Effect of estrogen suppression on the mineralization density of iliac crest biopsies in young women as assessed by backscattered electron imaging

The effects of estrogen suppression on bone mineralization in young women were studied by quantitative backscattered electron (BSE) imaging of transiliac biopsies taken before and after treatment for endometriosis. Treatment (6 months) was with analogs of gonadotrophin releasing hormone (GnRH) given either alone (six paired biopsies), which resulted in a marked reduction in the levels of circulating estrogen, or in conjunction with tibolone, a synthetic steroid with estrogenic, progestrogenic, and androgenic properties (four paired biopsies). Estrogen withdrawal increased (p < 0.01) and concomitant tibolone treatment decreased (p < 0.05) the overall mean bone density. Estrogen withdrawal increased the fraction of bone with a high mineralization density [pretreatment: 0.236+/-0.007; GnRH: 0.279+/-0.009, mean +/- standard error of the mean (SEM); p < 0.01]. The concomitant addition of tibolone reversed these effects and increased the proportion of bone with a low mineralization density (pretreatment: 0.198 +/- 0.005; tibolone: 0.230 +/-0.008, p < 0.01). Using previously published data, the mean bone density was inversely correlated with mean wall thickness in cancellous bone (p = 0.030) and with the percentage of active osteons (p = 0.023) in cortical bone. Although treatment had similar effects on the mean bone mineralization density of cortical and cancellous bone, there were different distributions of mineralization between the two sites, with cancellous bone having more skewed and kurtotic distributions both before and after estrogen withdrawal. This study indicates that a short-term estrogen suppression results in the accumulation of bone with a higher mineralization density. As bone with a high mineral content has a decreased impact resistance, this might increase fracture risk. Understanding the cellular and biochemical mechanisms responsible for the local distribution of bone mineral when estrogen is withdrawn may allow the development of new strategies for maintaining bone quality after menopause.

Sequencing and analysis of genes involved in the biosynthesis of a vancomycin group antibiotic

BACKGROUND

The emergence of resistance to vancomycin, the drug of choice against methicillin-resistant Staphylococcus aureus, in enterococci has increased the need for new antibiotics. As chemical modification of the antibiotic structure is not trivial, we have initiated studies towards enzymatic modification by sequencing the DNA coding for the biosynthesis of chloroeremomycin (also known as A82846B and LY264826).

RESULTS

Analysis of 72 kilobases of genomic DNA from Amycolatopsis orientalis, the organism that produces chloroeremomycin, revealed the presence of 39 putative genes, including those coding for the biosynthesis of the antibiotic. Translation and subsequent comparison with known proteins in public databases identified enzymes responsible for the biosynthesis of the heptapeptide backbone and 4-epi-vancosamine, as well as those for chlorination and oxidation reactions involved in the biosynthesis of chloroeremomycin.

CONCLUSIONS

The genes responsible for the biosynthesis of chloroeremomycin have been identified, and selective expression of these genes could lead to the synthesis of new potent glycopeptide antibiotics.

Effects of intravenous methylprednisolone on outcome in MRI-based prognostic subgroups in acute optic neuritis

Treatment of acute optic neuritis with steroids has been shown to hasten visual recovery without affecting the final degree of recovery. However, MRI-clinical studies indicate that patients with long optic nerve lesions, particularly those that involve the nerve within the optic canal, may have a worse prognosis for recovery of vision. Partly because such lesions could lead to swelling and subsequent ischemic optic nerve damage, steroids could have a selective beneficial effect on this subgroup of patients. The present randomized trial was designed to test this possibility. Sixty-six patients with acute optic neuritis received IV saline or IV methylprednisolone. The clinical, psychophysical, electrophysiologic, and MRI outcomes were assessed after 6 months. Patients with short lesions presented earlier than those with long lesions (involving three or more 5-mm-thick slices of any part of the optic nerve, as well as its intracanalicular portion), and lesion length was significantly less in patients presenting within a week of onset of symptoms. Lesions also tended to lengthen during follow-up in individual patients. Treatment did not limit lesion length in either the long or short lesion subgroup and had no significant effect on final visual outcome. We conclude that steroids do not improve visual outcome or lesion length in patients with acute optic neuritis.

