Morphological variation of layer III pyramidal neurones in the occipitotemporal pathway of the macaque monkey visual cortex

We compared the morphological characteristics of layer III pyramidal neurones in different visual areas of the occipitotemporal cortical 'stream', which processes information related to object recognition in the visual field (including shape, colour and texture). Pyramidal cells were intracellularly injected with Lucifer Yellow in cortical slices cut tangential to the cortical layers, allowing quantitative comparisons of dendritic field morphology, spine density and cell body size between the blobs and interblobs of the primary visual area (V1), the interstripe compartments of the second visual area (V2), the fourth visual area (V4) and cytoarchitectonic area TEO. We found that the tangential dimension of basal dendritic fields of layer III pyramidal neurones increases from caudal to rostral visual areas in the occipitotemporal pathway, such that TEO cells have, on average, dendritic fields spanning an area 5-6 times larger than V1 cells. In addition, the data indicate that V1 cells located within blobs have significantly larger dendritic fields than those of interblob cells. Sholl analysis of dendritic fields demonstrated that pyramidal cells in V4 and TEO are more complex (i.e. exhibit a larger number of branches at comparable distances from the cell body) than cells in V1 or V2. Moreover, this analysis demonstrated that the dendrites of many cells in V1 cluster along specific axes, while this tendency is less marked in extrastriate areas. Most notably, there is a relatively large proportion of neurones with 'morphologically orientation-biased' dendritic fields (i.e. branches tend to cluster along two diametrically opposed directions from the cell body) in the interblobs in V1, as compared with the blobs in V1 and extrastriate areas. Finally, counts of dendritic spines along the length of basal dendrites revealed similar peak spine densities in the blobs and the interblobs of V1 and in the V2 interstripes, but markedly higher spine densities in V4 and TEO. Estimates of the number of dendritic spines on the basal dendritic fields of layer III pyramidal cells indicate that cells in V2 have on average twice as many spines as V1 cells, that V4 cells have 3.8 times as many spines as V1 cells, and that TEO cells have 7.5 times as many spines as V1 cells. These findings suggest the possibility that the complex response properties of neurones in rostral stations in the occipitotemporal pathway may, in part, be attributed to their larger and more complex basal dendritic fields, and to the increase in both number and density of spines on their basal dendrites.     

Quantitative study of primitive pyramidal cells in rat anterior cingular cortex

In the present paper the primitive pyramidal cells of the Vthlayer of the anterior cingulate cortex in adult male white rats were analyzed quantitatively and compared statisticaly with large pyramidal cells of the same region. The number of dendrites, the total lengths of dendrites, the number of spines and the density of spines -- according to the order of dendrites -- show similarity between the primitive pyramidal cells and the large pyramidal cells the latter one exhibit the higher values. The curves of distribution of the various density of spines along the apical main dendrite of both cell types are similar in shape, too. The lengths of the dendritic fields and their basal spines-values are without significant distinction for both cell types, however there are more dendritic fields in large pyramidal cells. Refered to a complete pyramidal neuron they can say: there are significantly higher values in large pyramidal cells for the number of dendrites and their total lengths, the total number of spines, the number of branching sites sites and free endings. However the density of spines of the complete neuron has no significant differences between primitive and large pyramidal cells.     

Postnatal development of pyramidal dendritic and axonal bundles in the visual cortex of the rat

We studied the development and spatial organization of vertically arranged pyramidal dendritic and axonal bundles in the visual cortex of the rat by using extracellular biocytin injections into frontal brain slice preparations. Vertical bundles of intracortical axons could be clearly observed at time of birth with a initial center-to-center distance of 18 microns +/- 3.1 microns. At the same time a clustering of pyramidal cell apical dendrites was completely absent. Dendritic bundles were demonstrated for the first time at postnatal day 5 when the supragranular layer 2/3 begins to differentiate. In the following weeks both axonal as well as dendritic bundles grew continuously and completely in parallel with regard to their center-to-center distances, diameters and number of elements up to their adult values at around postnatal day 90. At adulthood both types of bundles showed a center-to-center distance of 50.1 microns +/- 20.1 microns (axons) and 52.6 microns +/- 18.1 microns (dendrites), respectively. Our results demonstrate that axonal and dendritic bundles originating from the same neurons in the visual cortex of the rat correspond very well with regard to their size and distances. Developing neurons migrating along radial glia fibers group their axons together in fascicles before the lamination of the cortex is completely matured. After all layers have been developed, the apical dendrites of pyramidal cells with aggregated axons also group in clusters. The following development of axonal and dendritic bundles is presumably concerned with the volume increase of the maturating neocortex. Evidence for activity dependent plasticity after eye opening could not be found.     

