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PubMed2026

Alternative splicing in layer 3 pyramidal neurons differs across regions of the human cortical hierarchy.

The primate neocortex is organized as hierarchical networks of functionally distinct regions. In the dorsal visual stream network, information is conveyed from primary visual (V1) to posterior parietal (PPC) and dorsolateral prefrontal (DLPFC) cortices. This information transfer is mediated primarily by layer 3 pyramidal neurons (L3PNs), which differ across these regions in morphology, excitability, and intracellular Ca2+ regulation. These region-specific L3PN properties may be influenced by alternative splicing (AS) of pre-mRNA, which occurs extensively in the human brain. To explore the potential impact of AS of region-specific L3PN properties, we analyzed RNA-seq data from pools of L3PNs dissected from human V1, PPC, and DLPFC. We found that <6% of genes with regional differences in expression also differed in AS. This finding indicates that the absence of transcriptional differences is insufficient to conclude that a gene does not contribute functional differences between regions. Additionally, there were numerous regional differences in AS, particularly between V1 and DLPFC or PPC L3PNs, which involved genes associated with neuron morphology and Ca2+ regulation; > 90% of these AS differences involved functionally relevant sequences (eg phosphorylation sites, etc.). These findings suggest AS contributes to region-specific L3PN properties relevant to the function of the dorsal visual stream.

Humans↗

PubMed1979

The projection of the lateral geniculate nucleus to area 17 of the rat cerebral cortex. V. Degenerating axon terminals synapsing with Golgi impregnated neurons.

The sites of termination of afferents from the lateral geniculate nucleus to layer IV and lower layer III in area 17 of the rat visual cortex have been determined by use of a combined degeneration--Golgi/EM technique. Degeneration of geniculocortical axon terminals was produced by making lesions in the lateral geniculate body. After the animals had been allowed to survive for two days, the ipsilateral visual cortex was removed and impregnated by the Golgi technique. Suitably impregnated neurons and their processes in layer IV and lower layer III were then gold-toned and deimpregnated for examination in the electron microscope. A search was made for synapses between degenerating axon terminals and the gold-labelled postsynaptic neurons. Geniculocortical synapses were found to involve: (1) the spines of basal dendrites as well as those of proximal shafts and collaterals of apical dendrites of layer III pyramidal neurons; (2) the spines of the apical dendritic shafts and collaterals of layer V pyramidal neurons; (3) the perikaryon and dendritic spines of a sparsely-spined stellate cell; and (4) the perikaryon and dendrites of a smooth, bitufted stellate cell. In view of this variety of postsynaptic elements it is suggested that all parts of the perikarya and dendrites of neurons contained in layer IV and lower layer III which are capable of forming asymmetric synapses can be postsynaptic to the thalamic input. Finally, an analysis of the known neuronal interrelations within the rat visual cortex is presented.

Afferent Pathways↗

PubMed1979

Intrinsic organization of snake dorsomedial cortex: an electron microscopic and golgi study.

The cellular populations present in dorsomedial cortex in the snakes Constrictor constrictor, Natrix sipendon and Thamnophis sirtalis are described at the light microscopic level using Nissl and Golgi preparations as well as at the ultrastructural level. This area plays a central role in cortical organization in snakes by participating in major commissural and association projections. Systematic analyses of Golgi preparations indicate that five populations of neurons are present in dorsomedial area and have a preferential laminar distribution. Layer 1 stellate cells have somata positioned in the center of the outermost cortical layer, layer 1. Their dendrites are confined to this layer. Double pyramidal cells have their somata loosely packed in layer 2. Their dendrites bear a moderate population of spines, ascending through layer 1 to the pial surface and descending partially through layer 3. Some double pyramidal cells have somata displaced downwards into the upper third of layer 3. These neurons closely resemble the layer 2 double pyramidal cells. Layer 3 stellate cells have somata positioned in the middle third of layer 3. Their dendrites extend in all directions throughout layer 3 and through layer 2 into layer 1. Finally, horizontal cells have their somata positioned deep in layer 3, near the ventricle, and dendrites aligned concentric with the ventricle. Comparison of the organization of the known afferents to dorsomedial area with the distribution of the five cell types suggests that the laminations of both afferent fibres and dorsomedial neurons places specific neuronal populations in synaptic contact with specific sets of afferents.

