Dendritic branch typing and spine expression patterns in cortical nonpyramidal cells

To understand the dendritic differentiation in various types of cortical nonpyramidal cells, we analyzed quantitatively their dendritic branching and spine expression. The dendritic internode and interspine interval obeyed exponential distributions with type-specific decay constants. The initial branching pattern, internode interval and spine density at the light microscopic level divided nonpyramidal cells into three dendritic types, correlated with axonal, neurochemical and firing types. The initial branching pattern determined the overall vertical spread of dendrites. Basket cell subtypes with different firing and chemical expression patterns were distinct in the vertical and horizontal spatial spread, providing diverse input territories. Internode densities of dendritic spines, as well as those of axonal synaptic boutons, did not correlate with the tortuosities and intervals, suggesting a tendency to distribute synapses homogeneously over the arbor. Dendritic spines identified at the electron microscopic level were different in length and shape among subtypes. Although the density was lower than that of pyramidal cells, spines themselves were also composed of several morphological types such as mushroom and multihead ones, which were expressed differentially among subtypes. Correlation of dendritic branching characteristics with differences in spine structure suggests distinct ways to receive specific inputs among the subtypes.     

Effects of synaptic activity on dendritic spine motility of developing cortical layer v pyramidal neurons

It is increasingly clear that dendritic spines play an important role in compartmentalizing post-synaptic signals and that their dynamic morphological properties have functional consequences. Here, we examine this issue using two-photon microscopy to characterize spine motility on layer V pyramidal neurons in acute slices of the developing mouse cortex. In this system, all spine classes except filopodia become less dynamic as development proceeds. General manipulations of activity (TTX or KCl treatment) do not alter spine dynamics, although increased glutamatergic transmission (AMPA or NMDA treatment) stabilizes developing cortical spines. These effects on spine dynamics do not appear to be related to AMPA or NMDA receptor expression as assessed with immunolabeling, as there is no correlation between spine motility and AMPA (GluR1/2) or NMDA (NR1/NR2B) receptor subunit expression on a spine by spine basis. These results indicate that activity through glutamatergic synapses is important for regulating spine motility in the developing mouse cortex, and that the relative complement of receptors, while different across morphological classifications, cannot account for differences in dynamic structural changes in dendritic spines.     

Repeated stress induces dendritic spine loss in the rat medial prefrontal cortex

The prefrontal cortex (PFC) plays an important role in higher cognitive processes, and in the regulation of stress-induced hypothalamic-pituitary-adrenal (HPA) activity. Here we examined the effect of repeated restraint stress on dendritic spine number in the medial PFC. Rats were perfused after receiving 21 days of daily restraint stress, and intracellular iontophoretic injections of Lucifer Yellow were carried out in layer II/III pyramidal neurons in the anterior cingulate and prelimbic cortices. We found that stress results in a significant (16%) decrease in apical dendritic spine density in medial PFC pyramidal neurons, and confirmed a previous observation that total apical dendritic length is reduced by 20% in the same neurons. We estimate that nearly one-third of all axospinous synapses on apical dendrites of pyramidal neurons in medial PFC are lost following repeated stress. A decrease in medial PFC dendritic spines may not only be indicative of a decrease in the total population of axospinous synapses, but may impair these neurons' capacity for biochemical compartmentalization and plasticity in which dendritic spines play a major role. Dendritic atrophy and spine loss may be important cellular features of stress-related psychiatric disorders where the PFC is functionally impaired.     

Kinematics of the scoliotic spine as related to the normal spine

A coupling between the lateral flexion and axial rotation as a result of the geometric arrangement of the motion segments is well known in a normal spine. The kinematic behavior of idiopathic scoliotic spines has been analyzed by means of a biomechanical model study and a radiologic study. The anteroposterior and lateral flexion radiographs of 40 patients with progressive adolescent idiopathic scoliosis were studied. In five of these patients, anteroposterior radiographs were also made with the spine in a ventrally flexed position. The kinematic behavior of a nonpathologic spine was examined by means of a three-dimensional, nonlinear geometric mathematical model of the spine. The frontal plane inclination of the facet joints in conjunction with the vertebral orientation in the sagittal plane influence the kinematic behavior in the normal spine. In a scoliotic spine, there is an axially rotated position and, in most cases, a dorsal inclination (lordotic) of the motion segments. Nevertheless, the direction of the axial rotation during lateral flexion does not differ from the direction of the axial rotation during lateral flexion in a normal spine. The existing axial rotation in idiopathic scoliosis cannot be explained on the basis of spinal kinematics. In contrast to normal spines, in scoliotic spines exists a coupling between ventral flexion or extension and axial rotation. This may be essential in the management of idiopathic scoliosis.     

