In the visual systems of insects, different types of photoreceptors contribute to specialized visual channels that mediate distinct functions and behaviors. Large compound eyes of Periplaneta americana contain photoreceptors of two spectral classes, broadband green-sensitive photoreceptors and narrow-band UV-sensitive photoreceptors. Here, we investigated how visual stimulation by UV and green light affects locomotor, resting, and grooming behaviors in P. americana under conditions when light avoidance is not possible. We show that green but not UV light stimulates locomotor activity, inducing paradoxical positive masking. Duration of resting and grooming decreased with increasing light intensity, consistent with development of behavioral stress in response to visual overstimulation. A reaction of full immobility is described under UV light and at higher intensities of green light, with relative periods of immobility and grooming strongly negatively correlated. Low-intensity UV was more effective than low-intensity green light in suppressing grooming and inducing immobility. Our results suggest that locomotor activity in P. americana is mainly regulated by green-sensitive photoreceptors, and that dim UV light can trigger behavioral immobility, whereas both wavelengths induce stress-like reactions at high intensities. Considering the intrinsic UV sensitivity of green-sensitive photoreceptors, the contrasting behavioral responses indicate antagonistic interactions between UV and green visual channels.
Absence of screening pigment in insect compound eyes has been linked to visual dysfunction. We investigated how its loss in a white-eyed mutant (W-E) alters the photoreceptor electrophysiological properties, opsin gene expression and the behavior of the cockroach, Periplaneta americana. Whole-cell patch-clamp recordings of green-sensitive photoreceptors in WE cockroaches gave reduced membrane capacitance, absolute sensitivity to light and light-induced currents. Decreased low-pass filtering increased voltage bump amplitudes in WE photoreceptors. Intracellular recordings showed that angular sensitivity of WE photoreceptors had two distinct components: a large narrow component with the same acceptance angle as wild-type, plus a relatively small wide component. Information processing was evaluated using Gaussian white-noise modulated light stimulation. In bright light, WE photoreceptors demonstrated higher signal gain and signal power than wild-type photoreceptors. Expression levels of the primary UV-and green-sensitive opsins were lower and of the secondary green-sensitive opsin significantly higher in WE than in wild-type retinae. In behaviour experiments, WE cockroaches were significantly less active in dim green light, consistent with the relatively low light sensitivity of their photoreceptors. Overall, these differences can be related to the loss of screening pigment function and to a compensatory decrease in the rhabdomere size in WE retinae.
roach Periplaneta americana under the effect of the stress hormone octopamine.2-3-week-old males after the imaginal ecdysis were placed in an experimental setup [3]. A day before the experiment, the drinking water was removed from the cage. Octopamine (D,Loctopamine hydrochloride, Sigma-Aldrich) was dissolved in drinking water (10 g/L) and placed into the test chamber in two 0.5 ml-vessels with 20 mg of sucrose added to one of them. In control experiments, the octopamine solutions were replaced by pure drinking water and aqueous su-
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