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PubMed2003

On the estimation variance for the specific Euler-Poincaré characteristic of random networks.

The specific Euler number is an important topological characteristic in many applications. It is considered here for the case of random networks, which may appear in microscopy either as primary objects of investigation or as secondary objects describing in an approximate way other structures such as, for example, porous media. For random networks there is a simple and natural estimator of the specific Euler number. For its estimation variance, a simple Poisson approximation is given. It is based on the general exact formula for the estimation variance. In two examples of quite different nature and topology application of the formulas is demonstrated.

Humans↗
PubMed1998

Interaction of frontal and perirhinal cortices in visual object recognition memory in monkeys.

Monkeys were trained preoperatively in visual object recognition memory. The task was delayed matching-to-sample with lists of trial-unique randomly generated visual stimuli in an automated apparatus, and the stimuli were 2D visual objects made from randomly generated coloured shapes. We then examined the effect of either: (i) disconnecting the frontal cortex in one hemisphere from the perirhinal cortex in the contralateral hemisphere by crossed unilateral ablations; (ii) disconnecting the magnocellular portion of the mediodorsal (MDmc) thalamic nucleus in one hemisphere from the perirhinal cortex in the contralateral hemisphere; or (iii) bilaterally ablating first the amygdala, then adding fornix transection, then finally perirhinal cortex ablation. We found that both frontal/perirhinal and MDmc/perirhinal disconnection had a large effect on visual object recognition memory, whereas both amygdalectomy and the addition of fornix transection had only a mild effect. We conclude that the frontal lobe needs to interact with the perirhinal cortex within the same hemisphere for visual object recognition memory, but that routes through the amygdala and hippocampus are not of primary importance.

Amygdala↗
PubMed1998

Characterization of neuronal migration disorders in neocortical structures: quantitative receptor autoradiography of ionotropic glutamate, GABA(A) and GABA(B) receptors.

Epileptiform activity was previously described [Luhmann et al. (1998) Eur. J. Neurosci., 10, 3085-3094] in the neocortex of the adult rat following freeze lesioning of the newborn neocortex. After a survival time of 3 months, a small area of dysplastic cortex surrounded by histologically normal (exofocal) neocortex was observed. The dysplastic cortex is characterized by the formation of a small sulcus and a three- to four-layered architecture. Two questions are addressed here: (i) is the hyperexcitability associated with changes in binding to major excitatory and inhibitory transmitter receptors in the dysplastic cortex?; and (ii) do such changes also occur in the exofocal cortex? Alterations in binding to glutamatergic N-methyl-D-aspartate (NMDA), (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), kainate and GABA(A) and GABA(B) (gamma-aminobutyric acid) receptors are demonstrated with quantitative in vitro receptor autoradiography by using the ligands [3H]MK-801, [3H]AMPA, [3H]kainate, [3H]muscimol and [3H]baclofen, respectively. In the dysplastic cortex, the binding to NMDA, AMPA and kainate receptors is significantly increased, whereas the binding to GABA(A) and GABA(B) receptors is reduced. Exofocal areas of the lesioned hemisphere show an imbalance between excitatory and inhibitory receptor binding with an up-regulation of the binding to AMPA and kainate, and a down-regulation to GABA(A) receptors. The binding to GABA(B) and NMDA receptors is not significantly changed in the exofocal areas. The imbalance between excitatory and inhibitory receptors may cause the hyperexcitability, as previously found in the identical experimental model, and may also induce epileptiform activity in the human cortex with migration disorders.

Animals↗
PubMed1998

Organization of projections of rat retrosplenial cortex to the anterior thalamic nuclei.

