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Biomedical subjects

M J Johnson

Publications and source records attributed to M J Johnson.

At least 55 records · Page 3Linked to original sources
PubMed1996

Fat embolism syndrome.

Since it was initially described, fat embolism syndrome (FES) has remained one of the least clearly understood complications of trauma. This article is a review of the classic and current literature on FES with regard to its causes, pathophysiology, clinical presentation, diagnosis, and treatment. FES is associated with many traumatic and nontraumatic conditions, but is most commonly associated with fractures of long bones of the lower extremity. The pathophysiology is thought to be a cascade of events which can lead to adult respiratory distress syndrome (ARDS). Signs and symptoms of clinical FES usually begin within 24 to 48 hours after trauma. The classic triad involves pulmonary changes, cerebral dysfunction, and petechial rash. Clinical diagnosis is key because laboratory and roentgenographic diagnosis is not specific. Treatment consists of careful initial handling, early stabilization of fractures, careful volume replacement, analgesia, respiratory support, and perhaps steroids. The vast majority of patients today survive FES without sequelae.

Embolism, Fat↗
PubMed1995

A comparative analysis of coordinated neuronal activity in the thalamic ventrobasal complex of rats and cats.

There are substantial differences in the incidence of inhibitory neurons in the ventrobasal complex of rat and cat thalamus. This marked dissimilarity in neuronal composition suggests that there should be corresponding differences in the orchestration of neural activity in these regions during cutaneous stimulation. To explore this possibility, we conducted a cross-correlation analysis of neuronal activity in the ventroposterolateral (VPL) nucleus of anesthetized rats and cats. Pairs of neurons representing hairy skin were recorded simultaneously with one or two electrodes during air jet stimulation of multiple sites throughout the receptive fields. Cross-correlation histograms indicated that correlated activity among adjacent neurons occurred in three distinct patterns. In one pattern, classified as narrow-unimodal, the discharge of one neuron preceded a discharge in the partner neuron over a narrow interval of time (< 5 ms). Narrow-bimodal patterns were characterized by responses in which the temporal order of discharges from the two neurons was variable, but the interspike intervals were always < 5 ms. In wide-unimodal patterns, the discharge of one neuron was correlated with subsequent discharges in the partner neuron over a wide interval of time (> 5 ms). In rat VPL, two-thirds of the 58 neuron pairs showing correlated responses were characterized by narrow-unimodal responses and nearly one-third of the neuron pairs displayed narrow-bimodal patterns. Only one pair of rat VPL neurons were characterized by a wide-unimodal pattern of coordination. By comparison, half of the 61 adjacent neuron pairs with coordinated responses in cat VPL were characterized by narrow-unimodal patterns. Slightly more than one-third of the correlated neuron pairs had narrow-bimodal patterns, while the remainder (13%) were classified as wide-unimodal responses. Pairs of neurons separated by 340-405 microns discharged synchronously in a pattern that was similar to the temporal relationship expressed in the narrow-bimodal patterns found among adjacent neurons. In both species, the wide-unimodal patterns had the strongest coordinated responses as measured by the correlation coefficient. Although inhibitory relationships did not appear in correlation histograms that had been corrected for stimulus coordination, cross-correlation analysis of the raw spike trains revealed brief (10-40 ms) periods of inhibition that were associated with cat VPL neurons exhibiting wide-unimodal coordination patterns. In rat VPL, most inhibition involved longer (30-60 ms) periods of inhibitory oscillations appearing amidst a much larger rhythmic pattern. These results suggest that correlation patterns transpiring over narrow (< 5 ms) time intervals represent the coordination of activity among neighboring thalamocortical relay neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1995

Evaluation of preterm delivery in a systemic lupus erythematosus pregnancy clinic.