Regional dendritic and spine variation in human cerebral cortex: a quantitative golgi study

The present study explored differences in dendritic/spine extent across several human cortical regions. Specifically, the basilar dendrites/spines of supragranular pyramidal cells were examined in eight Brodmann's areas (BA) arranged according to Benson's (1993, Behav Neurol 6:75-81) functional hierarchy: primary cortex (somatosensory, BA3-1-2; motor, BA4), unimodal cortex (Wernicke's area, BA22; Broca's area, BA44), heteromodal cortex (supple- mentary motor area, BA6beta; angular gyrus, BA39) and supramodal cortex (superior frontopolar zone, BA10; inferior frontopolar zone, BA11). To capture more general aspects of regional variability, primary and unimodal areas were designated as low integrative regions; heteromodal and supramodal areas were designated as high integrative regions. Tissue was obtained from the left hemisphere of 10 neurologically normal individuals (M(age) = 30 +/- 17 years; five males, five females) and stained with a modified rapid Golgi technique. Ten neurons were sampled from each cortical region (n = 800) and evaluated according to total dendritic length, mean segment length, dendritic segment count, dendritic spine number and dendritic spine density. Despite considerable inter-individual variation, there were significant differences across the eight Brodmann's areas and between the high and low integrative regions for all dendritic and spine measures. Dendritic systems in primary and unimodal regions were consistently less complex than in heteromodal and supramodal areas. The range within these rankings was substantial, with total dendritic length in BA10 being 31% greater than that in BA3-1-2, and dendritic spine number being 69% greater. These findings demonstrate that cortical regions involved in the early stages of processing (e.g. primary sensory areas) generally exhibit less complex dendritic/spine systems than those regions involved in the later stages of information processing (e.g. prefrontal cortex). This dendritic progression appears to reflect significant differences in the nature of cortical processing, with spine-dense neurons at hierarchically higher association levels integrating a broader range of synaptic input than those at lower cortical levels.     

Regulation of dendritic spine morphology by the rho family of small GTPases: antagonistic roles of Rac and Rho

Dendritic spines mediate most excitatory transmission in the mammalian CNS and have been traditionally considered stable structures. Following the suggestion that spines may 'twitch', it has been recently shown that spines are capable of rapid morphological rearrangements. Because of the role of the small GTPases from the Rho family in controlling neuronal morphogenesis, we investigated the effects of several members of this biochemical signaling pathway in the maintenance of the morphology of extant dendritic spines by combining biolistic transfection of pyramidal neurons in cultured cortical and hippocampal slices with two-photon microscopy. We find a variety of effects on the density and morphology of dendritic spines by expressing either constitutively active or dominant negative forms of several small GTPases of the Rho family, by blocking the entire pathway with Clostridium difficile toxin B or by blocking Rho with C3 transferase. We propose a model where Rac promotes spine formation, while Rho prevents it. We conclude that the small GTPases provide antagonistic control mechanisms of spine maintenance in pyramidal neurons.     

Estrogen replacement increases spinophilin-immunoreactive spine number in the prefrontal cortex of female rhesus monkeys

While studies have shown that estrogen affects hippocampal spine density and function, behavioral studies in humans and nonhuman primates have also implicated the prefrontal cortex in the effects of estrogen on cognition. However, the potential for similar estrogen-induced increases in spines and synapses in the prefrontal cortex has not been investigated in primates. Moreover, it is not known if such an estrogen effect would be manifested throughout the neocortex or primarily in the regions involved in cognition. Therefore, we investigated the effects of estrogen on dendritic spines in the prefrontal and primary visual cortices of young rhesus monkeys. Young female monkeys were ovariectomized and administered either estradiol cypionate or vehicle by intramuscular injection. Using an antibody against the spine-associated protein, spinophilin, spine numbers were estimated in layer I of area 46 and in layer I of the opercular portion of area V1 (V1o). Spine numbers in layer I of area 46 were significantly increased (55%) in the ovariectomy + estrogen group compared to the ovariectomy + vehicle group, yet spine numbers in layer I of area V1o were equivalent across the two groups. The present results suggest that estrogen's effects on synaptic organization influence select neocortical layers and regions in a primate model, and provide a morphological basis for enhanced prefrontal cortical functions following estrogen replacement.     