Purinergic transmitters inhibit bone formation by cultured osteoblasts

Adenosine triphosphate (ATP) and other purinoceptor agonists cause a transient rise in [Ca2+]i in cultured osteoblast-like cells and have a mitogenic effect, as does parathyroid hormone (PTH), and there is evidence that ATP and PTH can act synergistically on osteoblasts. The likelihood that nucleotides, acting through purinoceptors, are important local factors in bone remodeling is therefore considerable. However, their effect on bone formation is unknown. We recently developed a culture system in which appositional bone formation occurs only in narrow grooves cut in a substratum. We have used this as an assay to measure the effects of ATP (50 and 500 mumol/L), ATP gamma S (20 mumol/L), 2-MeSATP (2 and 20 mumol/L), uridine triphosphate (UTP) (0.2, 2, and 20 mumol/L), adenosine (20 mumol/L), bovine PTH (0.25 and 0.5 IU/mL), rat PTH1-34 (10(-8) and 10(-7) mol/L), and rat PTHrP1-40 (10(-9) and 10(-8) mol/L) on bone formation by rat calvarial osteoblasts. The culture medium was renewed 3 times/week (every 2 or 3 days), and the number of bone loci and length and area of Alizarin red-stained mineralized bone formed in the grooves of each specimen in 16-29 days were measured. Compared with controls, ATP gamma S, 2-MeSATP, and ATP reduced the amount of bone formed in a 2-3 week culture period. Adenosine had no effect, and UTP either had no effect or at 2 mumol/L stimulated bone formation. PTH and PTHrP completely abolished bone formation in 4 week cultures. Our findings are consistent with evidence for more than one P2 purinoceptor subtype in bone, and show for the first time that the effect of ATP on appositional bone formation by osteoblasts in vitro is, like PTH and PTHrP, inhibitory.

E2F as a regulator of keratinocyte proliferation: implications for skin tumor development

E2F and DP family members are established regulators of the cell cycle. In this study, we examined their activity/expression during keratinocyte growth arrest. Treating human epidermal keratinocytes with the growth inhibitors TPA or IFN-gamma or allowing the cells to reach confluence resulted in 90% inhibition of DNA synthesis, whereas a keratinocyte-derived squamous carcinoma cell line (SCC25) was resistant to growth inhibitors. Gel shift analysis of keratinocytes using an E2F response element indicated that growth arrest was associated with a decrease in all E2F binding complexes. This indicates that growth inhibition is not due to negative regulation by pocket proteins. Conversely, gel shift analysis of growth inhibitor-resistant SCC25 cells showed no decrease in E2F binding. If deregulated E2F expression/activity is involved in tumor development, then the deliberate deregulation of E2F activity may make keratinocytes resistant to growth inhibitors in much the same way as the SCC cells. The HPV16 E7 protein is known to activate E2F. Retroviral infection of keratinocytes with E7-expressing constructs resulted in growth inhibitor resistance, whereas infection with E6 constructs did not. E2F is a heterodimeric complex consisting of E2F family members (1-5) and DP proteins (1-3). Examination of the expression levels for E2F genes and other genes associated with the cell cycle indicated that E2F1 was profoundly decreased in growth-arrested keratinocytes (90%), whereas E2F3, E2F5, and DP1 were not. E2F2 and E2F4 were increased in IFN-gamma-treated keratinocytes but not in TPA-treated or confluent keratinocytes. In contrast, SCC25 cells did not undergo growth arrest and did not downregulate E2F1 mRNA expression in response to growth inhibitors. Our results indicate that E2F DNA binding and in particular E2F1 mRNA expression are associated with keratinocyte proliferation. Our results with the SCC25 cells and the E7-infected cells are consistent with the proposition that deregulated E2F expression/activity (in particular E2F1) may be involved in the unregulated proliferation of skin tumor cells.

