Takashi Shiga

Runx3 controls the axonal projection of proprioceptive dorsal root ganglion neurons

Dorsal root ganglion (DRG) neurons specifically project axons to central and peripheral targets according to their sensory modality. The Runt-related genes Runx1 and Runx3 are expressed in DRG neuronal subpopulations, suggesting that they may regulate the trajectories of specific axons. Here we report that Runx3-deficient (Runx3−/−) mice displayed severe motor discoordination and that few DRG neurons synthesized the proprioceptive neuronal marker parvalbumin. Proprioceptive afferent axons failed to project to their targets in the spinal cord as well as those in the muscle. NT-3-responsive Runx3−/− DRG neurons showed less neurite outgrowth in vitro. However, we found no changes in the fate specification of Runx3−/− DRG neurons or in the number of DRG neurons that expressed trkC. Our data demonstrate that Runx3 is critical in regulating the axonal projections of a specific subpopulation of DRG neurons.

Immunohistochemical demonstration of nerve fibers in the synovial fold of the human cervical facel joint

The role of the intra‐articular synovial fold as a source of facet joint pain is unclear, because the nature of nociceptive innervation in lumbar synovial folds is controversial, and there have been no such studies in cervical synovial folds. The present study aimed to demonstrate the presence of nerve fibers including nociceptive fibers in synovial folds of human cervical facet joints using immunohistochemistry. Synovial folds of cervical facet joints removed from patients undergoing cervical spine laminoplasty were analyzed immunohistochemically using antibodies to protein gene product 9.5, β III‐tubulin, substance P and calcitonin gene‐related peptide. Many nerve fibers immunoreactive for protein gene product 9.5 and β III‐tubulin were demonstrated both around blood vessels and as free fibers in the stroma of the synovial fold. Also, immunostaining showed the presence of free nerve fibers immunoreactive for substance P and calcitonin gene‐related peptide in the stroma. The presence of putative nociceptive fibers in cervical synovial folds supports a possible role for these structures as a source of cervical facet joint pain.

An enriched environment increases noradrenaline concentration in the mouse brain.

Exposure to an enriched environment has been shown to have many positive effects on brain structure and function. In the present study, we examined the effects of environmental enrichment on monoaminergic neurons in the mouse brain. After being exposed to an enriched environment for 40 days, noradrenaline content was increased significantly in the parieto-temporo-occipital cortex, the cerebellum and the pons/medulla oblongata. In contrast, no changes were observed in serotonin or dopamine levels in these same regions.

Runx transcription factors in neuronal development

Runt-related (Runx) transcription factors control diverse aspects of embryonic development and are responsible for the pathogenesis of many human diseases. In recent years, the functions of this transcription factor family in the nervous system have just begun to be understood. In dorsal root ganglion neurons, Runx1 and Runx3 play pivotal roles in the development of nociceptive and proprioceptive sensory neurons, respectively. Runx appears to control the transcriptional regulation of neurotrophin receptors, numerous ion channels and neuropeptides. As a consequence, Runx contributes to diverse aspects of the sensory system in higher vertebrates. In this review, we summarize recent progress in determining the role of Runx in neuronal development.

Dynamic regulation of the expression of neurotrophin receptors by Runx3

Sensory neurons in the dorsal root ganglion (DRG) specifically project axons to central and peripheral targets according to their sensory modality. However, the molecular mechanisms that govern sensory neuron differentiation and the axonal projections remain unclear. The Runt-related transcription factors, Runx1 and Runx3, are expressed in DRG neuronal subpopulations, suggesting that they might regulate the cell specification and the trajectories of specific axons. Here, we show that parvalbumin-positive DRG neurons fail to differentiate from the onset in Runx3-/- mice. By contrast, TrkC-positive DRG neurons differentiate normally at embryonic day (E) 11.5, but disappear by E13.5 in Runx3-/- mice. Subsequently, TrkC-positive DRG neurons reappear but in smaller numbers than in the wild type. In Runx3-/- mice, central axons of the TrkC-positive DRG neurons project to the dorsal spinal cord but not to the ventral and intermediate spinal cord, whereas the peripheral axons project to skin but not to muscle. These results suggest that Runx3 controls the acquisition of distinct proprioceptive DRG neuron identities, and that TrkC-positive DRG neurons consist of two subpopulations: Runx3-dependent early-appearing proprioceptive neurons that project to the ventral and intermediate spinal cord and muscle; and Runx3-independent late-appearing cutaneous neurons that project to the dorsal spinal cord and skin. Moreover, we show that the number of TrkA-positive DRG neurons is reduced in Runx3-/- mice, as compared with the wild type. These results suggest that Runx3 positively regulates the expression of TrkC and TrkA in DRG neurons.

Regulation of dendrite formation of Purkinje cells by serotonin through serotonin1A and serotonin2A receptors in culture.

Serotonergic fibers and receptors appear in the rat cerebellum during early postnatal development. In the present study, we investigated the actions of serotonin (5-HT) and its receptors in the dendrite formation of Purkinje cells in organotypic cultures of anterior and posterior lobes of the cerebellum at postnatal day 7. In anterior lobes after 4 days in vitro (4DIV), the dendritic areas and branchings of Purkinje cells were increased by the treatment of 2 microM 5-HT, but decreased by 20 microM 5-HT. In posterior lobes after 4DIV, the dendritic areas of Purkinje cells were increased by 5-HT (2, 20 and 200 microM). In contrast, 5-HT treatment decreased dendritic areas of Purkinje cells in both anterior and posterior lobes after 7DIV. Next, we determined the actions of specific 5-HT receptors in mediating the effects of 5-HT by treatment with selective 5-HT receptor agonists. In anterior lobes after 4DIV, dendritic areas of Purkinje cells were increased by a 5-HT1A receptor agonist (8-OH-DPAT), whereas decreased by a 5-HT2A receptor agonist (DOI). The present study suggested that the dendrite formation of Purkinje cells is promoted by 5-HT through 5-HT1A receptors, but inhibited by 5-HT through 5-HT2A receptors.

