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 Purely Optical Stimulation of Neurons
Electrical stimulation of nerve strands and individual neurons are well established methods in medical research and - to some degree - in therapy. However, the latter generally suffers from poor spatial resolution since the neccessary electrical fields extend across large areals rather than individual neurons.
Even in electrophysiological experiments under lab conditions, is the electrical `clamping´ of single cells a rather tedious task. It requires penetration of the cell membrane with a µm-sized pipette and extreme caution during the actual measurement.
Our group is currently investigating a non-contact, high resolution alternative to electrical stimulation, namely the stimulation of individual neurons with short laserpulses in the visible and NIR spectrum.
To this end, we are monitoring mamalian stammcells (rats ...) in a patch clamp setup, while focussing a tunable laser into the soma. Our main interest at this point lies on light induced changes in the cells´ rest potential and net currents across the membrane.
Our laser system consists of a frequency trippled Nd:YAG laser that is pumping an optical parametric oscillator (OPO). The OPO yields 10-ns pulses in the whole visible spectrum (400-780 nm) with some 10 mJ pulse energy. The light is delivered to the patch-clamp setup via optical fiber and then focussed to a 40 µm spot in the focal plane of a microscope.
Patch-clamp recordings are performed while tuning the OPO from 400 to 780 nm, thus obtaining action spectra of the neuron cell. This following page epicts our current experimental setup.
Some sample recordings, although taken from granulosa cells in rats, rather than excitable neurons can be found here. |