Using sponsorship to promote health messages to children

A survey of children aged 8 to 14 years attending a three-day football clinic was undertaken to examine the relative impact of different sponsorship strategies used to promote health messages. It was found that promotional clothing worn by role models was an effective method for promoting a specific health message (i.e., "Smoking? No Way!"). Personal endorsement of the health message by an external role model and, to a lesser extent, personal endorsement by clinic leaders and promotional clothing worn by clinic leaders and external role models were also effective in promoting a general health message (i.e., "Don't smoke"). The implications for health sponsorship and the promotion of commercial products to children are discussed.

Conditions for the culture of bovine embryonic myogenic cells

The objective of this experiment was to determine the growth characteristics of bovine embryonic muscle cells and to optimize the growth conditions for these cells using commercially-prepared media and sera. In the first study, the growth of muscle cells isolated from the hindlimb was determined by measuring DNA content. The DNA concentration was lowest (P < 0.001) at 24 h post-plating and increased to a maximum at approximately 60 h. The slopes of creatine kinase activity and fusion index curves were similar to the DNA; however, the creatine kinase activity achieved a maximum at 140 h post-plating, while the fusion index reached maximum at 120 h. In the second study, cells were cultured on different substrata, either plastic, gelatin, or collagen. There were no differences (P > 0.05) in the cell growth rates for any of the three substrata. In the third study, cells were grown in 10% fetal bovine serum (FBS) and either a balanced salt solution (BSS; 30 mM Hepes, 10 mM glucose, 120 mM NaCl, 2.5 mM Na2HPO4, and 3 mM KCl), McCoy's 5A, Dulbecco's Minimal Essential Medium/Ham's F12 (DMEM/F12), or 70% DMEM/20% M-199. Cell numbers adhering to the plate at 26 h post-plating were different (P > 0.001) between each medium (DMEM/M-199 > McCoy's 5A > DMEM/F12 > BSS). Cell proliferation rates for each treatment medium were greatest for DMEM/M-199, followed by McCoy's 5A, DMEM/F12, and BSS. Cell differentiation was highest (P < 0.05) in the DMEM/F12, followed by McCoy's 5A, DMEM/M-199, and BSS. In the final study, the cells were treated with different sources of serum added at 10% to DMEM/M-199. The sera consisted of FBS, newborn calf serum (NCS), horse serum (HS) and iron-supplemented calf serum (Fe(2+)-CS). The cells were added to each well at 10(4) cells. At 24 h post-plating, the serum-free, NCS, and FBS-treated cell numbers were greater (P < 0.05) than the cells treated with HS or Fe(2+)-CS, which may reflect the efficient adherence to the surface or faster adaptation to the serum by the cells. The proliferation rate was greatest (P < 0.001) for the cells treated with Fe(2+)-CS, followed by FBS = NCS, HS, and no serum. Therefore, the muscle cells obtained from bovine embryos grow and differentiate similar to muscle cells from other species. The optimal growth medium for growing these cells in vitro is DMEM/M-199 plus 10% Fe(2+)-CS, while the optimal differentiation medium is McCoy's 5A.

Cognitive screening in mild traumatic brain injuries: analysis of the neurobehavioral cognitive status examination when utilized during initial trauma hospitalization

Cognitive screening following mild traumatic brain injury (MTBI) remains variable with method of diagnosis, indications for testing, and utilization of results differing between institutions. The Neurobehavioral Cognitive Status Examination (NCSE) was originally developed for use in organic brain dysfunction and central nervous system (CNS) lesions. When attention is given to both the objective cognitive area scores and the "process features" component of the exam, it is an effective tool for identifying cognitive deficits associated with MTBI. One hundred seven MTBI patients underwent cognitive screening in the acute care setting. Memory was the function most frequently affected in patients with positive cognitive screens. Several of the NCSE deficits also correlated significantly with each other but not with memory. Age, length of stay, injury severity score (ISS), and cranial computed tomography scan were not associated with cognitive screen results. An admission Glasgow Coma Scale (GCS) of 13 or 14 was significantly associated with a positive cognitive screen, but a GCS of 15 did not predict a negative cognitive screen. All patients with MTBI require cognitive screening to identify deficits, ensure patient and family education, and when necessary facilitate treatment.

