The brain as a photoreceptor : intracerebral ocelli in the Coleoptera.

点击翻译按钮获取中文摘要

Light affects living beings in diverse ways and photic information is perceived not only through the eyes but also through extraocular photoreceptors. The physiological roles of the latter are manifold : e.g. control of biorhythms, copulation, escape, skin color. Morphological studies have revealed that the bean beetle Epilachna and caddisflies possess intracerebral ocelli in their optic ganglia which develop from the lateral ocelli of the larvae.A pair of bilaterally placed specialized pigmented organs was found at the caudal ends of the brains of the fireflies Luciola cruciata and L.lateralis. On the basis of serial semi thin sections of plastic-embedded brains of both male and female individuals, it was concluded that the pigmented organs in question, which existed close to the compound eye, seemed photoreceptive in nature. Further electron microscopical observations revealed that the cells in the center of the intracerebral ocelli had numerous microvilli and that the direction of t … More he microvilli was irregular.(1) Observations on 12 Coleoptera including fireflies revealed the presence of intracerebral structures in nine different species. Ladybird beetles, on the other hand, possessed structures similar in organization and position to those of the fireflies, namely in the caudal area of the brain. No pigmented areas were observed in three species.(2) Intracellular and extracellular recordings were obtained from the intracerebral ocelli of the fireflies with microelectrodes. The physiological evidence revealed that the cells found in the brain were, indeed, photoreceptors with high sensitivity comparing with the retinula cells in its compound eye. The spectral sensitivity curves obtained from 21 penetrated cell revealed the peak of the spectral sensitivity curve, λ max, was 530 nm. Values of λ max of the retinula cells have been given as 380 nm and 560 nm. The λ max of the spectral sensitivity of the intracerebral ocelli was different from that of the retinula cell.(3) The λ max of the spectral sensitivity curve obtained from the lateral eye of larvae was 530 nm, and the structure of the lateral ocelli resembled to the intracerebral ocelli of adults.(4) In order to confirm the origin of the intracerebral ocelli, we removed the lateral ocelli (1) and injected tracer into the lateral ocelli (2). Those experiment revealed that the origin of the intracerebral ocelli is, indeed, from the lateral ocelli of larvae. Less