Differential non-target-derived repulsive signals play a critical role in shaping initial axonal growth of dorsal root ganglion neurons.

Initial trajectories of dorsal root ganglion (DRG) axons are shaped by chemorepulsive signals from surrounding tissues. Although we have previously shown that axonin-1/SC2 expression on DRG axons is required to mediate a notochord-derived chemorepulsive signal, Dev. Biol. 224, 112-121), other molecules involved in the non-target-derived repulsive signals are largely unknown. Using coculture assays composed of tissues derived from the chick embryo or mutant mice treated with function-blocking antibodies and phosphatidylinositol-specific phospholipase C, we report here that the chemorepellent semaphorin 3A (Sema3A) and its receptor neuropilin-1 are required for mediating the dermamyotome- and notochord-derived, but not the ventral spinal cord-derived, chemorepulsive signal for DRG axons. The dermamyotome-derived chemorepulsion is exclusively dependent on Sema3A/neuropilin-1, whereas other molecules are also involved in the notochord-derived chemorepulsion. Chemorepulsion from the ventral spinal cord does not depend on Sema3A/neuropilin-1 but requires axonin-1/SC2 to repel DRG axons. Thus, differential chemorepulsive signals help shape the initial trajectories of DRG axons and are critical for the proper wiring of the nervous system.

Neuronglia cell adhesion molecule (Ng-CAM) expression in the chick embryo spinal cord: observations on the earliest developing intersegmental interneurons

The pattern of expression of the neuron-glia cell adhesion molecule (Ng-CAM) among the presumptive intersegmental interneurons in the early chick embryo spinal cord (stage 14-19) was examined using whole-mount and cryostat preparations double-stained with anti-Ng-CAM antibody and a neuron-specific anti-beta-tubulin antibody. In brachial segments, primitive longitudinal cells (PL-cells), located in the ventrolateral region of the spinal cord, express Ng-CAM both on their cell bodies and longitudinally growing axons, beginning at Hamburger-Hamilton stage 15 (embryonic day (E) 2.5). Shortly thereafter, at stage 16, circumferential cells (C-cells), composed of associational and commissural interneurons in the dorsolateral and lateral region of the spinal cord begin to express Ng-CAM both on their cell bodies and their axons which project ventrally along the lateral surface of the spinal cord. In the following stages. PL-cells express Ng-CAM strongly and begin to fasciculate to form a longitudinal fascicle in the ventrolateral marginal region of the spinal cord. C-Cells either extend their Ng-CAM-positive axons ventrally without fasciculation to join the Ng-CAM positive ipsilateral longitudinal fascicle at stage 17 (which has already been formed by PL-cell axons), or they cross the midline to join the Ng-CAM positive contralateral longitudinal fascicle after growing through the floor plate at stage 19. By stage 19, cell bodies and proximal segments of the C-cell axons exhibit decreased Ng-CAM expression, whereas the distal segment of these axons, including growth cones, strongly express Ng-CAM. Many contacts were observed between Ng-CAM-positive growth cones and axons in the ventral region of the spinal cord, both within the longitudinal fascicle and the floor plate region, suggesting the involvement of Ng-CAM in neurite-neurite interactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental regulation of notochord-derived repulsion for dorsal root ganglion axons

During the initial stages of development, the notochord provides repulsive signals for dorsal root ganglion (DRG) axons via semaphorin 3A/neuropilin-1, axonin-1/SC2, and other unknown repulsive molecules. The notochord is known to produce aggrecan, one of the chondroitin sulfate proteoglycans (CSPGs). We report here that adding aggrecan to the culture medium cannot only induce DRG growth cone collapse, but also inhibit DRG axonal growth. Using cocultures composed of tissues derived from chick embryos or neuropilin-1-deficient mice treated with chondroitinase ABC, we show the direct evidence that CSPGs are involved in notochord-derived repulsion for DRG axons. At later developmental stages, CSPGs are involved in perinotochordal sheath-derived axon repulsion, but not in notochord core-derived repulsion. We further demonstrate that TAG-1/axonin-1/SC2 is not involved in mediating repulsive activities by CSPGs, but is required for notochord core-derived axon repulsion. Thus, notochord-derived multiple axon repulsions act in a spatiotemporal-specific manner to shape the initial trajectories of DRG axons.

Immunolocalization of p38 MAP kinase in mouse brain

p38 has been implicated to play a critical role in regulating apoptosis in PC12 and cerebellar granule cells, and is inactivated in cultured fetal neurons in response to insulin. Though p38 is activated in microglia after ischemia, the physiological functions of p38 in the brain are not well understood. As a first step to elucidate the physiological functions of p38 in the central nervous system, we raised a polyclonal antibody against p38 and performed immunohistochemical examination to demonstrate the localization of p38 in mouse brain. Strong p38 immunoreactivity was apparent in fiber bundles including the olfactory tract, anterior commissure, corpus callosum, cingulum, internal capsule, stria terminalis, fimbria and alveus hippocampi, fornix, stria medullaris, optic chiasm and optic tract. Although similar regions were stained with both anti-p38 and anti-neurofilament antibodies, intense p38 immunoreactivity was often observed in myelin sheath-like structures but not in axons. This is the first demonstration of the localization of p38 in the central nervous system and provides an anatomical basis for understanding physiological roles of p38.