Somatosensory evoked potentials in adults with cortical dysgenesis and epilepsy

Cortical dysgenesis (CD) is a well-recognised cause of epilepsy, but its functional anatomy is not fully understood. We recorded cortical somatosensory evoked potentials (SEPs) in 13 adult patients with epilepsy and various CDs excluding diffuse gyral malformations as diagnosed by MRI. The CD involved the perirolandic/perisylvian region in 7 patients. Six patients had neurological signs but only 3 had sensory dysfunction (astereognosis). As compared with 12 control subjects, SEPs were considered definitely abnormal in 7 patients (including the 6 with neurological signs) and equivocally abnormal in 2. The abnormalities ranged from defects affecting single components to absence of all potentials of cortical origin in one patient with hemiparesis and astereognosis. In this case it appears that gross sensory function must have been mediated by subcortical structures or through diffuse cortical projections. The initial cortical potentials (N20/P20) were absent in 6 patients, 5 of whom had CD in zones involving or bordering on the primary sensory cortex. Parietal potentials following N20 were absent or attenuated in 4 patients and of abnormally wide distribution, spreading to frontal, midline and ipsilateral electrodes, in 3 frontal components following P20 were absent, attenuated, delayed or distorted by abnormal spread of the parietal activity in 5 patients. Five patients with unilateral CD showed definite or equivocal SEP abnormalities to stimulation of both arms, suggesting there may be more widespread disturbance of cortical organisation and/or synaptogenesis, beyond the resolution of present day neuroimaging.

Site-directed mutagenesis of the catalytic residues of bovine pancreatic deoxyribonuclease I

Bovine pancreatic deoxyribonuclease I (DNase I) is a well characterised endonuclease which cleaves double-stranded DNA to yield 5' phosphorylated polynucleotides. Co-crystal structures of DNase I with two different oligonucleotides have revealed the presence of several residues (R9, E78, H134, D168, D212 and H252) close to the scissile phosphate. The roles that these amino acids play in the catalytic mechanism have been investigated using site-directed mutagenesis. The following variants were used: R9A, E78T, H134Q, D168S, D212S and H252Q. The kinetics of all six mutants with both DNA and a small chromophoric substrate, thymidine-3',5'-di(p-nitrophenyl)-phosphate, were studied. Only R9A and E78T showed any significant turnover of the two substrates. D168S, H134Q, D212S and H252Q showed vanishingly low activities towards DNA and no detectable activity with thymidine-3',5'-di(p-nitrophenyl)-phosphate. These results demonstrate that H134, D168, D212 and H252 play a critical role in the catalytic mechanism. It is suggested that H134 and H252 (which are hydrogen-bonded to E78 and D212, respectively) provided general acid and general base catalysis. DNase I also requires Mg2+ and E39 has been identified as a ligand for this metal ion. We propose that D168 serves as a ligand for a second Mg2+, and thus DNase I, uses a two metal-ion hydrolytic mechanism. Both magnesium ions are used to supply electrophilic catalysis. Role assignment is based on the mutagenesis results, structural information, homologies between DNase I from different species and a comparison with exonuclease III. However, it is still not feasible to unequivocally assign a particular catalytic role to each amino acid/metal ion.

