Mechanisms of the inhibition of fast axonal transport by local anesthetics.

The present study attempted to clarify the mechanism(s) by which local anesthetics inhibit fast axonal transport. Spinal nerves of the bullfrog were incubated with local anesthetics under conditions known to inhibit transport and the effects of these exposures to local anesthetics on the content of adenosine triphosphate and creatine phosphate in nerves and on the density of microtubules in unmyelinated axons were examined. Lidocaine, at concentrations of 14 or 20 mM, did not reduce significantly the content of adenosine triphosphate (although significant reductions in creatine phosphate were observed); the density of microtubules was also not affected by 14 mM lidocaine. Some mechanism other than inhibition of oxidative metabolism or disruption of microtubules must therefore be responsible for the inhibition of fast axonal transport by 14 mM lidocaine. Significant reductions in the content of adenosine triphosphate were observed with 1 or 2 mM tetracaine and with 0.5 or 1 mM dibucaine (this latter concentration of dibucaine also reduced the content of creatine phosphate); however, comparison with the effects of 2,4-dinitrophenol indicated that these inhibitions of oxidative metabolism were insufficient to inhibit transport in the case of 0.5 mM dibucaine or could at best only partly explain the inhibition of transport in the other cases. Since the density of microtubules was not affected by 1 mM tetracaine and was not sufficiently reduced by 0.5 mM dibucaine to inhibit transport, some other effect must again largely contribute to or be solely responsible for the inhibition of fast axonal transport by these concentrations of dibucaine and tetracaine.

Ready evaluation of lung alveolar toxic damage with histological sections morphometry.

In this experiment we aimed at developping a method of ready evaluation of lung alveolar toxic damage using morphometric measurements. Swiss-Webster mice were treated with different doses of diquat (i.p.) and the left lung was fixed at 0, 3, and 5 days after treatment. The technique of morphometry of histological sections embedded in glycol methacrylate (GMA) was used to quantify possible modifications of alveolar cells. Quantitative evaluation includes: alveolar macrophages, polymorphonuclear cells, type II and intermediate pneumocytes. The results indicate a lung dose-dependent response, observed in both inflammatory and epithelial regeneration components of the alveolar primary reaction. This method could be used to readily evaluate the pulmonary toxic potential of any substance.

Comparison of clinical and real-life judgments of loudness discomfort.

The purpose of this study was to determine the relationship between the loudness discomfort level (LDL) and real-life impressions of loudness discomfort. LDLs were measured with an established procedure for a variety of stimuli including FM tones, speech noise, and stimuli recorded from two real-life environments, in two groups of subjects. Sound pressure level distributions were measured in each of two environments at the time of subject recruitment, and LDLs were subsequently measured. LDLs were then compared to the sound pressure levels measured in each environment, and to the impressions of loudness discomfort which subjects reported through the use of a questionnaire. Results indicated large discrepancies between LDLs and judgments of loudness discomfort in real-life environments. The LDL does not appear to be an accurate predictor of subjects' impression of loudness discomfort and may not be appropriate for setting the SSPL of hearing aids.

Absence of age-related optic disk changes in young children with optic nerve hypoplasia.

PURPOSE: To determine whether the ratio of optic disk diameter to disk-to-macula distance (DD/DM) in children with optic nerve hypoplasia (ONH) changes over time. PATIENTS AND METHODS: Fifteen subjects (29 eyes) enrolled in a prospective registry study on ONH had fundus photography performed under the age of 24 months and again at 60 months. Using the ratio of the DD/DM method, the relative size of the optic disk was assessed twice for each photo by one masked expert examiner to determine whether any change in relative disk size occurred over time. RESULTS: There was no change in relative optic disk size between initial and final fundus photographs. The average (± SD) age at the time of initial and final fundus photography was, respectively, 11.6 ± 5.2 months and 60.6 ± 1.3 months. Strong concordance was noted between the average DD/DM of the initial and the final photographs (ρ=0.939; 95% CI: 0.893, 0.981). There was negligible difference between the individual time point measurements (-0.011 ± 0.03) (95% LOA: -0.07, 0.04). CONCLUSION: There were no clinically significant changes in relative optic disk size over time in children with ONH; thus, DD/DM measurements need not be adjusted by age beyond 1 year in children with this disorder.

Clinical electrophysiology and visual outcome in optic nerve hypoplasia.

