Dendritic spinules detected by the peroxidase method]

The structure of marked associative pyramidal neurons, their dendrites, and spines in layer III of somato-sensory cortex in cats after HRP-injection into the motor cortex has been described. Secondary and tertiary branches of basal dendrites are revealed more often than the apical ones. But the spines, especially their heads, were more obvious on the apical dendrites. The marked associative neurons are displaced sparsely, making no accumulations.     

Activity-dependent regulation of dendritic spine density on cortical pyramidal neurons in organotypic slice cultures

In order to examine the effects of activity on spine production and/or maintenance in the cerebral cortex, we have compared the number of dendritic spines on pyramidal neurons in slices of PO mouse somatosensory cortex maintained in organotypic slice cultures under conditions that altered basal levels of spontaneous electrical activity. Cultures chronically exposed to 100 μM picrotoxin (PTX) for 14 days exhibited significantly elevated levels of electrical activity when compared to neurons in control cultures. Pyramidal neurons raised in the presence of PTX showed significantly densities of dendritic spines on primary apical, secondary apical, and secondary basal dendrites when compared to control cultures. The PTX-induced increase in spine density was dose dependent and appeared to saturate at 100 μM. Cultures exhibiting little or no spontaneous activity, as a result of growth in a combination of PTX and tetrodotoxin (TTx), showed significantly fewer dendritic spines compared to cultures maintained in PTX alone. These results demonstrate that the density of spines on layers V and VI pyramidal neurons can be modulated by growth conditions that alter the levels of spontaneous electrical activity. 1994 John Wiley & Sons, Inc.     

The anatomy of the cerebral cortex of the echidna (Tachyglossus aculeatus)

The cerebral cortex of the echidna is notable for its extensive folding and the positioning of major functional areas towards its caudal extremity. The gyrification of the echidna cortex is comparable in magnitude to prosimians and cortical thickness and neuronal density are similar to that seen in rodents and carnivores. On the other hand, many pyramidal neurons in the cerebral cortex of the echidna are atypical with inverted somata and short or branching apical dendrites. All other broad classes of neurons noted in therian cortex are also present in the echidna, suggesting that the major classes of cortical neurons evolved prior to the divergence of proto- and eutherian lineages. Dendritic spine density on dendrites of echidna pyramidal neurons in somatosensory cortex and apical dendrites of motor cortex pyramidal neurons is lower than that found in eutheria. On the other hand, synaptic morphology, density and distribution in somatosensory cortex are similar to that in eutheria. In summary, although the echidna cerebral cortex displays some structural features, which may limit its functional capacities (e.g. lower spine density on pyramidal neurons), in most structural parameters (e.g. gyrification, cortical area and thickness, neuronal density and types, synaptic morphology and density), it is comparable to eutheria.     

Quantitative histological studies of the variability of Golgi-impregnated cortical neurons in rats and cats]

Quantitative GOLGI-studies are executed about the layer V pyramidal neurons of the albino rat and the cat sensorimotor cortex. To this the length LP of the perikarya, the lenth LAD of the apical main dendrites, the spine-densities (spine-dendrite-quotients) DQ and the length NZ of the spineless ("nude") initial zone of the apical dendrites are measured in several male animals descending of the same litters. The neuronal signs are compared within the specimens of the same age. There are no statistical significant differences (level: 0,05) between these neuronal signs in all specimens of the same age and species. Relating to the examined marks of the cortical pyramids it is allowed to decline the hypothesis of variability between animals (rats or cats respectively) of the same age and sex. By this it is legal and sufficient to examine only one specimen (animal) for each stage of age in histological researches of ontogenetic series. This specimen is representative to this stage of evolution.     

Changes of Dendritic Spine Density and Morphology in the Superficial Layers of the Medial Entorhinal Cortex Induced by Extremely Low-Frequency Magnetic Field Exposure

