Optical inactivation of a proprioceptor in an insect by non-genetic tools

Abstract

BackgroundThe specific role of sensory organs in locomotor pattern generation is traditionally investigated by means of mechanical ablation in arthropods that currently do not allow genetic manipulation. Mechanical ablation is irreversible, and may lead to injury discharges and changes in the structural integrity of the cuticle. New methodHere, we present a new method to temporarily or permanently deprive parts of an insect nervous system of sensory feedback from leg proprioceptors by means of blue light application. We illuminated campaniform sensilla (CS) with a blue LED (420–480 nm) or a 473 nm laser at different light intensities to optically eliminate sensory and motor neuron responses to mechanical stimulation. ResultsWe were able to eliminate all stimulus-evoked responses of CS. Individual CS groups were precisely and selectively inactivated without affecting nearby proprioceptors, using an optical fiber (Ø 200 µm) to guide the light. Our results demonstrated that lower light intensities significantly increase the required exposure time, but also the chance for recovery, thus making the effect reversible. Comparison with existing methodsIn contrast to mechanical ablation, optical inactivation of individual sensory organs is non-invasive and does not affect the behavioral state of the animal, nor does it induce escape behavior. This is especially relevant in non-model system experimental animals where optogenetic manipulation cannot be used, due to a lack of established methods of access. ConclusionOur results show that the proposed method is a reliable alternative to mechanical ablation and can be successfully applied to the CS, as it fulfills all requirements regarding selectivity, efficiency, and reproducibility.