Abstract
For several decades, Drosophila has been widely used as a suitable model organism to study the fundamental processes of associative olfactory learning and memory. More recently, this condition also became true for the Drosophila larva, which has become a focus for learning and memory studies based on a number of technical advances in the field of anatomical, molecular, and neuronal analyses. The ongoing efforts should be mentioned to reconstruct the complete connectome of the larval brain featuring a total of about 10,000 neurons and the development of neurogenic tools that allow individual manipulation of each neuron. By contrast, standardized behavioral assays that are commonly used to analyze learning and memory in Drosophila larvae exhibit no such technical development. Most commonly, a simple assay with Petri dishes and odor containers is used; in this method, the animals must be manually transferred in several steps. The behavioral approach is therefore labor-intensive and limits the capacity to conduct large-scale genetic screenings in small laboratories. To circumvent these limitations, we introduce a training device called the Maggot Instructor. This device allows automatic training up to 10 groups of larvae in parallel. To achieve such goal, we used fully automated, computer-controlled optogenetic activation of single olfactory neurons in combination with the application of electric shocks. We showed that Drosophila larvae trained with the Maggot Instructor establish an odor-specific memory, which is independent of handling and non-associative effects. The Maggot Instructor will allow to investigate the large collections of genetically modified larvae in a short period and with minimal human resources. Therefore, the Maggot Instructor should be able to help extensive behavioral experiments in Drosophila larvae to keep up with the current technical advancements. In the longer term, this condition will lead to a better understanding of how learning and memory are organized at the cellular, synaptic, and molecular levels in Drosophila larvae.
Highlights
Various technical and conceptual successes have helped recent research to gradually understand how a brain organizes learning and memory
We aimed to develop a new, robust, and easy-to-handle device, which we named Maggot Instructor, to train Drosophila larvae in an automated fashion
Our initial study focused on a protocol that automatically conditions the larvae by optogenetic activation of olfactory receptor neuron (ORN) (CS) via blue light and stimulation through electric shock (US)
Summary
Various technical and conceptual successes have helped recent research to gradually understand how a brain organizes learning and memory. We still cannot understand and address a number of basic mechanisms, recent achievements are fascinating Part of this development is due to the work on less complex insect brains, such as that of the fruit fly Drosophila and its larva. The establishment of the larval connectome that includes the reconstruction of every individual neuron with all its synapses and synaptic partners (Ohyama et al, 2015; Berck et al, 2016; Jovanic et al, 2016; Schlegel et al, 2016; Eichler et al, 2017) These advantages allow, for the first time, projects that can purposefully investigate – by using thousands of newly established genetic tools – how learning and memory are organized at the level of the brain, the nerve cell and the synapse
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