The organization of the projections from the retrosplenial cortex (Brodmann's area 29) to the anterior thalamic nuclei was examined in the rat with retrograde transport of the cholera toxin B subunit and anterograde transport of biotinylated dextran amine. Areas 29a and 29b project mainly ipsilaterally to the rostral two-thirds of the anteroventral nucleus, with area 29a projecting more rostrodorsally than area 29b. Area 29c projects bilaterally to the ventromedial part of the anteroventral nucleus. The projections from area 29c are organized in a topographic pattern such that the rostral area 29c projects to the caudoventral part of the anteroventral nucleus, whereas the caudal area 29c projects to the more rostrodorsal parts. Caudal area 29d projects mainly ipsilaterally to the rostrodorsal part of the anteromedial nucleus, and the rostral and dorsal parts of the anteroventral nucleus, whereas rostral area 29d projects bilaterally to the caudodorsal part of the anteromedial nucleus and the caudolateral part of the anteroventral nucleus. All the areas of the retrosplenial cortex provide sparse projections, mainly ipsilateral, to the anterodorsal nucleus, with a crude topographic pattern such that the rostrocaudal axis of the retrosplenial cortex corresponds to the caudorostral axis of the anterodorsal nucleus. The results indicate that each area of the retrosplenial cortex has a distinct projection field within the anterior thalamic nuclei. This suggests that each of these projections transmits distinct information that is important for complex memory and learning functions, e.g. discriminative avoidance learning and spatial memory.

Animals↗
PubMed1998

The murine Y1 receptor 5' upstream sequence directs cell-specific and developmentally regulated LacZ expression in transgenic mice CNS.

The Y1 receptor for neuropeptide Y (NPY) is highly expressed in mammalian CNS where it mediates the activation of several neurobiological functions. We have previously demonstrated that a 1.3-kb fragment upstream of the transcription initiation sites of the murine Y1 receptor gene is able to direct specific expression of reporter genes in neuronal cell cultures. In the present study transgenic mice harbouring this putative promoter region linked to the LacZ reporter gene were generated and analysed for temporal and spatial distribution. Ten transgenic lines expressed beta-galactosidase in the CNS but not in other organs such as heart, liver and kidney. Histochemical analysis of brain from adult transgenic mice showed specific expression of the transgene in specific brain regions with little variation. Four transgenic lines showed characteristic patterns of beta-galactosidase activity in the brain that are consistent with the expression of the endogenous gene. Prominent LacZ activity was present in several telencephalic and diencephalic structures, including deeper layers of cerebral cortex, amygdaloid complex, hippocampus, preoptic area, several thalamic and hypothalamic nuclei and habenula. The ontogeny analysis indicates that the LacZ expression agrees with the temporal expression pattern of rat Y1 receptor mRNA. These data demonstrate that the 1.3-kb upstream region of the murine Y1 receptor gene contains the cis acting elements required for establishing a CNS-restricted and developmental stage-specific pattern of expression in vivo. Moreover they provide further information on the distribution of this NPY subtype receptor in mammalian brain.

Animals↗
PubMed1999

The surface contour of articular cartilage in an intact, loaded joint.

The friction coefficients measured in diarthrodial joints are small. Theories of joint lubrication attribute this efficiency to entrapment or movement of synovial fluid, yet anatomical models of the surface are based on studies of isolated fragments of cartilage, not functional joints. To investigate the functional interrelationship of joint surfaces and synovial fluid, the ultrastructure of loaded joints was examined. Twenty-four New Zealand white rabbit knee joints were loaded either statically or moved ex vivo using simulated muscle forces and then plunge-frozen under load. After fixation in the frozen/loaded state by freeze-substitution fixation, the medial joint compartments were embedded in epoxy resin while still articulated. Bone was trimmed away from the articular surfaces, permitting the cartilage to be sectioned for light and electron microscopy. These joint surfaces were then compared with controls which were not loaded, not moved or had been disarticulated prior to embedding. Articular surfaces of loaded joints were smooth at magnifications from x 35 to x 7500, whereas the tibial surfaces of nonloaded joints were irregular. Small pools of joint fluid were observed at the meniscal edge and beneath the anterior horn of the meniscus. At magnifications of x 40000, the joint surfaces were separated by a uniform 100 nm space containing fluid. An amorphous, electron dense articular surface lamina was present but, when loaded, was thicker and flatter than previously reported. No surface pits or bumps were visible in embedded, loaded joints. This is the first ultrastructural study of intact loaded joints. The findings suggest that fluid film lubrication is present in diarthrodial joints, but the fluid sequestration postulated in several models is not apparent.

