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At least 19 recordsLinked to original sources
PubMed2000

Mechanisms of calcium decay kinetics in hippocampal spines: role of spine calcium pumps and calcium diffusion through the spine neck in biochemical compartmentalization.

Dendritic spines receive most excitatory inputs in the CNS and compartmentalize calcium. Although the mechanisms of calcium influx into spines have been explored, it is unknown what determines the calcium decay kinetics in spines. With two-photon microscopy we investigate action potential-induced calcium dynamics in spines from rat CA1 pyramidal neurons in slices. The [Ca(2+)](i) in most spines shows two decay kinetics: an initial fast component, during which [Ca(2+)](i) in spines decays to dendritic levels, followed by a slower decay phase in which the spine follows dendritic kinetics. The correlation between [Ca(2+)](i) in spine and dendrite at the breakpoint of the decay kinetics demonstrates diffusional equilibration between spine and dendrite during the slower component. To explain the faster initial decay, we rule out saturation or kinetic effects of endogenous or exogenous buffers and focus instead on (1) active calcium extrusion and (2) buffered diffusion of calcium from spine to dendrite. The presence of an undershoot in most spines indicates that extrusion mechanisms can be intrinsic to the spine. Supporting the two mechanisms, pharmacological blockade of smooth endoplasmic reticulum calcium (SERCA) pumps and the length of the spine neck affect spine decay kinetics. Using a mathematical model, we find that the contribution of calcium pumps and diffusion varies from spine to spine. We conclude that dendritic spines have calcium pumps and that their density and kinetics, together with the morphology of the spine neck, determine the time during which the spine compartmentalizes calcium.

Action Potentials↗
PubMed2006

Falls from height: spine, spine, spine!

BACKGROUND: Falls from a height are a major cause of morbidity and hospital cost. Spinal injury is frequently associated with falls from height, but reliable predictive factors have not been identified. Diagnostic evaluation of the spine is complex and debated. Our objective was to characterize spinal injury after falls from height and identify predictive factors of spinal injuries. STUDY DESIGN: Medical records of patients with falls from height>10 feet admitted in a Level I trauma center during a period of 66 months were reviewed. Univariate and multivariate analyses were performed to identify independent risk factors of spinal injuries. RESULTS: Of 414 patients, 127 (31%) suffered 277 spinal injuries. Multiple spinal injuries at different levels were found in 62 (49%) patients; in 19 (15%) spinal injuries were at noncontinuous levels. The only independent predictor of spinal injury was alcohol intoxication (odds ratio=3.305; 95% CI, 1.75-6.242; p<0.001) but the number of intoxicated patients was low and the predictive ability weak. Level of falls from height did not correlate with likelihood of spinal injury. Twenty-four of 107 (22%) patients with spinal injuries and a reliable clinical examination had no symptoms related to the spine; all but 2 had distracting injuries. CONCLUSIONS: Spinal injury is frequent among survivors of falls from height>10 feet. Because of the absence of reliable predictors of spinal injury, the possibility of multiple noncontinuous fractures, and the presence of distracting injuries clouding the clinical presentation, aggressive evaluation of the entire spine is warranted.

Accidental Falls↗
PubMed2000

Anatomy of deer spine and its comparison to the human spine.

