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.
Acetylcholine receptors (AChRs) at the adult mouse and embryonic chick neuromuscular junctions were visualized by using erabutoxin b (Eb), one of the short-chain neurotoxins from Laticauda semifasciata, and antibody against AChRs of the electric organ from Narke japonica. Visualization of AChRs was performed by the following three methods: (1) staining with rhodaminelabeled Eb (TMR-Eb), (2) staining with horseradish peroxidase-labeled Eb (HRP-Eb), and (3) indirect immunofluorescence microscopy using the antibody against purified AChRs. At the light microscopic level, TMR-Eb offered the most simple and rapid procedure for producing clear images. The HRP-Eb method was suitable for viewing the distribution of AChRs at the ultrastructural level. These procedures revealed that adult neuromuscular junctions had a nearly uniform distribution of AChRs at their postsynaptic membrane, whereas embryonic ones possessed aggregations of small discrete regions of high AChR concentration. Similar regions of AChRs were observed on the nonjunctional myotube surface.
Assembled precast members and related connections should be economically feasible, bring ease of construction, and provide acceptable static properties as well as adequate dynamic characteristics in high seismic zones. The seismic performance of an assembled precast high-strength concrete beam with a simple and innovative lap splice connection in high-rise buildings is discussed. The flexibility variation along the lap splice connection of the beam, which involves a reduced profile, is also investigated. The lap splice connection, located at beam mid-span, was connected by transverse untensioned bolts. The simplicity of the form and developed mechanism are intended to be suitable for construction sites. The experimental test results confirmed the adequacy of such assemblies to satisfy a safe level under different loadings. The beam under reversed cyclic loading proved to be ductile and failure occurred outside the lap splice connection similarly to monolithic ordinary reinforced concrete beams. The flexural stiffness varied along the lap splice connection of the assembled beam and declined at the transition section of the reduced profile under large loading. Therefore, this reduction, within design limits, would not affect the performance of the assembled beam.
This book describes the developmental process of the brain of the medaka fish., aiming to understand the brain structure of vertebrates including humans.