In the present study, we investigated the effects of chronic exposure (14 and 28 days) to a 0.5 mT 50 Hz extremely low-frequency magnetic field (ELM) on the dendritic spine density and shape in the superficial layers of the medial entorhinal cortex (MEC). We performed Golgi staining to reveal the dendritic spines of the principal neurons in rats. The results showed that ELM exposure induced a decrease in the spine density in the dendrites of stellate neurons and the basal dendrites of pyramidal neurons at both 14 days and 28 days, which was largely due to the loss of the thin and branched spines. The alteration in the density of mushroom and stubby spines post ELM exposure was cell-type specific. For the stellate neurons, ELM exposure slightly increased the density of stubby spines at 28 days, while it did not affect the density of mushroom spines at the same time. In the basal dendrites of pyramidal neurons, we observed a significant decrease in the mushroom spine density only at the later time point post ELM exposure, while the stubby spine density was reduced at 14 days and partially restored at 28 days post ELM exposure. ELM exposure-induced reduction in the spine density in the apical dendrites of pyramidal neurons was only observed at 28 days, reflecting the distinct vulnerability of spines in the apical and basal dendrites. Considering the changes in spine number and shape are involved in synaptic plasticity and the MEC is a part of neural network that is closely related to learning and memory, these findings may be helpful for explaining the ELM exposure-induced impairment in cognitive functions.     

Experience‐dependent plasticity of dendritic spines of layer 2/3 pyramidal neurons in the mouse cortex

Previous studies have shown that sensory and motor experiences play an important role in the remodeling of dendritic spines of layer 5 (L5) pyramidal neurons in the cortex. In this study, we examined the effects of sensory deprivation and motor learning on dendritic spine remodeling of layer 2/3 (L2/3) pyramidal neurons in the barrel and motor cortices. Similar to L5 pyramidal neurons, spines on apical dendrites of L2/3 pyramidal neurons are plastic during development and largely stable in adulthood. Sensory deprivation via whisker trimming reduces the elimination rate of existing spines without significant effect on the rate of spine formation in the developing barrel cortex. Furthermore, we show that motor training increases the formation and elimination of dendritic spines in the primary motor cortex. Unlike L5 pyramidal neurons, however, there is no significant difference in the rate of spine formation between sibling dendritic branches of L2/3 pyramidal neurons. Our studies indicate that sensory and motor learning experiences have important impact on dendritic spine remodeling in L2/3 pyramidal neurons. They also suggest that the rules governing experience‐dependent spine remodeling are largely similar, but not identical, between L2/3 and L5 pyramidal neurons. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 277–286, 2016     

Noradrenergic enhancement of Ca2+ responses of basal dendrites in layer 5 pyramidal neurons of the prefrontal cortex

Although the excitatory effects of noradrenaline have been thoroughly studied in the central nervous system, there is relatively little known about the adrenergic effects on Ca2+ dynamics of dendrites. In the present study, we imaged basal dendrites of layer 5 pyramidal neurons in the prefrontal cortex using two-photon microscopy. In our experiments noradrenaline, applied in the bath, enhanced excitability of layer 5 pyramidal neurons. The number of evoked action potentials following current injection to the soma increased by 44.7% on average. In the basal dendrites and spines the evoked Ca2+ responses were also markedly enhanced. Noradrenaline-induced effects could be blocked by the beta-adrenergic blocker propranolol. Our data, that activation of the noradrenergic system increases excitability of layer 5 pyramidal neurons via beta-adrenergic receptors and enhances Ca2+ signaling in basal dendrites, suggest a cellular site of action for noradrenaline to improve the integrative capabilities of dendrites.     

Ontogeny of the mouse motor cortex. The polymorph layer or layer VI. A Golgi and electronmicroscopical study

Summary The development of neurons and their synapses of the mouse motor cortex has been studied from the first postnatal day up to an age of three weeks both electronmicroscopically and with the Golgi method. Special attention has been paid to the maturation of the different cell types in the sixth cortical layer and their dendritic organization within this layer.The polymorph layer is subdivided into two zones: an internal (VIb) and an external one (VIa). In these zones six different cell types can be identified both electronmicroscopically and with the Golgi method: large, small and inverted pyramidal cells in VIa; horizontal cells, star cells and small pyramidal cells in VIb.Spines of apical dendrites of large pyramidal cells in sublayer VIa can be detected as early as the 6th postnatal day. About the ninth day the basal dendrites as well show emerging spines. Somatic spines are found only on the large pyramidal cells and disappear slowly towards the end of the 3rd postnatal week.The small pyramidal cells show developing spines on their apical dendrite in the first half of the second postnatal week. The final density and distribution of spines is reached by the stem dendrites towards the end of the second week, by the basal dendrites during the third week. The maturation process of the improperly orientated neurons occurs in time in between the large and the small pyramidal cells.The axo-somatic synapses appear in general at a later date than the axo-dendritic ones. In the horizontal cells axo-somatic synapses are visible already at the seventh postnatal day.At the end of the first week especially in layer VIb many immature neurons with an ovoid or round nucleus are present having little if any endoplasmic reticulum organised as ergastoplasm.Towards the end of the second week however most neurons in the polymorph layer have a well developed endoplasmic reticulum.Electronmicroscopical pictures reveal in outgrowing dendrites many enlargements filled with vesicles, these correspond to the varicosities seen in Golgi pictures. At nine days postnatally the first myelinated fibres appear.Aided by grant (R-209-67) from the United Cerebral Palsy Research and Educational Foundation, New York.     