Cloning of a cDNA encoding the human transforming growth factor-beta type II receptor: heterogeneity of the mRNA

A combined study of anterograde axonal degeneration and Golgi electron microscopic technique was designed to examine the distribution and density of axon terminals from the mediodorsal thalamic nucleus (MD) over layer III pyramidal cells in the prelimbic cortex of the rat. The reconstructive analysis of serial ultrathin sections of gold-toned apical and basal dendrites of layer III pyramidal cells showed that degenerating thalamocortical axon terminals from MD formed asymmetrical synaptic contacts predominantly with dendritic spines of the identified basal dendrites as well as apical dendrites. There was little difference in the numerical density of thalamocortical synapses from MD per unit length of both apical and basal dendrites.     

Morphology of pyramidal neurones in cytochrome oxidase modules of the S-I bill representation of the platypus

The primary somatosensory cortex of the platypus (Ornithorhynchus anatinus) is characterized by a distinct array of functionally specific cytochrome oxidase (CO) modules, forming alternate CO-rich and CO-poor bands. In the current study, we undertook to establish whether the cellular morphology of layer V pyramidal neurones reflects this modular organization. To this end, we injected neurones with Lucifer Yellow in 250 microm thick, flat-mounted cortical slices and processed the tissue to reveal a light-stable reaction product. By aligning blood vessels in serial sections in which we injected individual neurones with sections processed for CO, we were able to establish the exact location of injected cells with respect to the pattern of CO bands. Pyramidal neurones in the CO-poor bands (which are responsive to both mechano- and electroreceptive stimuli) had basal dendritic fields that were larger than those in the CO-rich bands. The large basal dendritic fields of layer V pyramidal neurones in the CO-poor bands may allow for integration of a greater number of more diverse inputs, thus allowing for averaging of stimuli to improve the signal-to-noise ratio or enhance spatial discrimination of peripheral stimuli. In some instances, neurones located within approximately 100 microm of the boundaries of the CO bands had dendritic fields that appeared to conform to the CO bands, the dendrites preferentially arborizing within a single band and avoiding the neighbouring band. However, the bias was not absolute, as we observed many examples of cells with dendrites that crossed the boundary between bands. Furthermore, many cells had dendrites that showed distinct dendritic bias that bore no obvious relationship to the CO boundaries.     

Progressive atrophy of pyramidal neuron dendrites in autoimmune MRL-lpr mice

The autoimmune-prone MRL-lpr substrain of mice develop an autoimmunity-associated behavioral syndrome (AABS) which resembles in many respects the behavior of animals exposed to chronic stress. The present study examined whether these mice show changes in the morphology of neuronal dendrites, as found in animals exposed to chronic stress. A modified Golgi-Cox procedure was used to visualize the dendrites of pyramidal neurons in the parietal cortex and in the CA1 hippocampal field of 5-week and 14-week old MRL-lpr mice and MRL + / + controls. Reduced dendritic branching and length, and an up to 20% loss of dendritic spines were observed in parietal and hippocampal pyramidal neurons of MRL-lpr mice at both ages. In the parietal cortex, there was an age-dependent potentiation in the reduction of basilar, but not apical, dendrite branching and length, as well as in the loss of spines on basilar segments. Loss of spines in the hippocampus followed an age-related course for apical but not basilar dendrites. Moreover, compared to age-matched controls, brain weight was smaller in MRL-lpr mice at 14 but not 5 weeks of age. Considering that dendritic atrophy becomes more extensive when autoimmune disease is florid in MRL-lpr mice, it is proposed that immune/inflammatory factor(s) produce dendritic loss. Reduced dendritic complexity may represent, at least in part, a structural basis for the altered behavioral profile of MRL-lpr mice.     

