The rules by which odor receptors encode odors and allow behavior are still largely unexplored. Although large data sets of electrophysiological responses of receptors to odors have been generated, few hypotheses have been tested with behavioral assays. We use a data set on odor responses of Drosophila larval odor receptors coupled with chemotaxis behavioral assays to examine rules of odor coding. Using mutants of odor receptors, we have found that odor receptors with similar electrophysiological responses to odors across concentrations play non-redundant roles in odor coding at specific odor concentrations. We have also found that high affinity receptors for odors determine behavioral response thresholds, but the rules for determining peak behavioral responses are more complex. While receptor mutants typically show loss of attraction to odors, some receptor mutants result in increased attraction at specific odor concentrations. The odor receptor mutants were rescued using transgenic expression of odor receptors, validating assignment of phenotypes to the alleles. Vapor pressures alone cannot fully explain behavior in our assay. Finally, some odors that did not elicit strong electrophysiological responses are associated with behavioral phenotypes upon examination of odor receptor mutants. This result is consistent with the role of sensory neurons in lateral inhibition via local interneurons in the antennal lobe. Taken together, our results suggest a complexity of odor coding rules even in a simple olfactory sensory system.

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An increasing number of states are legalizing marijuana use for medicinal purposes despite marijuana use remaining criminalized at the federal level and continued Schedule I status by the US Food and Drug Administration. Many of those states in which medical marijuana is legal require physician involvement to facilitate patient access. In addition, physicians may have ethical objections to medical marijuana use or may not believe there is adequate scientific evidence to support its use. The constellation of these factors creates an ethical quandary for physicians when approached by patients for assistance in accessing medical marijuana. This article provides an ethical framework that provides guidance to physicians in managing these patient requests taking into consideration the above ethically relevant factors. (J Am Board Fam Med 2020;33:147-151.)