The anatomical parameters of the thoracic and lumbar regions of the deer spine were evaluated and compared with the existing data of the human spine. The objective was to create a database for the anatomical parameters of the deer spine, with a view to establish deer spine as a valid model for human spine biomechanical experiments in vitro. To date, the literature has supported the use of both calf and sheep spines as a suitable model for human spine experiments as the difficulty in procuring the human cadaveric spines is well appreciated. With the advent of Bovine Spongiform Encephalopathy (BSE) and its likely transmission to human in form of new variant Creutzfeld Jakob disease (CJD), there is a slight risk of transmission to humans through food chain if proper precautions for disposal of specimen are not adhered to. There is also a significant risk of transmission through direct inoculation to the researchers (Wells et al. Vet. Rec., 1998:142:103-106), working with infected bovine and sheep spine. The deer spines are readily available and there are no reported cases of deer being carriers of prion diseases (Ministry of Agriculture, Fisheries and Food, 1998). Six complete deer spines were measured to determine 22 dimensions from the vertebral bodies, endplates, disc, pedicles, spinal canal, transverse and spinous processes, articular facets. This was compared with the existing data of the human spine in the literature. The deer and human vertebrae show many similarities in the lower thoracic and upper lumbar spine, although they show substantial differences in certain dimensions. The cervical spine was markedly different in comparison. The deer spine may represent a suitable model for human experiments related to gross anatomy of the thoracic and lumbar spine. A thorough database has been provided for deciding the validity of deer spine as a model for the human spine biomechanical in vitro experiments.

Animals↗
PubMed2002

Functional anatomy of the deer spine: an appropriate biomechanical model for the human spine?

The object of this study was to create a database for the biomechanical and certain functional anatomical parameters of the deer spine, for comparison with the human spine. This was done with a view toward using the deer spine as an alternative model for various biomechanical experiments, as it is difficult to procure nonembalmed, fresh human spine specimens. Bovine spongiform encephalopathy (BSE) and its human variant, Creutzfeld Jakob disease (CJD), prevent us from using bovine and sheep spine. There is a risk of transmission of disease through direct inoculation to the researcher working with infected bovine or sheep spine, and a theoretical possibility of transmission through the food chain if proper precautions for specimen disposal are not taken. We chose deer spine as an alternative for testing nonembalmed fresh human spine because, to date, there have been no reported cases of deer being carriers of prion diseases. Fifteen deer spine specimens were sectioned appropriately to obtain six functional spinal units for each level in the thoracic and lumbar spine. Each unit was tested in a Dartec materials testing machine (Dartec Ltd., Stourbridge, UK) under pure moments in three main anatomical planes. The range of motion (ROM), neutral zone (NZ), and stiffness parameters of the functional unit were determined in flexion-extension, right/left lateral bending, and axial rotation. The data obtained were compared with the corresponding human spine data in the literature. Deer spine specimens were also studied for bone mineral density (BMD) using a DEXA scan. The results revealed the overall ROM was greater for deer spine compared to the human spine in the upper thoracic region, but less compared to human spine in the lower lumbar spine region. The only comparable region for ROM was in the lower thoracic/upper lumbar region. The stiffness coefficients were also comparable in this region. The BMD was also comparable in the two species. We conclude that the lower thoracic/upper lumbar region in the deer spine can be used as a model for some human biomechanical experiments because of its biomechanical and material similarities to the human spine of the corresponding region.

Absorptiometry, Photon↗
PubMed2006

Clearing the cervical spine in critically injured patients: a comprehensive C-spine protocol to avoid unnecessary delays in diagnosis.

