Combined two-photon calcium imaging and single-ommatidium visual stimulation to study fine-scale retinotopy in insects

Abstract

Individual neurons in several sensory systems receive synaptic inputs organized according to subcellular topographic maps, yet the fine structure of this topographic organization has not been studied in detail. The lobula giant movement detector (LGMD) neuron in the locust visual system is known to receive topographic (retinotopic) excitatory inputs on part of its dendritic tree. To study the fine structure of this retinotopic mapping of visual inputs onto the excitatory dendritic field of the LGMD, we designed a custom microscope allowing visual stimulation at the native sampling resolution of the locust compound eye (defined by a single ommatidium or facet) while simultaneously performing two-photon calcium imaging on excitatory dendrites. Our goal is to provide the reader with detailed guidelines on how to build a custom two-photon microscope and a single-facet stimulation setup and to show experimental results on the detailed retinotopic structure of the projection of excitatory inputs onto the LGMD based on these tools.