OBJECTIVE: To identify the primary etiology of preterm birth in women with systemic lupus erythematosus, analyzing prospective data collected on 66 pregnancies in 58 women followed-up at a lupus pregnancy center. METHODS: Hospital records were reviewed and subjects were interviewed for pregnancies delivered after 23 completed weeks' gestation in women cared for at the Hopkins Lupus Pregnancy Center. A control group consisted of all women delivered at the same hospital during 2 years of the study period. RESULTS: Preterm premature rupture of membranes (PROM) occurred in 13 of 33 (39%) pregnancies delivered at 24-36 weeks' gestation. In addition, term PROM also occurred with high incidence in ten of 33 (30.3%) pregnancies delivered after 36 weeks' gestation. The rate of PROM in study subjects differed from that in controls at 34-36 weeks' gestation and after 36 weeks. CONCLUSION: Premature rupture of membranes is more common in pregnancies occurring in women with systemic lupus erythematosus than in control pregnancies. Disease activity, prednisone use, and serologic studies are not predictive. Premature rupture of membranes is the major etiology of preterm birth in this cohort.

Case-Control Studies↗
PubMed1995

Techniques for controlling variability in gram staining of obligate anaerobes.

Identification of anaerobes recovered from clinical samples is complicated by the fact that certain gram-positive anaerobes routinely stain gram negative; Peptostreptococcus asaccharolyticus, Eubacterium plautii, Clostridium ramosum, Clostridium symbiosum, and Clostridium clostridiiforme are among the nonconformists with regard to conventional Gram-staining procedures. Accurate Gram staining of American Type Culture Collection strains of these anaerobic bacteria is possible by implementing fixing and staining techniques within a gloveless anaerobic chamber. Under anaerobic conditions, gram-positive staining occurred in all test organisms with "quick" fixing techniques with both absolute methanol and formalin. The results support the hypothesis that, when anaerobic bacteria are exposed to oxygen, a breakdown of the physical integrity of the cell wall occurs, introducing Gram stain variability in gram-positive anaerobes.

Bacteria, Anaerobic↗
PubMed1995

Evidence for synchronous activation of neurons located in different layers of primary somatosensory cortex.

Although many studies have examined the columnar organization of primary somatosensory (SI) cortex, the functional relationship among neurons in different layers remains unclear. To understand how activity is coordinated among different cortical layers, the present investigation tested the hypothesis that the initial part of a peripheral stimulus produces a serial pattern of laminar activation in SI cortex. Extracellular discharges of 334 histologically recovered neurons were recorded from the medial bank of the coronal sulcus in nine anesthetized cats during electrical or cutaneous stimulation of the distal forelimb. Mean responses during the initial 50-msec period following stimulus onset were largest in layers IIIb or IV for both types of stimulation, but laminar differences in the magnitude of onset responses were not statistically significant. Among 175 neurons with responses exceeding 0.5 spikes per stimulus, electrical stimulation consistently produced shorter response latencies than mechanical indentation in the extragranular (II, IIIa, V, VI), but not in the middle (IIIb, IV), cortical layers. The average minimum latencies for different cortical layers ranged from 7.4 to 10.1 msec for responses to electrical stimulation and from 10.3 to 11.6 msec for responses to mechanical indentations, but these laminar differences were not statistically significant. In some experiments, neurons in different layers of a cortical column were recorded simultaneously with dual-electrode assemblies; among 37 neuron pairs in which both neurons responded with more than 0.5 spikes per stimulus, response latencies were similar, even though the neurons were separated by several hundred microns. Cross-correlation analysis of the onset responses for neurons recorded simultaneously from different layers also indicated that many cells throughout a cortical column were activated nearly simultaneously by the initial phase of a peripheral stimulus. Results from the present study are compared with previous reports examining laminar patterns of activation.

Afferent Pathways↗
PubMed1995

Resistance training modes: specificity and effectiveness.

There is considerable demand for information on the effectiveness of various resistance exercises for improving physical performance, and on how exercise programs must match functional activities to produce the greatest performance gains (training specificity). Evidence supports exercise-type specificity; the greatest training effects occur when the same exercise type is used for both testing and training. Range-of-motion (ROM) specificity is supported; strength improvements are greatest at the exercised joint angles, with enough carryover to strengthen ROMs precluded from direct training due to injury. Velocity specificity is supported; strength gains are consistently greatest at the training velocity, with some carryover. Some studies have produced a training effect only for velocities at and below the training velocity while others have produced effects around the training velocity. The little, mainly isokinetic, evidence comparing different exercise velocities for improving functional performance suggests that faster exercise best improves fast athletic movements. Yet isometric exercise can improve actions like the vertical jump, which begin slowly. The rate of force application may be more important in training than actual movement speed. More research is needed into the specificity and efficacy of resistance exercise. Test populations should include both males and females of various ages and rehabilitation patients.