Animals↗

PubMed1979

Ultrastructure of neurons in the auditory cortex of ageing rats: a morphometric study.

The cell bodies of pyramidal cells in layers II and V of rat auditory cortex were quantitatively examined in groups of rats 3, 6, 15, 23, 27 and 34-36 months of age. The mean diameters of cell bodies of both layer II and layer V neurons, as measured in 1 micron plastic sections, increased between 3 and 15 months of age, then decreased to a diameter that was less in the 36-month-old than in the 3-month-old rats. Morphometry of the nuclei of the cells was done by measuring nuclear area and nuclear envelope length directly on electron micrographs. In the layer II cells, neither parameter changed with advancing age. In the layer V cells, the mean nuclear area decreased significantly in the old animals and the mean envelope length increased. Point-counting techniques were applied to electron micrographs of cell bodies to determine the relative volume of selected organelles, inclusions and ground substance in the perikaryal cytoplasm. In this part of the study the chronological pattern of change in layer II and layer V pyramidal cells was similar. The relative volume of dense bodies increased linearly with advancing age, with a slightly more accelerated rate in layer II cells. The relative volume of ground substance remained essentially constant through 27 months, and then at 34-36 months decreased to 83% and 89% of the three-month level in layer V and layer II, respectively. The relative volume of the rough endoplasmic reticulum (RER) did not change significantly until after 15 months, at which time it began to occupy increasingly a larger fraction of the perikaryal cytoplasm. Finally, the relative volumes of mitochondria, multivesicular bodies and Golgi apparatus did not show clear trends of change during the 33-month period.

Aging↗

PubMed1975

Corticothalamic neurons and thalamocortical terminal fields: an investigation in rat using horseradish peroxidase and autoradiography.

Subsequent to thalamic injections in rats of horseradish peroxidase (HRP) alone or HRP and [3H]leucine in combination, the cells of origin of the corticothalamic projections and the terminal fields of the thalamocortical projections were identified. HRP-labeled corticothalamic neurons were uniformly found in layers V and VI. They were medium to small in size and always pyramidal in shape with the larger neurons being found in layer V. On the other hand, 3 different patterns for the distribution of thalamocortical terminal fields were observed. The autoradiographic material indicated that in prefrontal cortex the bulk of thalamocortical fibers terminate in layer III while in motor cortex they terminate primarily in layer V. A third pattern was shared by temporal, occipital and parietal cortex where the bulk of thalamocortical fibers terminate preferentially in layer IV. The data derived from the rats which had received thalamic injections of HRP and [3H]leucine in combination indicated that the connections between cortex and thalamus are in general reciprocal. These results are discussed with regard to earlier studies using classical or more recently developed neuroanatomical methods.

Animals↗

PubMed1977

Complexity of branching dendritic trees: dependence on number of trees per cell and effects of branch loss during sectioning.

We have investigated whether the complexity of dendritic trees is correlated with the number of primary dendrites per neuron (trees per cell). In estimating the average number of branches of centrifugal orders 1-5 per tree we used statistical methods to compensate for loss of parts of trees during sectioning. Limitations of these methods are discussed. Neurons from four populations, stained by the Golgi-Cox method, were examined: stellate cells from layer IV, area 17 of visual cortex, in normal and dark-reared cats; the pyramidal cells from layer V, somatosensory cortex, in two strains of rats. In all four groups of neurons the average number of branches of higher orders (3, 4, 5) per tree tended to be smaller in neurons bearing more trees. Thus all trees from a population of neurons should not be assumed to be equivalent. The decreasin high-order branches per tree tended to offset the increase in number of trees per cell. In three of the four groups these opposed tendencies maintained the average number of high-order branches per neuron nearly independent of the number of trees per cell. Natural selection may have favoured near-constancy in the number of high-order branches to reduce dispersion among neurons of one type in functional input-output rleations.