Neural recognition molecules CHL1 and NB-3 regulate apical dendrite orientation in the neocortex via PTP alpha

Apical dendrites of pyramidal neurons in the neocortex have a stereotypic orientation that is important for neuronal function. Neural recognition molecule Close Homolog of L1 (CHL1) has been shown to regulate oriented growth of apical dendrites in the mouse caudal cortex. Here we show that CHL1 directly associates with NB-3, a member of the F3/contactin family of neural recognition molecules, and enhances its cell surface expression. Similar to CHL1, NB-3 exhibits high-caudal to low-rostral expression in the deep layer neurons of the neocortex. NB-3-deficient mice show abnormal apical dendrite projections of deep layer pyramidal neurons in the visual cortex. Both CHL1 and NB-3 interact with protein tyrosine phosphatase alpha (PTPalpha) and regulate its activity. Moreover, deep layer pyramidal neurons of PTPalpha-deficient mice develop misoriented, even inverted, apical dendrites. We propose a signaling complex in which PTPalpha mediates CHL1 and NB-3-regulated apical dendrite projection in the developing caudal cortex.     

Close homolog of L1 modulates area-specific neuronal positioning and dendrite orientation in the cerebral cortex

We show that the neural cell recognition molecule Close Homolog of L1 (CHL1) is required for neuronal positioning and dendritic growth of pyramidal neurons in the posterior region of the developing mouse neocortex. CHL1 was expressed in pyramidal neurons in a high-caudal to low-rostral gradient within the developing cortex. Deep layer pyramidal neurons of CHL1-minus mice were shifted to lower laminar positions in the visual and somatosensory cortex and developed misoriented, often inverted apical dendrites. Impaired migration of CHL1-minus cortical neurons was suggested by strikingly slower rates of radial migration in cortical slices, failure to potentiate integrin-dependent haptotactic cell migration in vitro, and accumulation of migratory cells in the intermediate and ventricular/subventricular zones in vivo. The restriction of CHL1 expression and effects of its deletion in posterior neocortical areas suggests that CHL1 may regulate area-specific neuronal connectivity and, by extension, function in the visual and somatosensory cortex.     

Intrinsic organization of the medial cerebral cortex of the lizard Lacerta pityusensis: A golgi study

The morphology of cells and the organization of axons were studied in Golgi-Colonnier and toluidine blue stained preparations from the medial cerebral cortex of the lizard Lacerta pityusensis. In the medial cortex, six strata were distinguished between the superficial glial membrane and the ependyma. Strata I and II formed the outer plexiform layer, stratum III formed the cellular layer, and strata IV go VI the inner plexiform layer. The outer plexiform layer contained smooth bipolar neurons; their dendrites were oriented anteroposteriorly and their axons were directed towards the posterior zone of the brain. Five neuronal types were observed in the cellular layer. The spinous pyramidal neurons had well-developed apical dendrites and poorly developed basal ones. Their axons entered the inner plexiform layer and gave off collaterals oriented anteroposteriorly. The small, sparsely spinous pyramidal neurons had poorly developed dendrites and their axons entered the inner plexiform layer. The spinous bitufted neurons had well-developed apical and basal dendritic tufts. Their axons gave off collaterals that reached the outer and inner plexiform layers of both the dorsomedial and dorsal cortices. The sparsely spinous horizontal neurons had dendrites restricted to the outer plexiform layer. Their axons entered the inner plexiform layer. The sparsely spinous, multipolar neurons had their soma close to stratum IV and their axons entered the outer plexiform layer. In stratum V of the inner plexiform layer were large, spiny polymorphic neurons; they had dendrites with long spines, and their axons reached the cellular layer. On the basis of these results, we have subdivided the medial cortex into two subregions: the superficial region, which contains the neurons of the cellular layer and their dendritic domains, and the deep region, strata V and VI, which contains the large, spiny polymorphic neurons. The neurons in the medial cortex of these lizards resembles those in the area dentata of mammals. On this basis, the superficial region may be compared to the dentate gyrus and the deep region to the hilar region of the hippocampus of mammals.     

