Uptake of 3H-GABA (gamma-aminobutyric acid) and 3H-leucine in the pancreatic islets and substantia nigra of the rat

Isolated pancreatic islets and thin slices of substantia nigra (SN) of the rat were incubated in a medium containing 3H-GABA or 3H-leucine to test the activity of both tissues in the uptake of those substances. Pancreatic islets showed a low uptake of both 3H-GABA and 3H-leucine, but SN had a high activity in the uptake of 3H-GABA, though not for 3H-leucine. This suggests that GABA contained at high levels in the pancreatic islets some functional role other than in neurotransmission as in the central nervous system (CNS).

Cells of origin of the spinocerebellar tract in the rat, studied with the method of retrograde transport of horseradish peroxidase

Following injections of horseradish peroxidase into the cerebellum, the distribution of labeled neurons was studied in the whole length of the spinal cord of the rat. To find the ascending side of the axons, injections were made following hemisections at C1 or between C1 and C2. Labeled spinocerebellar tract neurons were classified into two groups according to the axonal course in the spinal cord; one is composed of neurons with uncrossed ascending axons and the other, neurons with crossed ascending axons. Neurons of origin of the uncrossed tracts were located in the medial part of lamina VI of C2 to C8, the central part of lamina VII of C4 to C8, lamina V of C7 to L3 and Clarke's column. Neurons of origin of the crossed tracts were found in the central cervical nucleus of C1 to C3, the intermediate zone and the ventral horn of the lower thoracic and the lumbar segments (T11 to L3), and in the dorsal horn, the medial part of lamina VII and the ventrolateral part of the ventral horn of the sacral and caudal spinal cord. In comparison with our previous results in the cat, it was suggested that the spinocerebellar system in the rat is organized in the same fashion as in the cat, in terms of the location and the intraspinal axonal course of the cells of origin.

Comparative study of the monoamine neuron system in the spinal cord of the lamprey and hagfish

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.

Identification and distribution of the spinal and hypophyseal projection neurons in the paraventricular nucleus of the rat. A light and electron microscopic study with the horseradish peroxidase method

The distribution of labeled neurons in the paraventricular nucleus of the hypothalamus (PVN) was studied following injections of horseradish peroxidase (HRP) into the spinal cord (C8 to T1) or the hypophysis in the rat. Injections were also made in the spinal cord in another group of animals, which were subjected to water deprivation for a period of 3 days, and the PVN of these animals was examined with the electron microscope. Spinal projection neurons (paraventriculospinal tract, PVST, neurons) formed two groups; the dorsal and the ventral groups. They were located within the parvocellular part of the PVN and fused into one at the caudal level. The neurons of the dorsal group were well assembled whereas those of the ventral group were intermingled with paraventriculohypophyseal tract (PVHT) neurons, which were concentrated in the magnocellular part. Electron microscopic observations revealed that HRP-labeled neurons after spinal injections did not contain neurosecretory granules and that they were not affected by water deprivation. On the other hand, neurons containing a number of neurosecretory granules displayed a significant degree of dilatation of the endoplasmic reticulum as the result of water deprivation. These neurons contained no HRP granules. The present findings suggest that the PVST neurons are distinct from the PVHT neurons and that the neuronal groups of both systems form different cell columns within the nucleus.

Anatomical organization of the spinocerebellar system in the cat, as studied by retrograde transport of horseradish peroxidase

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 crossed 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 uncrossed 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.

The location of spinal neurons with long descending axons (long descending propriospinal tract neurons) in the cat: a study with the horseradish peroxidase technique

The distribution spinal neurons with long descending axons was studied in the cat by means of retrograde transport of horseradish peroxidase. Labeled neurons appeared bilaterally in the cervical and the thoracic cord following injections in the lumbosacral cord. In some cases hemisections were made rostrally and contralaterally to the injections in an attempt to determine whether or not the axons crossed. Neurons with uncrossed descending axons were located in laminae I, V, VII and VIII. Lamina I neurons were present in all the spinal segments. In lamina V labeled neurons were distributed mainly laterally in the cervical cord but medially and laterally in the thoracic cord. In the upper cervical and the thoracic cord laminae VII and VIII neurons were distributed very densely along the lateral cord, accounting for 30 and 40 of the total labeled neurons, respectively. In the cervical enlargement they were located in the middle part of lamina VII and in lamina VIII, accounting for about 25% of the total labeled neurons. Neurons with crossed descending axons were found in laminae V, VII and VIII, in the medial part of lamina VII including the intermediomedial nucleus of the thoracic levels and close to the central canal. Lamina V neurons were very small in number. The largest collections of labeled neurons were present in the medial part of laminae VII and VIII. They accounted for about 45% to 55% and 37% of the total in the cervical and the thoracic cord. These neurons may function as the long spinal reflex paths for forelimb-hindlimb synergies and the intercalated paths between the supraspinal descending tracts and the spinal motor centers.

The location of spinal projection neurons in the cerebellar nuclei (cerebellospinal tract neurons) of the cat. A study with the horseradish peroxidase technique

The distribution of spinal projection neurons was studied in the cerebellar nuclei of the cat following injections of horseradish peroxidase (HRP) into the cervical, thoracic and lumbar cord. HRP-positive (labeled) neurons were found in the medial (fastigial) and the posterior interpositus nuclei on the side contralateral to the cervical injection, being most numberous in cases with injections between the C2 and the C3 segments. In the medial nucleus (M) labeled neurons were distributed in the central to the caudal portions, and there was a conspicuous group of labeled small neurons extending from the ventrolateral part to the intermediate zone between the M and the anterior interpositus nucleus. With an increasing number of medium-sized neurons, this neuronal group persisted caudally in a similar position, ventromedial to the posterior interpositus nucleus (IP). Labeled large neurons were seen in the medial third of the IP. In the two cases labeled neurons of medium and small sizes were equal in number, and the neurons of the IP constituted about 10% of the total number of the spinal projection neurons. The present study suggests that the neurons of the M and the IP, including those of the intermediate group located between the two, project the bulk of the crossed descending fibers as far caudally as the C2 and the C3 segments.

Scanning electron microscopy of the third ventricular wall in the lamprey, Lampetra japonica

The third ventricular wall and its adjacent region of the arctic lamphrey, Lampetra japonica, were studied by scanning electron microscopy to elucidate their surface fine structures. The specimens were caught in the mouth of the river during their anadromous migration. The ventricular wall is covered entirely with the cilia of ependymal cells, with the exception of the ventral side of the lateral wall, the floor of the recessus infundibuli and a portion of the recessus posteriosus. In the ependymal layer covering the ventral side of the lateral wall, numerous protrusions of neurons are found equipped with microvilli and cilia. These neurons seem to correspond to the liquor-contacting neurons. Ependymal cells identified as tanycytes occur in the posterior portion of the floor of the recessus infundibuli. The apex of the tanycyte is provided with numerous microvilli and a bundle of cilia, while its basal projection extends towards the outer layer of neurohypophysis to make contact with the capillary wall. A small spherule considered to be a secretory substance is observed near the root of the ciliary bundle. tthe recessus posteriosus consists of a layer of ependymal cells and neurons with an apical projection into the ventricular cavity. Possible intraventricular macrophage (Kolmer cell) is found in the lamprey.