Clearing the cervical spine in polytrauma patients still presents a challenge to the trauma team. The risk of an overlooked cervical spine injury is substantial since these patients show painful and life-threatening injuries to one or more organ systems so that clinical examination is usually not reliable. A generally approved guideline to assess the cervical spine in polytrauma patients might significantly reduce delays in diagnosis, but a consistent protocol for evaluating the cervical spine has not been uniformly accepted or followed by clinicians. One purpose of this study was to analyse the common methods for cervical spine evaluation in critically injured patients and its safety and efficacy at this trauma centre. The second purpose was to present a comprehensive diagnostic C-spine protocol, based on the authors' experiences with documented cases. From a prospectively gathered polytrauma database, we retrospectively analysed the clinical records of all polytrauma patients, with skeletal and/or non-skeletal cervical spine injuries, who were admitted to this level I trauma centre between 1980 and 2004. All patients were assessed following the trauma algorithm of our unit (modified by Nast-Kolb). Standard radiological evaluation of the cervical spine consisted of either a single lateral view or a three-view cervical spine series (anteroposterior, lateral, odontoid). Further radiological examinations (functional flexion/extension views, oblique views, CT scan, MRI) were carried out for clinical suspicion of an injury or when indicated by the standard radiographs. Sixteen patients (14%) had a single cross-table lateral view for radiological assessment of the cervical spine during initial trauma evaluation, Twenty-nine patients had a three-view cervical spine series (anteroposterior, lateral, odontoid) and 81 patients underwent extended radiological examinations by cervical CT scan (n=52), functional flexion/extension views (n=26) or MRI (n=3). Correct diagnosis was made in 107 patients (91%) during primary trauma evaluation, whereas in 11 patients (9%) our approach to clear the cervical spine failed to detect significant cervical spine injuries. In six patients skeletal injuries were missed by a single lateral view and in two patients by a three-view standard series because inadequate radiographs with poor technical quality or incomplete visualization of the cervical spine did not show the extent of the injury. In three cases ligamentous injuries were missed despite complete sets of standard radiographs and cervical CT scan, but without functional radiography. Common methods for cervical spine evaluation in critically injured patients were plain radiographs, cervical CT scan and functional flexion/extension views. Cervical CT scan was the most efficient imaging tool in detecting skeletal injuries, showing a sensitivity of 100%. A single cross-table lateral view appeared to be insufficient, as we found a sensitivity of only 63%. Functional radiography or MRI was also necessary, as plain radiographs and CT scan failed to detect significant ligamentous injuries in 6% of the patients. For more comprehensive assessment of the C-spine, we presented a new C-spine protocol based on the authors' experiences, with the aim to avoid unnecessary delays in diagnosis.

Adolescent↗
PubMed2004

Impact of time-dependent changes in spine density and spine shape on the input-output properties of a dendritic branch: a computational study.

Populations of dendritic spines can change in number and shape quite rapidly as a result of synaptic activity. Here, we explore the consequences of such changes on the input-output properties of a dendritic branch. We consider two models: one for activity-dependent spine densities and the other for calcium-mediated spine-stem restructuring. In the activity-dependent density model we find that for repetitive synaptic input to passive spines, changes in spine density remain local to the input site. For excitable spines, the spine density increases both inside and outside the input region. When the spine stem resistances are relatively high, the transition to higher dendritic output is abrupt; when low, the rate of increase is gradual and resembles long-term potentiation. In the second model, spine density is held constant, but the stem dimensions are allowed to change as a result of stimulation-induced calcium influxes. The model is formulated so that a moderate amount of synaptic activation results in spine stem elongation, whereas high levels of activation result in stem shortening. Under these conditions, passive spines receiving modest stimulation progressively increase their spine stem resistance and head potentials, but little change occurs in the dendritic output. For excitable spines, modest stimulation frequencies cause a lengthening of both stimulated and neighboring spines and the stimulus eventually propagates. High-frequency stimulation that causes spines to shorten in the stimulated region decreases the amplitude of the dendritic output slightly or drastically, depending on initial spine densities and stem resistances.

Cell Count↗
PubMed1994

Spine fracture risk is predicted by non-spine fractures.

A prospective cohort study of 1098 postmenopausal Japanese-American women evaluated the relationship between baseline non-spine fractures and new (incident) spine fractures. At the baseline examination in 1981, prevalent non-spine fractures were ascertained by interview, and prevalent spine fractures by radiograph. Bone mass measurements of the distal radius, proximal radius, calcaneus (1981), the lumbar spine (1984) were obtained and repeated at 1- to 2-year intervals. Women with existing non-spine fractures have a threefold greater risk of subsequent spine fractures, independent of bone mass, and independent of the known association between prevalent spine fractures and subsequent spine fractures. Women with both a prevalent non-spine fracture and low bone mass (50th percentile or lower) have an eightfold greater risk of new spine fractures compared with women above the 50th percentile of bone mass and no prevalent fractures. In addition to low bone mass, both prevalent spine fractures and prevalent non-spine fractures are strong risk factors for subsequent spine fracture. These data suggest that not all osteoporotic risk factors are expressed via bone mass, and that other, unmeasured risk factors, such as bone quality defects, may explain these results. In clinical terms, women with both prevalent fractures and low bone mass should be recognized as being at extremely high risk, and treatment potency should be commensurate with this level of risk.