Recovery of a 62-year-old man from prolonged cold water submersion

Layer III pyramidal neurones were injected with Lucifer Yellow in cortical slices taken from the medial subdivision of the frontal eye field (FEF) of the macaque monkey. The average area covered by basal dendritic fields, in the dimension parallel to the cortical layers, was 115.1 +/- 2.9 x 10(3) microm2, significantly larger than that observed among layer III cells in eye movement-related visual areas of the parietal lobe. Furthermore, the dendritic fields of pyramidal cells in the FEF were considerably more complex than those of their counterparts in the parietal lobe, as evaluated by Sholl analysis. Spine density varied along the basal dendritic tree, reaching a maximum of 8.5 +/- 0.8 spines/10 microm at a distance of 70-90 microm from the centre of the cell body. Such highly complex basal dendritic fields of layer III pyramidal neurones in the FEF may enable the integration of a diverse set of inputs from visual, motor, polysensory and memory-related periprincipal cortical areas.     

A quantitative analysis of the dendritic organization of pyramidal cells in the rat hippocampus

The three dimensional organization of the dendritic trees of pyramidal cells in the rat hippocampus was investigated using intracellular injection of horseradish peroxidase in the in vitro hippocampal slice preparation and computer-aided reconstruction. The total dendritic length, dendritic length in each of the hippocampal laminae, and the number of dendritic branches were measured in 20 CA1 pyramidal cells, 7 neurons in CA2 and 20 CA3 pyramidal cells. The total dendritic length of CA3 pyramidal cells varied in a consistent fashion depending on their position within the field. Cells located close to the dentate gyrus had the smallest dendritic trees which averaged 9,300 microns in total length. Cells in the distal part of CA3 (near CA2) had the largest dendritic trees, averaging 15,800 microns. The CA2 field contained cells which resembled CA3 pyramidal cells in most respects except for the absence of thorny excrescences on their proximal dendrites. There were also smaller pyramidal cells that resembled CA1 neurons. CA1 pyramidal cells tended to be more homogeneous. Pyramidal neurons throughout the transverse extent of CA1 had a total dendritic length on the order of 13,500 microns. The quantitative analysis of the laminar distribution of dendrites demonstrated that the stratum oriens and stratum radiatum contained significant portions of the pyramidal cell dendritic trees. In Ca3, for example, 42-51% of the total dendritic length was located in stratum oriens; about 34% of the dendritic tree was located in stratum radiatium. The amount of dendritic length in stratum lacunosum-moleculare of CA3 varied depending on the location of the cell. Many CA3 cells located within the limbs of the dentate gyrus, for example, had no dendrites extending into stratum lacunosum-moleculare whereas those located distally in CA3 had about the same percentage of their dendritic tree in stratum lacunosum-moleculare as in stratum radiatum. In CA1, nearly half of the dendritic length was located in stratum radiatum, 34% was in stratum oriens and 18% was in stratum lacunosum-moleculare. These studies identified distinctive dendritic branching patterns, in the stratum radiatum and stratum lacunosum-moleculare, which clearly distinguished CA3 from CA1 neurons.     

Regulation of dendritic growth and remodeling by Rho, Rac, and Cdc42

The acquisition of cell type-specific morphologies is a central feature of neuronal differentiation and has important consequences for nervous system function. To begin to identify the underlying molecular mechanisms, we have explored the role of Rho-related GTPases in the dendritic development of cortical neurons. Expression of dominant negative mutants of Rac or Cdc42, the Rho-inhibitory molecule C3 transferase, or the GTPase-activating protein RhoGAP p190 causes a marked reduction in the number of primary dendrites in nonpyramidal (multipolar) neurons and in the number of basal dendrites in neurons with pyramidal morphologies. Conversely, the expression of constitutively active mutants of Rho, Rac, or Cdc42 leads to an increase in the number of primary and basal dendrites. In cortical cultures, as in vivo, dendritic remodeling leads to an apparent transformation from pyramidal to nonpyramidal morphologies over time. Strikingly, this shift in favor of nonpyramidal morphologies is also inhibited by the expression of dominant negative mutants of Cdc42 and Rac and by RhoGAP p190. These observations indicate that Rho, Rac, and Cdc42 play a central role in dendritic development and suggest that differential activation of Rho-related GTPases may contribute to the generation of morphological diversity in the developing cortex.     