Development of long-term dendritic spine stability in diverse regions of cerebral cortex

Synapse formation and elimination occur throughout life, but the magnitude of such changes at distinct developmental stages remains unclear. Using transgenic mice overexpressing yellow fluorescent protein and transcranial two-photon microscopy, we repeatedly imaged dendritic spines on the apical dendrites of layer 5 pyramidal neurons. In young adolescent mice (1-month-old), 13%-20% of spines were eliminated and 5%-8% formed over 2 weeks in barrel, motor, and frontal cortices, indicating a cortical-wide spine loss during this developmental period. As animals mature, there is also a substantial loss of dendritic filopodia involved in spinogenesis. In adult mice (4-6 months old), 3%-5% of spines were eliminated and formed over 2 weeks in various cortical regions. Over 18 months, only 26% of spines were eliminated and 19% formed in adult barrel cortex. Thus, after a concurrent loss of spines and spine precursors in diverse regions of young adolescent cortex, spines become stable and a majority of them can last throughout life.     

Calcium dynamics of spines depend on their dendritic location

Dendritic spines are morphologically and functionally heterogeneous. To understand this diversity, we use two-photon imaging of layer 5 neocortical pyramidal cells and measure action potential-evoked [Ca(2+)]i transients in spines. Spine calcium kinetics are controlled by (i) the diameter of the parent dendrite, (ii) the length of the spine neck, and (iii) the strength of spine calcium pumps. These factors produce different calcium dynamics in spines from basal, proximal apical, and distal apical dendrites, differences that are more pronounced without exogenous buffers. In proximal and distal apical dendrites, different calcium dynamics correlate with different susceptibility to synaptic depression, and modifying calcium kinetics in spines changes the expression of long-term depression. Thus, the spine location apparently determines its calcium dynamics and synaptic plasticity. Our results highlight the precision in design of neocortical neurons.     

Cortical area and species differences in dendritic spine morphology

Dendritic spines receive most excitatory inputs in the neocortex and are morphologically very diverse. Recent evidence has demonstrated linear relationships between the size and length of dendritic spines and important features of its synaptic junction and time constants for calcium compartmentalisation. Therefore, the morphologies of dendritic spines can be directly interpreted functionally. We sought to explore whether there were potential differences in spine morphologies between areas and species that could reflect potential functional differences. For this purpose, we reconstructed and measured thousands of dendritic spines from basal dendrites of layer III pyramidal neurons from mouse temporal and occipital cortex and from human temporal cortex. We find systematic differences in spine densities, spine head size and spine neck length among areas and species. Human spines are systematically larger and longer and exist at higher densities than those in mouse cortex. Also, mouse temporal spines are larger than mouse occipital spines. We do not encounter any correlations between the size of the spine head and its neck length. Our data suggests that the average synaptic input is modulated according to cortical area and differs among species. We discuss the implications of these findings for common algorithms of cortical processing.     

Neuronal organization of field 4 of the motor cortex of the cat brain

By means of the silver nitrate impregnation method after Golgi-Kopsch in kittens and young cats the field 4 in the cerebral motor cortex has been studied. The motor cortex of the field 4 possesses certain heteromorphism. Besides usual stellate and pyramidal neurons, that differ from real ones by some morphological signs: their body is often round, the apical dendrite is much thinner than the corresponding dendrite of a pyramidal neuron, it does not produce oblique branches along the course, never gets into the I layer, the spines arrange less densely. According to the mode of dendrites setting off, the atypical pyramidal neurons can be divided into multipolar and spindle-like with horizontal or vertical branching of the dendrites. According to the spines distribution, the multipolar atypical neurons can be divided into spinous, rare-spinous and aspinous. With respect to various cellular forms and distribution of various types of neurons in layers, every of the areas (gamma, alpha, sfu, fu) possesses specific peculiarities. The greatest variability of the neurons have the field 4 gamma and 4 alpha, where, besides stellate and pyramidal, atypical neurons can be found. The stellate neurons of the field 4 gamma are characterized with a deep arrangement, their number is essentially less, than in other areas of the field 4. In the field 4 alpha they are situated in the layers II-III. Suprafundal and fundal parts of the field do not possess pyramidal atypical neurons and are characterized with presence of large amount of the stellate neurons. In respect to the axonal branching in the suprafundal part of the field 4, 2 types of the stellate cells are distinguished.     