Adult↗
PubMed1996

Vertebral deformity in the thoracic spine in post-menopausal women: value of lumbar spine bone density.

Differential bone loss in the thoracic and lumbar spine is known to occur in some patients with osteoporosis. However, the discriminant value of lumbar spine bone densitometry in the detection of thoracic spine fractures in healthy, population-based women has not been established. The relationship between lumbar spine bone mineral density and thoracic spine vertebral deformities in a prospective study of 79 post-menopausal population-based women aged 45-65 years has been investigated. Lumbar spine bone mineral density was measured using dual energy X-ray absorptiometry, and vertebral morphometry was assessed from lateral thoracic spine radiographs. Seven women (9%) were found to have one or more vertebral deformities in the thoracic spine (reduction in anterior or posterior height > 25%). Only one of these had a lumbar spine bone mineral density T score below -2.5, whilst the T score was between -1 and -2.5 in three and greater than -1 in three. Two of these women also had lumbar spine vertebral deformity but lumbar spine radiographs were normal in the remaining five. There were no significant differences in age, height, weight, hormone replacement therapy use or bone mineral density between women with and without thoracic spine fractures. These results demonstrate that vertebral deformities in the thoracic spine occur in a proportion of healthy post-menopausal women in the absence of densitometric or radiographic evidence of osteoporosis in the lumbar spine. Although often asymptomatic, the significance of these fractures lies in the increased risk of further fractures. In the future, morphometric X-ray absorptiometric techniques may prove valuable in the detection of these fractures and avoid the need for conventional radiography.

Absorptiometry, Photon↗
PubMed1985

Three-dimensional analysis of dendritic spines. II. Spine apparatus and other cytoplasmic components.

A total of 342 dendritic spines (193 from the visual and 149 from the cerebellar cortex of the mouse) were analyzed in serial and several hundred of thousands of them in single sections, with respect to the presence and organization of the spine apparatus and other cytoplasmic components. The continuity of the spine apparatus with the smooth endoplasmic reticulum of the dendritic trunk was shown in three-dimensional reconstructions. The dense material of the spine apparatus was divided into "inner dense plate" and "outer dense plate". The close relationship between the outer dense plate and the postsynaptic density suggests that the spine apparatus functions as a postsynaptic protein synthesizing centre. The material from the outer dense plate could be used for a dynamic extension of the synaptic active zone. An extraspinous spine apparatus of the axon initial segment was partially reconstructed. Polyribosomes were found in all large spines of the visual cortex but were not so frequent in small spines and in Purkinje cell dendritic spines. Microfilamentous network and intermediate filaments occurred in the spines. The smooth endoplasmic reticulum of Purkinje cell dendritic spines was reconstructed. No spine apparatus and dense material were present in these spines.

Animals↗
PubMed2005

Prospective performance assessment of an out-of-hospital protocol for selective spine immobilization using clinical spine clearance criteria.