The growth of the dendritic trees of Purkinje cells in irradiated agranular cerebellar cortex

The heads of noenatal Wistar rats were irradiated with 200 rads daily from birth to the 10th day post-partum. Ten litters each containing 5 animals were killed at 30 days post-partum and their brains treated by the Golgi-Cox technique. The dendritic trees of 24 Purkinje cells were analysed using the quantitative technique of network analysis, and comparisons made between parameters obtained from 20 normal Purkinje cells. All dendritic trees in agranular irradiated cortex were markedly reduced in size (as indicated by total dendritic length and total number of segments) although mean path lengths were normal. Segment lengths were normal over proximal branches, but uniformly increased over distal branches. Abnormal appendages, called 'giant spines' were observed on many dendrites. They were often some 10 mum in length and their presence effectively reduced segment lengths, increased the frequency of trichotomy and deviated growth from the normal random terminal pattern so that long collateral branching topologies were formed. Nevertheless, trichotomy was uniformly reduced in those trees without 'giant spines' and the distribution of branching patterns suggested that growth had proceeded by random terminal dichotomy. These results demonstrate that the development of dendritic trees is retarded in the agranular irradiated cerebellum, where synaptogenesis is very greatly reduced below normal. The quantitative changes in segment lengths, size of trees, and trichotomy accord with those predicted by the filopodial synaptogenic hypothesis of dendritic growth formulated by Vaughn et al. 99, whilst the results of the topological analysis suggest that branching is established by a degree of non-random interaction between growing dendrites and their substrate. 'Claw-like' dendritic complexes within some Purkinje cell trees may have been induced by aberrent fibre bundles of few surviving granule cells.     

Usefulness of redux properties in acid-resistant bacilli for rapid detection of their growth in culture

The mechanism by which (-) deprenyl enhances cognitive function in Alzheimer's disease (AD) is not yet understood. (-) Deprenyl (0.2 mg/kg/day) was administered intramuscularly to adult male monkeys (n = 6) for 25 days. Control monkeys (n = 6) received physiological saline by the same route. The activity of acetylcholinesterase (AChE) in different brain regions and the dendritic arborization in CA3 pyramidal neurons of hippocampus were analysed. (-) Deprenyl-treated monkeys showed a significant increase in the AChE activity by 43% (p < 0.001) in the frontal cortex, by 39% (p < 0.025) in the motor cortex, by 66% (p < 0.001) in the hippocampus and by 26% (p < 0.05) in the striatum compared to controls. The branching points and the intersections of both apical and basal dendrites of CA3 hippocampal pyramidal neurons were also significantly increased in (-) deprenyl-treated monkeys. Enhanced AChE activity may increase dendritic arborization in the hippocampus and it may also play a role in improving cognitive functions observed in AD, following (-) deprenyl treatment.     

Imaging the structure of the striatum: a fractal approach to SPECT image interpretation

Specimens of human cerebral cortex were obtained during neurosurgical operations and studied by immunocytochemistry and electron microscopy, using antibodies to the metabotropic glutamate receptor subunit mGluR1a and the ionotropic glutamate receptor GluR2/3. A small number of non-pyramidal neuronal cell bodies were labelled for mGluR1a. Double immunolabelling with mGluR1a and GluR2/3 showed that most pyramidal cell bodies were labelled for GluR2/3 but not for mGluR1a. Despite the non-colocalisation of these two receptor subtypes in cell bodies, however, many dendrites and dendritic spines were double-labelled for mGluR1a and GluR2/3 at electron microscopy. As there is evidence that most neurons positive for GluR2/3 are pyramidal cells, this suggests that mGluR1a is present in dendrites of pyramidal neurons, despite absent or low levels of immunoreactivity in their cell bodies.     

