The ability to sense and respond to a rewarding stimulus is a key advantage for animals in their natural environment. The circuits that mediate these responses are complex, and it has been difficult to identify the fundamental principles of reward structure and function. However, the well-characterized brain anatomy and sophisticated neurogenetic tools in Drosophila melanogaster make the fly an ideal model to understand the mechanisms through which reward is encoded. Drosophila find food, water, intoxicating substances, and social acts rewarding. Basic monoaminergic neurotransmitters, including dopamine (DA), serotonin (5-HT), and octopamine (OA), play a central role in encoding these rewards. DA is central to sensing, encoding, responding, and predicting reward, whereas 5-HT and OA carry information about the environment that influences DA circuit activity. In contrast, slower-acting neuromodulators such as hormones and neuropeptides play a key role in both encoding the pleasurable stimulus and modulating how the internal environment of the fly influences reward sensation and seeking. Recurring circuit motifs for reward signaling identified in Drosophila suggest that these key principles will help elucidate understanding of how reward circuits function in all animals.
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Drosophila Reward Circuits
John S. Hernandez, Tariq M. Brown, and Karla R. Kaun
Article
Invertebrate Nociception
Nathaniel J. Himmel, Atit A. Patel, and Daniel N. Cox
Nociception is a protective mechanism that mediates behavioral responses to a range of potentially damaging stimuli, including noxious temperature, chemicals, and mechanical stimulation. Nociceptive mechanisms are found throughout metazoans. Noxious stimuli are transduced by specialized, high-threshold peripheral nociceptors, which fire action potentials to elicit adaptive behavioral responses. Nociception is essential for survival and provides a mechanism for sensory perception of noxious stimuli, which alerts the organism to potential environmental dangers. When coupled with pain sensation and complex behavioral responses, this mechanism protects the organism from incipient damage. Moreover, acute and chronic pain may manifest as altered nociception in neuropathic pain states. Elucidating the neural bases of nociception is therefore important for identifying and implementing novel strategies for the treatment of neuropathic pain, as well as uncovering the mechanistic bases by which the nervous system integrates information to produce specific behaviors in response to a range of noxious stimuli. Invertebrate organisms, such as Drosophila melanogaster and Caenorhabditis elegans, have emerged as powerful, genetically tractable platforms for exploring these questions. Here, we concisely review the current state of knowledge regarding the cells, molecules, neural circuits, and behaviors associated with invertebrate nociception in the fruit fly and nematode worm.
Article
Drosophila Olfaction
Quentin Gaudry and Jonathan Schenk
Olfactory systems are tasked with converting the chemical environment into electrical signals that the brain can use to optimize behaviors such as navigating towards resources, finding mates, or avoiding danger. Drosophila melanogaster has long served as a model system for several attributes of olfaction. Such features include sensory coding, development, and the attempt to link sensory perception to behavior. The strength of Drosophila as a model system for neurobiology lies in the myriad of genetic tools made available to the experimentalist, and equally importantly, the numerical reduction in cell numbers within the olfactory circuit. Modern techniques have recently made it possible to target nearly all cell types in the antennal lobe to directly monitor their physiological activity or to alter their expression of endogenous proteins or transgenes.
