Drosophila larvae are able to associate odor stimuli with gustatory reward. Here we describe a simple behavioral paradigm that allows the analysis of appetitive associative olfactory learning.
In the following we describe the methodological details of appetitive associative olfactory learning in Drosophila larvae. The setup, in combination with genetic interference, provides a handle to analyze the neuronal and molecular fundamentals of specifically associative learning in a simple larval brain.
Organisms can use past experience to adjust present behavior. Such acquisition of behavioral potential can be defined as learning, and the physical bases of these potentials as memory traces1-4. Neuroscientists try to understand how these processes are organized in terms of molecular and neuronal changes in the brain by using a variety of methods in model organisms ranging from insects to vertebrates5,6. For such endeavors it is helpful to use model systems that are simple and experimentally accessible. The Drosophila larva has turned out to satisfy these demands based on the availability of robust behavioral assays, the existence of a variety of transgenic techniques and the elementary organization of the nervous system comprising only about 10,000 neurons (albeit with some concessions: cognitive limitations, few behavioral options, and richness of experience questionable)7-10.
Drosophila larvae can form associations between odors and appetitive gustatory reinforcement like sugar11-14. In a standard assay, established in the lab of B. Gerber, animals receive a two-odor reciprocal training: A first group of larvae is exposed to an odor A together with a gustatory reinforcer (sugar reward) and is subsequently exposed to an odor B without reinforcement 9. Meanwhile a second group of larvae receives reciprocal training while experiencing odor A without reinforcement and subsequently being exposed to odor B with reinforcement (sugar reward). In the following both groups are tested for their preference between the two odors. Relatively higher preferences for the rewarded odor reflect associative learning – presented as a performance index (PI). The conclusion regarding the associative nature of the performance index is compelling, because apart from the contingency between odors and tastants, other parameters, such as odor and reward exposure, passage of time and handling do not differ between the two groups9.
The described setup in Drosophila larvae allows for the investigation of associative olfactory learning within a comparably elementary brain. The approach is simple, cheap, easy to establish in a lab and does not require high-tech equipment9. We present a version of the experiment, to study appetitive associative learning reinforced by fructose reward11. The described setup is based on a series of parametrical studies that comprehensively investigated variations in the number of trai…
The authors have nothing to disclose.
We especially want to thank the members of the Gerber lab for technical instructions on their experimental setup and comments on the manuscript. We also thank Lyubov Pankevych for fly care and maintenance of the wild type CantonS stock. This work is supported by the DFG grant TH1584/1-1, the SNF grant 31003A_132812/1 and the Zukunftskolleg of the University of Konstanz (all to AST).
Name of the reagent | Company | Catalogue number | CAS number |
Fructose | Sigma | 47740 | 57-48-7 |
NaCl | Fluka | 71350 | 7647-14-5 |
Agarose | Sigma | A5093 | 9012-36-6 |
1-octanol | Sigma | 12012 | 111-87-5 |
Amylacetate | Sigma | 46022 | 628-63-7 |
Paraffin oil | Sigma | 18512 | 8012-95-1 |