气管插管对颈椎的影响

背景麻醉医师在气管内插管和其他气道管理操作时都常规涉及到颈部,这些操作对颈椎运动的影响,特别是对颈椎损伤患者的颈椎及神经的影响,是麻醉医师值得重视的问题。 目的简述颈椎解剖结构和各种操作对颈椎运动的影响,从而更好地指导临床工作以及提高麻醉的安全性。 内容从颈椎解剖、颈椎运动、气管内插管时的颈椎活动、插管辅助设备对颈...     

Heterogeneous spine loss in layer 5 cortical neurons after spinal cord injury

A large thoracic spinal cord injury disconnects the hindlimb (HL) sensory-motor cortex from its target, the lumbar spinal cord. The fate of the synaptic structures of the axotomized cortical neurons is not well studied. We evaluated the density of spines on axotomized corticospinal neurons at 3, 7, and 21 days after the injury in adult mice expressing yellow fluorescence protein in a subset of layer 5 neurons. Spine density of the dendritic segment proximal to the soma (in layer 5) declined as early as 3 days after injury, far preceding the onset of somatic atrophy. In the distal segment (in layer 2/3), spine loss was slower and less severe than in the proximal segment. Axotomy of corticospinal axons in the brainstem (pyramidotomy) induced a comparable reduction of spine density, demonstrating that the loss is not restricted to the neurons axotomized in the thoracic spinal cord. Surprisingly, in both forms of injury, the spine density of putative non-axotomized layer 5 neurons was reduced as well. The spine loss may reflect fast rearrangements of cortical circuits after axotomy, for example, by a disconnection of HL cortical neurons from synaptic inputs that no longer provide useful information.     

Load-displacement properties of the thoracolumbar calf spine: Experimental results and comparison to known human data

The availability of human cadaveric spine specimens for in vitro tests is limited and the risk of infection is now of vital concern. As an alternative or supplement, calf spines have been used as models for human spines, in particular to evaluate spinal implants. However, neither qualitative nor quantitative biomechanical data on calf spines are available for comparison with data on human specimens. The purpose of this study was to determine the fundamental biomechanical properties of calf spines and to compare them with existing data from human specimens. Range of motion, neutral zone, and stiffness properties of thoracolumbar calf spines (T6-L6) were determined under pure moment loading in flexion and extension, axial left/right rotation and right/left lateral bending. Biomechanical similarities were observed between the calf and reported human data, most notably in axial rotation and lateral bending. Range of motion in the lumbar spine in flexion and extension was somewhat less in the calf than that typically reported for the human, though still within the range. These results suggest that the calf spine can be considered on a limited basis as a model for the human spine in certain in vitro tests.     

Role of afferent innervation and neuronal activity in dendritic development and spine maturation of fascia dentata granule cells

By using slice cultures of hippocampus as a model, we have studied the development of dendritic spines in fascia dentata granule cells. We raised the question as to what extent spine development is dependent on a major afferent input to these neurons, the fibers from the entorhinal cortex and neuronal activity mediated by these axons. Our results can be summarized as follows: (i) the entorhino-hippocampal projection develops in an organotypic manner in co-cultures of entorhinal cortex and hippocampus. Like in vivo, entorhinal fibers, labeled by anterograde tracing with biocytin, terminate in the outer molecular layer of the fascia dentata. (ii) The layer-specific termination of entorhinal fibers is not altered by the blockade of neuronal activity with tetrodotoxin. Likewise, the differentiation of the dendritic arbor of postsynaptic granule cells does not require neuronal activity. Blockade of neuronal activity did not affect the mean spine number of granule cell dendrites in entorhino-hippocampal co-cultures, but led to a relative increase in thin, long filiform spines that are characteristic of immature neurons. (iii) The maturation of the granule cell dendritic arbor is, however, controlled by the afferent fibers from the entorhinal cortex in an activity-independent manner. In single slice cultures of hippocampus lacking entorhinal input, Golgi-impregnated granule cells have much shorter, less branched dendrites when compared with granule cells in entorhino-hippocampal co-cultures. This reduction in dendritic length in granule cells lacking entorhinal input results in a lower mean total number of spines per neuron, but the mean number of spines per microm is not reduced in the absence of entorhinal innervation. These results indicate that innervation by fibers from the entorhinal cortex, but not neuronal activity mediated via these axons, is essential for the normal development of the granule cell dendritic arbor. Neuronal activity is required, however, for the maturation of dendritic spines.     

