, 2010, Kong et al., 2010, Krashes et al., this website 2009, Lebestky et al., 2009 and Mao and Davis, 2009). Our work demonstrates that a single dopaminergic neuron in the SOG potently modulates

proboscis extension behavior. Other dopaminergic neurons have cell bodies near TH-VUM and extensive projections in the SOG, yet activation of these neurons is not associated with proboscis extension. It is possible that additional dopaminergic neurons regulate other aspects of taste behavior, but they are insufficient to drive proboscis extension. In mammals, dopamine levels in the nucleus accumbens, the target of the mesolimbic pathway, increase upon sugar detection in the absence of consumption (Hajnal et al., 2004) or upon nutrient consumption in the absence of detection (de Araujo et al., 2008), suggesting that dopamine encodes multiple rewarding aspects of sugar: intensity on the tongue and nutritional value. Recent studies in Drosophila also show that they sense nutritional content independent of taste detection, and this influences ingestion (

Burke and Palbociclib cell line Waddell, 2011, Dus et al., 2011 and Fujita and Tanimura, 2011). It will be interesting to determine whether dopamine plays a role in sensing internal nutritional state and regulates other aspects of ingestion in addition to its role in proboscis extension. The anatomical location of the dopaminergic interneuron highlights the central role of the SOG in taste processing and suggests that local SOG circuits

may control proboscis extension behavior. Future studies identifying the downstream targets of TH-VUM will ultimately enable a deeper understanding of how dopamine achieves spatial and temporal modulation of extension probability. Our current study identifies an essential role for dopamine in gain control of proboscis extension to sucrose and underscores the exquisite second specificity of single neurons as thin threads to behavior. w1118 flies were used as control wild-type flies. The following Gal4 lines were used: Akh-Gal4 ( Lee and Park, 2004), dilp3-Gal4 ( Buch et al., 2008), tdc2-gal4 ( Cole et al., 2005), hugin-Gal4 ( Melcher and Pankratz, 2005), TH-Gal4 ( Friggi-Grelin et al., 2003), hs-flp, MKRS (Bloomington stock collection), Npf-Gal4 ( Wu et al., 2003), UAS-Kir2.1 ( Baines et al., 2001), tub-Gal80ts ( McGuire et al., 2004), ptub-FRT-Gal80-FRT and Gr5a-lexA ( Gordon and Scott, 2009), UAS-mCD8::GFP ( Lee and Luo, 1999), and UAS-dTRPA1 ( Hamada et al., 2008). DopR mutants (f02676) and D2R mutants (f06521) were obtained from the Exelixis collection ( Bellen et al., 2004 and Thibault et al., 2004). Flies were grown on standard fly food. Measurement of PER was performed as described using females (Wang et al., 2004), except that flies were glued to glass slides using nail polish. Flies were stimulated with water on their tarsi and allowed to drink ad libitum.