Maggot Instructor: Semi-Automated Analysis of Learning and Memory in Drosophila Larvae

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.

Cognitive limits of larvalDrosophila: testing for conditioned inhibition, sensory preconditioning, and second-order conditioning

“…These results do not provide evidence of secondorder conditioning as an associative phenomenon (preliminary experiments in the aversive domain, using a modified protocol and associations between odor and electric shock during first-order conditioning, likewise yielded no such evidence: Supplemental Fig. S3A-D; Saumweber et al 2011;Tomasiunaite et al 2018).…”

Sex in a virtual reality: experimental evidence for sexual isolation due to variation in perception of the environment

“…Therefore, it might be argued that the flies in our experiment did not make decisions based on actual ecological performance and expected fitness. However, input obtained from sensory neurons is perceived as real by these flies when assessing habitat quality [44][45][46] . Hence, avoiding the perceived CO 2 is in principle an adaptive response of the fly in their virtual reality, even if CO 2 is not present in their actual reality.…”

“…Half of the flies perceive optogenetic stimulation as the smell of a harmful concentration of CO 2 [58][59][60][61] and are expected to avoid the illuminated habitat. The other half of the flies perceive it as the smell of food-related compounds 46,59,60,62 and are expected to be attracted to the illuminated habitat.…”

“…The repellent stimulus was induced using a Gr21a-GAL4 optogenetic driver 44,60,63 (Bloomington fly strain #23890). The attractive stimulus was induced using an Or42b-GAL4 driver 46,60,62,64 (Bloomington strain #9971). We used the responder UAS-Chrimson 39 (Bloomington fly strain #55136).…”

Quantitative imaging of sleep behavior in Caenorhabditis elegans and larval Drosophila melanogaster

“…For fly larvae, numerous methods have been described for monitoring short-term behaviors in a high-throughput manner 32,38,39 . However, to our knowledge no other method exists to monitor behavior over periods of hours to days.…”