Postnatal differentiation of firing properties and morphological characteristics in layer V pyramidal neurons of the sensorimotor cortex

The maturational profile of the firing characteristics of 217 layer V pyramidal neurons of rat sensorimotor cortex, injected with biocytin for morphological reconstruction, was analysed by means of intracellular recordings made between postnatal day (P)3 and 22. Starting from the onset of the second postnatal week, the pyramidal neurons could be differentiated as adapting or non-adapting regular spiking on the basis of the presence or absence of spike frequency adaptation. The percentage of non-adapting regular spiking neurons was very high during the second postnatal week (53%) and progressively decreased with age, concurrently with the appearance of the new class of intrinsically bursting neurons (beginning of the third week) whose percentage progressively increased from 23%, found in P14-P16 rats, to 46% in adult rats. Non-adapting regular spiking neurons were found to share with intrinsically bursting neurons several physiological characteristics comprehending faster action potentials, more prominent effect of anomalous rectification and consistent depolarizing afterpotentials, that differentiated them from the adapting regular spiking neurons. Moreover, intrinsically bursting and non-adapting regular spiking neurons were characterized by a round-shaped distribution of basal dendrites and expanded apical dendritic arborization, that differentiated them from the adapting regular spiking neurons showing a simpler dendritic arborization. These morphological hallmarks were seen in immature intrinsically bursting neurons as soon as they became distinguishable, and in immature non-adapting regular spiking neurons starting from the onset of the second postnatal week. These findings suggest that a significant subpopulation of immature non-adapting regular spiking neurons are committed to becoming bursters, and that they are converted into intrinsically bursting neurons during the second postnatal week, as soon as the ionic current sustaining the burst firing is sufficiently strong. The faster action potentials in both immature non-adapting regular spiking and intrinsically bursting neurons suggest a higher density of Na+ channels in these neuronal classes: the maturational increase in Na+-current, namely of its persistent fraction, may represent the critical event for the conversion of the non-adapting regular spiking neurons into the intrinsically bursting ones.     

The exponentiation formula of reliability and survival: does it always hold?

The dendritic branching pattern of cultured hippocampal neurons was analyzed to obtain mathematical parameters that fit the time-dependent growth of dendrites under limited extrinsic influence. Cultured neurons were stained with a non-toxic carbocyanine dye (diO) and pyramidal-shaped neurons that were physically separated from one another were analyzed at post-plating days 1, 2, 3, 4, 6 and 7. The geometric branching pattern of the dendrites was analyzed using a mathematical model that incorporates random effects in the form of a Galton-Watson branching process where splitting of one branch is statistically independent of the splitting of all other branches, and deterministic effects in the form of a parameter that measures the extent to which dense patterns (clusters) or sparse patterns (elongated trees) are formed. The geometric branching pattern of the dendrites was analyzed using a mathematical model that incorporates random and deterministic effects. The model parameters were estimated via the method of maximum likelihood. The data suggest that in vitro basal dendrites grow according to a purely random branching process without pronounced dense or sparse patterns, while apical dendrites tend to form elongated trees with fewer secondary bifurcations. This trend is quantified, and it depends on the culture conditions in which the neurons are grown. The quantitative assessment of various influences on dendritic growth patterns are discussed.     

