Octopaminergic modulation of neuronal responses to flight-induced naturalistic image sequences

Abstract

Event Abstract Back to Event Octopaminergic modulation of neuronal responses to flight-induced naturalistic image sequences Diana Rien1, Roland Kern1 and Rafael Kurtz1* 1 Bielefeld University, Neurobiology, Germany Sensory input experienced by animals during behavioral action may differ fundamentally during different states of locomotor activity. Given the limited working range of neurons, adjustments of their sensitivity and stimulus tuning to the current locomotor state might be advantageous. Such state-dependent modulation, which has recently received much attention in various animal models (1), was demonstrated in visual motion-sensitive neurons of different fly species (2-4). The modulation of these neurons is mediated by octopamine, as was recently shown directly by manipulating the activity of a set of octopaminergic neurons (5). Flight or walking activity, as well as application of an octopamine agonist caused enhanced resting activity, shorter latencies in the response to abrupt motion onsets, and larger stimulus-induced responses (2,3,5-10). The strongest response boosts were observed with sustained presentation of high temporal frequencies, thus leading in some studies to a shift in the temporal frequency tuning toward higher values (2,7). However, the functional relevance of these state-dependent changes is unclear, because experimenter-defined stimuli have been used instead of natural optic flow. We assessed the functional significance of octopaminergic neuromodulation for the processing of optic flow as experienced during flight. Naturalistic image sequences were reconstructed based on the head position and gaze orientation during flight (11) and replayed with a panoramic stimulus device (12). We studied how the responses of the V1 neuron in Calliphora vicina to these stimuli are modified by octopaminergic modulation. Spontaneous as well as stimulus- induced spike rates were increased by the octopamine agonist CDM and decreased by an antagonist, epinastine. Moreover, small but consistent shifts in the peak positions of cross- correlograms between the different drug-induced states were present, consistent with an octopamine-induced acceleration of responses to optic flow cues. However, cross-correlations as well as coherence values between the responses recorded in different states of octopaminergic modulation were almost as high as those between traces obtained within one state. Thus, our results suggest that naturalistic optic-flow processing is slightly modified, but not fundamentally altered, by state-dependent neuromodulation. Figure 1