Spectral properties of identified polarized-light sensitive interneurons in the brain of the desert locustSchistocerca gregaria

Abstract

SUMMARY Many migrating animals employ a celestial compass mechanism for spatial navigation. Behavioral experiments in bees and ants have shown that sun compass navigation may rely on the spectral gradient in the sky as well as on the pattern of sky polarization. While polarized-light sensitive interneurons(POL neurons) have been identified in the brain of several insect species,there are at present no data on the neural basis of coding the spectral gradient of the sky. In the present study we have analyzed the chromatic properties of two identified POL neurons in the brain of the desert locust. Both neurons, termed TuTu1 and LoTu1, arborize in the anterior optic tubercle and respond to unpolarized light as well as to polarized light. We show here that the polarized-light response of both types of neuron relies on blue-sensitive photoreceptors. Responses to unpolarized light depended on stimulus position and wavelength. Dorsal unpolarized blue light inhibited the neurons, while stimulation from the ipsilateral side resulted in opponent responses to UV light and green light. While LoTu1 was inhibited by UV light and was excited by green light, one subtype of TuTu1 was excited by UV and inhibited by green light. In LoTu1 the sensitivity to polarized light was at least 2 log units higher than the response to unpolarized light stimuli. Taken together, the spatial and chromatic properties of the neurons may be suited to signal azimuthal directions based on a combination of the spectral gradient and the polarization pattern of the sky.

Neural Organization and Visual Processing in the Anterior Optic Tubercle of the Honeybee Brain

“…Both constitute the largest AOTu volume and are composed of two subunits (outer and inner lobes in locusts; MU-VL and MU-DL in honeybees). Our results suggest a spatial information content at the MU inter-tubercle output, and likewise, upper unit interneurons in locusts respond in a strongly stimulus position-dependent manner (Pfeiffer and Homberg, 2002;Pfeiffer et al, 2005;Kinoshita et al, 2007). We thus believe that this bi-lobed major AOTu compartment serves similar spatial processing functions in honeybees and locusts.…”

“…The VLU of the honeybee AOTu shows remarkable similarity with the lower unit of the locust AOTu (Homberg et al, 2003), which processes polarized light information and conveys it via the LAL to the central body (Pfeiffer et al, 2005;Homberg 2007, 2009;Kinoshita et al, 2007). Both are positioned ventrodorsally and posterior to the more prominent AOTu unit (MU in honeybees; upper unit in locusts) and receive input from the dorsal medulla.…”

“…The most prominent optic glomerulus is the anterior optic tubercle (AOTu). AOTu neurons involved in sky-compass, polarized light, and spectral processing have been characterized in the locust by means of intracellular recordings (Pfeiffer et al, 2005;Kinoshita et al, 2007). In honeybees, little is known about the neural architecture and function of the AOTu.…”

Light-dependent orientation responses in animals can be explained by a model of compass cue integration

“…Including the outlier gives the statistics R adj = 0.47 and p = 0.04 which still is 439 significant, but not surprisingly with a much lower R adj value. There is evidence that 440 polarization cues and possibly the correlated color gradients can be suppressed at high 441 irradiances (Kinoshita et al, 2007) and in such case, the model would actually predict 442 normal orientation. At a constant wavelength of 565 nm there was good fit of the model to 443 the r-values with R adj = 0.74 and p < 0.0001 (Fig.…”

“…It has been suggested that light in the blue or mid wavelength range may serve as 182 some sort of reference color in a color gradient compass (Kinoshita et al, 2007). In that 183 case Eq.…”