Spectral and polarized light sensitivity of photoreceptors in the compound eye of the cricket (Gryllus bimaculatus)

Summary

Retinula cells in the compound eye of the cricket (Gryllus bimaculatus) were recorded intracellularly and stained with Lucifer yellow. Two different methods were used to determine the spectral sensitivity of these cells: a) the spectral scanning method, and b) the conventional flash method. Three spectral types, with S(λ)-curves close to the rhodopsin-absorption functions, were found withλ _max at 332 nm (UV), 445 nm (blue) and 515 nm (green), respectively.

Blue receptors were only recorded in the anatomically specialized dorsal rim area (DRA), and UV and green receptors in the dorsal region of the pigmented part of the eye, whereby green receptors were only found in the ventral eye. On the basis of these results, model calculations are presented for di- and trichromatic colour vision in the cricket.

The fluorescence markings revealed green receptors whose axons project with short visual fibres to the lamina, and a UV receptor with a long visual fibre which projects through the lamina to the medulla. The blue receptors send their axons either to the lamina and medulla (long visual fibres) or only to the lamina (short visual fibres).

The temporal dynamics of the three receptor types were examined. The blue receptors lack a phasic component of the receptor potential, and the time from stimulus on-set to peak potential is strongly increased compared to the UV and green receptors. Light adaptation reduces the latency to less than half of the dark adapted state.

Spectral adaptation experiments revealed an ‘unidirectional coupling’ between UV and green receptors, and it was found that polarization sensitivity (PS) in blue cells was much higher (PS= 6.5±1.5) than that of UV (PS=1.76±0.05) and green (2.26±0.57) receptors. The functional aspects of the three receptor types are discussed with respect to the presented physiological and morphological data.