Dynamic neutralisation of the lumbar spine confirmed on a new lumbar spine simulator in vitro

A new dynamic neutralisation system for lumbar spine segments has been developed and tested on four cadaveric lumbar spines. Segments L4/5 (3 cases) and L3/4 (1 case) were tested on a new lumbar spine simulator which allowed the simultaneous application of bending moments, compressive and shear loads. The average applied loads were 18.3 Nm flexion moment, 2296 N compressive and 458 N anterior shear load for flexion, and 12.5 Nm extension moment, 667 N compressive and 74 N posterior shear load for extension. The relative motion of the upper vertebra in respect to the lower vertebra was measured with the three-dimensional FASTRAK system, using an advanced computer software. The endplate centres as well as the centre of the screw heads were taken as reference points, identified by orthogonally taken radiographs. The dynamic neutralisation system described reduces bending angles and horizontal translations, but it expands vertical translations. The bulging of the posterior annulus is also reduced. Received: 4 May 1998     

Dendritic spine structural anomalies in fragile-X mental retardation syndrome

Fragile-X syndrome is the most common single-gene inherited form of mental retardation. Morphological studies suggest a possible failure of the synapse maturation process. Cerebral cortical spine morphology in fragile-X syndrome and in a knockout mouse model of it appears immature, with long, thin spines much more common than the stubby and mushroom-shaped spines more characteristic of normal development. In human fragile-X syndrome there is also a higher density of spines along dendrites, suggesting a possible failure of synapse elimination. While variously misshapen spines are characteristic of a number of mental retardation syndromes, the overabundance of spines seen in fragile-X syndrome is unusual. Taken with evidence of neurotransmitter activation of the synthesis of the fragile-X protein (FMRP) at synapses in vitro and evidence for behaviorally induced FMRP expression in vivo, and with evidence compatible with a role for FMRP in regulating the synthesis of other proteins, it is possible that FMRP serves as an 'immediate early protein' at the synapse that orchestrates aspects of synaptic development and plasticity.     

Age-related dendritic and spine changes in corticocortically projecting neurons in macaque monkeys

Alterations in neuronal morphology occur in primate cerebral cortex during normal aging, vary depending on the neuronal type, region and cortical layer, and have been related to memory and cognitive impairment. We analyzed how such changes affect a specific subpopulation of cortical neurons forming long corticocortical projections from the superior temporal cortex to prefrontal area 46. These neurons were identified by retrograde transport in young and old macaque monkeys. Dendritic arbors of retrogradely labeled neurons were visualized in brain slices by intracellular injection of Lucifer Yellow, and reconstructed three-dimensionally using computer-assisted morphometry. Total dendritic length, numbers of segments, numbers of spines, and spine density were analyzed in layer III pyramidal neurons forming the projection considered. Sholl analysis was used to determine potential age-related changes in dendritic complexity. We observed statistically significant age-related decreases in spine numbers and density on both apical and basal dendritic arbors in these projection neurons. On apical dendrites, changes in spine numbers occurred mainly on the proximal dendrites but spine density decreased uniformly among the different branch orders. On basal dendrites, spine numbers and density decreased preferentially on distal branches. Regressive dendritic changes were observed only in one particular portion of the apical dendrites, with the general dendritic morphology and extent otherwise unaffected by aging. In view of the fact that there is no neuronal loss in neocortex and hippocampus in old macaque monkeys, it is possible that the memory and cognitive decline known to occur in these animals is related to rather subtle changes in the morphological and molecular integrity of neurons subserving identifiable neocortical association circuits that play a critical role in cognition.     

The effects of decompression and exogenous NGF on compressed cerebral cortex

Using a rat epidural bead implantation model, we found that compression alone could reduce the overall and individual layer thicknesses of cerebral cortex with no apparent cell death. The dendritic lengths and spine densities of layer II/III and V pyramidal neurons started to decrease within 3 days of compression. Decompression for 14 days resulted in near complete to partial recovery of the cortical thickness and of the dendritic lengths of layer II/III and V pyramidal neurons, depending on the duration of the preceding compression. The recoverability was better following short (3-day) than long (1- or 3-month) periods of compression. The loss of dendritic spines nevertheless persisted. An intraventricular infusion of NGF was performed after decompressing the lesions following 3 days of cortical compression, and this increased the recovery of the spines but not the dendritic length of the cortical pyramidal neurons, nor did it alter the recovery of the cortical thickness. NGF also promoted the increase of the dendritic spines, but not the dendritic length of the cortical pyramidal neurons of normal animals. In short, the data show that a few days of compression alone can cause permanent cortical damage. Exogenous NGF, if applied topically, may restore the dendritic spine density of cortical neurons subjected to compression.     

