Opsins are the photoreceptive proteins which trigger phototransduction cascades in visual and non-visual photoreceptor cells. I have conducted the following studies on the opsin genes to elucidate the function and evolution of the animal photoreceptor cells: 1) All the retinal photoreceptor cells are rod-shaped in a nocturnal gecko (Gekko gekko). Phylogenetic and biochemical analyses revealed that the gecko visual opsins are cone-type, suggesting that the gecko rods originate from their ancestral cones. 2) I identified a novel subtype of opsin and a Go-type G-protein in the ciliary photoreceptor cells of an invertebrate, scallop (Patinopecten yessoensis). The result suggests that the novel Go-mediated phototransduction cascade is responsible for the hyperpolarizing photoresponse in the scallop photoreceptor cells, and that multiple phototransduction systems emerged before the species divergence between vertebrates and arthropods. 3) Non-visual photosensitivity has been found in the brain of vertebrates. A search for brain opsin genes in zebrafish (Danio rerio) identified two kinds of novel opsins: exo-rhodopsin in the pineal gland and VAL-opsin in the deep brain. VAL-opsin was also found in the retinal horizontal cells, suggesting its contribution to retinal physiology. Transgenic experiments on the exo-rhodopsin promoter led to the discovery of a novel pineal-specific cis element, PIPE.

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Most of adult butterflies feed on flower nectar. Certain flower colors are important signals to stimulate their flower-visiting (foraging) behavior. Flower scents also affect its behavior but it remains unclear what components in the scent serve as the releasing factors. When Pieris rapae and Vanessa indica were examined for responses to flower volatiles of certain nectaring plants, several aromatic compounds including phenylacetaldehyde and benzaldehyde strongly stimulated proboscis extension reflex and orientation to artificial models from the butterflies. Such bioactive aromatic compounds are omnipresent as flower volatiles in the plant kingdom, suggesting that butterflies commonly use these olfactory signals for food recognition. On the other hand, several flower volatiles suppress foraging behavior of butterflies, e.g. γ -decalactone present in fragrant olive flowers was identified as a repellent for P. rapae. Several nymphalid butterflies such as Kaniska canace and V. indica feed on tree sap and rotting fruits. Fermentative odors, e.g. ethanol and acetic acid, from these foods evoked their foraging behavior. However, other nymphalid species feeding only on flower nectar never showed positive responses to such odors. These results suggest that butterflies use different olfactory signals depending on their feeding habits.

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The paraventricular organ (PVO), which is located in the lateral walls of the third ventricle of the posterior hypothalamus, is well conserved among non-mammalian vertebrates such as birds, reptiles, amphibians, teleost and lamprey. The PVO is composed of cerebrospinal fluid (CSF) contacting neurons, whose characteristic knob-like terminals protrude into the lumen of the third ventricle and whose lateral processes form a fine plexus in the neuropile. The PVO neurons form CSF-contacting dendritic terminals that bear solitary 9x2+0 clia and resemble chemoreceptors and photoreceptors cytologically. The CSF-contacting neurons in the PVO of non-mammalian vertebrates show serotonin immunoreactivity. Recently, we suggested that serotonin-immunoreactive (ir) PVO neurons regulate gonadotropin-releasing hormone (GnRH) and/or gonadotropin-inhibitory hormone ir cells in birds and reptiles. On the basis of these previous studies, we speculated that in non-mammalian, the serotonin-ir PVO neurons modulate the functions of the pituitary gland.

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Part 6. Entropy cost of information in living neuron is estimated to be very close to the thermodynamic limit at 0.7k_B per bit of information. Parallel transmission and principle of summation average with stochastic sampling is explained as the essential way of adaptation under the inevitable thermal noise. Theoretical arguments on Maxwell's demon and the negative entropy principle of information or the irreversibility of measurement are explained. Origin of life and the evolution of life are discussed from the information theoretic standpoint, in reference to the actual values of rate of information and the energy threshold of living cell.

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