STUDY OBJECTIVE: We determine whether the use of an emergency medical services (EMS) protocol for selective spine immobilization would result in appropriate immobilization without spinal cord injury associated with nonimmobilization. METHODS: A 4-year prospective study examined EMS and hospital records for patients after the implementation of an EMS protocol for selective spine immobilization. EMS personnel were trained to perform and document a spine injury assessment for out-of-hospital trauma patients with a mechanism of injury judged sufficient to cause a spine injury. The assessment included these clinical criteria: altered mental status, evidence of intoxication, neurologic deficit, suspected extremity fracture, and spine pain or tenderness. The protocol required immobilization for patients with a positive assessment on any of those criteria. Outcome characteristics included the presence or absence of spine injury and spine injury management. RESULTS: The study collected data on 13,483 patients; 126 of the patients were subsequently excluded from the study because of incomplete data, leaving a study sample of 13,357 patients with complete data. Spine injuries were confirmed in the hospital records for 3% (n=415) of patients, including 50 patients with cord injuries and 128 patients with cervical injuries. Sensitivity of the EMS protocol was 92% (95% confidence interval [CI] 89.4 to 94.6%) resulting in nonimmobilization of 8% of the patients with spine injuries (33 of 415). None of the nonimmobilized patients sustained cord injuries. The specificity was 40% (95% CI 38.9 to 40.5%). CONCLUSION: The use of our selective immobilization protocol resulted in spine immobilization for most patients with spine injury without causing harm in cases in which spine immobilization was withheld.

Adolescent↗
PubMed2004

Regulation of dendritic spine motility and stability by Rac1 and Rho kinase: evidence for two forms of spine motility.

Dendritic spines are major sites of excitatory synapses in the brain and display rapid motility, which is believed to be important for synapse formation and plasticity. Spine morphology was previously shown to be regulated by the Rho GTPases Rac1 and RhoA. Here, we analyzed the roles of Rac1 and a downstream effector of RhoA, Rho kinase, in controlling spine morphogenesis and their effects on spine motility and stability. Blockade of Rac1 induced long, thin spines and inhibited spine head growth, morphing, and stability. Spine head growth was more severely affected in mature spines. On the other hand, inhibition of Rho kinase induced new, long spines and protrusive motility. These data demonstrate that Rac1 and RhoA/Rho kinase pathways regulate different aspects of spine morphology, motility, and stability and presumably also different aspects of synaptic functions. Moreover, our data show that there are two different types of spine motility: protrusive motility and head morphing, which are differentially regulated by Rac1 and Rho kinase. We propose that these two different types of spine motility serve different functions in synaptogenesis and synapse maturation.

Animals↗
PubMed1997

Anatomy of the sheep spine and its comparison to the human spine.

BACKGROUND: The sheep spine is often used as a model for the human spine, although the degree to which these spines are anatomically comparable has yet to be categorically established. The purpose of this study was to investigate the characteristic anatomical dimensions of the sheep spine and to compare these with existing human data. METHODS: Five complete spines were measured to determine 21 dimensions from the pedicles, spinal canal, transverse and spinous processes, facets, endplates, and disc. RESULTS: The results showed that sheep and human vertebrae are most similar in the thoracic and lumbar regions, although they show substantial differences in certain dimensions. Morphological variations as a function of spine level typically were well matched in the two species. CONCLUSIONS: Sheep spine may be a useful model for experiments related to the gross structure of the thoracic or lumbar spine, with certain limitations for the cervical spine. A thorough database has been provided for deciding the appropriateness of using the sheep spine as a model for the human spine.

Animals↗
PubMed1997

Are sheep spines a valid biomechanical model for human spines?

STUDY DESIGN: Range of motion, neutral zone, and stiffness parameters of the complete cervical, thoracic, and lumbar sheep spine were determined in flexion and extension, axial left/right rotation, and right/left lateral bending. OBJECTIVES: To determine quantitative biomechanical properties of the sheep spine and compare them with those from the human spine. SUMMARY OF BACKGROUND DATA: Sheep spines often serve as a model for experimental in vivo and in vitro studies in spine research, but few quantitative biomechanical data from sheep spines for comparison with human specimens are available. METHODS: Complete spines were sectioned into single-joint segments and tested in a spine tester under pure moments in the three main anatomic planes. RESULTS: The craniocaudal variation in range of motion in all load directions was qualitatively similar between sheep spines and values reported in the literature for human specimens. CONCLUSIONS: Based on the biomechanical similarities of sheep and human spines demonstrated in this study, it appears that the use of the sheep spine, which already includes evaluation of surgical techniques and bone healing processes, might be extended to spinal implants.

