Shoji Tabata

An anterograde and retrograde tract-tracing study on the projections from the thalamic gustatory area in the rat: distribution of neurons projecting to the insular cortex and amygdaloid complex.

Projections from the thalamic gustatory nucleus, i.e. the parvicellular part of the posteromedial ventral thalamic nucleus (VPMpc) to the forebrain regions were studied in the rat by the tract-tracing methods with anterograde tracer (biotinylated dextran amine, BDA) and anterograde/retrograde tracer (wheat-germ agglutinin-horseradish peroxidase, WGA-HRP). After BDA injection into the VPMpc, terminal labeling was observed in the insular cortex, amygdaloid complex, and fundus striati. The terminal labeling in the amygdaloid complex was distributed in dorsolateral area of the rostral part of the lateral amygdaloid nucleus and the rostral part of the lateral subdivision of the central amygdaloid nucleus. The terminal labeling in the central amygdaloid nucleus extended to the fundus striati. The retrograde tracing study with WGA-HRP revealed that the projection fibers from the VPMpc to the amygdaloid complex originated from the medial part of the VPMpc and also from the thalamic area medial to the VPMpc. In the rats injected with Fluoro-Gold and WGA-HRP, respectively into the insular cortex and amygdaloid complex, no double-labeled neuronal cell bodies were found in the VPMpc, although neurons labeled singly with Fluoro-Gold were intermingled with those singly labeled with WGA-HRP in the medial part of the VPMpc. The results indicated that VPMpc neurons projecting to the amygdaloid complex constituted a population different from VPMpc neurons projecting to the insular cortex.

Early development of the peripheral nervous system in a lancelet species

The developmental pattern of the lancelet (amphioxus) peripheral nervous system from embryos to larvae has been studied by using wholemount immunostaining and transmission electron microscopy. The peripheral nerves first appeared on the anterior dorsal surface of the medulla at the middle neurula stage, when the anterior nerve cord was just closing. A single axon with a large growth cone was the progenitor of each nerve. The nerve roots adopted an asymmetric arrangement soon after. The first nerve, likely a pair of pure sensory nerves, sprouted from the anterior tip of the nerve cord. This nerve may be comparable topographically to the preoptic nerve (the posterior branch of the terminal nerve) in lungfishes. However, the neuron that first extends its axon was located in the medulla, as in the other posterior nerves. One of the extramedullary primary sensory neurons, the corpuscles of de Quatrefages, appeared in larvae with the mouth and two anterior gill pores. Their axons were seemingly fasciculated with the efferent axon of the first nerve. The second nerve, the most complex one to appear during embryonic and early larval development, innervated the preoral pit and the buccal region. The third and fourth nerves on the left side also innervated the buccal region. The larval innervation patterns in the anterior region differed from the adult organization, suggesting a segmental rearrangement of the nerve supply during development. There was no evidence to dichotomize the peripheral nerves into cranial and spinal nerves, as exist in vertebrates. These characteristics of the peripheral nervous system in the lancelet indicate that this animal has a rather derived or primitive developmental system of peripheral nerves, making the analysis of homology with vertebrates difficult. J. Comp. Neurol. 393:415–425, 1998.

Collagen Fibrils in the Odontoblast Layer in the Teeth of the Rat and the House Shrew, Suncus murinus by Scanning Electron Microscopy Using a Maceration Method

It is not well known whether there are gaps in the tight junctions between odontoblasts and whether the fluid flows from the pulp to the predentin through these gaps. The collagen fibrils in the odontoblast layer were investigated using a maceration method in order to show the existence of the gaps between tight junctions of the odontoblasts. The mandibles containing teeth of the rat and the house shrew were digested by NaOH maceration and revealed the architecture of the collagen fibrils under scanning electron microscopy. The collagen fibrils went from the pulp, through the odontoblast layer, and were woven into the collagen network of the predentin in all teeth used in this study. Thick bundles of collagen were seen in the odontoblast layer at the pulp horn of the rat molars. Because there are many collagen fibrils in the odontoblast layer, it is considered that the tight junction of the odontoblast is of the discontinuous type.