Alteration of GABAergic neurotransmission by pulsed infrared laser stimulation

Transient electrical impulses are conventionally used to elicit physiological responses in excitable tissues. While electrical stimulation has many advantages, it requires an electrode–tissue interface, exhibits relatively low spatial selectivity and always produces a “stimulus artifact”. Recently, it has been shown that pulsed, low-energy infrared laser light can evoke nerve, muscle and sensory responses similar to those induced by traditional electrical stimulation in a contact-free, damage-free, artifact-free and spatially selective manner. However, the effect of transient infrared laser light on neurotransmission in the CNS is still largely unknown. Here, we tested the effect of infrared laser light on GABAergic neurotransmission. We recorded spontaneous inhibitory postsynaptic currents (sIPSCs) from cultured rat cortical neurons prior to and after infrared laser stimulation. Using transient infrared laser light, we either stimulated the neuronal soma that had axonal projections to the recorded neuron or directly stimulated the axons that projected to the recorded neuron. Optical stimulation led to enhanced amplitude, decreased decay time constant and increased frequency of sIPSCs. These alterations of sIPSC properties produced by optical stimulation were specifically mediated by GABAA receptors and caused by the transient laser light per se since no exogenous substances such as caged compounds were used. These data show that optical stimulation using transient infrared laser light can alter GABAergic neurotransmission and demonstrate that it may be an alternative approach to electrical stimulation in studying GABAergic function.