Animals↗
PubMed2002

The arrector pili muscle and the follicular unit of the scalp: a microscopic anatomy study.

BACKGROUND: The arrector pili muscle is a smooth muscle bundle that attaches to the bulge region of the follicle and extends to its superior attachment in the upper dermis. Hair follicles in the scalp are grouped, forming well-defined anatomic structures known as follicular units, which are composed of terminal and vellus hairs, the associated sebaceous glands, and the arrector pili muscles. OBJECTIVE: To describe the microscopic anatomy of the arrector pili muscles in relation to the follicular units, using horizontal sections of scalp skin. METHODS: Normal scalp skin was obtained from 20 adult cadavers. Tissue specimens were horizontally sectioned at all levels of depth, including the infundibulum, isthmus, and inferior segment. Sections were stained with hematoxylin and eosin, and Masson's trichrome. RESULTS: The distribution of hair follicles in follicular units was only present above the insertions of the arrector pili muscles, at the infundibulum and isthmus. Masson's trichrome proved to be a very useful stain to delineate the follicular units. At the isthmus level, bulky cords of arrector pili muscle were located specifically at one pole of the follicular unit. These bulky cords appeared to be located at the same pole in different follicular units. CONCLUSION: At the isthmus level, above their follicular attachments, the arrector pili muscles that originate from their respective follicles join together, forming a single muscular structure that extends upward to its superior attachment zone. An anatomic model is proposed in which a single arrector pili muscular structure is shared by all the follicles contained within the follicular unit.

Hair Follicle↗
PubMedDate not supplied

Modeling the effects of transforming growth factor-beta on extracellular matrix alignment in dermal wound repair.

We present a novel mathematical model for collagen deposition and alignment during dermal wound healing, focusing on the regulatory effects of transforming growth factor-beta (TGFbeta.) Our work extends a previously developed model which considers the interactions between fibroblasts and an extracellular matrix composed of collagen and a fibrin based blood clot, by allowing fibroblasts to orient the collagen matrix, and produce and degrade the extracellular matrix, while the matrix directs the fibroblasts and control their speed. Here we extend the model by allowing a time varying concentration of TGFbeta to alter the properties of the fibroblasts. Thus we are able to simulate experiments which alter the TGFbeta profile. Within this model framework we find that most of the known effects of TGFbeta, i.e., changes in cell motility, cell proliferation and collagen production, are of minor importance to matrix alignment and cannot explain the anti-scarring properties of TGFbeta. However, we find that by changing fibroblast reorientation rates, consistent with experimental evidence, the alignment of the regenerated tissue can be significantly altered. These data provide an explanation for the experimentally observed influence of TGFbeta on scarring.

Cell Movement↗
PubMed2000

In vitro validation of a new approach for quantitating regurgitations using proximal isovelocity surface area.

The present work has been designed to validate the calculation of the effective regurgitant orifice (ERO) area with the use of a new formula that takes into account the velocity profile (V(r) vs r) and that is insensitive to errors in the determination of the position of the orifice. Assuming a hemispheric model, ERO = 2 pi r(2). V(r)/V(o) (with V(o) = velocity at the orifice) and (V(o)/V(r))(0.5) = (2 pi/ERO)(0.5) r. Thus, the slope of the corresponding linear regression allows ERO to be calculated as: ERO = 2 pi/slope(2). This approach was tested in vitro in pulsatile conditions on circular, conical, and slit-like orifices. The calculated ERO was compared with the actual jet cross sectional area derived from the transverse velocity profile at the jet origin. For the purpose of comparison, the "classical" ERO was calculated for all the configurations, angulations, and threshold velocities. The relationship between (V(o)/V(r))(0.5) was linear (r > 0.98) over a wide range of velocities. The nonhemispheric components were found to modify the constant and not the slope. The mean variation of the calculated ERO was 6.5%. The correlation between the calculated and the actual ERO was very close (>0.97) with slope equal to 0.96. By comparison with the new method, the classical formula gave an underestimation of the ERO that dramatically increased when studying the flow closer to the orifice or in the case of error on the measurement of r. In conclusion, a method using velocity profiles instead of isolated values improves the accuracy of the proximal isovelocity surface area (PISA) method for measuring the ERO.

