Satoru Onodera

Schwann cell basal lamina and nerve regeneration

Nerve segments approximately 7 mm long were excised from the predegenerated sciatic nerves of mice, and treated 5 times by repetitive freezing and thawing to kill the Schwann cells. Such treated nerve segments were grafted into the original places so as to be in contact with the proximal stumps. The animals were sacrificed 1, 2, 3, 5, 7 and 10 days after the grafting. The grafts were examined by electron microscopy in the middle part of the graft, i.e. 3-4 mm distal to the proximal end and/or near the proximal and distal ends of the graft. In other instances, the predegenerated nerve segments were minced with a razor blade after repetitive freezing and thawing. Such minced nerves were placed in contact with the proximal stumps of the same nerves. The animals were sacrificed 10 days after the grafting. Within 1-2 days after grafting, the dead Schwann cells had disintegrated into fragments. They were then gradually phagocytosed by macrophages. The basal laminae of Schwann cells, which were not attacked by macrophages, remained as empty tubes (basal lamina scaffolds). In the grafts we examined, no Schwann cells survived the freezing and thawing process. The regenerating axons always grew out through such basal lamina scaffolds, being in contact with the inner surface of the basal lamina (i.e. the side originally facing the Schwann cell plasma membrane). No axons were found outside of the scaffolds. One to two days after grafting, the regenerating axons were not associated with Schwann cells, but after 5-7 days they were accompanied by Schwann cells which were presumed to be migrating along axons from the proximal stumps. Ten days after grafting, proliferating Schwann cells observed in the middle part of the grafts had begun to sort out axons. In the grafts of minced nerves, the fragmented basal laminae of the Schwann cells re-arranged themselves into thicker strands or small aggregations of basal laminae. The regenerating axons, without exception, attached to one side of such modified basal laminae. Collagen fibrils were in contact with the other side, indicating that these modified basal laminae had the same polarity in terms of cell attachment as seen in the ordinary basal laminae of the scaffolds.(ABSTRACT TRUNCATED AT 400 WORDS)

A Comparative Neuroanatomical Study of the Red Nucleus of the Cat, Macaque and Human

Background The human red nucleus (Nr) is comparatively less well-studied than that of cats or monkeys. Given the functional importance of reticular and midbrain structures in control of movement and locomotion as well as from an evolutionary perspective, we investigated the nature and extent of any differences in Nr projections to the olivary complex in quadrupedal and bipedal species. Using neuroanatomical tract-tracing techniques we developed a “neural sheet” hypothesis allowing us to propose how rubro-olivary relations differ among the three species. Methods and Findings Wheat germ agglutinin-horseradish peroxidase staining supports findings that the cats nucleus accessories medialis of Bechtrew (NB) projects mainly to the lateral bend of the principal olive. We clarified boundaries among nucleus of Darkschewitsch (ND), NB and parvicellular red nucleus (pNr) of the cats neural sheet. The macaques ND-medial accessory olivary projection is rostro-caudally organized and the dorsomedial and ventrolateral parts of the macaques pNr may project to the principal olives rostral and caudal dorsal lamella; in cat it projects as well to pNr. Myelin- and Nissl-stained sections show that a well-developed dorsomedial part of the human Nr consists of densely packed cells, deriving small myelinated fibers that continue into the medial central tegmental tract. Conclusions Based on these findings we suggest there are distinct bipedal-quadrupedal differences for Nr projections to the olivary complex. We propose the Nr of cats and monkeys comprise the ND, NB and pNr in a zonal sheet-like structure, retaining clear nuclear boundaries and an isolated, well-developed mNr. The human NB may be distinguished from its more specialised ND (ND lies alongside a well-developed pNr) in the human central gray. Phylogenetically, the NB may have been translocated into a roll-shaped Nr in the reticular formation, the dorsomedial portion of which might correspond to the cats and monkeys NB.