AIMS: In optic nerve hypoplasia (ONH), the extent of functional loss of retinal ganglion cells cannot be determined by ophthalmoscopic examination. The prognostic value of visual electrodiagnostic tests in infants and toddlers with ONH was assessed by comparison with visual outcome. METHODS: 85 participants with ONH had electroretinogram (ERG) and visual-evoked potential (VEP) testing to flash and to pattern-reversal checks and ocular fundus photography prior to 36 months of age. These initial measures were compared with visual acuity outcomes at 5 years of age in the better-seeing eye. RESULTS: Visual outcomes ranged from normal to no light perception. Electrodiagnostic tests with prognostic value were: the amplitude of the flash VEP (Spearman's rank correlations, p<0.001), the threshold category of stimulus (flash or check size) that elicited a VEP (p<0.001) and the amplitude of the N95 component of the pattern ERG (PERG) to 4-degree checks (p<0.02). Optic nerve size and co-existing pallor were also significant correlates. Stepwise regression analysis composed a best prediction model from VEP threshold category, optic nerve size and optic disc pallor (R(2)=58%; p<0.001). CONCLUSIONS: Optic disc diameter, observation of disc pallor, VEP and PERG testing in infancy are useful for establishing the visual prognosis at 5 years of age in children with ONH. This is consistent with the notion that these parameters are related to the anatomic and functional preservation of retinal ganglion cells.

Nonoperative management of blunt liver and spleen injury in children: evaluation of the ATOMAC guideline using GRADE

BACKGROUND: Nonoperative management of liver and spleen injury should be achievable for more than 95% of children. Large national studies continue to show that some regions fail to meet these benchmarks. Simultaneously, current guidelines recommend hospitalization for injury grade + 2 (in days). A new treatment algorithm, the ATOMAC guideline, is in clinical use at many centers but has not been prospectively validated. METHODS: A literature review conducted through MEDLINE identified publications after the American Pediatric Surgery Association guidelines using the search terms blunt liver trauma pediatric, blunt spleen trauma pediatric, and blunt abdominal trauma pediatric. Decision points in the new algorithm generated clinical questions, and GRADE [Grading of Recommendations, Assessment, Development, and Evaluations] methodology was used to assess the evidence supporting the guideline. RESULTS: The algorithm generated 27 clinical questions. The algorithm was supported by six 1A recommendations, two 1B recommendations, one 2B recommendation, eight 2C recommendations, and ten 2D recommendations. The 1A recommendations included management based on hemodynamic status rather than grade of injury, support for an abbreviated period of bed rest, transfusion thresholds of 7.0 g/dL, exclusion of peritonitis from a guideline, accounting for local resources and concurrent injuries in the management of children failing to stabilize, as well as the use of a guideline in patients with multiple injuries. The use of more than 40 mL/kg or 4 U of blood to define end points for the guideline, and discharging stable patients before 24 hours received 1B recommendations. CONCLUSION: The original American Pediatric Surgery Association guideline for pediatric blunt solid organ injury was instrumental in improving care, but sufficient evidence now exists for an updated management guideline.(AU)

Retinal function in infants with optic nerve hypoplasia: electroretinograms to large patterns and photopic flash.

AIMS: Optic nerve hypoplasia (ONH), which is defined as a congenital deficiency of retinal ganglion cells, may also involve more distal layers of the retina. We investigated electrophysiological function of the retina in ONH using electroretinograms (ERGs). METHODS: ERGs were recorded from 48 subjects (3.5-35 months) with unilateral or bilateral ONH. Pattern reversal (4 degrees checks) was presented under chloral hydrate sedation, using an optical system to correct a cycloplegic refraction. A photopic flash stimulus was also used. Fundus photographs were used to measure the disk diameter/disk macula ratio (DD/DM), and to document other clinical signs. Eyes were classified as moderate (0.15-0.3) or severe (<0.15) ONH, and those with DD/DM greater than 0.3 were used as reference eyes. RESULTS: Pattern ERG recording was completed in 89 eyes and was detectable in 80% of eyes with ONH (61/76 tested) and in all 13 reference eyes. Photopic flash ERGs were of good quality in all eyes. The severity of ONH correlates with the amplitude of the photopic flash b-waves and with the amplitude of the N95 component of the pattern ERG (P<0.01). However, the ERGs to large patterns were well preserved (>3.5 microV) in 10 of 35 eyes with severe ONH. Tortuous retinal vessels in eyes with either moderate or severe ONH were associated with smaller amplitude photopic b-waves and markedly diminished or undetectable pattern ERGs. CONCLUSIONS: This study supports the hypothesis that retinal dysfunction distal to the ganglion cells is common in ONH, but is not predictable on the basis of ONH severity alone. Additionally, tortuous retinal vessels in ONH may be a sign associated with retinal dysfunction.

Histomorphometric study of the pulmonary response of guinea pigs to chronic cotton dust inhalation.