The organization of double bouquet cells in monkey striate cortex

In previous publications we proposed a model of cortical organization in which the pyramidal cells of the cerebral cortex are organized into modules. The modules are centred around the clusters of apical dendrites that originate from the layer 5 pyramidal cells. In monkey striate cortex such modules have an average diameter of 23 μm and the outputs originating from the modules are contained in the vertical bundles of myelinated axons that traverse the deeper layers of the cortex. The present study is concerned with how the double bouquet cells in layer 2/3 of striate cortex relate to these pyramidal cell modules. The double bouquet cells are visualized with an antibody to calbindin, and it has been shown that their vertically oriented axons, or horse tails, are arranged in a regular array, such that there is one horse tail per pyramidal cell module. Within layer 2/3 the double bouquet cell axons run alongside the apical dendritic clusters, while in layer 4C they are closely associated with the myelinated axon bundles. However, the apical dendrites are not the principal targets of the double bouquet cell axons. Most of the neuronal elements post-synaptic to them are the shafts of small dendrites (60%) and dendritic spines, with which they form symmetric synapses. This regular arrangement of the axons of the double-bouquet cells and their relationship to the components of the pyramidal cells modules supports the concept that there are basic, repeating neuronal circuits in the cortex.     

The postnatal development of lamina V pyramidal cells in the sensomotor cortex of the albino rat. 2. Quantitative studies on Golgi preparations]

Using Golgi-Cox preparates the postnatal development (1st to 90th day after birth) of the patterns of apical dendrite spines in layer V pyramids in albino rat sensorimotor cortex is represented. Especially it is reported about the evolution of the total amount of apical dendrite spines, of length of apical dendrites, of spine density (spine dendrite quotients, DQ), of interspinous distance (space between two adjacent visible spines, in the proximal dendrite with increasing spine distribution and in the district with crest of spine distribution separately) and finally of cell body length.     

Systematic regulation of spine sizes and densities in pyramidal neurons

Dendritic spines receive most excitatory inputs in the CNS. Recent evidence has demonstrated that the spine head volume is linearly correlated with the readily releasable pool of neurotransmitter and the PSD size. These correlations can be used to functionally interpret spine morphology. Using Golgi impregnations and light microscopy, we reconstructed 23000 spines from pyramidal neurons in layers 2/3, 4, 5 and 6 of mouse primary visual cortex and CA1 hippocampal region and measured their spine head diameters and densities. Spine head diameters and densities are variable within and across cells, although they are similar between apical and basal dendrites. When compared to other regions, layer 5 neurons have larger spine heads and CA1 neurons higher spine densities. Interestingly, we detect a correlation between spine head diameter and interspine distance within and across cells, whereby larger spines are spaced further away from each other than smaller spines. Finally, in CA1 neurons, spine head diameters are larger, and spine density lower, in distal apical dendrites (>200 microm from soma) compared to proximal regions. These results reveal that spine morphologies and densities, and therefore synaptic properties, are jointly modulated with respect to cortical region, laminar position, and, in some cases, even the position of the spine along the dendritic tree. Individual neurons also appear to regulate their apical and basal spine densities and morphologies in concert. Our data provide evidence for a homeostatic control of excitatory synaptic strength.     

Transient and persistent dendritic spines in the neocortex in vivo

Dendritic spines were imaged over days to months in the apical tufts of neocortical pyramidal neurons (layers 5 and 2/3) in vivo. A fraction of thin spines appeared and disappeared over a few days, while most thick spines persisted for months. In the somatosensory cortex, from postnatal day (PND) 16 to PND 25 spine retractions exceeded additions, resulting in a net loss of spines. The fraction of persistent spines (lifetime > or = 8 days) grew gradually during development and into adulthood (PND 16-25, 35%; PND 35-80, 54%; PND 80-120, 66%; PND 175-225, 73%), providing evidence that synaptic circuits continue to stabilize even in the adult brain, long after the closure of known critical periods. In 6-month-old mice, spines turn over more slowly in visual compared to somatosensory cortex, possibly reflecting differences in the capacity for experience-dependent plasticity in these brain regions.