Toshiko Tsumori

Topographical projection from the hippocampal formation to the amygdala: A combined anterograde and retrograde tracing study in the rat

The hippocampal formation and amygdala are responsible for regulating emotion, learning, and behavior. The hippocampal projection to the amygdala has been demonstrated to originate in the subiculum and adjacent portion of field CA1 of the Ammons horn (Sub/CA1) in the rat; however, the topographical organization of this pathway is still understudied. To make it clear, we performed anterograde and retrograde tracing with biotinylated dextran amine (BDA) and cholera toxin B subunit (CTb), respectively, in the rat. A series of BDA experiments revealed that the temporal‐to‐septal axis of origin determined a medial‐to‐lateral axis of termination in the amygdala. Briefly, the temporal region of the Sub/CA1 projects preferentially to the medial amygdaloid region including the medial, intercalated, and basomedial nuclei and the amygdalohippocampal transition area, and progressively more septal portions of the Sub/CA1 distribute their efferents in more lateral regions of the amygdala. Sub/CA1 fibers distributed in the central amygdaloid nucleus were relatively few. Retrograde tracing with CTb confirmed this topography and revealed little hippocampal innervation of the central nucleus of the amygdala. These observations suggest that distinct Sub/CA1 regions arranged along the longitudinal hippocampal axis may influence distinct modalities of the amygdala function. J. Comp. Neurol. 496:349–368, 2006.

Topographical organization of projections from the subiculum to the hypothalamus in the rat.

The projections from the subiculum to the hypothalamus were comprehensively examined in the rat by using the anterograde Phaseolus vulgaris leucoagglutinin (PHA‐L) and retrograde cholera toxin B subunit (CTb) methods. Tracing of efferents with PHA‐L indicated that the medial preoptic region received projection fibers from the temporal two‐thirds of the subiculum, whereas the anterior, tuberal, and mammillary regions received those from the full longitudinal extent of the subiculum. The subicular projections to the anterior and tuberal hypothalamic regions were also found to be organized in a topographical manner such that the temporal‐to‐septal axis of origin in the subiculum determined a ventromedial‐to‐dorsolateral axis of termination in the medial zone of the hypothalamus: Massive labeled fibers from the temporalmost part of the subiculum terminated in the subparaventricular zone and its caudal continuum around the dorsal and medial aspects of the ventromedial nucleus, and those from progressively more septal parts terminated in progressively more dorsolateral parts of the medial zone. In addition, the temporal‐to‐septal axis of origin in the subiculum tended to determine a medial‐to‐lateral axis of termination in the preoptic region as well as a ventral‐to‐dorsal axis of termination in the mammillary region. Furthermore, the temporal‐to‐septal axis of origin in the septal two‐thirds of the subiculum corresponded to a ventrolateral‐to‐dorsomedial axis of termination in the medial mammillary nucleus. The topographical projections from the subiculum to the medial zone of the hypothalamus were confirmed by CTb experiments, representatively in the subicular projections to the anterior hypothalamic region. These results suggest that different populations of neurons existing along the longitudinal axis of the subiculum may exert their influences on the execution of different hypothalamic functions. J. Comp. Neurol. 419:205–222, 2000.

Early development of the oligodendrocyte in the embryonic chick metencephalon

It has been demonstrated that the spinal cord oligodendrocytes in the vertebrates arise in the ventral ventricular zone adjacent to the floor plate in their early development. Because of the similarities of basic structures in the spinal cord and metencephalon, it is probable that the mode of early oligodendrocyte development in the metencephalon is the same as that in the spinal cord. We examined this possibility in chick embryos, using monoclonal antibodies O1 and O4, markers for oligodendrocyte lineage. An O4‐positive (O4+) cell focus was observed in the medial ventricular zone of E5 chick ventral metencephalon (the earliest stage examined), adjacent to the floor plate. At E6, O4+ cells were dispersed from the medial to the lateral pons and, at E7, to the cerebellar anlagen. O4+ cells in the E6 brainstem and in the E7 cerebellum were unipolar in shape, whereas one day later, some of the labeled cells were multipolar with a few thin processes. O1 + oligodendrocytes first appeared at E8 in the ventromedial part of the pons and were distributed throughout the pons at E10 and in the cerebellum at E12. Explants from three subdivisions of the metencephalon (medial and lateral pons, and cerebellum) from E5 to E8 chick embryos were separately cultured to confirm the potential for generation of oligodendrocyte lineage. O4+ cells appeared in the culture of the E5 medial pons (the earliest stage examined), in the E6 lateral pons, and in the E7 cerebellum. In addition, E7 was the youngest stage from which cerebellar explants were able to generate O1+ oligodendrocytes. Our results clearly demonstrated the in vivo morphology of oligodendrocyte precursors in the metencephalon and their developmental appearance in a ventral‐to‐dorsal manner. From the bipolar morphology of O4+ cells and the spacio‐temporal continuity of the dispersion, it is inferred that the initial dispersion of O4+ cells may involve oligodendrocyte migration from the focus of the medial pons to the lateral and dorsal parts of the metencephalon. J. Neurosci. Res. 48:212–225, 1997.

