Dissection of Gain Control Mechanisms inDrosophilaMechanotransduction

Abstract

Mechanoreceptor cells respond to a vast span of stimulus intensities, which they transduce into a limited response-range using a dynamic regulation of transduction gain. Weak stimuli are detected by enhancing the gain of responses through the process of active mechanical amplification. To preserve responsiveness, the gain of responses to prolonged activation is rapidly reduced through the process of adaptation. We investigated long-term processes of mechanotransduction gain control by studying responses from single mechanoreceptor neurons in Drosophila. We found that mechanical stimuli elicited a sustained reduction of gain that we termed long-term adaptation. Long-term adaptation and the adaptive decay of responses during stimuli had distinct kinetics and they were independently affected by manipulations of mechanotransduction. Therefore, long-term adaptation is not associated with the reduction of response gain during stimulation. Instead, the long-term adaptation suppressed canonical features of active amplification which were the high gain of weak stimuli and the spontaneous emission of noise. In addition, depressing amplification using energy deprivation recapitulated the effects of long-term adaptation. These data suggest that long-term adaptation is mediated by suppression of active amplification. Finally, the extent of long-term adaptation matched with cytoplasmic Ca 2ϩ levels and dTrpA1-induced Ca 2ϩ elevation elicited the effects of long-term adaptation. Our data suggest that mechanotransduction employs parallel adaptive mechanisms: while a rapid process exerts immediate gain reduction, long-term adjustments are achieved by attenuating active amplification. The slow adjustment of gain, manifest as diminished sensitivity, is associated with the accumulation of Ca 2ϩ .

Cell-intrinsic mechanisms of temperature compensation in a grasshopper sensory receptor neuron

“…The former may directly arise from the temperature dependence of the transduction channels' maximal conductance. The latter may require additional heat-sensitive channels with a modulatory influence on the transduction process, such as thermosensitive transient receptor channels (TRPA) ( Kang et al, 2012 ), which in principle could down-regulate the saturation level of the transduction function via their increased calcium response ( Chadha and Cook, 2012 ).…”

Mechanosensation and Adaptive Motor Control in Insects

“…Recordings from macrochaete bristles on the head of blowflies [24] and the notum of Drosophila [18, 21, 29, 30] have identified only slowly adapting bristles with a very low mechanical threshold of ~1° (Figure 2). These bristles are probably not sensitive to wind or sound [24], but rather respond to transient mechanical deflections such as those created by contact with external objects or during grooming behavior.…”

NOMPC-dependent mechanotransduction shapes the dendrite of proprioceptive neurons

“…The nompC 4 allele responds with faster adaptation kinetics [22], leading to a reduced charge inflow into bristle mechanoreceptor neurons upon mechanical activation [23]. Therefore, we propose that, like the bristle mechanoreceptor neuron, the joint proprioceptive neurons respond in the nompC 4 mutant, but with a less robust response than we observe in wild type flies.…”