Animals↗

PubMed1979

The cochlear nuclei in man.

The human cochlear nuclei are composed of a ventral and a dorsal nucleus which are similar, though not identical, in their cytoarchitecture to those of other mammals. The ventral cochlear nucleus (VCN) consists of a rostral area of spherical cells, a central area of multipolar and globular cells, a posterior area of octopus cells, and laterodorsal cap of small neurons. The interareal boundaries are less distinct in man than in the cat. The central region of multipolar cells and the cap area of small cells constitute the bulk of the human VCN. The spherical, globular, and octopus cells appear relatively less numerous in man than in other mammals. The dorsal cochlear nucleus (DCN) in man is relatively large, but lacks the typical stratification seen in other mammals, with only vestiges of the granular and molecular layers remaining. Virtually the entire DCN consists of an area of cochlear fiber neuropil containing pyramidal cells, small neurons, and occasional giant cells. The pyramidal cells have lost their typical radial orientation and lie scattered within the cochlear neuropil. Thus the entire human DCN may be equivalent to layers 2 and 3 of this nucleus in other mammals. In spite of the relatively large DCN, the acoustic striae appear small. This is in contrast to the large trapezoid body leaving the VCN. Intrinsic and descending fiber pathways to the cochlear nuclei are not clearly defined and may be less prominent in man than in the cat.

Acetylcholinesterase↗

PubMed1978

Projection from area 3a to the motor cortex by neurons activated from group I muscle afferents.

Two receiving areas in the pericruciate cortex are known for inputs from group I muscle afferents of forelimb nerves. One focus is near the postcruciate dimple of area 3a, and the other in the lateral sigmoid gyrus of the motor cortex (area 4gamma). The cortico-cortical projection of area 3a to 4gamma, and the relay by this projection of group I muscle afferent input to the motor cortex were investigated in cats. The following results were obtained. 1. Seventy-four neurons within area 3a were antidromically activated by intracortical microstimulation of the motor cortex. 2. Although excitation evoked by stimulation of group I muscle afferents could be demonstrated for only a few (8 of 48) cortico-cortical neurons in extracellular recordings, due to the methodological limitations discussed, this input evoked EPSPs in 8 of 9 cortico-cortical neurons recorded intracellularly. Therefore, it is likely that the majority of neurons projecting from area 3a to the motor cortex have an excitatory synaptic input from group I afferents. 3. Neurons projecting from area 3a to the motor cortex were most commonly found in cortical layer III, although some were found in layer V. 4. Five of nine pyramidal tract neurons of area 3a had a strong excitatory synaptic input from group I muscle afferents. 5. A new type of pyramidal tract neuron was found which has cortico-cortical axon collaterals connecting the two cytoarchitectonic regions. These various neurons may be part of a feedback system from muscle afferents to the motor cortex.

Afferent Pathways↗

PubMed1978

Quantitative visualization of gamma-aminobutyric acid receptors in hippocampus and area dentata demonstrated by [3H]muscimol autoradiography.