Projections of extraocular muscle primary afferent neurons to the trigeminal sensory complex in the cat as studied with the transganglionic transport of horseradish peroxidase

The central projections of extraocular muscle primary afferent neurons were examined in the cat by means of transganglionic axonal transport of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). Injections of the extraocular muscle with WGA-HRP resulted in transganglionic terminal labeling within the ipsilateral trigeminal sensory complex. Although the density of trigeminal projections varied among cases, labeled axons and terminals were heavily and consistently found within the rostroventral portion of the pars oralis of the spinal trigeminal nucleus. The caudal part of the trigeminal principal sensory nucleus occasionally contained moderate labeling but very few deposits of HRP reaction product were noted in the pars interporalis and pars caudalis of the spinal trigeminal nucleus.

Review : Evolution of the Motor System: Why the Elephant's Trunk Works Like a Human's Hand

The nucleus of Darkschewitsch, the nucleus accessorius medialis of Bechterew, and the parvicellular red nucleus in the mammalian mesodiencephalon fuse with each other and thus have borders that are not always distinct. These structures project topographically to the inferior olive and receive inputs from motor cortex, premotor cortex, substantia nigra, and cerebellar nuclei, which suggests that these nuclei play an important role in mammalian motor control. Furthermore, the nuclei show developmental differences that correspond with species-specialized body parts, such as the humans hand, the axial muscular system of the whale, and the elephants trunk, to name just a few. We focus here on the differences in these meso diencephalo-olivo-cerebellar projections among certain mammals and propose that these brain structures are altered as the animals gross anatomy alters. We also suggest that well-developed mesodiencephalo olivo-cerebellar projections may be an important factor for the differentiation of the large neocortex of the human, primate, elephant, and whale during evolutionary progress. NEUROSCIENTIST 5:217-226, 1999

Carbocyanine Dye Usage in Demarcating Boundaries of the Aged Human Red Nucleus

Background Though the adult human magnocellular Red nucleus (mNr) is essentially vestigial and its boundaries with neighbouring structures have never been well demarcated, human studies in utero have shown a well developed semilunar mNr wrapping around the caudal parvicellular Red nucleus (pNr), similar to what is seen in quadrupeds. In the present study, we have sought to better delineate the morphological determinants of the adult human Red nucleus (ahRn). Methods and Findings Serial sections of ahRn show fine myelinated fibers arising from pNr and turning toward the central tegmental tract. DiI was deposited within a well restricted region of ahRn at the fasciculus retroflexus level and the extent of label determined. Nissl-stained serial sections allowed production of a 3-D mNr model, showing rudimentary, vestigial morphology compared with its well developed infant homologue. DiI within this vestigial mNr region at the level of the oculomotor nerve showed labeled giant/large mNr neurons, coarse fiber bundles at the ventral tegmental decussation and lateral lemniscal label. Conclusions Large amounts of DiI and a long incubation time have proven useful in aged human brain as a marker of long axons and large cell bodies of projecting neurons such as the rubrospinal projection and for clarifying nuclear boundaries of closed nuclei (e.g., the large human pNr). Our 3D model of adult human mNr appeared shrunken in shape and axially rotated compared with the infant mNr, the rotation being a common feature among mammalian mNr.

Chapter 6 A projection linking motor cortex with the LM-suprageniculate nuclear complex through the periaqueductal gray area which surrounds the nucleus of Darkschewitsch in the cat

