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Notes: Summary To reveal the organization and relative magnitude of connections from various parts of the cerebral cortex to the cerebellar paramedian lobule via the pontine nuclei, horseradish peroxidase conjugated to wheat germ agglutinin was injected in the paramedian lobule in conjunction with injection of the same tracer in various parts of the cerebral cortex in 14 cats. Termination areas of cortical fibres (anterogradely labelled) and pontine neurons projecting to the paramedian lobule (retrogradely labelled) were carefully plotted in serial sections through the pons. On the average 89% of all labelled cells were found in the pontine nuclei contralateral to the cerebellar injection, 11% in the ipsilateral pontine nuclei. The highest degree of overlap between anterograde and retrograde labelling was found after injections in the posterior sigmoid gyrus (SmI), while less overlap was found after injections of the anterior sigmoid gyrus (MsI). Injections of the second somatosensory area (SmII) and the parietal association cortex (areas 5 and 7) gave moderate degrees of overlap. Very little or no overlap was found after injections of the premotor cortex (area 6), the visual areas 17, 18 and 19 and the auditory cortex (AI and AII). It is concluded that a major cortical input to the paramedian lobule arises in the posterior sigmoid gyrus (SmI), but that additional contributions arise in the anterior sigmoid gyrus (MsI), the parietal areas 5 and 7 and the second somatosensory cortex (SmII). Among the latter regions probably the parietal areas contribute most. Overlap between terminal regions of cortical fibres and cells projecting to the paramedian lobule takes place at numerous discrete sites at virtually all rostrocaudal levels of the pons. Cerebrocortical afferents via the pontine nuclei to the intermediate zone of the posterior lobe are organized according to the same principles as described previously for cortical afferents to the hemispheral parts of the posterior lobe (crus I and II).

Notes: Summary This study deals with three different aspects of the organization of connections from the cingulate gyrus to the cerebellum. (1) With the use of wheat germ agglutinin-horseradish peroxidase as a retrograde tracer, the distribution of cingulate neurons projecting to the pontine nuclei was studied. Retrogradely labeled cells were found in layer 5 in all parts of the cingulate gyrus. Average densities of cingulopontine cells were similar in the different cytoarchitectonic subdivisions, although some density gradients were observed. The projection was found to be remarkably strong. Average densities of corticopontine cells in the cingulate gyrus ranged from 500–700 cells per mm2 cortical surface, and the total number of neurons was in the range of 75000–105000 (n=4). (2) A topographical organization of terminal fields of fibers originating in different parts of the cingulate gyrus was demonstrated with the combined use of anterograde degeneration and anterograde transport of wheat germ agglutinin-horseradish peroxidase. Terminal fibers originating in different zones of the cingulate gyrus were distributed in a patchy mosaic within a narrow band along the ventromedial aspect of the pontine nuclei. (3) We confirm, with the combined use of lesions in the cingulate gyrus and injections of wheat germ agglutinin-horseradish peroxidase in the ventral paraflocculus, that there is considerable overlap between terminal fibers originating in the cingulate gyrus, and cells retrogradely labeled from the ventral paraflocculus. The role of the ventral paraflocculus as a receiver of “limbic” input is discussed.

Notes: Summary The distribution of degenerating fibres in the nucleus reticularis tegmenti pontis (N.r.t.) has been examined in Nauta (1957) impregnated sections from cats with discrete lesions of various cortical regions. The following cortical regions send fibres to the N.r.t.: Ms I, Sm I, Sm II, the orbital gyrus, the proreate gyrus, the parietal cortex and parts of the medial surface of the frontal lobe. The projection is bilateral, but mainly ipsilateral. The main terminal area of fibres from all cortical regions mentioned is the ventral part of the N.r.t. at middle rostrocaudal levels. Within this territory most cortical regions have their particular terminal sites in the N.r.t., but there is considerable overlapping. The anatomical organization and the role of the N.r.t. as a cerebrocerebellar relay station are discussed. The regions of the N.r.t. not receiving cortical fibres are supplied by fibres from other sources. These fibre groups have their preferential, although overlapping, areas of termination. In its organization the N.r.t. differs markedly from the pontine nuclei proper. Like the two other precerebellar reticular nuclei the N.r.t. appears to provide possibilities for an integration of impulses from the cerebral cortex with those from many other sources before they influence the cerebellum.