Blood Flow Velocity↗
PubMed2003

Atrial excitation assuming uniform propagation.

INTRODUCTION: We investigated the spread of the excitation wave over the atria following initiation in a given focus in an atrial model containing its overall geometry only, i.e., without atrial bundles. METHODS AND RESULTS: The propagation velocity of the excitation wave was taken to be uniform, and the wall thickness was discarded. The timing of excitation of any point on the atrium thus becomes directly proportional to its shortest distance over the atrial wall to the focus. Despite these gross simplifications, the general nature of the excitation sequence found corresponded closely to clinical data reported in the literature. This suggests that the complex overall geometry of the atria dominates the timing of the excitation. A highly intriguing observation from this study was that, when looking at the pathways from the sinus node to all other points on the atrium, prominent routes became visible even though no such pathways formed part of the model of the atrial geometry used. The locations of these prominent routes coincide with those of various distinct bundles in the atria. Possible inferences of these observations are discussed. CONCLUSION: Based upon comparison with data from other studies, it is concluded that, during stable heart rhythms, propagation of the atrial excitation wave is well approximated by an assumption of uniform velocity, even though no atrial bundles were included in the model. The overall geometry seems to be the dominant factor in the spread of excitation.

Algorithms↗
PubMed2000

An in vitro study of the accuracy of a new protocol for planning distraction osteogenesis of the mandible.

PURPOSE: The purpose of this study was to determine the in vitro accuracy of a new protocol for distraction osteogenesis of the mandible that involves a planning process and a surgical technique. MATERIALS AND METHODS: An experimental design was developed to simulate distraction osteogenesis on stereolithographic models of patients with craniofacial deformities. All patients had previously undergone 3-dimensional computerized scans of the craniofacial skeleton. The data from these scans were used to generate stereolithographic models. Before the fabrication of the models, the computed tomography (CT) data were manipulated to add a series of rulers and markers to the models. The 3-dimensional computerized scans were also used as the basis of the planning process. They were imported into an animation software (3D-Studio Max; Discreet, Montreal, Canada), and a virtual distractor was built and installed on the model, and the osteotomies and distraction processes were simulated. Finally, a recipe for sequencing the linear and angular changes of the distractor were calculated. A surgical technique was developed to facilitate the precise installation of the distractor as indicated in the presurgical plan. The transfer of information regarding pin position and orientation from the computer model to the patient was accomplished by creating a surgical template. This template was designed in the computer and fabricated by use of stereolithography. Mock surgery was performed on the stereolithographic models, and the results were compared with those predicted by the computer. The difference between the actual position and the predicted position was recorded. RESULTS: On the X-axis, the difference between the predicted position for the condylar marker and the actual position of the marker on the stereolithographic models was 0.6 +/- 1.1 mm. On the Y-axis, the difference between the predicted position for the condylar marker and the actual position of the marker on the stereolithographic models was -0.9 +/- 2.6. On the Z-axis, the difference between the predicted position for the condylar marker and the actual position of the marker on the stereolithographic models was 0.04 +/- 0.8 mm. There was excellent correlation between the predicted and the actual measurements for the X, Y, and Z axes: 0.98, 0.93, and 0.98, respectively. CONCLUSIONS: The results indicate that the combination of this planning process and surgical technique was very accurate. This in vitro study is the first step in determining the clinical usefulness of this protocol. If the results of this study are validated in clinical practice, this protocol will allow clinicians to improve the clinical outcomes of patients treated with distraction osteogenesis.