In this study we describe, through stereological methods, the lung morphology following inhalation exposure of guinea pigs to 21 mg/m3 cotton dust (CD) for 1 year. Various stereological parameters were determined on semithin histological sections, through a multistage sampling approach, to study the reaction of the whole lung, alveolar parenchyma, and bronchioles to CD inhalation. After 1 year of exposure, the lung volume was increased. Two distinct patterns of lung response were identified among the exposed animals. In type I responders, most of the morphometric parameters measured to describe the alveolar parenchymal reaction were within control value limits (means +/- 2 SD). In type II responders, the volume density (Vv) of the parenchymal zone was decreased, while the Vv, mean thickness, and absolute volume of the alveolar septa were increased. These changes caused the surface density (Sv) of alveolar epithelium to decrease, and an estimate of the percentage of alveolar septa remaining functional for gas exchange was also significantly lowered in these animals. In both types of responders, fifth to ninth orders of bronchioles had a raised wall to lumen ratio; the Vv and mean thickness of the bronchiolar epithelium were markedly increased, denoting hyperplastic changes. Thus, chronic exposure to cotton dust induced definite morphological changes on the peripheral conducting airways in most of the exposed animals, and induced pronounced changes at the alveolar level in 8 of 17 CD-exposed guinea pigs.

Biphasic mode of epithelial regeneration in murine pulmonary alveoli.

After administration to mice of butylated hydroxytoluene, the pulmonary alveolar epithelium adopts a biphasic pattern of regenerative proliferation. This hitherto-unnoticed pattern of epithelial repair in the lung was revealed by the investigation of stereologic parameters. The earliest evidence of epithelial injury involved the type I pneumocytes, whose necrosis and disappearance from the septal surface was shown by a lowered surface density (SV). Proliferation of the type II pneumocytes ensued: the volume density (VV) rose above normal soon after the onset of necrosis, only to decrease as the cells slowly differentiated into intermediate and then type I pneumocytes. A second peak of type II pneumocytes appeared as the denuding of septa persisted. This twofold proliferation was also shown by the numerical density count (NV). Differentiation into an intermediate pneumocyte was itself documented by the raised VV and SV values. These observations of a biphasic mode of proliferation of type II pneumocytes raise the question of an unsuspected, persistent action of the toxic agent within pulmonary alveoli and serve to document the homeostasis of epithelial regeneration.

A histomorphometric assessment of BHT-induced pulmonary toxicity.

The morphological heterogeneity of the lung and the poor extent of knowledge concerning alveolar repair following toxic insult have made morphology, and especially morphometry, a most suitable approach for the study of the injured lung. In this study we aimed to further develop a rapid and quantitative morphological approach to evaluate the sequence of lesion-repair in the aggressed alveolus. Swiss-Webster mice were treated with butylated hydroxytoluene (BHT, 400 mg/kg ip) and the lung was sampled at 1, 3, 5, 7, and 14 d after treatment. A morphometric evaluation, carried out on histological sections, was used to quantify the inflammatory and epithelial regenerative components of the alveolar primary reaction. Classical morphometric parameters such as the Aa and Na ratios, and the mean cellular surface were determined by planimetry. Following BHT administration, the alveolar stem cells (type II pneumocytes) proliferate and differentiate according to a biphasic pattern, with proliferative peaks at d 3 and 7. Furthermore, the challenged pulmonary alveolus retains increased numerical and surface density of macrophages and type II pneumocytes as late as d 14 after initial aggression.

Dissociation of the inhibition of fast axonal transport by chlorimipramine from an effect on axonal microtubules.

The effect of in vitro exposure of bullfrog spinal nerves to 0.2 mM chlorimipramine on the density of axonal microtubules was studied in an attempt to clarify the mechanism by which chlorimipramine inhibits fast axonal transport. A 17-h exposure to chlorimipramine reduced the density of microtubules in unmyelinated axons by only 18%; this microtubular loss does not reach the upper limit of the range of microtubule reduction associated with inhibition of fast axonal transport. A 23-h exposure to chlorimipramine, which had decreased microtubular density in unmyelinated axons by 40% in a previous study, did not decrease microtubular density in myelinated axons in the present study. These results rule out microtubular destruction as the mechanism responsible for inhibition of fast orthograde axonal transport by chlorimipramine, and greatly reduce the likelihood that microtubular destruction plays a significant role in the inhibition of fast retrograde transport by chlorimipramine.

Intensity discrimination determined with two paradigms in normal and hearing-impaired subjects.

