Depressive Symptom Profiles Predict Specific Neurodegenerative Disease Syndromes in Early Stages

Background: During early stages, patients with neurodegenerative diseases (NDG) often present with depressive symptoms. However, because depression is a heterogeneous disorder, more precise delineation of the specific depressive symptom profiles that arise early in distinct NDG syndromes is necessary to enhance patient diagnosis and care. Methods and Findings: Five-hundred and sixty four participants self-reported their depressive symptoms using the Geriatric Depression Scale (GDS), including 111 healthy older control subjects (NC) and 453 patients diagnosed with one of six NDGs who were at the mild stage of disease (CDR® Dementia Staging Instrument ≤ 1) [186 Alzheimer's disease (AD), 76 behavioral variant frontotemporal dementia (bvFTD), 52 semantic variant primary progressive aphasia (svPPA), 46 non-fluent variant PPA (nfvPPA), 49 progressive supranuclear palsy syndrome (PSPS), 44 corticobasal syndrome (CBS)]. The GDS was divided into subscales based on a previously published factor analysis, representing five symptoms (dysphoria, hopelessness, withdrawal, worry, and cognitive concerns). Mixed models were created to examine differences in depression subscale by group, and logistic regression analyses were performed to determine if patterns of depressive symptoms could predict a patient's NDG syndrome. PSPS patients presented with a hopeless, dysphoric, and withdrawn pattern, while patients with CBS presented with a similar but less severe pattern. Worry was a key symptom in the profile of patients with svPPA, while ADs only had abnormally elevated cognitive concerns. Depressive profile accurately predicted NDG diagnosis at a rate of between 70 and 84% accuracy. Conclusions: These results suggest that attention to specific depressive symptom profile can improve diagnostic sensitivity and can be used to provide more individualized patient care.

Strategy use and verbal memory in older adults: The role of intellectual functioning and the preferential impact of semantic clustering

Objective: The relative importance of various mechanisms supporting declarative verbal memory among older adults remains uncertain. The present study examined the impact of strategy use (specifically semantic clustering) versus other variables known to impact memory performance (age, sex, education, FSIQ, processing speed, and executive functioning) on verbal memory functioning among healthy older adults.Methods: Healthy older adults from the California Verbal Learning Test, Second Edition standardization sample were selected (N = 242). Relationships between verbal memory, demographics variables, and neuropsychological factors were established, and a hierarchical regression analysis was conducted to examine the individual contributions of these variables in predicting memory performance.Results: Bivariate correlations suggested that memory was significantly related to demographic factors, IQ, executive functioning, and semantic clustering. Importantly, hierarchical regression analysis revealed that semantic clustering significantly and independently contributed to recall performance beyond the demonstrated impacts of FSIQ, speed, executive functioning, and demographic variables. Furthermore, FSIQ did not moderate the relationship between semantic clustering and memory indicating that this strategy is an important factor in bolstering recall, independent of FSIQ.Conclusions: Our results highlight the critical importance of semantic clustering utilization in enhancing memory performance among healthy older adults.

Long-term test-retest reliability of the California Verbal Learning Test - second edition

OBJECTIVE

Aging is often associated with declines in episodic memory. Reliable tracking of memory requires assessment instruments that are stable over time to better understand changes potentially attributable to neurodegenerative disease. While prior studies support the test-retest reliability of memory instruments over brief intervals, follow-up testing in clinical settings typically occurs at least one-year later. The present study evaluated the long-term test-retest reliability of the California Verbal Learning Test - second edition (CVLT-2), a widely used measure of episodic learning and memory.

METHOD

One hundred and fifty seven healthy older adults (mean age = 68.47 years; education = 17.28 years) underwent repeat assessment at an average of 1.30 years apart. Participants underwent repeat assessment using either parallel or alternate forms at follow-up. We utilized a standardized regression-based (SRB) approach to determine statistically significant changes in test scores over time.

RESULTS

This study revealed modest 1-year test-retest correlation coefficients for the primary CVLT-2 measures (range = .57-.69) Results of SRB formulae are provided to assist clinicians with defining clinically relevant cognitive change on the CVLT-2 while controlling for confounding factors.

CONCLUSIONS

Findings from this study support repeat test administration of the CVLT-2 over longer periods, and may enhance its applicability in determining longitudinal change in memory performance.

