Spinal cords of the lamprey and hagfish were fluorescence histochemically and electron microscopically examined. Ventrally to the central canal of both cyclostomes, yellow fluorescence bound to small to medium sized neurons was observed. In the lamprey only, weakly blue-green fluorescent subependymal cells were seen just beneath the central canal. In the ventral floor of their spinal cord, yellow fluorescent varicosities were observed; their density was much higher in the lamprey than in the hagfish. The lateral surface of the hagfish spinal cord was marginated by a chain of yellow fluorescent varicosities. The yellow fluorescence was microspectrofluorometrically identified as fluorescence due to 5-HT. Electron microscopically, the 5-HT neurons contained many large dense-core vesicles. The 5-HT varicosities or terminals seen in the ventral zone of both cyclostomes possessed the large dense-core vesicles and small clear synaptic vesicles, which appeared as small dense-core vesicles after KMnO4 fixation. The terminal of the lamprey was nakedly situated on the ventral surface, while that of the hagfish was always covered by the superficial glial layer. This finding seems to favor the view that lamprey and hagfish should be divided into two different classes.
The choroid plexus and the third ventricle wall of the rat brain were observed by scanning electron microscopy.Macrophages of various shapes known as Kolmer cells were attached to the ependymal surface of the choroid plexus densely covered with microvilli. Some cells possessed numerous fine processes radiating from the centrally located cell body and ending, often with an attenuated web-like tip, among the ependymal microvilli. Others were cells with a few pseudopod-like processes of considerable thickness and length. The latter type was thought to be in locomotion.The same cells were occasionally also found in the third ventricle wall far from the choroid plexus. The Kolmer cells are thought to be scavengers belonging to the whole ventricular system, though they are gatherd mainly on the choroid plexus.
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.