Descending projections from the superior colliculus to the reticular formation around the motor trigeminal nucleus and the parvicellular reticular formation of the medulla oblongata in the rat

We observed by the anterograde and retrograde tracing techniques in the rat that the lateral part of the superior colliculus (SC), where the nigrotectal fibers from the dorsolateral part of the substantia nigra pars reticulata (SNr) terminated, sent projection fibers to the reticular region around the motor trigeminal nucleus (RFmt) and parvicellular reticular formation (RFp) of the medulla oblongata, where many premotor neurons for the orofacial motor nuclei were known to be distributed. The SC neurons sending their axons to the RFmt and RFp were mainly located in the stratum griseum intermedium, and additionally in the stratum griseum profundum. Our results suggest that neuronal signals conveyed through the nigro-tecto-bulbar pathway to the RFmt and RFp may exert control influences upon oral behavior.

Developmental appearance of oligodendrocytes in the embryonic chick retina

The axons of the optic nerve layer are known to be myelinated by oligodendrocytes in the chick retina. The development of the retinal oligodendrocytes has been studied immunohistochemically with antibodies against oligodendrocyte lineage: monoclonal antibodies O4 and O1, and an antibody against myelin basic protein. O4 positive (O4+) cells were first detected in the retina on the tenth day of incubation (embryonic day (E)10, stage 36). The labeled cells were located in the optic nerve layer close to the optic fissure. Most were unipolar in shape, extending a leading process with a growth cone toward the periphery of the retina. By E12, unipolar O4+ cells had spread to the middle of the retina. Many O4+ cells close to the optic fissure showed radial arrangement with extension of processes toward the inner limiting membrane. O1+ oligodendrocytes were first observed in the E14 retina positioned just above (interiorly to) retinal ganglion cells. These labeled cells extended fine processes in the optic nerve layer. Limited numbers of myelin basic protein‐positive cells were present by E16 and located interiorly to the retinal ganglion cells. In addition to the oligodendrocyte in the optic nerve layer, a limited number of O4+ cells were observed in the inner nuclear layer by E14, and they became O1+ by E18. Furthermore, explant culture experiments showed E10 to be the youngest stage at which the retina contained oligodendrocyte precursors. An intraventricular injection of fluorescent dye 1,1′,dioctadecyl‐3,3,3′,3‐tetramethylindocarbocyanine perchlorate (DiI) at E6 yielded O4+/DiI+ cells in the retina at E10, which provided direct evidence to support migration of oligodendrocyte precursor into the retina. The present results demonstrated the sequential appearance of the cells of oligodendrocyte lineage and the detailed morphology of the developing oligodendrocytes in the retina. These morphologic features strongly suggested that retinal oligodendrocytes were derived from the optic nerve and spread by migration through the optic nerve layer. J. Comp. Neurol. 398:309–322, 1998.

Morphological evidence for a vestibulo-thalamo-striatal pathway via the parafascicular nucleus in the rat

We observed by anterograde and retrograde tracing techniques that projection fibers originating from the medial vestibular nucleus (MVe) of the rat terminated in the dorsal two-thirds of the lateral part of the parafascicular thalamic nucleus (PF), where neurons sending their axons to the dorsolateral part of the striatum existed. It was further revealed that the vestibular fibers made asymmetrical synaptic contacts mainly with dendrites and additionally with soma of the striatum-projecting PF neurons. These data suggest that output signals from the MVe may be transmitted disynaptically to the striatal neurons via the PF neurons.

