Hiroki S. Ozaki

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.

The fibers which leave the Probst's longitudinal bundle seen in the brain of an acallosal mouse: a study with the horseradish peroxidase technique

The congenital absence of the corpus callosum, a brain anomaly frequently noted in humans, has been recently found to occur in some mice of the ddN strain in our laboratory. In the brains of these mice, the Probsts longitudinal bundle is always present on both cerebral hemispheres and gives rise to some aberrant fibers toward the midline. In this research, the neuroanatomical features of these fibers were studied by iontophoretical injections of horseradish peroxidase (HRP) into the neocortex of acallosal mouse brains. The results revealed that the fibers which leave the Probsts longitudinal bundle are, at least, of 3 kinds: namely, the fibers that run out from the anterior portion of the bundle and take a U-turn ipsilaterally without crossing the midline through the septal tissue to go back again into the longitudinal bundle at the level where they have left it; the commissural fibers that leave the bundle from its middle portion and cross through a tiny bridge of tissue associated with the ventral hippocampal commissure to the opposite hemisphere; and the fibers that arise from the posterior portion of the bundle and accumulate as an anomalous fascicle below the cingulum. The observation that no labeled fibers were seen within the anterior commissure in the present HRP materials suggests that the axons from neocortex which are prevented from crossing the midline in mice with congenital absence of the corpus callosum cannot find an alternative pathway via the anterior commissure.

The fibers which course within the Probst's longitudinal bundle seen in the brain of a congenitally acallosal mouse: a study with the horseradish peroxidase technique

The congenital absence of the corpus callosum, a brain anomaly frequently noted in humans, has been recently found to occur in some mice of the ddN strain in our laboratory. In the brains of these mice, the Probsts longitudinal bundle is always present on both cerebral hemispheres. In this research, the neuroanatomical features of the constituent fibers of this bundle were studied by iontophoretical injections of horseradish peroxidase into different loci in the neocortex of acallosal mouse brains. The results revealed that (1) certain cortical fibers of the Probsts bundle terminate in the ipsilateral neocortex; (2) some commissural fibers in the longitudinal bundle originate from the cells in the wide neocortical regions, and project to the opposite hemisphere in homotopic as well as heterotopic regions over the ventral hippocampal commissure; (3) the fibers from different cortical regions are arranged in a topographic manner within this bundle. The present data clearly demonstrate that a good portion of fibers in the Probsts longitudinal bundle seen in the congenitally acallosal mouse brain are corticocortical in nature, which indicates that this bundle has an ipsilateral neocortical association function.

Agenesis of the corpus callosum in ddN strain mouse associated with unusual facial appearance (flat-face)

In the course of an experiment involving brother-sister matings between ddN strain mice, mice occurred with an unusual facial appearance (flat-face). Subsequently, 4 mice with flat-face were bred from the litters of the second birth (ca. 10% frequency). This flat-face was assumed to be the result of a malformed short nose, hypoplastic maxilla and mandible, and hypertelorism. These 4 flat-face mice exhibited no significant delays in growth, motor ability or the development of learning ability. Histologically, they were all characterized by an almost total absence of callosal fibers and the presence of abnormal longitudinal neuromatous bundles. Therefore, the flat-face mice may be useful as experimental animals for brain research, as one can easily judge that they lack the corpus callosum from the facial appearance.

Innervation of blood vessels in the rat incisor pulp: A scanning electron microscopic and immunoelectron microscopic study

Although two types of nerve endings have been proposed to innervate blood vessels in the dental pulp, the precise innervation pattern is not well understood. This is mainly due to the lack of information regarding the positional relationships of nerve fibers with blood vessels at the electron microscopic level.

Genetic controls of susceptibility and resistance to 4-Nitroquinoline 1-oxide-induced tongue carcinomas in rats

We analyzed the incidence of infiltrative mass‐type tongue carcinomas (IMTC) induced in 550 rats by continuous oral administration of 0.001% 4‐nitroquinoline 1‐oxide solution for 180 days. The study included various crosses of susceptible Dark‐Agouti rats (DA) and resistant Wistar/Furth rats (WF). DA showed a 93.6% incidence of IMTC measuring more than 5 mm in their largest diameter, while WF showed only a 4% incidence. Reciprocal F1 and F2 hybrids mated by DA and WF showed 47.5% and 45.8% incidences, respectively. Meanwhile, reciprocal backcrossed hybrids to DA and WF showed 73.7%, and 24.6% incidences, respectively. Segregation of the incidences suggests that there are two autosomal dominant genes, one linked to the susceptibility of DA and the other to the resistance of WF.

Effects of 3-acetylpyridine on local cerebral glucose utilization

Local cerebral glucose utilization was observed in mice treated with 3-acetylpyridine (3-AP), one of the nicotinamide antagonists. This drug resulted in loss of pyramidal cells and gliosis restricted almost exclusively to Spielmeyers resistant sector (area CA3) in the dorsal hippocampus. On the other hand, the most striking feature in the autoradiographic observations was that optical density in the impaired CA3 region of the dorsal hippocampus was significantly increased (P less than 0.01). Therefore, when the 2-deoxyglucose method is employed under pathological conditions, one must pay attention to these glial reactions.