The brain of mammals can hardly regenerate once it is physically damaged. Its constituent neurons are terminally differentiated, and have essentially ceased to divide. On the other hand, the central nervous system of the gastropod Limax can spontaneously regenerate, and recover its structure and function even if it is damaged or ablated. Tentacles, for example, are able to regenerate their original structure if they are amputated. Moreover, two pairs of tentacles have functional redundancy each other. The spontaneous regeneration can also be observed in the procerebra, bilaterally equipped brain parts involved in the higher olfactory functions. Here again, the bilateral procerebra exhibit a kind of functional redundancy where only either right or left procerebrum functions at a time. Finally, the neurons are able to amplify their genomic DNA to meet the increasing demand for the macromolecules during the body growth. In this review article, I introduce the central nervous system of Limax that shows exquisite feats of flexible change far exceeding the conceptual framework that is taken for granted by researchers in the field of mammalian neuroscience.

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Animals sense environmental temperatures and adapt via behavioral and physiological responses, therefore the thermoperceptions are likely to play crucial roles in adaptive evolution. The temperature receptors are the thermosensitive channels that belong to transient receptor potential (TRP) superfamily in animals. Since evolutionary changes of temperature-sensitive TRP channels directly alter the thermoperceptions, elucidation the evolutionary process of these genes is essential for understanding the adaptation to thermal environments. We collected the genes for temperature-sensitive TRP channels from the genome sequence databases of various vertebrates and conducted molecular phylogenetic analysis and estimated the evolutionary process. We showed that the most of the temperature-sensitive TRP channels were already existed in the ancestral vertebrates, while gene duplication and loss events occurred in the respective lineages resulted in the diversity of thermoTRP repertoires among species. In addition, to estimate the functional evolution, we cloned TRPV3 from western clawed frog belonging to amphibians that are phylogenetically distantly related to mammals and examined the functional properties by electrophysiological approaches. The temperature sensitivity of western clawed frog TRPV3 differed considerably from that of mammalian TRPV3, suggesting that temperature-sensitive TRP channels can dynamically change their functions through evolutionary process.

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While instinctive behavior is adaptive for animals in terms of survival and reproductive success, we sometimes find non-adaptive variant behaviors in observing instinctive behaviors. However, the questions “How are variant behaviors generated?” and “What is the functional meaning of the mechanism of variant behaviors?” have not been focused in ethology. Especially in neuroethology and physiology, variant behaviors seem to have been excluded for investigation of the neural mechanism of instinctive behaviors. In the present paper, by the behavioral experiments of pill bug and giant isopod, we illustrate that animals have capacity to generate variant behaviors and can create novel adaptive behaviors by the capacity when their surroundings change for a short time.

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