Animals↗
PubMed2000

Actin-associated protein synaptopodin in the rat hippocampal formation: localization in the spine neck and close association with the spine apparatus of principal neurons.

Dendritic spines are sites of synaptic plasticity in the brain and are capable of remodeling their shape and size. However, little is known about the cellular mechanisms that regulate spine morphology and motility. Synaptopodin is a recently described actin-associated protein found in renal podocytes and dendritic spines (Mundel et al. J Cell Biol. [1997] 139:193-204), which is believed to play a role in spine plasticity. The present study analyzed the distribution of synaptopodin in the hippocampal formation. In situ hybridization histochemistry revealed a high constitutive expression of synaptopodin mRNA in the principal cell layers. Light microscopic immunohistochemistry showed that the protein is distributed throughout the hippocampal formation in a region- and lamina-specific manner. Postembedding immunogold histochemistry demonstrated that synaptopodin is exclusively present in dendrites and spines, specifically in the spine neck in close association with the spine apparatus. Spines lacking a spine apparatus are not immunoreactive for synaptopodin. These data suggest that synaptopodin links the spine apparatus to actin and may thus be involved in the actin-based plasticity of spines.

Actins↗
PubMed2000

Potential role of synaptopodin in spine motility by coupling actin to the spine apparatus.

Dendritic spines are dynamic structures that rapidly remodel their shape and size. These morphological adaptations are regulated by changes in synaptic activity, and result from rearrangements of the postsynaptic cytoskeleton. A cytoskeletal molecule preferentially found in mature spines is the actin-associated protein synaptopodin. It is strongly expressed by spine-bearing neurons in the olfactory bulb, striatum, cerebral cortex, and hippocampus. In the hippocampus, principal cells express synaptopodin mRNA and sort the protein to the spine compartment. Within the spine microdomain, synaptopodin is preferentially located in the spine neck and is closely associated with the spine apparatus. On the basis of these data we hypothesize that synaptopodin could affect spine motility by bundling actin filaments in the spine neck. In addition, it could link the actin cytoskeleton of spines to intracellular calcium stores, i.e., the spine apparatus and the smooth endoplasmic reticulum.

Actins↗
PubMed2006

New or worsening lumbar spine vertebral fractures increase lumbar spine bone mineral density and falsely suggest improved skeletal status.

Changes in lumbar spine bone mineral density (BMD) are determined by follow-up dual-energy x-ray absorptiometry (DXA) assessments. Inclusion of new or worsening vertebral fractures in follow-up measurements may increase BMD. To test this hypothesis, we examined pooled data from the placebo groups of two clinical trials that involved postmenopausal women with osteoporosis. DXA measurements of lumbar spine BMD, bone mineral content (BMC), and area were obtained at baseline and at two years in the Multiple Outcomes of Raloxifene Evaluation (MORE) Trial and at baseline and study endpoint in the Fracture Prevention Trial. In these trials, fractured vertebrae identified by expert radiologists during posterioranterior (PA) spine DXA assessment were excluded from the BMD assessment. Lateral spine radiographs were graded using a semi-quantitative (SQ) scale. Most new or worsening vertebral fractures (84%) diagnosed from lateral spine radiographs were not identified by PA spine DXA. While the follow-up BMD of vertebrae without new or worsening fractures did not change significantly, each unit increase in SQ grade was associated with an approximate 7.0% increase in the BMD of affected vertebrae (p < 0.001). Increases in BMD were highly correlated with increases in BMC (r = 0.87, p < 0.001). Inclusion of new or worsening vertebral fractures increased PA spine BMD measurements at follow-up, with the impact being related to the magnitude of change in SQ score. It is difficult to reliably identify vertebral fractures from PA spine DXA assessments. Inclusion of new or worsening vertebral fractures in follow-up DXA measurements may falsely suggest an improvement in spine BMD. Our suggestion is to perform lateral spine imaging concurrently with any assessment of PA spine BMD in patients who, in the opinion of the health care provider, may have vertebral fractures.

