Neuroethological study of the wavelength-discriminat ion in the extraocular phtoreceptor.

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It is widely accepted that pineal organ is photosensitive in lower vertebrates. The pineal organ contains photoreceptor cells and photic information obtained by the photoreceptors is transmitted to the central nervous system via second-order neurons, ganglion cells, in the pineal organ. Two types of ganglion cells have been identified, namely, achromatic-and chromatic-type ganglion cell. The achromatic-type ganglion cell is spontaneously active in darkness and is inhibited by visible light. The spike discharge from pineal ganglion cells of chromatic type is suppressed by UV light and excited by light of middle to long wavelengths. The chromatic responses allow the pineal complex to detect the ratio of UV light to visible light in environmental light, which achieves the wavelength-discrimination in the pineal complex independently of eyes. However, the function of the chromatic-type ganglion cell is unknown. We investigated the effect of UV and green light on swimming action using the sand lamprey, Lethenteron reissneri. At first, we electrophysiologically demonstrated that the chromatic ganglion cell was found in the pineal of the sand lamprey. Subsequently, we recorded the swimming movement of the lamprey under irradiation of UV and green light by use of video camera, and analyzed it by the computer. As results, The UV irradiation activated the swimming movement, and the UV-induced swimming movement disappeared by the pinealectomy. Those suggested that the chromatic information form the pineal organ regulated the swimming locomotor activity in the lamprey.