Muscimol, a potent gamma-aminobutyric acid (GABA) agonist, was used in a radioactively labeled form for the quantitative localization of GABA receptors in the rat's hippocampus (CA(1) to CA(4)) and area dentata. [(3)H]Muscimol was injected directly in vivo or used in the incubation medium of tissue slices, and the tissues were then fixed and prepared for autoradiography. [(3)H]Muscimol-bound GABA receptors are weakly though evenly distributed over the fimbria of the fornix. There was a laminar distribution in CA(1) to CA(4) and the area dentata, with an increasing density of the GABA receptors in that order. The lowest density was found in the alveus of CA(1) and CA(2) and the highest in the stratum granulosum of the area dentata. The greatest density was found in the neuropil between granule cells, in which are found dendrites and the basket-like plexuses of the inhibitory GABA-containing local circuit neurons. The molecular layers of the area dentata, CA(1), and CA(2) also have a high density of GABA receptors, indicating a probable distribution over the dendrites of granule and pyramidal cells. The laminar distribution of GABA receptors in the hippocampus and area dentata is similar to the distributions of the GABA-synthesizing enzyme, glutamate decarboxylase, and of GABA previously published. Neurons with label of various density are found in the polymorphic cell layer of the area dentata, in the stratum radiatum of CA(3), and in CA(4). These are possibly the GABA-containing basket local circuit neurons.

Amanita↗

PubMed1977

Age-related deterioration of pyramidal cell basal dendrites in rat auditory cortex.

The basal dendritic trees of layer V pyramidal cells in the rat auditory cortex were examined quantitatively in a group of 3-month-old and a group of 34- and 36-month-old rats. Two forms of analysis were used on the Golgi preparations: (1) the number of intersections between the basal dendrites and a series of concentric circles whose common center lies over the perikaryon center, and (2) the number of dendritic branches, by order, per neuron. The data indicate that in the old animals the density of the dendritic tree has decreased significantly within a radius of about 150mu of the perikaryon, yet the extent of the dendritic domain has not changed appreciably. Analysis of the dendritic branching suggests that there has been a deterioration not only in the peripheral branches of the dendritic tree, but also that entire dendrites have been lost. This loss of primary branches was confirmed through the reconstruction of layer V neuronal perikarya and their proximal dendrites from 1-mu plastic serial sections of auditory cortex. Concomitant with the loss of dendrites which accompanies advancing age is a tendency for the perikaryon to be smaller, but not distorted, in the old animals.

Aging↗

PubMed1979

[Classification of nerve cell forms in lamina IV of the visual cortex of albino rats using Nissel preparation with the help of automatic picture processing].

1) Using the automatical picture processing device "MORPHOQUANT", VEB Carl Zeiss Jena, layer IV of the adult albino rat's area 17 was investigated in Nissl-preparations to classify pyramidal and stellate cells on the basis of quantitative features. 2) A review is given about the applied computer programme. 3) 30 seconds are necessary for adjustment, measurement and statistical calculation. 4) Five features per neuron soma were registered and statistical calculated: neuron area in picture points (KOFL), mean value of extinction (EXTM), total extinction (EXTS), shape (i.e. dia ratio, DMVH), and the distribution of strong coloured particles (i.e. centricity, ZNTR). 5) High statistical significance could be achieved only with regard to the neuron area and the distribution of strong coloured particles. 6) The causes for different results obtained in previous and present measurements and the importance of differentiation between several types of neurones are discussed as well.

Animals↗

PubMed1975

Cytoplasmic inclusions of neurons in the monkey visual cortex (area 19).

Several unusual neuronal inclusions were found in certain cells of the rhesus monkey visual cortex (Area 19): 1. Filamentous bodies, present in the small stellate cells of layer IV, globoid, 0.3-0.6 mum in diameter, consisting of fine 50 A filaments in a hexagonal meshwork. These are often associated with the labyrinthine bodies. 2. Labyrinthine bodies found exclusively in the small stellate cells of layer IV, including certain neurons with dispersed ribosomes. These are 0.4-0.7 mum in diameter and consist of 900 A wide tubes which interconnect with one another. The walls of these tubes are continuous and made up of a sheet or honeycomb lacework of small hexagonal 150 A subunits. 3. This inclusion, an aggregate 0.3-0.7 mum in size, consists of small membrane-bounded vesicles with a single dense granule associated with other non-membrane bound small dense droplets. The inclusions are always associated with the maturing face of the Golgi complex of certain layer IV pyramidal cells; as such, they may be an unusual product of the Golgi apparatus. These observations were confirmed by examination of stereo pairs of electron micrographs. Speculations are made with regard to possible functions for these inclusions.