Exercise↗
PubMed1994

Sensory modulation of synchronous thalamocortical interactions in the somatosensory system of the cat.

Neuronal responses to hairy skin stimulation were simultaneously recorded in the ventral posterolateral nucleus (VPL) of the thalamus and primary somatosensory cortex (SI) of halothane-anesthetized cats. Among 233 thalamocortical neuron pairs, cross-correlation analysis revealed significant interactions in 120 pairs. Excitatory interactions were most prevalent and included influences occurring exclusively in the thalamocortical (41 pairs) or corticothalamic (23 pairs) directions as well as multiphasic interactions (40 pairs) in both directions. Only 16 pairs exhibited inhibitory interactions and 7 of these involved multiphasic combinations of excitation and inhibition. In 14 of these neuron pairs, inhibition was exerted in the corticothalamic direction. Receptive field (RF) overlap between thalamic and cortical neurons varied considerably, and neuronal interactions were more likely for neuron pairs sharing large portions of their combined RFs. Computer-controlled stimulation was delivered to multiple RF sites but only 46% of the neuron pairs displayed interactions at more than one stimulation site and only four neuron pairs showed interactions at all stimulus positions. When interactions occurred at multiple stimulus sites, 40% of these interactions were characterized by timing shifts where the time interval between VPL and SI discharges varied as much as 20 ms because of stimulus relocation. In nine neuron pairs, systematic shifts in stimulus position produced reversals in the temporal sequence of thalamic and cortical neuronal discharges. Functional interactions between thalamic and cortical neurons were detected during both spontaneous and stimulus-induced activity. Matched-sample comparisons of connection strength and half-widths of thalamocortical peaks during spontaneous and stimulus-induced activity indicated that functional interactions produced by cutaneous stimulation were significantly stronger and had less temporal variability than those occurring spontaneously.

Animals↗
PubMed1994

Cross-correlation analysis of cuneothalamic interactions in the rat somatosensory system: influence of receptive field topography and comparisons with thalamocortical interactions.

1. We simultaneously recorded neuronal responses to cutaneous stimulation from matched somatotopic representations in the nucleus cuneatus and ventrobasal complex of intact, halothane-anesthetized rats. A total of 95 cuneate and 86 thalamic neurons representing hairy skin on the forelimb were activated by hair movements produced by air jets at multiple skin sites. Mean responsiveness was higher among neurons in nucleus cuneatus (34.4 spikes per stimulus) than in thalamus (23.7 spikes per stimulus), a result that was consistent with the greater proportion of "sustained" responses recorded in nucleus cuneatus (80%) than in the thalamus (62%). 2. Cross-correlation analysis of 166 pairs of cuneate and thalamic neurons showed that 56 neuron pairs displayed time-locked correlations in activity that were characterized primarily by excitatory interactions (44 pairs) or a combination of excitatory and inhibitory interactions (10 pairs). Unilateral interactions in the cuneothalamic direction (31 pairs) and reverse direction (11 pairs) were observed, as well as multiphasic interactions in both directions (14 pairs). Most excitatory interactions involved intervals of 1-7 ms between successive cuneate and thalamic discharges, whereas most inhibitory influences involved intervals > 7 ms. Connection strength, defined by the ratio of time-linked interactions to the number of cuneate discharges, varied widely among neuron pairs but was largest for interactions involving interspike intervals of < or = 15 ms. 3. The relationship between connection strength and receptive field topography was analyzed in 103 cuneate-thalamic neuron pairs. The region of skin shared by both neurons varied substantially among neuron pairs and the probability of detecting interactions increased proportionately with larger amounts of receptive field overlap. Neuron pairs with moderate (25-50%) amounts of receptive field overlap had connection strengths 3-4 times greater than neuron pairs with minimal (0-25%) overlap. Connection strength was essentially identical, however, for neuron pairs with moderate or large (> 50%) amounts of overlap. 4. Cuneate-thalamic neuron pairs displaying functional connections were usually tested at multiple peripheral sites, but only 37% (18 of 49) of these neuron pairs displayed interactions at more than one stimulation site. Stimulation at different sites altered the timing of interactions in seven neuron pairs, including three that showed timing shifts across time zero in the cross-correlation histogram. In neuron pairs displaying interactions at multiple sites, connection strengths for 67% of the cases were strongest when stimulation was delivered within the region of receptive field overlap.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Loss of muscle mass is poorly reflected in grip strength performance in healthy young men.

