Taste Perception and Modulation in a Miniature Brain – APITASTE

Taste allows distinguishing between chemical compounds and the sensations they produce based on contact with chemoreceptors. It allows animals and humans to discriminate edible from non-edible items and is, therefore, crucial for survival. The question of how taste information is encoded and modulated in the central nervous system is important both for the field of neurosciences and for managing food intake in species that play a major role in agriculture and animal production. This is the case of the honey bee, an insect that is both a well-established model for neuroscience studies and a key species for crop pollination.
In the honey bee, the sense of taste has remained largely unexplored despite intensive studies on her other sensory modalities (olfaction, vision). This is surprising given the extraordinary impact of taste on honey bee foraging and survival in an era in which colonies are under massive threats due to human impact on natural food sources.
In insects, peripheral taste detection occurs within cuticular hairs, the gustatory sensilla, which are mostly located on the antennae, the mouthparts and the tarsi. These sensilla host gustatory receptor cells and, usually a mechanoreceptor cell. Electrophysiological recordings showed that gustatory receptors respond with varying sensitivity to sugars, salts, and possibly amino acids, proteins and water. So far, responses to bitter substances were unclear or inexistent, although inhibitory effects of these substances on sucrose receptor cells were found. The sequencing of the bee genome revealed a surprising scarcity of gustatory receptor genes compared to most other insect species, which possess several dozens of such genes. How taste sensations arise from such a reduced number of gustatory input channels remains unknown and calls for a thorough analysis of central taste processing in the bee brain.
In the APITASTE project, we will perform this analysis and uncover mechanisms of central gustatory processing in an insect model. Using calcium imaging, we will characterize gustatory maps in the subesophagic zone (SEZ), the first central area of gustatory processing in the insect brain, and determine whether they follow a hedonic-principle organization. We will couple in vivo imaging of the SEZ with a novel protocol of gustatory conditioning in immobilized bees that we recently established, in order to determine if and how neural taste representation varies with aversive learning and with different phases of memory formation. We will decrypt central-taste neuromodulation by focusing on the facilitatory or inhibitory effects of biogenic amines and the neuropeptide sNPF, whose receptors have been characterized in the bee genome. Taking advantage of the accessibility of the bee’s nervous system to optophysiological recordings and other invasive procedures, and of its remarkable learning and memory capacities, we will be able to provide an integrative view about how taste is encoded in simple nervous circuits and how taste representations are modified by experience.