Mice lacking tartrate-resistant acid phosphatase (Acp 5) have disrupted endochondral ossification and mild osteopetrosis

Mature osteoclasts specifically express the purple, band 5 isozyme (Acp 5) of tartrate-resistant acid phosphatase, a binuclear metalloenzyme that can generate reactive oxygen species. The function of Acp 5 was investigated by targeted disruption of the gene in mice. Animals homozygous for the null Acp 5 allele had progressive foreshortening and deformity of the long bones and axial skeleton but apparently normal tooth eruption and skull plate development, indicating a role for Acp 5 in endochondral ossification. Histomorphometry and mineralization density analysis of backscattered electron imaging revealed widened and disorganized epiphyseal growth plates with delayed mineralization of cartilage in 6- to 8-week-old mutant mice. The membrane bones of the skull showed increased density at all ages examined, indicating defective osteoclastic bone turnover. Increased mineralization density was observed in the long bones of older animals which showed modelling deformities at their extremities: heterozygotes and homozygous Acp 5 mutant mice had tissue that was more mineralized and occupied a greater proportion of the bone in all regions. Thus the findings reflect a mild osteopetrosis due to an intrinsic defect of osteoclastic modelling activity that was confirmed in the resorption pit assay in vitro. We conclude that this bifunctional metalloprotein of the osteoclast is required for normal mineralization of cartilage in developing bones; it also maintains integrity and turnover of the adult skeleton by a critical contribution to bone matrix resorption.

Somatosensory evoked potential monitoring in cervical surgery: identification of pre- and intraoperative risk factors associated with neurological deterioration

Cortical and subcortical somatosensory evoked potentials (SSEPs) were noninvasively monitored in 191 surgical procedures involving the cervical spine. In nine patients in the poorest neurological condition, SSEPs could not be monitored. Lower limb SSEPs were often too degraded to be useful. Upper limb responses were reliably recorded in 182 procedures, with a sensitivity of 99% and a specificity of 27% in 10 patients who developed neurological signs postsurgery. The aim of monitoring was to detect changes in spinal cord function at a time when neurological deterioration could be prevented or reversed, and these studies alerted the authors to certain clinical and SSEP risk factors associated with deterioration. Clinical and operative risk factors were: 1) poor pre-operative neurological function (one-third of Ranawat Class IIIb patients deteriorated); 2) use of instrumentation (the risk doubled in preoperatively unimpaired patients); 3) upper cervical and clival surgery (the risk tripled); and 4) and multisegmental surgery (increased risk with each additional level). There were SSEP changes in 33 patients. Fifty percent of patients with a complete loss had neurological damage, unlike those who had incomplete loss or whose electrical changes had recovered by the end of surgery. In the authors' view these "false positives" may represent real physiological changes, the effects of which might have been minimized by an alteration in the surgeon's response as a result of the warning. Although these initial studies have made this surgical team more alert to potential problems, the role of intraoperative SSEP monitoring is still being debated.

The speed of post mortem change to the human skeleton and its taphonomic significance

The aim of this study was to assess the potential speed of post mortem alteration to skeletal microstructure by examining human material drawn from differing environmental contexts and time periods. The material was taken from terrestrial, intertidal and lacustrine contexts and extended over a range of 3 months to 83 years post mortem. The examination was conducted using backscattered electron imaging which provided information on microstructure and relative density. The results from this study have significantly brought forward the time of known onset for post mortem alteration for 3 morphological types of microstructural change, the earliest of which was 3 months post mortem. The contribution of the depositing environment was also shown to influence significantly the microstructural/ morphological type of post mortem alteration. It is hypothesized that microstructural changes to bone could occur within days of death as a result of endogenous bacterial migration to the skeleton. Further studies are required to establish definitively the earliest moment that such change can occur prior to skeletonisation.