Isometric maximal handgrip strength (GSmax) has been used as an expedient test of overall muscle strength and index of fat-free mass (FFM). We tested this relationship in 55 fit young men undergoing high rates of FFM loss in an 8.5-wk military training course involving multiple stressors including nutritionally uncomplicated energy deficit. GSmax was measured by a hand dynamometer interfaced with a computer providing visual feedback; another strength test, measuring dynamic strength of larger muscle groups (Cleansim), was also performed. GSmax did not change (530 +/- 57 vs 529 +/- 63 N) in the face of a 15.6% loss of body weight (12.1 +/- 3.4 (SD) kg), including 6.9% loss of FFM (4.6 +/- 2.6 kg), but Cleansim decremented significantly (77.4 +/- 9.6 to 58.7 +/- 8.9 kg) and changes were significantly correlated with delta FFM for GSmax (r = 0.31) and Cleansim (r = 0.49). We conclude that GSmax is not a good representation of changes in total FFM in healthy young men even though it appears to be useful in more severely catabolic patients with extreme losses of FFM and in pubertal boys making large gains in FFM. Other aspects of physical performance are clearly affected by high rates of weight loss, as demonstrated by decrements in the Cleansim and its stronger relationship to delta FFM.

Adult↗
PubMed1993

Cervical spine evaluation: efficacy of open-mouth odontoid view for nontraumatic radiography.

PURPOSE: The open-mouth odontoid view has been a standard component of radiographic cervical spine series regardless of setting or indication. This study examines the prevalence of disease in C-1 to C-2 in an outpatient setting for nontraumatic neck evaluations. MATERIALS AND METHODS: Reports of 1,033 nontraumatic cervical spine series on file at two large medical centers and at a large multispecialty clinic were reviewed retrospectively for patient characteristics, indications, and radiologic evaluations. RESULTS: The odontoid view in 10 patients demonstrated radiographic abnormalities in C-1 to C-2. Four of these patients had rheumatoid arthritis, two had metastatic carcinoma, one had Down syndrome, and the remaining three had no predisposing conditions for disease in C-1 to C-2. CONCLUSIONS: Odontoid view radiography is warranted in patients with conditions with increased risk for disease in C-1 to C-2, but for the vast majority of outpatients it is not worth the technical difficulty, radiation exposure, or expense.

Adolescent↗
PubMed1993

Thalamocortical interactions in the somatosensory system: interpretations of latency and cross-correlation analyses.

1. Isolated extracellular neuronal responses to cutaneous stimulation were simultaneously recorded from corresponding peripheral representations in the ventrobasal nucleus and primary somatosensory cortex of intact, halothane-anesthetized rats. Thalamic and cortical neurons representing hairy skin on the forelimb were activated by hair movements produced by a series of 50 or 100 discrete air jets. A corresponding set of neurons representing the glabrous pads of the hind paw were activated by a similar number of punctate mechanical displacements. 2. Cortical electrode penetrations were histologically reconstructed, and 118 neurons in the glabrous skin representation exhibited cutaneous responses that were categorized into supragranular, granular, or infragranular groups according to their laminar position. Minimum latencies of cortical neurons responding to glabrous skin displacement were analyzed, and significant differences were found in the distribution of minimum latencies for the different cortical layers. Mean values for minimum latencies in the infragranular and granular layers were 15.8 and 16.3 ms, respectively, whereas supragranular neurons were characterized by minimum latencies having a mean of 20 ms. The differences between these groups suggests that stimulus-induced afferent activity reaches infragranular and granular layers before contacting supragranular neurons. Average latencies were also calculated on responses occurring during the 1st 20 trials, but the cortical distributions of these values overlapped considerably, and differences between the laminar groups were not statistically significant. 3. In several recording sites, two cortical neurons were recorded simultaneously, and the response latencies of these matched pairs were often substantially different despite the similarity in laminar position. This result indicates that laminar location is not the only determinant of response latency and that serially organized circuits are distributed within, as well as between, cortical layers. 4. From a sample of 302 neurons exhibiting cutaneous responses within histologically identified regions of thalamus or cortex, a set of 143 pairs of neurons recorded simultaneously from both regions was available for cross-correlation analysis. Significant thalamocortical interactions were found in 38 neurons pairs. Analysis of these significant interactions revealed that thalamocortical connection strength, as measured by neuronal efficacy, was two to four times larger for neuron pairs having the cortical cell in granular layer IV than for neuron pairs having an extragranular layer cortical neuron. There was no difference in thalamocortical connection strength between neuron pairs containing supra- or infragranular cortical neurons. 5. Summed peristimulus time histograms revealed stimulus-locked inhibition of spontaneous activity in 4% (8/195) or cortical and 18% (20/107) of thalamic neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

