We propose here a novel interpretation of the embryonic origin of cells of diencephalic sensory relay nuclei in teleosts based on our recent studies of gene expression patterns in the medaka <i>(Oryzias latipes)</i> embryonic brain and comparative hodological studies. It has been proposed that the diencephalic sensory relay system in teleosts is unique among vertebrates. Teleost relay nuclei, the preglomerular complex (PG), have been assumed to originate from the basal plate (the posterior tuberculum) of the diencephalon, whereas relay nuclei in mammals are derived from the alar plate (dorsal thalamus) of the diencephalon. Our results using in situ hybridization show, however, that many <i>pax6-</i> or <i>dlx2-</i>positive cells migrate laterally and ventrocaudally from the diencephalic alar plate to the basal plate during development. Massive clusters of the migrated alar cells become localized in the mantle layer lateral to the posterior tubercular neuroepithelium, from which main nuclei of the PG appear to differentiate. We therefore consider most if not all neurons in the PG to be of alar, not basal, origin. Thus, the teleost PG, at least in part, can be regarded as migrated alar nuclei. Developmental and hodological data strongly suggest that the teleost PG is homologous to a part of the mammalian dorsal thalamus. The organization and origin of the diencephalic sensory relay system might have been conserved across vertebrates.
There are numerous species of teleosts in the world. In their widespread distribution in divergent environments, different teleost species have employed variable strategies for survival. The diversity in niches and habits is reflected in the morphology of teleost brains, although all the major brain parts are present that are common to other vertebrates. Species differences are particularly remarkable in the external morphology of sensory brain regions. Generally speaking, the brain part bulges, which is involved in the processing of the most "important" sensory modality for that species. Thus, one can imagine, to a certain extent, the lifestyle of a teleost species, just by looking at its external brain morphology. However, there are also cases of amazing diversity, the reasons for which remain unknown. The diversity of teleost brain morphology is introduced in this chapter, presenting selected cases among the virtually infinite variety. In addition to the intra-teleostean diversity just mentioned, there are features in brain organization that are specific to teleosts (and related non-teleostean actinopterygians) but are lacking in other vertebrates, which is also demonstrated in this chapter. Diversity can be also found in such teleost-specific structures.
This book describes the developmental process of the brain of the medaka fish., aiming to understand the brain structure of vertebrates including humans.
Dahl-Iwai salt-sensitive (S) and salt-resistant (R) rat strains were newly established as inbred strains. To characterize the strains, the Dahl-Iwai S and R rats were fed low-salt (0.3% NaCl) and high-salt (8.0% NaCl) diets from 5 weeks after birth, and systolic blood pressure and pathologic findings were examined at intervals. The distributions of alleles at 19 biochemical and immunologic loci also were examined in the aforementioned strains, together with those for the inbred SS/Sea and SR/Sea strains, which were derived from inbred SS/Jr and SR/Jr strains, respectively. The Dahl-Iwai S rats were hypertensive after 3 weeks of consuming the 8.0% NaCl diet and died from 6 to 10 weeks after the diet was initiated. Renal lesions developed after 4 weeks' consumption of the high-salt diet. The Dahl-Iwai S rats were not hypertensive until at least the age of 21 weeks while they consumed the 0.3% NaCl diet, whereas it was reported that the SS/Jr rats became hypertensive at about 20 weeks of age when they consumed the low-salt diet. The Dahl-Iwai R rats were normotensive whether fed the 0.3 or 8.0% NaCl diet. Hydronephrosis was not observed in the Dahl-Iwai R rats, though it develops in SR/Jr rats with high frequency. Different distributions were detected for kidney alkaline phosphatase-1 (Akp-1) and amylase-1 (Amy-1) alleles between the Dahl-Iwai S and SS/Sea strains, and for esterase-14 (Es-14) and seminal vesicle protein-1 (Svp-1) alleles between the Dahl-Iwai R and SR/Sea strains. The phenotypic differences between the substrains of inbred Dahl rats could be ascribed to different genetic backgrounds.
The Raman spectra of bovine corneas and lenses irradiated to the ultra violet radiation at Syowa station of Antarctica were observed. The bovine crystallin occurred photo‐induced cataract by the exposure to the solar radiation of mid‐summer at Antarctica. Photo‐induced decrease of Raman signals assigned to Trp residues suggests that the structural change of crystallin is correlated with the decomposition of them. The Raman spectra of the collagen of cornea showed little change, however FT‐IR measurements showed that the IamideII/IamideI decreased much by the exposure to the solar radiation of mid‐summer at Antarctica.
Abstract The threat of predation is a driving force in the evolution of animals. We have previously reported that Xenopus laevis enhanced their tail muscles and increased their swimming speeds in the presence of Japanese larval salamander predators. Herein, we investigated the induced gene expression changes in the brains of tadpoles under the threat of predation using 3′-tag digital gene expression profiling. We found that many muscle genes were expressed after 24 h of exposure to predation. Ingenuity pathway analysis further showed that after 24 h of a predation threat, various signal transduction genes were stimulated, such as those affecting the actin cytoskeleton and CREB pathways, and that these might increase microtubule dynamics, axonogenesis, cognition, and memory. To verify the increase in microtubule dynamics, DiI was inserted through the tadpole nostrils. Extension of the axons was clearly observed from the nostril to the diencephalon and was significantly increased ( P ≤ 0.0001) after 24 h of exposure to predation, compared with that of the control. The dynamic changes in the signal transductions appeared to bring about new connections in the neural networks, as suggested by the microtubule dynamics. These connections may result in improved memory and cognition abilities, and subsequently increase survivability.