Analysis of Variance↗
PubMed2001

A biomechanical evaluation of mandibular angle fracture plating techniques.

PURPOSE: The purpose of this investigation was evaluate the biomechanical behavior of a vast array of fixation philosophies and techniques that address mandibular angle fractures. MATERIALS AND METHODS: A total of 150 polyurethane synthetic mandible replicas (Synbone, Laudquart, Switzerland,) were used in this investigation. Five controls and 5 each of 14 different fixation philosophies and techniques were subjected to vertical loading at the incisal edge and then repeated for contralateral loading in the molar region by an Instron 1331 (Instron, Canton, MA) servohydraulic mechanical testing unit. The fixation philosophies and techniques evaluated were the lag screw technique, monocortical superior border plating techniques with varying sizes of plates and screws, monocortical 2-plate techniques with varying forms of fixation, monocortical tension band systems with associated bicortical stabilization plates of various types, and various forms of reconstruction plates. Load/displacement data within a 0 to 200 N range were recorded. Yield load, yield displacement, and stiffness were determined. Mean and standard deviations were calculated, and statistically significant differences within and among categories were determined using an analysis of variance (P <.05). Second-order polynomial best-fit curves were also created for each group to further evaluate and compare the mechanical behavior. RESULTS: For incisal edge loading, statistically significant differences (P <.05) were found for stiffness between some of the monocortical superior border fixation techniques, as well as for yield displacement between several forms of monocortical 2-plate fixation techniques. No other differences were found within categories or among the groups that best represented their categories. For contralateral molar loading, statistically significant differences existed within and among categories. CONCLUSIONS: Under the conditions of this experiment, all systems met or exceeded currently identified postoperative functional requirements for incisal edge loading, but failed to meet them for contralateral molar loading.

Biomechanical Phenomena↗
PubMed2002

Reproducibility of maxillary positioning in Le Fort I osteotomy: a 3-dimensional evaluation.

PURPOSE: In the present study, we evaluated the difference between the model surgery movement and the actual surgical movement in the horizontal (X), vertical (Y), and transverse (Z) directions using the same reference coordinates. PATIENTS AND METHODS: Twelve patients (6 male and 6 female, mean age of 24.3 years) who underwent Le Fort I osteotomy and sagittal split ramus osteotomy were included in the study. The maxillary position was controlled by an intermediate splint and face-bow/bite-fork combination system. A coordinate transformation system with transition matrices was developed, which enabled objective comparison between the planned surgical change of the maxilla on the articulator and the actual surgical change assessed by the 3-dimensional cephalogram. RESULTS: The absolute mean difference was 2.2 mm. The difference between the model surgery and the surgical result ranged from -7.7 mm to 6.6 mm. The surgical result differed from the planned surgical movement by more than 2 mm in more than 45% of the measured coordinate values. CONCLUSION: Although all of the patients were satisfied with their postsurgical appearance and occlusion, the result shows that further development is required in the maxillary positioning system.

Adult↗
PubMed2003

A new technique for the creation of a computerized composite skull model.

PURPOSE: The goals of this study were to develop a technique for creating a computerized composite skull model and to test its accuracy. The computerized composite skull model is the combination of a 3-dimensional (3D) computed tomography (CT) bone model with digital dental models. MATERIALS AND METHODS: A dry skull with intact dentition was used in development of the technique. The creation of the computerized composite skull model was divided into 3 steps. The first step was to create digital dental models. The second step was to create a 3D CT bone model of the craniomaxillofacial skeleton. The last step was to incorporate the digital dental models into the 3D CT skull model, creating a computerized composite skull model. The accuracy of the computerized composite skull model was assessed. Bone-to-bone, tooth-to-tooth, and bone-to-tooth measurements were made on the computerized composite skull model and the dry skull. Pearson correlation coefficient and linear regression tests were performed. RESULTS: A technique to create a computerized composite skull model was developed. This computerized model not only represented bony structures from CT data but also reproduced dentition from digital dental models. For the bone-to-bone measurements, the mean difference between the computerized composite skull model and the dry skull was 0.5 +/- 0.6 mm. For the tooth-to-tooth measurements, the mean difference was 0.1 +/- 0.2 mm. For the bone-to-tooth measurements, the mean difference was 0.2 +/- 0.3 mm. CONCLUSIONS: This study showed the feasibility of creating a computerized composite skull model as well as its accuracy.