The endogenous inhibitor of protein kinase-C in the rat ovary is a protein phosphatase.

Calcium- and lipid-dependent protein kinase (PKC) activity in the ovary of the pseudopregnant rat is masked by an endogenous inhibitor of PKC. These studies were undertaken to examine the mechanism of action of the endogenous inhibitor of PKC in the rat ovary. The addition of the phosphatase inhibitors calyculin-A (0.09 nM), microcystin-LR (6.4 nM), and okadaic acid (10 nM) resulted in the loss of PKC inhibitory activity and an increase in basal PKC activity in rat ovarian cytosol. In phosphatase assays, significant dephosphorylation of histone-III-S or myelin basic protein that had been phosphorylated by PKC occurred within 4 min after the addition of ovarian cytosol from the pseudopregnant rat. This dephosphorylation was prevented from the pseudopregnant rat. This dephosphorylation was prevented by the addition of calyculin-A (0.73 nM) and was removed by fractionation of ovarian cytosol on diethylaminoethyl cellulose. No inhibition of PKC activity was observed when the PKC-specific peptides AcMBP-(4-14) and [Ser25]PKC-(19-31) were used as the substrate for phosphorylation. In addition, rat ovarian cytosol did not exhibit phosphatase activity when the peptide AcMBP-(4-14) was used as the substrate. Addition of ovarian cytosol resulted in dephosphorylation of phosphorylase-alpha phosphorylated by phosphorylase kinase, but not dephosphorylation of histone-II-A or histone-VIII-S phosphorylated by PKA. The data suggest that the endogenous inhibitor of PKC in the rat ovary is a protein phosphatase.

Animals↗
PubMed1992

Nucleotide sequence of a cDNA for canine amylin.

Canine amylin cDNA was cloned and sequenced from a dog pancreas library using oligonucleotide probes corresponding to portions of human amylin. The sequence reported here is significantly different from an incomplete sequence previously reported. The non-amyloidogenic canine mature peptide is 89% and 95% identical to its amyloidogenic human and cat homologues, respectively. Both the dog and cat peptides are identical over the proposed amyloidogenic region, amino acids 20-29. Hydropathy plots comparing these three peptides are nearly identical suggesting that the primary sequence of amylin is in itself insufficient to explain pancreatic amyloid formation.

Amino Acid Sequence↗
PubMed1992

Population differences of fetal biophysical and behavioral characteristics.

Population differences in nonstress test reactivity have been reported with a threefold increase in the likelihood of nonreactive nonstress tests observed in black fetuses as compared with white fetuses. We analyzed fetal behavioral states and fetal heart rates in 14 black and 15 white fetuses at term to explain this observed difference in nonstress test reactivity. Two-hour Doppler and real-time ultrasonographic examination of each patient revealed no differences in percent time spent in the four behavioral states between the two populations. A 9.5 beats/min difference between black and white fetuses was found. The higher baseline heart rate of the black fetuses persisted in each behavioral state and may affect nonstress test reactivity because of rate-dependent decreases in short-term variability and rate-dependent limitations of maximal acceleration amplitude.

Behavior↗