The molecular and cellular basis of thirst behavior

• Applicant: Dr. Marion Hartl
• Subject Area: Cognitive, Systems and Behavioural Neurobiology ; Sensory and Behavioural Biology
• Term: from 2013 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 241524787

The motor response of an animal in a given context depends on sensory inputs as well as its internal state, such as hunger or thirst. Many studies have focused on how sensory inputs trigger certain behavioral motor output, while the impact of the animal s internal physiological state on behavioral responses is much less studied. In case of drinking and feeding, behavioural decisions must be appropriate to the body s requirements for food and water. Drinking behavior is not very well studied in any model organism. In Drosophila, the unmatched availability of genetic tools that allow the specific targeting and manipulation of distinct cell types and molecules provides the opportunity to dissect the neural control of drinking behavior. Osmotic balance, thirst and drinking behaviour are far less studied than feeding behaviour in Drosophila, although drinking is as fundamental for survival as eating. With the proposed experiments, I aim to unravel how flies process the gustatory detection of water and how thirst is signalled through neuropeptides to influence motor output.Water is sensed by the fly s gustatory system. The osmosensitive ion channel ppk28, a member of the Degenerin/ Epithelial Sodium family, is expressed in chemosensory neurons on the legs and proboscis that detect water. The ppk28 ion channel mediates cellular and behavioral response to water (Cameron et al., 2010). The sensory neurons target the first relay for gustatory information in the fly brain, the subesophagal ganglion (SOG). The motor neurons that drive drinking behaviour are also in the SOG but do not directly contact water sensory projections. To determine how water taste detection leads to drinking behavior, I will identify the second-order neurons which process water taste detection. In the proposed work, I will screen for second-order neurons through an anatomical approach using GFP reconstitution across synaptic partners (GRASP) (Feinberg et al., 2008, Gordon and Scott, 2009) to select synaptic partners of the gustatory water neurons. These candidates will be further evaluated by calcium imaging experiments and behavioral assays for their impact in water taste and drinking behavior. These studies will begin to elucidate the neural circuits for water intake.As a second major goal, I will search for neuropeptides which signal thirst. In flies, as in mammals, water drinking is not stable over time but instead depends on the osmotic state of the animal. Although vasopressin is one molecule that has been implicated in osmotic balance in mammals, molecules that signify the osmotic state have not been identified in Drosophila. I hypothesize that the concentration of specific neuropeptides reflects the inner water balance and, thus, modulates the probability of drinking. These neuropeptides might be released by interneurons integrating signals from upstream neurons.

• DFG Programme: Research Fellowships
• International Connection: United Kingdom, USA
• Hosts: Professorin Dr. Irene Miguel-Aliaga; Professorin Dr. Kristin Scott