Cephalometry↗
PubMed2001

Importance of positioning and technical factors in anatomic localization of sporting injuries in scintigraphic imaging.

Sports medicine is becoming increasingly important as more people take up exercise for health and well-being. It is adding to the spectrum of acute and chronic injuries that have traditionally been seen in elite or professional athletes. Because of its high sensitivity and lesion contrast, bone scintigraphy has traditionally played a key role in the detection of such injuries. This role has been reduced in recent times by the increased use of magnetic resonance imaging (MRI), which has functional capability, high-contrast resolution, and high-spatial resolution. Bone scintigraphy has the capability of detecting early cortical ligament avulsion and enthesopathic disease before the onset of edema or changes in bone marrow that are detected by MRI. If this capability is added to more precise anatomic localization of lesions, we may see a resurgence in its use in sports medicine. A number of techniques are presented in this article, encompassing positioning, special views, and tomographic reconstructions, that can significantly improve the accuracy of localization of scintigraphic abnormalities with reference to anatomic models or sources of cross-sectional anatomy.

Ankle Injuries↗
PubMed2001

Stress analysis in the TMJ during jaw opening by use of a three-dimensional finite element model based on magnetic resonance images.

This study was designed to investigate temporomandibular joint (TMJ) stress distribution during mouth opening using a finite element (FE) model of an individual TMJ based on magnetic resonance (MR) images. A dry skull with a silicon disk was used to test the three-dimensional reconstruction procedure, and showed enough accuracy and reproducibility in linear dimensions and disk volume for the following FE modelling for stress analysis in the TMJ. From an individual FE analysis of a normal subject, relatively high stresses were observed in the anterior and posterior regions of the disk during mouth opening, and furthermore, the superior boundary contacting with the glenoid fossa exhibited lower stresses than those on the inferior boundary facing the condyle. During transmission of stress through the disk, mechanical stress may be reduced by the stress redistribution function of the disk.

Adult↗
PubMed2001

Navigational precision of drilling tools preventing damage to the mandibular canal.

PURPOSE: The use of CT-based intraoperative navigation has greatly improved surgical control in many specialities. In this study the precision of the SMN system (Zeiss, Oberkochen, Germany) for navigated drilling before implant insertion is evaluated. MATERIAL AND METHOD: One hundred test drillings were carried out on 10 standardized acrylic lower jaw models with the aid of the navigation system after CT scanning. The CT scans were taken using a slice thickness of 1 mm. Then the CT data were transferred to the workstation of the SMN system and referentiation with the help of reference points (fiducials) of the mandibular models for superposition of the acrylic and the CT models were carried out. Referentiation of the model and the drilling were performed by a drilling tool. The limit of drilling was the upper border of the mandibular canal. The aim was to come as near as possible without perforation of the canal roof. RESULTS: An average drilling depth of 6.23 mm and a mean distance to the mandibular canal of 0.14 mm (s=0.05) was found. In 11 cases the upper border of the canal was perforated. The average penetration of the mandibular canal measured 0.19 mm. Eighty-nine drill holes were accomplished without perforation. The average distance to the alveolar canal measured 0.13 mm. CONCLUSION: A high precision of CT-based navigation for controlled drilling of mandibles for dental implants was seen.

Cranial Nerve Injuries↗