Notes: Summary Small lesions (in some cases bilateral) were made in the cerebral primary sensorimotor region in altogether 21 adult cats and the ensuing degeneration in the pontine nuclei was studied with the silver impregnation methods of Nauta and Glees. Using thermocoagulation it was possible to obtain lesions restricted entirely to particular cortical regions (for example the “hindlimb region” in the posterior sigmoid gyrus). The main results are as follows: 1. All parts of the primary sensorimotor region send fibres to the pontine nuclei. The projections from the posterior part of the posterior sigmoid gyrus and the posterior part of the coronal gyrus are relatively scanty. 2. The cortical “motor” area (the anterior sigmoid gyrus and the anterior part of the coronal gyrus) and the “sensory” area (the posterior sigmoid gyrus and the posterior part of the coronal gyrus) do not project to identical pontine regions, although both projections are organized in principally the same way. 3. The “motor” and “sensory” areas both project in a somatotopical manner onto two longitudinally oriented sharply delimited columns. In both projections one column is located medial and one lateral to the longitudinal fibre bundles of the corticospinal and corticobulbar tracts. Within the medial columns the “hindlimb” is represented ventrally with “face” most dorsally, within the lateral columns the “hindlimb” is located most caudally, with “forelimb” and “face” successively more rostrally. 4. The present results are in agreement with physiological observations on the cerebrocerebellar relations, but show that the pontine projection from the primary sensorimotor cortex is organized in a more complex manner than hitherto assumed.

Notes: This study deals with the three-dimensional arrangement of populations of pontocerebellar cell bodies projecting to the parafloccular complex. The fluorescent tracers rhodamine B isothiocyanate, fluoro-gold and fast blue were injected in either adjacent or separated cerebellar folia. A set of coordinates (x, y, z) was assigned to each retrogradely labelled cell and the total distribution reconstructed and displayed on a graphics workstation. At a large scale, we found that the majority of the cells of each labelled population (all projecting to the same folium) were confined to a lamella-shaped tissue volume. Each lamella extended from medial to lateral, and accordingly followed the curving of the pontine grey around the corticospinal and corticobulbar fibre tracts. At a smaller scale, i.e. within each lamellar subspace, the neurons belonging to one labelled population were distributed in aggregates of various shapes. To enable further analysis of the shapes of the intralaminar aggregates, we developed a computer program for unfolding of the lamellae, based on cubic B-spline approximation. The flattened reconstructions were three-dimensional polygonal windows, circumscribing the large majority of the labelled cell swarm (usually 70–80% of the total number of labelled cells in one population). The present findings, taken together with previous data on a gradual, rather than disjunctive, shift of pontocerebellar neuronal position in relation to a gradual shift of target region (Bjaalie et al., Anat Rec, 231, 510–523, 1991), suggest that the cerebropontocerebellar system may be organized according to a set of fairly simple topographic rules.

Notes: The pathway from the mamillary complex to the cerebellum via the pontine nuclei has been studied using several anterograde and retrograde tracing techniques in the cat. We have also compared the pontine terminal regions of fibres from the mamillary complex and from the cingulate gyrus.Implantations of crystalline horseradish peroxidase wheat germ agglutinin (HRP-WGA) in the mamillary complex and lesions of the cingulate gyrus were combined in the same animal with injections of HRP-WGA, rhodamine-B-isothiocyanate (RITC), and Fluoro-Gold in different parts of the cerebellar hemisphere.Fibres from both the mamillary complex and the cingulate gyrus terminate mainly within a transversely oriented, c-shaped band in the ipsilateral, rostral pontine nuclei. Within this band the terminal fields of fibres from the mamillary complex and the cingulate gyrus form a mosaic-like pattern of partly overlapping patches. Pontine regions receiving a mamillary input project mainly to the ventral paraflocculus, and to a lesser degree to the dorsal paraflocculus, but apparently not to the uvula or crus II. Judging from the literature it seems highly unlikely that other parts of the cerebellar hemispheres receive projections from these pontine regions. Fibres from the ventral paraflocculus were shown to terminate in the parvicellular part of the lateral cerebellar nucleus only.The present findings would seem to imply that inputs from the mamillary complex and a related cortical region, the cingulate gyrus, are partly integrated, partly kept separate at the precerebellar level. This would ensure that small groups of cells in the rostral pontine nuclei receive a specific set of afferents. Conceivably, the information transmitted to the cerebellum by these groups of pontine cells might be related to functions of the mamillary complex, such as learning, motivation, and spatial memory.

Notes: Summary The electron microscopical changes occurring in the pontine nuclei following unilateral lesions of the primary sensorimotor cortex have been studied in 7 cats with a survival time from 2–23 days. A description is also given of the fine structure of the pontine regions in receipt of the fibres. These regions are shown in Fig. 1. The study shows that the boutons are practically only in synaptic contact with dendrites. The bouton density on these is only 16%. The boutons are of the en passage and terminal type, with the latter as the most common (Figs. 4a-e). The synaptic vesicles are rounded or elongated. The formaldehyde fixed material had 17.8% boutons with vesicles of the elongated type; the material fixed with a mixture of formaldehyde and glutaraldehyde had only 11.5% of such boutons. The degenerating boutons show the dark type of reaction and the majority of the corticopontine fibres are of the type shown in Figs. 4d and 4e. Astrocytes and microglial cells participate in the removal of degenerating boutons and terminal fibres. Degenerating boutons are present even at the 23 day stage and some have apparently only started to degenerate.