Motor evoked potential monitoring during spinal surgery: responses of distal limb muscles to transcranial cortical stimulation with pulse trains

During spinal surgery, motor evoked potentials (MEPs) were recorded from distal upper and lower limb muscles following multipulse transcranial electrical stimulation of the cortex. Twenty-two patients, 9 of them myelopathic, were anaesthetised with propofol +/- nitrous oxide. Using trains of 3-6 pulses separated by 2 ms, consistent responses generally measuring more than 100 microV were obtained from every patient except one, and persisted with nitrous oxide concentrations as high as 74%. Responses could usually be elicited from 3 or more limbs simultaneously, although the location of the stimulating anode was sometimes critical. The lower limb responses of one patient disappeared transiently during excision of an intramedullary tumour; his leg weakness was increased for a few days after surgery. Three other patients experienced increased weakness or spasticity, two without concomitant MEP changes and one with no recordable responses. Although other methods may be preferable in some circumstances, we believe this represents an advance over previously reported non-invasive techniques for peroperative MEP monitoring, and may be particularly useful for monitoring patients with myelopathy in the thoracic region.

Activation of the protease from human adenovirus type 2 is accompanied by a conformational change that is dependent on cysteine-104

Adenovirus codes for a protease the activity of which can be regulated in vitro by an 11 residue peptide (GVQSLKRRRCF) derived from another viral protein, pVI. Three cysteine residues, one in the activating peptide and two in the protease (C104 and C122), play a central role in both activation and catalysis. Expression of protease mutants in insect cells has shown that C104 is not essential for proteolytic activity. GVQSLKRRRCF also caused a concentration-dependent increase in tryptophan fluorescence of protease expressed in Escherichia coli that paralleled the increase in proteolytic activity, indicating that activation was accompanied by a conformational change. Tryptophan fluorescence of C104S was not increased by the addition of GVQSLKRRRCF, nor was the fluorescence of wild-type protease increased by the addition of the peptide analogues where cysteine is replaced by aspartic acid or serine, suggesting that C104 is involved in activation and C122 in catalysis.

Effects of dexamethasone and anabolic agents on proliferation and protein synthesis and degradation in C2C12 myogenic cells

The objective of this experiment was to determine the dose response of dexamethasone (DEX) on C2C12 myogenic cells and to examine the effects of the anabolic compounds estradiol (E), testosterone (T), and dihydrotestosterone (D) alone and in combination with DEX on proliferation and protein turnover in cultured C2C12 myogenic cells. In the first study, cells were treated with seven concentrations (0, 25, 50, 75, 100, 150, or 200 nM) of DEX in medium with or without 5% horse serum (HS) for the determination of protein synthesis and degradation, and six concentrations (0, 50, 100, 150, 200, or 250 nM) of DEX in medium with 5% fetal bovine serum for cell proliferation measurements. Proliferation of myoblasts decreased (P < .05) with DEX. As DEX concentration increased, protein degradation in myotubes increased (P < .05) up to 100 nM, then declined. Protein synthesis decreased linearly (P < .01) as DEX concentration increased. The presence of HS in the medium decreased (P < .01) protein degradation by 32% as compared with no HS and increased (P < .05) protein synthesis. In the second study, cells were treated with E, T, or D at four concentrations (0, 100, 500, or 1,000 nM) in medium containing 0 or 100 nM DEX. Cells were assayed for protein synthesis or protein degradation. Synthesis decreased (P < .01) and degradation increased (P < .01) with DEX. No differences (P > .05) were found between E, T, or D hormone treatments or concentrations. To measure proliferation, myoblasts were treated 1 d after plating with the same anabolic hormone treatments in medium containing 0 to 100 nM DEX. Cells were grown to confluence and assayed for proliferation. Proliferation decreased (P < .01) in the presence of DEX in each treatment compared with controls. Cells treated with E had significantly lower (P < .05) proliferation rates than cells treated with T and D. The presence of concentrations of DEX at 100 nM inhibited proliferation and protein synthesis and increased protein degradation. Anabolic agents at pharmacological doses do not inhibit the DEX effects on C2C12 myogenic cells, nor do they directly affect proliferation or protein turnover.