Whereas a previous study by one of us (Hicks et al., 1986) suggested that periaqueductal gray (PAG) neurons projecting to the lateralis medialis-suprageniculate (LM-SG) complex might mediate transmission of affective-related nociceptive information, our present work suggests instead, a function in processes related to movement. Cells of the nucleus of Darkschewitsch (ND) are known to have reciprocal projections with the motor cortex (MX), in particular with the hand area of MX, and also to project to the rostral medial accessory olivary (MAO) nucleus (Onodera and Hicks, 1995a). That the ND might be related to saccadic oculomotor function, as well as to the control of hand movements through its connections via the olivo-cerebellar circuit, is indicated by the fact that ND receives a strong projection from the substantia nigra pars reticulata and zona incerta (SNR/ZI) and projects directly and/or indirectly to eye movement nuclei (Onodera and Hicks, 1995b). Thus, ND may function in permitting integration of eye-hand motor coordination. This study focussed on the area of PAG surrounding ND. WGA-HRP was injected into MX and many labelled terminals and large neurones were in ND, with lesser numbers being observed in the area of the PAG surrounding ND. After injections into ND and closely adjacent areas, labelled terminals were observed sparsely distributed with a restricted area of the LM-SG complex. After injections into LM-SG area, small neuronal somata were seen in the area of the PAG surrounding ND, but no labelled somata were detected in ND. Thus if the cells of this PAG area, like those of ND, have similar functions owing to their common reciprocal connections with MX, then the small neurones in PAG projecting to LM-SG may constitute an important link in the circuitry subserving visual processing and/or the regulation of orienting movements of the hand, head and eye.

Tentative identification of arterial baroreceptors associated with arteriovenous anastomoses

Nerve endings of the trigeminal nerve were examined in the lip, nostril, upper jaw and supraorbital skin of cat by the horseradish peroxidase (HRP) tracing method. Wheatgerm agglutinin-HRP (WGA-HRP) as injected into the spinal trigeminal nucleus was transported transganglionically to nerve endings. The present study deals with presumptive baroreceptive nerve endings found on arteriovenous anastomoses and on some other large arteries. By light microscopy HRP-labeled, complexly arborized nerve endings were found on the walls of arteries located deep in the subcutaneous tissue of the lip and nostril. These arteries were identified in serial sections to be an arterial segment of an arteriovenous anastomosis. By electron microscopy characteristic nerve endings were located in the adventitia and partly extended into the adjacent connective tissue of the arterial wall. These terminals had no connective tissue capsule. Axon terminals were somewhat enlarged (1-2 microns in diameter) and extended through bundles of collagen fibrils. The terminals contained an abundance of mitochondria and some vesicles. Axon terminals were typically covered by thin Schwann cell processes, but parts of the axolemma were sometimes devoid of such Schwann cell coverings, being invested only by basal laminae. Cell bodies of Schwann cells were located apart from axons. These light and electron microscopic features of the endings resembled those of other well-defined baroreceptors reported in the carotid sinus, aortic arch and endocardium, as well as of Ruffini terminals and Golgi tendon organs, suggesting that they would be baroreceptors of arteriovenous anastomosis. In addition HRP-labeled single nerve fibers with varicosities were found in the walls of some large arteries in the facial skin. By electron microscopy, such a HRP-positive nerve fiber contained some mitochondria and vesicles in varicosities and coursed with a bundle of HRP-negative fine fibers in the adventitia of arteries. These HRP-labeled single fibers were considered to be sensory derived from trigeminal nerves.

Schwann cell basal lamina and central nerve regeneration

It has been demonstrated that the basal lamina scaffolds of Sehwann cells are effective pathways for regenerating peripheral nerves (Ide, et al, 1988). The present study was carried out to examine whether the Schwann cell basal laminae can be effective for regenerating fibers of the central nervous system. The rat sciatic nerve was transected for predegeneration, and after one week a part of the distal portion of the transected nerve was excised and treated several times by freezing and thawing to kill the Schwann cells. The treated nerve segment was then implanted into the spinal cord of the same animal. About 7 days after implantation, macrophages phagocytized dead Schwann cells, leaving basal lamina scaffolds of Schwann cells in the implant. Regenerating fibers entered such basal lamina scaffolds, being accompanied by cells resembling Schwann cells in appearance. After 20 days, most of the regenerating fibers were myelinated. The cells forming myelin sheaths resembled Schwann cells, being surrounded with basal laminae. Some astrocytic processes were found within the basal lamina scaffolds, enclosing one to several myelinated f~bers of the central nerve type. These findings suggest at least the possibility of the effectiveness of Schwann cell basal laminae for central nerve regeneration.