Animals↗

PubMed1975

Long-lasting facilitation of a synaptic potential following tetanization in the in vitro hippocampal slice.

Field potentials evoked by stimulation of afferent fibers in stratum radiatum were recorded in the CA1 region of the hippocampal slice maintained in vitro. Stimulation rates of 3-50/sec produced a large increase in amplitude of the population spike in CA1. This increase was maintained for several hours after the tetanization. The facilitation phenomenon appeared to be specific to the synapse of stratum radiatum afferents onto CA1 pyramidal cells since: (1) stimulation outside the radiatum layer did not produce the effect, (2) antidromic field potentials recorded in CA3 were unchanged, (3) EPSP threshold in CA1 was unchanged, and (4) alveus tetanization did not produce a facilitatory effect.

Animals↗

PubMed1979

Differential radiosensitivity of neurons and neuroglia of the hippocampus in the adult rabbit.

Adult rabbits were subjected to 4.5 Gy of whole-blody or brain alone gamma-irradiation, and their hippocampus was examined with the light and electron microscope. Pycnotic cells were found at the base of the granular layer of the dentate gyrus in the so-called subgranular zone, as soon as 3 h after irradiation, and were cleared up by active phagocytosis after 48 h. Some of these cells appeared as undifferentiated, whereas others were differentiating granule cells, and possibly immature neuroglia. The extent of cell necrosis was contingent upon the age of the animal, the oldest animal studied (27 months) showing only sparse lesion of that type. Astrocytes and microglia were responsible for the phagocytosis of dead cells. Another type of lesion was found in the nuclei of the mature granule cells and consisted of light spots which appeared 1 h after the irradiation and disappeared almost completely after 48 h. Pyramidal cells did not show any of these two lesions. It is concluded that the laterations in the electrical activity of pyrimidal cells, following irradiation, are at least partly due to lesions affecting the dentate gyrus. Radionecrosis in the subgranular zone is related to the presence of immature cells in this region.

Age Factors↗

PubMed1979

Anatomical and functional aspects of the associative projections from somatic area SI to SII.

1. Electrophysiological and morphological (retrograde axonal transport of horseradish peroxidase, HRP) experiments have been carried out in the cat in order to study the associative projections from area SI to ipsilateral SII. 2. Microelectrode recordings were performed in the forepaw focus of SII both in normal (64 units) and in SI-undercut (51 units) cats. 29.6% of the neurons recorded in the unoperated and 29.4% of those collected in the operated cats were excited by electric stimulation of the ipsilateral SI (forepaw focus). In both preparations almost all such units were endowed with large (either contra- or bilateral) receptive fields (RF). Cell population recorded in the SI-undercut cats showed no significant impairment to peripheral stimuli and/or changes in the size of the RFs. 3. From the forepaw focus of SI, 150 units have been recorded and tested by stimulation of the homologous focus of the ipsilateral SII. Eight of them were fired antidromically and thus identified as association cells. Their RFs were very small and located only in the digits of the contralateral forepaw. 4. Both single or multiple HRP injections were performed in SII. Retrogradely labelled cells were found in the ipsilateral SI. The great majority of association cells are pyramids and dwell mainly in layer III. In spite of the large diffusion of the exogenous reaction product in the injected SII and of the presence of retrogradely labelled cells anywhere in the ipsilateral thalamic VB complex, the distribution of association cells is unequal throughout SI since they strongly predominate in the digit zone of the forepaw representation.

Animals↗

PubMed1978

Properties of the pyramidal tract neuron system within the precentral wrist and hand area of primate motor cortex.

