Submitted on January 23, 2009
Revised on March 2, 2009
Accepted on March 28, 2009
Temporal dynamics of neuronal activation by Channelrhodopsin-2 and TRPA1 determine behavioral output in <I>Drosophila</I> larvae
Stefan R. Pulver1, Stanislov L. Pashkovski1, Nicholas J. Hornstein1, Paul A. Garrity1, and Leslie Claire Griffith1*
1 Brandeis University
* To whom correspondence should be addressed. E-mail: griffith{at}brandeis.edu.
In recent years, a number of tools have become available for remotely activating neural circuits in <I>Drosophila</I>. Despite widespread and growing use, very little work has been done to characterize exactly how these tools affect activity in identified fly neurons. Using the <I>GAL4-UAS</I> system, we expressed blue light-gated Channelrhodopsin-2 (ChR2) and a mutated form of ChR2 (H134R-ChR2; Nagel et al. 2005) in motor and sensory neurons of the <I>Drosophila</I> third instar locomotor circuit. Neurons expressing H134R-ChR2 show enhanced responses to blue light pulses and less spike frequency adaptation than neurons expressing ChR2. While H134R-ChR2 was more effective at manipulating behavior than ChR2, the behavioral consequences of firing rate adaptation were different in sensory and motor neurons. For comparison, we examined the effects of ectopic expression of the warmth-activated cation channel <I>Drosophila</I> TRPA1 (dTRPA1). When dTRPA1 was expressed in larval motor neurons, heat ramps from 21-27oC evoked tonic spiking at ~25oC that showed little adaptation over many minutes. dTRPA1 activation had stronger and longer lasting effects on behavior than ChR2. These results suggest that dTRPA1 may be particularly useful for researchers interested in activating fly neural circuits over long time scales. Overall, this work suggests that understanding the cellular effects of these genetic tools and their temporal dynamics is important for the design and interpretation of behavioral experiments.