Notes: Summary A quantitative electron microscopic immunocytochemical method was used to study the synaptic handling of glutamate and GABA in slice preparations from the rat pontine nuclei. Slices were subjected to a depolarizing stimulus (55 mM K+, 20 min) in the presence of a physiological or low Ca2+concentration. Depolarization at physiological [Ca2+] evoked a depletion of glutamate-like immunoreactivity from nerve terminals that contain round vesicles and establish asymmetric synaptic contacts. When depolarization was induced in the presence of only 0.1 mM Ca2+ (10 mM Mg2+ added), the loss of glutamate was significantly reduced or abolished, indicative of a Ca2+dependent component of glutamate release. By means of a double labeling immunocytochemical method we could identify a population of nerve terminals that displayed strong GABA-like immunoreactivity, and a level of glutamate like immunoreactivity that was low but yet clearly above background level. This type of terminal contains elongated or pleomorphic vesicles and establishes symmetric synaptic contacts. In these terminals, depolarization evoked a Ca2+-dependent depletion of GABA like immunoreactivity, but failed to change the level of glutamate like immunoreactivity. The present study demonstrates that two different types of nerve terminal in the rat pontine nuclei contain releasable pools of glutamate and GABA, respectively, and that the GABA releasing terminals also contain a non releasable pool of glutamate. The glutamate of the latter pool could act as precursor of GABA.

Notes: This study applies terms and methods for describing spatial interactions between multivariate spatial point patterns, which are, to our knowledge, new in neurobiology. We consider two categories of points, type 1 and 2, distributed within a certain reference volume (such as a nucleus of the brainstem or a cortical area). The points may, for example, represent different categories of labelled cells or axonal fields of termination. We say that there is spatial neutrality between points of type 1 and 2 if the types are signed by random labelling. If a mechanism drives the two point categories together, we say that the point patterns are positively associated. Conversely, if a mechanism drives type 1 and 2 points apart, we say that they are segregated. By comparing two cumulative distribution functions of distances between points, we can distinguish neutrality, positive association, and segregation. One function, H12(t), is the cumulative distribution function of the distance t between a pair of randomly selected points of type 1 and 2. The other, H00(t), is the corresponding function for a pair of points randomly selected without reference to type. Plots of the estimated difference between these two functions give an indication of positive association, neutrality, or segregation. A statistical test, based on simulations of random (neutral) distributions, can be used to see whether deviations from neutrality are significant.We apply the analysis described above to a major pathway of the brain, namely the ponto-cerebellar projection. Different types of cells in the pontine nuclei are retrogradely labelled with the fluorescent tracers Rhodamine-B-isothiocyanate, Fluoro-Gold, and Fast Blue. The tracers are injected in adjacent or more distant folia of the cerebellar paraflocculus. The location of the somata of labelled cells are recorded and the total distribution reconstructed in three dimensions and displayed on a dynamic graphics workstation. We ask whether different units (folia) in the paraflocculus receive information from the same population, from two different positively associated populations, or from segregated cell populations. We find a statistically significant tendency for cell populations projecting to adjacent folia to be positively associated, although there are few cells containing multiple labels. Populations of neurons projecting to folia wider apart are significantly segregated. From inspections of the reconstructions, using real-time rotations, we find that the swarms of labelled neurons tend to accumulate in shells or lamellae in the pons. Within the lamellae, the cells are aggregated in clusters and bands with empty holes (containing unlabelled ponto-cerebellar cell bodies, presumably projecting to other cerebellar targets) in between. By determining the average distance to a reference plane for each cell population, we find that cell populations shift in a ventro-medial direction as the injection sites move from the medial part of the dorsal paraflocculus toward the lateral part and into the ventral paraflocculus. We therefore conclude that there is a continuous shift in location of ponto-cerebellar cell populations, corresponding to specific shifts in cerebellar target regions.

Notes: Summary Muscle fiber diameters and number of capillaries per fiber, per mm2 and around each fiber were determined in needle biopsies from the lateral part of the quadriceps muscle of 11 young women. Six subjects were untrained (UT) and five were endurance-trained athletes (ET). Average values for maximal oxygen uptake were 43.9 (UT) and 62.1 ml/kg×min (ET). Mean fiber diameter was somewhat smaller in the UT than in the ET group (39.1 and 42.7 Μm), but the difference was not statistically significant. Fibers with the highest content of mitochondria were on the average 9 Μm thicker than those with the lowest content. The capillary per fiber ratios were 1.11±0.07 (mean±S.E.) and 1.69±0.13 in the UT and ET groups, respectively. The number of capillaries around each fiber was 3.04±0.17 (UT) and 4.42±0.31 (ET). After correction for shrinkage the number of capillaries per mm2 was 301 (UT) and 404 (ET). The capillary per fiber ratio increased with increasing fiber diameter and with the content of mitochondria.