A comparison of the mineral content of enamel and dentine in human premolars and enamel pearls measured by X-ray microtomography

Mineral content gradients in two composite enamel pearls from permanent human upper molars were measured by X-ray microtomography (XMT) at a resolution of 15-30 microns. This non-destructive microscopic technique was used to make 15-microns thick XMT slices with 100-microns separation through one pearl and 250-microns separation through the other. Average mineral contents were calculated from the linear absorption coefficients determined from regions of the XMT slices assuming the inorganic component to be calcium hydroxyapatite. These values were compared with similar XMT studies of coronal enamel and dentine of upper permanent premolars. A mineral content gradient in the pearls, reducing from the enamel surface to the amelodentinal junction, was found; this was similar to that observed in the coronal enamel of the upper premolar. The mineral contents in the surface and deeper enamel regions of the pearl were similar to those observed in premolar enamel. In contrast, the mineral content for the dentine of the pearl was greatest at the amelodentinal junction, i.e. the gradient was in the opposite direction to that observed in premolar dentine. These results suggest that the process of mineralization of the pearl dentine differs from that in permanent control dentine. In addition, gradients in enamel and dentine mineral contents reducing from the tip of the pearl to the base of the pearl were found.

Topographically induced bone formation in vitro: implications for bone implants and bone grafts

We have investigated the influence of substrate topography on the timing and location of bone formation by rat osteoblasts. 250 mu m thick slabs of dental tissues were used intact or had a rectangular grid of grooves (350 mu m wide and of variable depth) cut with a diamond wheel. They were then seeded with rat calvarial osteoblasts and cultured in MEM with 10% FCS at 37 degrees C in 5% CO(2). Ascorbic acid 50 mu g/mL and beta-glycero-phosphate 2 mmol/L were added at confluence. Cultures were observed daily from 2 to 4 weeks, until fixation (and storage) in 70% ethanol. Most were stained with alizarin red S to visualize the newly formed bone. The presence of gap junctions in the bone nodules was determined using connexin-43 immunolabeling and confocal microscopy. Two specimens were embedded in polymethylmethacrylate (PMMA): micromilled blockfaces were coated with carbon and examined by digital backscattered electron (BSE) microscopy. Bone formation began in the second week, preferentially wherever cellular condensation was favored: these locations were (a) within the grooves; (b) at the junction between the slab and the bottom of the culture dish; (c) at the periphery of the dish; and (d) in cracks where dissimilar tissues had separated. In the grooves, a grid of aligned bone developed, the deeper trenches showing bone formation earlier than shallower ones, with bone formation tapering off as a groove became shallower. BSE images showed that the bone formed was well mineralized and contained a high volume proportion of osteocytes. Mean and median values for the mean BSE coefficients were: in vitro bone in grooves 0.138528, 0.141484; in vivo aged bone (2 year old rat mandible) 0.143431, 0.144206; and in vivo young bone (neonate rat cranium) 0.129011, 0.132696. Connexin-43 gap junctions were immunolocalized on osteocytes fully enclosed within bone and on osteoblasts overlying it. We conclude first that local topography is an important factor in the location and timing of bone formation in vitro, and that it is likely to be equally important in vivo in normal bone turnover, fracture repair and the incorporation of bone grafts. Second, the mineral density of the bone formed in vitro is consistent with its being true bone.

Scanning electron microscopy of bone: instrument, specimen, and issues

There are many ways available now to maximise and analyse the information that can be obtained on the structure and constitution of bone using SEM. This paper considers a range of methods and the problems that arise relating to instrumentation and methodology as they apply to the use of SEM in the study of bone. In addition to the review content, some novel technical approaches to the SEM of bone are considered here for the first time; these include low kV imaging for the detection of new surface bone packets (and residual demineralized matrix after resorption), low kV BSE imaging of uncoated, embedded, and unembedded samples, environmental SEM for the study of wet tissue, low distortion, very low magnification imaging for the study of cancellous bone architecture, the use of multiple detectors for fast electrons in improving the imaging of porous samples, and high resolution, low voltage imaging for the study of collagen degradation during bone resorption.

