Mapping neural circuits in the mammalian brain: scanning laser photostimulation in vitro

摘要

Abstract: Determination of the organization, sign and strength ofneuronal circuitry has resisted conventional anatomicaland electrophysiological methods; it has provedparticularly difficult to discretely activate isolatedsingle circuits within the network of connections inthe mammalian brain slice. Traditional electricalstimulating electrodes are poor tools for a detailedinvestigation of the organization of functionalconnections within brain slices, as they lack goodspatial resolution and activate multiple neuronalcircuits simultaneously. Scanning laserphotostimulation offers many advantages over this andother current approaches: spatial resolution is superb,fibers of passage are not activated, and thousands ofpresynaptic locations can be stimulated. With thisapproach, caged neurotransmitters are activated in arestricted region of the brain slice by photolysis witha UV argon laser. Combining computer-controlledpositioning of the laser light and whole cell recordingin brain slices allows the construction of detailedmaps of the position, strength, sign and number ofinputs converging on a single postsynaptic neuron. Wedescribe the technique of photostimulation, outline theinstrumentation necessary to implement it, and discussthe interpretation of photostimulation- derived data.Finally, we will present examples of mapping circuitsin the mammalian visual cortex using this approach.Although only recently developed, scanning laserphotostimulation offers neuroscientists a powerful toolfor determining the organization and function of localbrain circuits.!24