Neurons can be rendered more active by increasing sodium or calcium conductance or by reducing potassium conductance. The temperature activated cation channel UAS-dTrpA1 (Rosenzweig et al., 2005 and Rosenzweig et al., 2008) has been a powerful reagent to acutely activate neural activity and has been used to identify

neurons involved in sleep and courtship behavior (Parisky et al., 2008 and von Philipsborn et al., 2011). An assessment of efficacy of continued expression of UAS-dTrpA1 shows that increased excitation can be maintained in some cells (Pulver et al., 2009). The acute activation in response to moderate temperature increase and the sustained depolarization have made UAS-dTrpA1 a favorite tool in many labs. UAS-TrpM8 encodes a cold-sensitive cation channel (Peabody et al., 2009); it can be used to confirm that neurons identified with UAS-dTrpA1

cause TSA HDAC molecular weight phenotypes in response to increased activity rather than the increase in temperature required to activate the channel. The chemical High Content Screening ligand capsaicin can activate mammalian TrpV1 channels expressed in flies and has been used to map gustatory inputs (Marella et al., 2006). Finally, overexpression of a bacterial sodium channel, NaChBac, can increase neural excitability (Nitabach et al., 2006) but may have other effects in other cell types or over longer timescales (Sheeba et al., 2008). Reduction of the potassium current can also increase neural activity. Dominant-negative versions of the tetrameric potassium channels Shaker, Eag, Shaw, and Shal have been made by truncation of the wild-type channels, usually after the much N-terminal multimerization domain (Broughton et al., 2004,

Hodge et al., 2005, Mosca et al., 2005 and Ping et al., 2011). RNAi constructs against Shaw also increase neural activity (Hodge and Stanewsky, 2008). These reagents have been reviewed (Hodge, 2009). A drawback is that the dominant-negative ion channels are only effective in neurons that express the normal versions of these ion channels. Optogenetics was pioneered by UAS-P2X2, a cation channel activated by caged ATP released by light. This channel has been used to identify neurons sufficient to induce jump-escape ( Lima and Miesenböck, 2005), courtship song ( Clyne and Miesenböck, 2008), and olfactory conditioning ( Claridge-Chang et al., 2009). One drawback is that the caged ATP must be injected into the hemolymph and then activated by light exposure, limiting the kind of behavior that can be studied and reducing the number of flies that can be screened. The advent of genetically encoded proteins that activate or silence neural activity in response to light has been an exciting development for the neuroscience field (Deisseroth, 2011, Peron and Svoboda, 2011 and Toettcher et al., 2011).