel approach to mapping glutamate receptors

• Shepherd Svoboda 2003 Circuit analysis of experience-dependent plasticity in the developing rat barrel cortex

• Wieboldt Hess 1994 Photolabile precursors of glutamate: synthesis, photochemical properties, and activation of glutamate receptors on a microsecond time scale.

• Yoshimura Callaway 2005 Excitatory cortical neurons form fine-scale functional networks.