Temperature-dependent activation of neurons by continuous near-infrared laser.

Optical control of neuronal activity has a number of advantages over electrical methods and can be conveniently applied to intact individual neurons in vivo. In this study, we demonstrated an experimental approach in which a focused continuous near-infrared (CNI) laser beam was used to activate single rat hippocampal neurons by transiently elevating the local temperature. Reversible changes in the amplitude and kinetics of neuronal voltage-gated Na and K channel currents were recorded following irradiation with a single-mode 980 nm CNI-laser. Using single-channel recordings under controlled temperatures as a means of calibration, it was estimated that temperature at the neuron rose by 14 degrees C in 500 ms. Computer simulation confirmed that small temperature changes of about 5 degrees C were sufficient to produce significant changes in neuronal excitability. The method should be broadly applicable to studies of neuronal activity under physiological conditions, in particular studies of temperature-sensing neurons expressing thermoTRP channels.