The literature on auditory intensity jnd's is ambiguous with respect to the relationship between the jnd's measured with gated and continuous pedestals and with respect to changes in this relationship in the presence of loudness recruitment accompanying cochlear pathology. In an attempt to clarify these issues and to lay a foundation for systematic investigations of the dependence on the jnd's on loudness functions, the jnd's for pure tones with gated- and continuous-pedestal paradigms of two groups of subjects, one with normal hearing and one with hearing loss of cochlear origin, were measured. The experiments were performed at 0.5, 2, and 6 kHz, and at a wide range of sensation levels (SLs) by means of an adaptive two-alternative, forced-choice (2IFC) procedure. The jnd's obtained with the continuous-pedestal method were smaller than those obtained with the gated-pedestal method for both groups of subjects. They also had smaller intersubject standard deviations. When jnd's of the two groups were compared on the basis of equal SLs, the group with hearing loss showed smaller jnd values than the group with normal hearing for both pedestal paradigms. When the comparisons were made on the basis of equal sound-pressure levels (SPLs), both groups showed similar values for moderate and high SPLs. At relatively low SPLs, the group with hearing loss tended to have somewhat higher values.

Pulmonary toxicity of inhaled aerosolized prostacyclin therapy--an observational study.

Large white/landrace piglets (mass 11 to 21 kg) were exposed to aerosolized alkaline glycine diluent (n = 2) or inhaled aerosolized prostacyclin (n = 2) for five to eight hours. Pigs receiving these aerosols developed mild acute sterile tracheitis, involving the superficial layers of the trachea, shown histologically and ultrastructurally. Pigs receiving the diluent aerosol also showed mild inflammatory changes in the bronchioles. These findings suggest caution with the use of high volumes of aerosolized alkaline glycine diluent during inhaled aerosolized prostacyclin therapy.

A splice variant of the ITF-2 transcript encodes a transcription factor that inhibits MyoD activity.

Proteins of the basic helix-loop-helix (bHLH) family are transcription factors that bind DNA containing the E box motif (CANNTG) found in the promoters of many muscle-specific genes. ITF-2 is a bHLH protein with widespread expression that is thought to form active heterodimers with MyoD, a muscle-specific bHLH transcription factor. We have isolated cDNAs derived from two alternatively spliced forms of mouse ITF-2, termed MITF-2A and -2B. These proteins differ in their N termini. Neither MITF-2A nor -2B transactivated the cardiac alpha-actin promoter, which contains an E box, when transfected into nonmuscle cells. In fact, MITF-2B inhibited MyoD activation of the cardiac alpha-actin promoter. This inhibitory activity required the N-terminal 83 amino acids since MITF-2A showed no inhibitory activity, and a mutant MITF-2B with deletion of the N-terminal 83 amino acids failed to inhibit MyoD-mediated transcriptional activation. MyoD activity was also inhibited by Id, a HLH protein, and this inhibition was reversed by the addition of excess E12 or MITF-2A. However, the inhibition of MyoD activity by MITF-2B was not reversed with E12 or MITF-2A. While Id is thought to inhibit MyoD by binding and sequestering potential dimerization partners, MITF-2B appears to inhibit MyoD activity by forming an inactive heterodimer with MyoD. Thus, differentially spliced transcripts of mouse ITF-2 encode different proteins that appear to dimerize with MyoD and activate or repress transcription.

Comparison of measures of exposure to asbestos in former crocidolite workers from Wittenoom Gorge, W. Australia.

Determinations of exposure-response relationships between crocidolite and the major asbestos-related diseases in the Wittenoom cohort have previously depended on the validity of estimates of airborne exposure to asbestos. This work aims to validate the airborne exposure measurements by obtaining measurements of the concentrations of uncoated crocidolite fibers and asbestos bodies retained in the lungs of individual workers, and to estimate the half-life of crocidolite fibers in the lungs. Samples of lung tissue, excluding tumor, of all former Wittenoom workers known to have died in Western Australia (WA) were sought from teaching hospitals, pathology departments, and the Coroner's pathologist. The lung specimens were processed using Pooley's method with TEM for counts of fibers of all types and using Smith and Naylor's method with conventional light microscopy for asbestos bodies (AB). Multiple linear regression was utilized to examine the associations between crocidolite concentrations in the lung and duration of employment at Wittenoom, time since last employed at Wittenoom, nature of job, estimated average fiber concentration at the worksite, and estimated cumulative crocidolite exposure (CCE) in fiber-years/ml for each subject. Lung tissue from 90 cases was processed and there was good agreement between counts of crocidolite fibers, asbestos bodies, and CCE. Correlations were 0.77 for AB and fibers, 0.54 for AB and CCE, and 0.58 for CCE and fibers, after log transformation. The half-life of crocidolite fibers in the lung was estimated at 92 months (95% CI 55-277 months). Previous estimates of airborne exposure to Wittenoom crocidolite have been reasonably reliable. The relatively simple technique of light microscopy for counting ABs in lung tissue also provides a useful and reliable indication of the level of past occupational exposure to crocidolite in subjects whose exposure has been only to crocidolite. The half-life of crocidolite fibers in the lungs of former Wittenoom workers is about 7-8 years.