Absorptiometry, Photon↗
PubMed1999

Estradiol increases spine density and NMDA-dependent Ca2+ transients in spines of CA1 pyramidal neurons from hippocampal slices.

To investigate the physiological consequences of the increase in spine density induced by estradiol in pyramidal neurons of the hippocampus, we performed simultaneous whole cell recordings and Ca2+ imaging in CA1 neuron spines and dendrites in hippocampal slices. Four- to eight-days in vitro slice cultures were exposed to 17beta-estradiol (EST) for an additional 4- to 8-day period, and spine density was assessed by confocal microscopy of DiI-labeled CA1 pyramidal neurons. Spine density was doubled in both apical and basal dendrites of the CA1 region in EST-treated slices; consistently, a reduction in cell input resistance was observed in EST-treated CA1 neurons. Double immunofluorescence staining of presynaptic (synaptophysin) and postsynaptic (alpha-subunit of CaMKII) proteins showed an increase in synaptic density after EST treatment. The slopes of the input/output curves of both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) postsynaptic currents were steeper in EST-treated CA1 neurons, consistent with the observed increase in synapse density. To characterize NMDA-dependent synaptic currents and dendritic Ca2+ transients during Schaffer collaterals stimulation, neurons were maintained at +40 mV in the presence of nimodipine, picrotoxin, and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). No differences in resting spine or dendritic Ca2+ levels were observed between control and EST-treated CA1 neurons. Intracellular Ca2+ transients during afferent stimulation exhibited a faster slope and reached higher levels in spines than in adjacent dendrites. Peak Ca2+ levels were larger in both spines and dendrites of EST-treated CA1 neurons. Ca2+ gradients between spine heads and dendrites during afferent stimulation were also larger in EST-treated neurons. Both spine and dendritic Ca2+ transients during afferent stimulation were reversibly blocked by D, L-2-amino-5-phosphonovaleric acid (D,L-APV). The increase in spine density and the enhanced NMDA-dependent Ca2+ signals in spines and dendrites induced by EST may underlie a threshold reduction for induction of NMDA-dependent synaptic plasticity in the hippocampus.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1991

Methods of estimation of spine density--are spines evenly distributed throughout the dendritic field?

Dendritic spines are small protrusions extending from the dendrites of nerve cells, which bear the majority of synapses. In the past, researchers quantified spine density as the number of visible spines per estimated micrometre of dendrite. This estimate ignores all those spines hidden from view due to their position on the dendrite. Dendrites vary in diameter and the underestimation in some will be greater than others. Estimation of dendritic length is also subjective and difficult in those which are tortuous. The Felman & Peters (1979) geometrical equation takes account of these criteria and provides a method of estimating 'true' spine numbers which does not involve slow and laborious reconstruction. This study compares ratios derived from both methods of estimation (spine density 2:1) at three loci in three experimental groups. Mean values of dendritic diameters and spine dimensions show the major cause for variation in the ratios between loci to be the shaft diameter of the dendrite. However, the greater ratio for apical as compared with basal and oblique dendrites is not as great as expected, bearing in mind that apical dendrites are approximately 2.5 times larger than oblique and basal dendrites. Therefore the spine distribution may not be the same throughout the dendritic field. Estimations of spine density based on visible spine counts are quicker, easier and sufficient for comparisons within the same locus. 'True' estimates (spine density 2) are more accurate and should be used when comparisons are being made between loci, cell types and species.

Animals↗