Gustatory processing and taste memory inDrosophila

Abstract

Taste allows animals to discriminate the value and potential toxicity of food prior to ingestion. Many tastants elicit an innate attractive or avoidance response that is modifiable with nutritional state and prior experience. A powerful genetic tool kit, well-characterized gustatory system, and standardized behavioral assays make the fruit fly, Drosophila melanogaster, an excellent system for investigating taste processing and memory. Recent studies have used this system to identify the neural basis for acquired taste preference. These studies have revealed a role for dopamine-mediated plasticity of the mushroom bodies that modulate the threshold of response to appetitive tastants. The identification of neural circuitry regulating taste memory provides a system to study the genetic and physiological processes that govern plasticity within a defined memory circuit.

A subset of sweet-sensing neurons identified by IR56d are necessaryand sufficient for fatty acid taste

“…Sweet sensing neurons project to the antennal mechanosensory and motor center (AMMC) and downstream PAM dopaminergic neurons that are activated by sugar [39,59]. In addition, a separate populations of dopamine neurons, the PPL1 cluster, is required for olfactory appetitive memory and taste aversive conditioning [60–62]. A central question will be whether these higher order neurons downstream of the SEZ are also sensitive to FAs, or selectively tuned to sugar.…”

Activation of specific mushroom body output neurons inhibits proboscis extension and sucrose consumption

“…Feeding decisions may be altered by learned associations, and importantly, there is a clear behavioral readout: the proboscis extension response (PER). For example, during conditioned taste aversion, a paired application of sugar to the tarsi and bitter to the proboscis results in a reduction of PER to sugar alone [18][19][20][21]. During conditioned aversion, taste information is transmitted from the subesophageal zone (SEZ) to the MBs for learned associations [21][22][23].…”

Targeted manipulation of neuronal activity in behaving adult flies

“…Collectively, these different tools and approaches can be used to study the rich set of innate behaviors performed by flies such as walking, flight, grooming, feeding, mating, fighting, and escape. Moreover, behavioral and circuit-based studies in flies have provided new insights into basic topics in neuroscience such as learning and memory, sensory-motor integration, neuromodulation, sleep, behavioral choice, behavioral sequencing, motor control, and sensory systems (Huston and Owald et al 2015;Hoopfer 2016;Masek and Keene 2016;McKellar 2016). Given that many of the tools used to study neural circuits have only recently become available, we anticipate that the coming years will experience a rapid growth in our understanding of how neural circuits within the fruit fly nervous system are organized to produce particular behaviors.…”