Determination of 3-methylhistidine by capillary electrophoresis

The post-translational methylation of histidine to form 3-methylhistidine (3MH) is a modification principally found in contractile proteins, and thus, the level of free 3MH has been used to monitor muscle protein turnover. This work describes procedures for the capillary electrophoretic separation and determination of the phenylthiohydantoin (PTH) derivative of 3MH using uncoated fused-silica capillaries. The procedure described here utilized UV detection and resulted in a linear standard curve in the range of 2-15 pmole, which is more sensitive than previously reported HPLC methods using fluorescent detection. In addition, good agreement for theoretical amounts of 3MH in hydrolyzed rabbit skeletal muscle actin and myofibril preparations from bovine skeletal muscle cells was found.

Clinical evaluation of VEPs to interleaved checkerboard reversal stimulation of central, hemi- and peripheral fields

The VEPs of 195 patients referred for supportive evidence of multiple sclerosis or optic neuritis were studied by a new method of interleaved checkerboard reversal stimulation of different areas of the visual field. In the first group of 95 patients checks of 40' subtense reversed in the whole field (28 degrees x 20 degrees), alternatively in the left and right hemifields and alternately in the central (5 degrees radius) and peripheral fields. In the second group of 100 patients checks reversed in the whole field and in interleaved mode in 3 visual field areas, comprising the central (4 degrees radius) and left and right hemisurround fields. In the first group abnormal responses were recorded from 52 eyes and there was partial disagreement among the stimulus conditions in 10 of the 52. Abnormalities were seen uniquely to central field stimulation in 3 eyes but never to whole field stimulation alone. In the second group abnormal responses were recorded in 58 eyes, again never uniquely to whole field stimulation, while abnormalities confined to one or two areas of the visual field were seen in 24, providing evidence of peripheral field involvement alone in 8 eyes. In the first group, waveforms created from the sum of the left and right hemifield and central and peripheral field responses showed quite close conformity to the whole field VEP, although amplitudes were significantly lower and latencies significantly shorter. In 7 eyes responses would have been differently classified (normal or abnormal) using the sum as compared with the whole fields.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetisation transfer ratios and transverse magnetisation decay curves in optic neuritis: correlation with clinical findings and electrophysiology

Conventional MRI sequences do not permit the distinction between the different pathological characteristics (oedema, demyelination, gliosis, axonal loss) of the multiple sclerosis plaque. Magnetisation transfer imaging and transverse magnetisation decay curve (tMDC) analysis may be more specific. These techniques have been applied to the optic nerves in 20 patients with optic neuritis and the results correlated with clinical and visual evoked potential (VEP) findings. tMDC analysis failed to identify separate intracellular and extracellular water compartments within the optic nerve but gave a measure of transverse relaxation time (T2) without the confounding effects of CSF in the nerve sheath. Both T2 and magnetisation transfer ratio (MTR) were abnormal after an episode of optic neuritis. T2 did not correlate with visual function or with VEP latency or amplitude. There was a significant correlation between MTR reduction and prolongation of VEP latency: this increased latency may reflect an effect of myelin loss on MTR. Longer lesions were associated with worse visual outcome, implying that the overall extent of pathological involvement is likely to influence the degree of functional deficit.

Characterization of the let-653 gene in Caenorhabditis elegans

A mutation in the let-653 gene of Caenorhabditis elegans results in larval death. The lethal arrest is concurrent with the appearance of a vacuole anterior to the lower pharyngeal bulb. The position of the vacuole is consistent with a dysfunction of the secretory/excretory apparatus. Germline transformation rescue experiments were able to position the let-653 gene to two overlapping cosmid subclones. Sequence data generated from both cDNA and genomic DNA subclones indicated that let-653 encodes a mucin-like protein. Our characterization suggests that a mucin-like protein is essential for effective functioning of the secretory/excretory apparatus within C. elegans.