1. To obtain basic anatomical data that will be useful in interpreting the results of studies of primate pyramidal tract neurons (PTNs), extracellular, single-unit recording techniques were used to determine a number of the properties of the PTN population within the electrically defined, precentral wrist zone of the monkey's motor cortex. 2. Recordings were obtained from a total of 1,375 antidromically identified PT and corticospinal tract (CST) cells. A mathematical model was then used to correct the statistics of the sample for variations in the probability of unit detection, which arise from variations in neuronal size and extracellular field dimensions. 3. Both the experimentally observed and theoretically corrected results suggest that the PT projection from this cortical zone is derived principally from slowly conducting, and presumably small to medium-sized cells (an estimated 85% of the resident PTN population). 4. Both the fast and slow cell subpopulations were found to be concentrated within cortical layer V, where they tend to congregate in small, mixed clusters of 2 to 5 neurons. Estimates of the total packing density of PTNs within layer V of this cortical zone suggest that they account for only 10-20% of the neurons within this major efferent layer. 5. 70% of the slow and 82% of the fast PT neurons within this cortical area were found to send their axons into the contralateral, lateral corticospinal tract. Thus, in futur functional studies of PTNs in this cortical area, it can be assumed that three of every four neurons will in fact influence segmental cells of one category or another directly. 6. Extensive data are also presented on the incidence of axon collateral branching from PT and CST cells to the red nucleus, the medial medullary reticular formation and the cuneate nucleus. 7. Some general implications of these findings for the design of future functional studies of anatomically identified motor cortex cell systems are then discussed.

Action Potentials↗

PubMed1979

Cortical neurons projecting to the pontine nuclei in the cat. An experimental study with the horseradish peroxidase technique.

Horseradish peroxidase (HRP) injections in various portions of the cat pontine nuclei resulted in retrograde labeling of neurons in layer V of the ipsilateral cerebral cortex. Corticopontine neurons, pyramidal in type, have been found to be labeled in the entire cortex, confirming the previous findings of anterograde degeneration studies. Most (91%) of the labeled cells were 14--26 micrometer in diameter (mean 19.4 +/- 4.5 micrometer SD). Small (10--20 micrometer) and medium (20--40 micrometer) cells represent 51.5% and 47.7%, respectively, of the total number of the labeled neurons. The populations of the neurons of various sizes were almost identical in different cortical areas, and were different from the populations of corticoreticular and corticospinal cells. Corticopontine cells were well labeled in experimental cases of 3-days' survival time, confirming the topographical organization established previously by degeneration studies for this projection system. However, in cases of shorter survival time (20--27 h), the number of labeled neurons was very small. The relative paucity of labeled corticopontine neurons in the sigmoid and lateral gyri is discussed with reference to other cortical descending neurons (e.g., the corticotectal, corticoreticular and corticospinal) which have hitherto been identified morphologically as well as physiologically.

Animals↗

PubMed1979

The projection of the visual cortex on the Clare-Bishop area in the cat. A degeneration study with the electron microscope.

Following large lesions of the cat visual cortex, the distribution of degenerating terminal boutons in the Clare-Bishop area was studied electron microscopically. Degenerating boutons were found throughout the cortical layers but mostly in layer III (51% of the total number of degenerating boutons) and layer V (24%). A smaller number of boutons were found in layers II (12%) and IV (9%), and very few in layers VI (3%) and I (1%). No degenerating terminals were observed in the upper two-thirds of layer I. Seventy-six per cent of the total degenerating boutons terminated on dendritic spines, 22% on dendritic shafts, and 2% on somata. Some degenerating boutons made synaptic contacts with somata and dendrites of nonpyramidal neurons. For example, one degenerating bouton was observed in contact with an apical dendrite of a fusiform cell. Three examples of dendritic spines, with which degenerating boutons made synaptic contracts, were found to belong to spinous stallate cells. No degenerating boutons were observed making synaptic contacts with profiles that could conclusively be traced to pyramidal cell somata.

Animals↗