Co-localization of nitric oxide synthase and vasoactive intestinal peptide immunoreactivity in neurons of the major pelvic ganglion projecting to the rat rectum and penis

Nitric oxide synthase (NOS)- and vasoactive intestinal peptide (VIP)-immunoreactive neurons projecting to the upper rectum or penis were examined using retrograde tracing combined with immunohistochemistry in the major pelvic ganglion of male rats. Five days after injection of Fluoro-Gold (FG) into the upper rectum or penis, the major pelvic ganglion was treated with colchicine. FG injected into the upper rectum labelled many ganglion neurons in the major pelvic ganglion. Immunohistochemistry showed that 37% of FG-labelled neurons were immunoreactive for NOS and 33% for VIP. After injection of FG into the penis, 41% of FG-labelled neurons were immunoreactive for NOS and 25% for VIP. Serial cryostat sections stained for NOS and VIP, respectively, showed the co-localization of NOS and VIP in the ganglion cells projecting to the rectum and penis. In the major pelvic ganglion of the colchicinetreated animals, about 17% of the ganglion cells were immunoreactive for NOS and 32% were immunoreactive for VIP. These neurons were small in diameter (less than 30 μm). A histogram showing cell sizes in cross-sectional areas of NOS-immunoreactive neurons coincided with that of VIP-immunoreactive neurons. Most of the NOS-and VIP-immunoreactive neurons were less than 600 μm2. These results indicate that small neurons containing both NOS and VIP in the major pelvic ganglion project to the rectum and penis. In the penile erectile tissues and enteric ganglia, NO and VIP may be released from the same axons and may act concomitantly on the target tissue.

Amygdaloid axon terminals are in contact with trigeminal premotor neurons in the parvicellular reticular formation of the rat medulla oblongata

After ipsilateral injections of biotinylated dextran amine (BDA) into the central nucleus of the amygdala (ACe) and cholera toxin B subunit (CTb) into the motor trigeminal nucleus (Vm) in the rat, numerous BDA-labeled axons with bouton-like varicosities were distributed bilaterally with a clear-cut ipsilateral dominance in the parvicellular reticular formation (RFp), where many CTb-labeled neurons existed bilaterally with slightly ipsilateral dominance. The prominent overlapping distribution of these labeled axons and neurons was found in the RFp region just ventral to the nucleus of the solitary tract and medial to the spinal trigeminal nucleus throughout the caudalmost part of the pons and the rostral half of the medulla oblongata. Within the neuropil of the RFp region in the rostral half of the medulla oblongata, BDA-labeled axons made symmetrical synaptic contacts predominantly with the dendrites and additionally with the somata of RFp neurons, some of which were labeled with CTb. These data suggest that output signals from the ACe may be transmitted disynaptically to the Vm via the RFp neurons in the medulla oblongata for the control of jaw movements.

Morphological features of microglial cells in the hippocampal dentate gyrus of Gunn rat: a possible schizophrenia animal model

BackgroundSchizophrenia is a debilitating and complex mental disorder whose exact etiology remains unknown. There is growing amount of evidence of a relationship between neuroinflammation, as demonstrated by microglial activation, and schizophrenia. Our previous studies have proposed that hyperbilirubinemia plays a role in the pathophysiology of schizophrenia. Furthermore, we suggested the Gunn rat, an animal model of bilirubin encephalopathy, as a possible animal model of schizophrenia. However, the effects of unconjugated bilirubin on microglia, the resident immune cell of the CNS, in Gunn rats have never been investigated. In the present study, we examined how microglial cells respond to bilirubin toxicity in adult Gunn rats.MethodsUsing immunohistochemical techniques, we compared the distribution, morphology, and ultrastructural features of microglial cells in Gunn rats with Wistar rats as a normal control. We also determined the ratio of activated and resting microglia and observed microglia-neuron interactions. We characterized the microglial cells in the hippocampal dentate gyrus.ResultsWe found that microglial cells showed activated morphology in the hilus, subgranular zone, and granular layer of the Gunn rat hippocampal dentate gyrus. There was no significant difference between cell numbers between in Gunn rats and controls. However, there was significant difference in the area of CD11b expression in the hippocampal dentate gyrus. Ultrastructurally, microglial cells often contained rich enlarged rich organelles in the cytoplasm and showed some phagocytic function.ConclusionsWe propose that activation of microglia could be an important causal factor of the behavioral abnormalities and neuropathological changes in Gunn rats. These findings may provide basic information for further assessment of the Gunn rat as an animal model of schizophrenia.

Demonstration of axon collateral projections from the substantia nigra pars reticulata to the superior colliculus and the parvicellular reticular formation in the rat

It was revealed in the rat that single neurons in the substantia nigra pars reticulata (SNr) innervated both the superior colliculus (SC) and the parvicellular reticular formation (RFp) in the pons and medulla oblongata by way of axon collaterals. After injecting Fluoro-gold into the lateral part of the SC and Fluoro-ruby into the RFp on the same side, some SNr neurons were double-labeled with both tracers. They were localized in the dorsolateral part of the caudal half of the SNr ipsilateral to the injection sites.