Morphological features of the entorhinal-hippocampal connection

The goal of this review in an overview of the structural elements of the entorhinal-hippocampal connection. The development of the dendrites of hippocampal neurons will be outlined in relation to afferent pathway specificity and the mature dendritic structure compared. Interneurons will be contrasted to pyramidal cells in terms of processing of physiological signals and convergence and divergence in control of hippocampal circuits. Mechanisms of axonal guidance and target recognition, target structures, the involvement of receptor distribution on hippocampal dendrites and the involvement of non-neuronal cellular elements in the establishment of specific connections will be presented. Mechanisms relevant for the maintenance of shape and morphological specializations of hippocampal dendrites will be reviewed. One of the significant contexts in which to view these structural elements is the degree of plasticity in which they participate, during development and origination of dendrites, mature synaptic plasticity and after lesions, when the cells must continue to maintain and reconstitute function, to remain part of the circuitry in the hippocampus. This review will be presented in four main sections: (1) interneurons-development, role in synchronizing influence and hippocampal network functioning; (2) principal cells in CA1, CA3 and dentate gyrus regions-their development, function in terms of synaptic integration, differentiating structure and alterations with lesions; (3) glia and glia/neuronal interactions-response to lesions and developmental guidance mechanisms; and (4) network and circuit aspects of hippocampal morphology and functioning. Finally, the interwoven role of these various elements participating in hippocampal network function will be discussed.     

Synaptic target selectivity and input of GABAergic basket and bistratified interneurons in the CA1 area of the rat hippocampus

To assess the position of interneurons in the hippocampal network, fast spiking cells were recorded intracellularly in vitro and filled with biocytin. Sixteen non-principal cells were selected on the basis of 1) cell bodies located in the pyramidal layer and in the middle of the slice, 2) extensive labeling of their axons, and 3) a branching pattern of the axon indicating that they were not axo-axonic cells. Examination of their efferent synapses (n = 400) demonstrated that the cells made synapses on cell bodies, dendritic shafts, spines, and axon initial segments (AIS). Statistical analysis of the distribution of different postsynaptic elements, together with published data (n = 288) for 12 similar cells, showed that the interneurons were heterogeneous with regard to the frequency of synapses given to different parts of pyramidal cells. When the cells were grouped according to whether they had less or more than 40% somatic synaptic targets, each population appeared homogeneous. The population (n = 19) innervating a high proportion of somata (53 +/- 10%, SD) corresponds to basket cells. They also form synapses with proximal dendrites (44 +/- 12%) and rarely with AISs and spines. One well-filled basket cell had 8,859 boutons within the slice, covering an area of 0.331 mm2 of pyramidal layer tangentially and containing 7,150 pyramidal cells, 933 (13%) of which were calculated to be innervated, assuming that each pyramidal cell received nine to ten synapses. It was extrapolated that the intact axon probably had about 10,800 boutons innervating 1,140 pyramids. The proportion of innervated pyramidal cells decreased from 28% in the middle to 4% at the edge of the axonal field. The other group of neurons, the bistratified cells (n = 9), showed a preference for dendritic shafts (79 +/- 8%) and spines (17 +/- 8%) as synaptic targets, rarely terminating on somata (4 +/- 8%). Their axonal field was significantly larger (1,250 +/- 180 microns) in the medio-lateral direction than that of basket cells (760 +/- 130 microns). The axon terminals of bistratified cells were smaller than those of basket cells. Furthermore, in constrast to bistratified cells, basket cells had a significant proportion of dendrites in stratum lacunosum-moleculare suggesting a direct entorhinal input. The results define two distinct types of GABAergic neuron innervating pyramidal cells in a spatially segregated manner and predict different functions for the two inputs. The perisomatic termination of basket cells is suited for the synchronization of a subset of pyramidal cells that they select from the population within their axonal field, whereas the termination of bistratified cells in conjunction with Schaffer collateral/commissural terminals may govern the timing of CA3 input and/or voltage-dependent conductances in the dendrites.     

Morphological changes in the hippocampal CA3 region induced by non-invasive glucocorticoid administration: a paradox

Repeated stress induces atrophy, or remodeling, of apical dendrites in hippocampal CA3 pyramidal neurons. In rats, the stress effect is blocked by adrenal steroid synthesis inhibitors, and mimicked by daily injection of corticosterone. We report that non-invasive administration of corticosterone in the drinking water (400 micrograms/ml) also produced atrophy of apical dendrites in CA3. Unexpectedly, the combination of daily stress and oral corticosterone negated the effects of either treatment alone, and no changes in the apical dendritic length or branching pattern of CA3 pyramidal neurons were observed compared to control unstressed rats.     

