Spino-cerebellar fibers of the opossumDidelphis marsupialis virginiana
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Summary In this study, the vertical, transverse and oblique diameters of the spinal cord segments (C 1 , C 6 , C 12 , C 18 , T 1 , T 4 , L 1 , L 4 , L 6 and L 8 ) and the ratio of gray matter to white matter in chick (l month) and adult (18 months) male ostriches, each group consisted of 3 animals, were measured with standard micrometric method using 6 µm thick sections by light microscope. With advancement of age, the ratio of gray matter to white matter was reduced but the diameters of spinal cord segments were increased. Statistically, there were significant differences in parameters measured between the two age groups (P<0.05). Key words: Spinal cord segments, Gray matter, White matter, Ostrich Introduction According to Streeter (1919), in the early stages of development in human, the spinal cord and the vertebral column grow side by side in a metameric manner but this growth at 30 millimeter embryonic stage interrupts and the vertebral column grows more rapidly than the spinal cord. The widest spinal cord segments of adult human were identified at 6th cervical segment and 12th thoracic segment, 38 and 36 millimeters, respectively (Williams
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Abstract The distribution of spinocerebellar tract (SCT) neurons has been studied in the entire length of the spinal cord of the cat following injections of horseradish peroxidase into the cerebellum, and whether or not the axons of the labeled neurons crossed within the spinal cord was determined in cases with injections preceded by hemisections at the cervical levels. The SCTs were classified into the following corssed and uncrossed tracts according to the cell origin and the fiber course; The crossed SCTs originate from (1) the central cervical nucleus (the CCN‐SCT), (2) lamina VIII neurons of the cervical to the lumbar cord (the lamina VIII‐SCT), (3) spinal border cells (the border cell‐SCT), (4) neurons in the medial lamina VII of the lumbar to the caudal spinal segments (the medial lamina VII‐SCT), (5) ventral horn neurons (laminae VII and VIII) of the sacral and caudal segments (the ventral horn‐SCT) and (6) dorsal horn neurons (lamina V) of the sacral and the caudal segments (the dorsal horn‐SCT). The uncorssed tracts originate from (1) neurons of the medial lamina VI of C2 to T1 (the medial lamina VI‐SCT of the cervical cord), (2) neurons in the central part of lamina VII of C6 to T1 (the central lamina VII‐SCT of the cervical enlargement), (3) lamina V neurons of the lower cervical to the lumbar cord (the lamina V‐SCT), (4) Clarke's column (the Clarke's column‐SCT) and (5) neurons in the medial lamina VI of L5 and L6 (the medial lamina VI‐SCT of the lumbar cord). The present study suggests that the spinocerebellar system originates from more diverse laminae than has previously been known, and further refined studies on the topographic projections of each tract will yield more important and valuable information in this field.
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Transition metal concentrations in the central nervous system (CNS) are altered in neurodegenerative diseases such as Alzheimer's, Parkinson's and multiple sclerosis. A common symptom of these diseases is demyelination, which is the degradation of the myelin sheath that encapsulates the neurons in vertebrates. Transition metal concentrations were measured in Long Evans Shaker (LES) rodent model and compared to healthy age-matched controls to investigate the relationship between transition metals and myelination. Micro probe Synchrotron Radiation X-ray Fluorescence (µSRXRF) was used to measure concentrations of manganese (Mn), iron (Fe), copper (Cu), and zinc (Zn) in regions of grey matter and white matter in Shaker rodents and their age-matched Long Evans (LE) controls in the cerebellum and spinal cord. In the cerebellum, the concentrations of all elements were significantly increased in the white matter of the Shaker model, and decreased in the gray matter of the Shaker model in comparison to their age and region matched controls. In the spinal cord samples, concentrations of all metals were higher in white matter and grey matter of Shaker rat spinal cord compared to those in the control rat spinal cord. This study demonstrated that the sensitivity of µSRXRF is sufficient to discriminate between the elemental distributions of gray and white matter of the brain sections and spinal cords in the two groups. The observed significant increase of Mn, Fe, Zn and Cu in the white matter of the Shaker animals in the cerebellum and spinal cord compared to controls could be the result of astrocytic glial cells replacing the myelin in the CNS. Unlike other imaging techniques, the fine resolution of µSRXRF enables specific regions of gray matter structures namely, the molecular layer and the granule layer to be identified in the rat CNS, and their transition metal concentrations to be quantified. This work will further establish µSRXRF as a powerful analytic technique for compositional studies in brain sections from models of brain disease.
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The neuronal organization of the spinal cord in red stingray was studied using the rapid Golgi method. The gray matter of the spinal cord was divided into seven laminae: RS-I, RS-II, RS-III, RS-IV, RS-V, RS-VI and RS-VII. RS-I is cell dense lamina which occupies the major part of the dorsal horn and corresponds to laminae I and II of the spinal cord of mammals, birds and reptiles. The neurons of the lamina I are interspersed with those of lamina II, without forming a discrete lamina. RS-II is located at the base of the dorsal horn and is considered to correspond to the nucleus proprius. RS-III and IV form the intermediate zone and are highly reticulated. A few neurons of various shapes and sizes are distributed among the numerous fibers. The nuclei such as the intermediolateral, intermediomedial or Clarke's nucleus cannot be identified in the intermediate zone. RS-V and VI constitute the ventral horn. RS-V occupies the major part of the ventral horn and contains motoneurons which are distributed diffusely, without forming any distinct cell groups. RS-VI is located in the ventromedial part of the ventral horn, contains commissural neurons and correspond to lamina VIII. RS-VII is a small area surrounding the central canal and corresponds to lamina X. Thus, while the major features of the spinal cord of the red stingray can be correlated with those of the spinal cord of mammals, birds and reptiles, the neuronal organization of the spinal cord of the red stingray remains in an undifferentiated state.
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Sacral projections of neurones located in the C6 segment of the spinal cord were electrophysiologically investigated in alpha-chloralose anaesthetized cats. The cell bodies were found mainly in lamina VIII and in the ventromedial part of lamina VII of the C6 segment. At the thoracic level their axons descended in lateral funiculi, mostly on both sides and only exceptionally contra- or ipsilaterally. However, bilateral projection to sacral segments was less frequent (25 neurones). It is concluded that axons terminate at different levels on both sides of the spinal cord and only part of them project bilaterally to S1/S2 segments. Conduction velocities calculated for all the axons varied from 38 to 80 m/s and were significantly slower for their distal parts. Therefore it is suggested that descending axons send collaterals at various spinal levels. The presented data indicate the importance of these neurones for interlimb coordination.
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The ventral horn of the rat spinal cord was investigated with respect to the somatotopic organization of the motor neurons that innervate the lumbar muscles. Neurotracer 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) was applied to specific sites in lumbar muscles. Spinal cord segments at L1 through L4 levels were cut into 40-mum serial transverse sections. Labeled neurons were located in the ventromedial nucleus (VM) and lateromedial nucleus (LM) nuclei of Rexed's lamina IX. Motor neurons innervating the m. interspinales lumborum and m. multifidus were without exception present in the VM, whereas all motor neurons innervating the m. rectus abdominis were present in the LM. Forty percent of motor neurons innervating the m. quadratus lumborum were present in the VM and the other 60% were in the LM. Although most of the motor neurons innervating the m. psoas major were present in the LM, a few labeled neurons existed in the VM. These results suggest that the border zone demarcating the areas of innervation of the dorsal and ventral rami of spinal nerves crosses the m. quadratus lumborum.
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