Subcellular distribution of neurabin immunolabeling in primate prefrontal cortex: comparison with spinophilin

Prefrontal cortical functioning depends on dopaminergic neurotransmission, which in turn depends on a complex signal transduction pathway including protein phosphatase-1 (PP1). Targeted localization of PP1 by the scaffolding proteins, spinophilin and neurabin, is critical for dopaminergic modulation of glutamate neurotransmission. In this study, we report the preparation of an antiserum to neurabin, use it to study the subcellular localization of neurabin and compare that to our previous study of spinophilin, a closely related PP1 scaffold. Neurabin is found predominately in dendritic spines, but is also found in other compartments, including dendrites, axons, terminals and glia. This distribution contrasts with that of spinophilin in that neurabin is found in axon terminals where spinophilin is absent, and in parvalbumin-containing interneuron dendrites there is no significant neurabin though these dendrites contain substantial spinophilin. Within the dendritic spine compartment, however, the two proteins are similarly distributed. Both neurabin and spinophilin are concentrated in spines, and double-labeling reveals that they co-localize in most spines. Furthermore, post-embedding immunogold labeling demonstrates that within a spine, neurabin is distributed in the same pattern as spinophilin, concentrated in the postsynaptic density and the 100 nm just below. These results indicate that neurabin and spinophilin share important similarities and differences in their patterns of distribution. Varying patterns of scaffold localization may play an important role in determining the content and action of signal transduction pathways in different neuronal populations or compartments.     

Lower cervical spine facet cartilage thickness mapping

OBJECTIVE: Finite element (FE) models of the cervical spine have been used with increasing geometric fidelity to predict load transfer and range of motion (ROM) for normal, injured, and treated spines. However, FE modelers frequently treat the facet cartilage as a simple slab of constant thickness, impeding the accuracy of FE analyzes of spine kinematics and kinetics. Accurate prediction of facet joint contact forces and stresses, ROM, load transfer, and the effects of facet arthrosis require accurate representation of the geometry of the articular cartilage of the posterior facets. Previous research has described the orientations of the facet surfaces, their size and aspect ratio, and mean and maximum thickness. However, the perimeter shape of the cartilaginous region and the three-dimensional distribution of cartilage thickness remain ill-defined. As such, it was the intent of this research to further quantify these parameters. METHOD: Vertebrae from seven fresh-frozen unembalmed human cadavers were serially sectioned and the osteochondral interface and the articulating surface of each facet on each slice were identified. The cartilage thickness was recorded at nine equidistant points along the length of each facet. It was observed that facets tended to have elliptic or ovoid shapes, and best-fit ovoid perimeter shapes were calculated for each facet. The thickness distribution data were used to represent the entire three-dimensional cartilage distribution as a function of one variable, and a thickness distribution function was optimized to fit the thickness distribution. The antero-posterior and medial/lateral shifts of the thickness center relative to the geometric were calculated and reported. RESULTS: High correlation was observed between the ovoid perimeter shapes and the measured facet shapes in radial coordinates, indicating that the ovoid approximation is able to accurately represent the range of facet geometries observed. High correlation between the measured and fitted thickness distributions indicates that the fitting function used is able to accurately represent the range of cartilage thickness distributions observed. CONCLUSION: Utilization of a more physiologic cartilage thickness distribution in FE models will result in improved representation of cervical spine kinematics and increased predictive power. The consistency observed in the thickness distribution function in this study indicates that such a representation can be generated relatively easily.     

Biomechanical in vitro evaluation of the complete porcine spine in comparison with data of the human spine

The purpose of this study was to provide quantitative biomechanical properties of the whole porcine spine and compare them with data from the literature on the human spine. Complete spines were sectioned into single joint segments and tested in a spine tester with pure moments in the three main anatomical planes. Range of motion, neutral zone and stiffness parameters of the spine were determined in flexion/extension, right/left lateral bending and left/right axial rotation. Comparison with data of the human spine reported in the literature showed that certain regions of the porcine spine exhibit greater similarities than others. The cervical area of C1–C2 and the upper and middle thoracic sections exhibited the most similarities. The lower thoracic and the lumbar area are qualitatively similar to the human spine. The remaining cervical section from C3 to C7 appears to be less suitable as a model. Based on the biomechanical similarities of certain regions of the porcine and human spines demonstrated by this study results, it appears that the use of the porcine spine could be an alternative to human specimens in the field of in vitro research. However, it has to be emphasized that the porcine spine is not a suitable biomechanics surrogate for all regions of the human spinal column, and it should be carefully considered whether other specimens, for example from the calf or sheep spine, represent a better alternative for a specific scientific question. It should be noted that compared with human specimens each animal model always only represents a compromise.     

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.