Comparison of projection neurons in the pontine nuclei and the nucleus reticularis tegmenti pontis of the rat

Dendritic features of identified projection neurons in two precerebellar nuclei, the pontine nuclei (PN) and the nucleus reticularis tegmenti pontis (NRTP) were established by using a combination of retrograde tracing (injection of fluorogold or rhodamine labelled latex micro-spheres into the cerebellum) with subsequent intracellular filling (lucifer yellow) in fixed slices of pontine brainstem. A multivariate analysis revealed that parameters selected to characterize the dendritic tree such as size of dendritic field, number of branching points, and length of terminal dendrites did not deviate significantly between different regions of the PN and the NRTP. On the other hand, projection neurons in ventral regions of the PN were characterized by an irregular coverage of their distal dendrites by appendages while those in the dorsal PN and the NRTP were virtually devoid of them. The NRTP, dorsal, and medial PN tended to display larger somata and more primary dendrites than ventral regions of the PN. These differences, however, do not allow the differentiation of projection neurons within the PN from those in the NRTP. They rather reflect a dorso-ventral gradient ignoring the border between the nuclei. Accordingly, a cluster analysis did not differentiate distinct types of projection neurons within the total sample. In both nuclei, multiple linear regression analysis revealed that the size of dendritic fields was strongly correlated with the length of terminal dendrites while it did not depend on other parameters of the dendritic field. Thus, larger dendritic fields seem not to be accompanied by a higher complexity but rather may be used to extend the reach of a projection neuron within the arrangement of afferent terminals. We suggest that these similarities within dendritic properties in PN and NRTP projection neurons reflect similar processing of afferent information in both precerebellar nuclei.     

Postnatal maturation of the layer III pyramidal neurons in the human prefrontal cortex: a quantitative Golgi analysis

In this study we examined the morphological maturation of the basal dendritic field of layer III pyramidal neurons located in the human dorsolateral prefrontal cortex in subjects ranging from 7.5 months after birth up to 27 years. The sections were stained with the Golgi-Cox method and the three-dimensional branching pattern was measured with a semi-automatic dendrite measuring system. Results show a rapid growth phase of the dendritic field from 7.5 months after birth up to one year. A marked increase in total dendritic length is observed, for which elongation of the terminal segments, longer intermediate segments and an increase in number of segments is an explanation. The dendritic length appears to have stabilized after one year, leading us to conclude that the postnatal morphological maturation of the layer III pyramidals does not continue well into childhood, but is completed at a much younger age. Additionally we analyzed the effect of varying section thickness on dendritic parameters and found no tendency for higher dendritic values with increasing section thickness for the range of thickness values of the histological sections used.     

The origin of efferent pathways from the primary visual cortex, area 17, of the macaque monkey as shown by retrograde transport of horseradish peroxidase

The retrograde transport of horseradish peroxidase has been used to identify efferent cells in area 17 of the macaque. Cells projecting to the lateral geniculate nucleus are small to medium sized pyramidal neurons with somata in lamina 6 and the adjacent white matter. The projection to the parvocellular division arises preferentially from the upper half of lamina 6, while that to the magnocellular division arises preferentially from the lower part of the lamina. The projection to both superior colliculus and inferior pulvinar arises from all sizes of pyramidal neurons lying in lamina 58 (Lund and Boothe, '75); at least pyramidal neurons of lamina 5B send collateral axon branches to both destinations. Injections with extensive spread of horseradish peroxidase show that many cells of lamina 4B and the large pyramidal neurons of upper lamina 6 also project extrinsically but their terminal sites have not been identified. Other studies have indicated that cells of laminae 2 and 3 project to areas 18 and 19. Therefore every lamina of the visual cortex, with the exception of those receiving a direct thalamic input, contains cells projecting extrinsically. Further, each lamina projects to a different destination and from Golgi studies can be shown to contain cells with specific patterns of dendritic branching which relate to the distribution of thalamic afferents and to the patterns of intracortical connections. These findings emphasise the significance of the horizontal organisation of the cortex with relation to the flow of information through it and contrast with the current concept of columnar organisation shown in physiological studies.