White matter hyperintensities correlate to cognition and fiber tract integrity in older adults with HIV

Our aim was to examine the clinical relevance of white matter hyperintensities (WMH) in HIV. We used an automated approach to quantify WMH volume in HIV seropositive (HIV+; n = 65) and HIV seronegative (HIV-; n = 29) adults over age 60. We compared WMH volumes between HIV+ and HIV- groups in cross-sectional and multiple time-point analyses. We also assessed correlations between WMH volumes and cardiovascular, HIV severity, cognitive scores, and diffusion tensor imaging variables. Serostatus groups did not differ in WMH volume, but HIV+ participants had less cerebral white matter (mean: 470.95 [43.24] vs. 497.63 [49.42] mL, p = 0.010). The distribution of WMH volume was skewed in HIV+ with a high proportion (23%) falling above the 95th percentile of WMH volume defined by the HIV- group. Serostatus groups had similar amount of WMH volume growth over time. Total WMH volume directly correlated with measures of hypertension and inversely correlated with measures of global cognition, particularly in executive functioning, and psychomotor speed. Greater WMH volume was associated with poorer brain integrity measured from diffusion tensor imaging (DTI) in the corpus callosum and sagittal stratum. In this group of HIV+ individuals over 60, WMH burden was associated with cardiovascular risk and both worse diffusion MRI and cognition. The median total burden did not differ by serostatus; however, a subset of HIV+ individuals had high WMH burden.

Increased subcortical neural activity among HIV+ individuals during a lexical retrieval task

BACKGROUND

Deficits in lexical retrieval, present in approximately 40% of HIV+ patients, are thought to reflect disruptions to frontal-striatal functions and may worsen with immunosuppression. Coupling frontal-striatal tasks such as lexical retrieval with functional neuroimaging may help delineate the pathophysiologic mechanisms underlying HIV-associated neurological dysfunction.

OBJECTIVE

We examined whether HIV infection confers brain functional changes during lexical access and retrieval. It was expected that HIV+ individuals would demonstrate greater brain activity in frontal-subcortical regions despite minimal differences between groups on neuropsychological testing. Within the HIV+ sample, we examined associations between indices of immunosuppression (recent and nadir CD4+ count) and task-related signal change in frontostriatal structures. Method16 HIV+ participants and 12 HIV- controls underwent fMRI while engaged in phonemic/letter and semantic fluency tasks. Participants also completed standardized measures of verbal fluency

RESULTS

HIV status groups performed similarly on phonemic and semantic fluency tasks prior to being scanned. fMRI results demonstrated activation differences during the phonemic fluency task as a function of HIV status, with HIV+ individuals demonstrating significantly greater activation in BG structures than HIV- individuals. There were no significant differences in frontal brain activation between HIV status groups during the phonemic fluency task, nor were there significant brain activation differences during the semantic fluency task. Within the HIV+ group, current CD4+ count, though not nadir, was positively correlated with increased activity in the inferior frontal gyrus and basal ganglia.

CONCLUSION

During phonemic fluency performance, HIV+ patients recruit subcortical structures to a greater degree than HIV- controls despite similar task performances suggesting that fMRI may be sensitive to neurocompromise before overt cognitive declines can be detected. Among HIV+ individuals, reduced activity in the frontal-subcortical structures was associated with lower CD4+ count.

A Diagnostic Dilemma: Similarity of Neuroradiological Findings in Central Nervous System Hemophagocytic Lymphohistiocytosis and Aspergillosis

Central nervous system (CNS) involvement in the context of hemophagocytic lymphohistiocytosis (HLH) is not uncommon. Given the immunosuppressive nature of HLH therapy, infectious complications are also seen. We describe a 9-year-old male who developed acute neurological decline secondary to aspergillosis while undergoing HLH therapy. The significant overlap observed in CNS neuroimaging of HLH and aspergillosis and the subtleties that may help differentiate the two are discussed. The importance of obtaining tissue for definitive diagnosis is underscored.

Mild Cognitive Impairment is Associated With White Matter Integrity Changes in Late-Myelinating Regions Within the Corpus Callosum

Degenerative brain changes in Alzheimer's disease may occur in reverse order of normal brain development based on the retrogenesis model. This study tested whether evidence of reverse myelination was observed in mild cognitive impairment (MCI) using a data-driven analytic approach based on life span developmental data. Whole-brain high-resolution diffusion tensor imaging scans were obtained for 31 patients with MCI and 79 demographically matched healthy older adults. Comparisons across corpus callosum (CC) regions of interest (ROIs) showed decreased fractional anisotropy (FA) in the body but not in the genu or splenium; early-, middle-, and late-myelinating ROIs restricted to the CC revealed decreased FA in late- but not early- or middle-myelinating ROIs. Voxelwise group differences revealed areas of lower FA in MCI, but whole-brain differences were equally distributed across early-, middle-, and late-myelinating regions. Overall, results within the CC support the retrogenesis model, although caution is needed when generalizing these results beyond the CC.

Glucose Dysregulation Interacts With APOE-∊4 to Potentiate Temporoparietal Cortical Thinning

We examined the interactive effects of apolipoprotein ∊4 (APOE-∊4), a risk factor for Alzheimer's disease (AD), and diabetes risk on cortical thickness among 107 healthy elderly participants; in particular, participants included 27 APOE-∊4+ and 80 APOE-∊4- controls using T1-weighted structural magnetic resonance imaging. Regions of interests included select frontal, temporal, and parietal cortical regions. Among APOE-∊4, glucose abnormalities independently predicted reduced cortical thickness among temporoparietal regions but failed to predict changes for noncarriers. However, among noncarriers, age independently predicted reduced cortical thickness among temporoparietal and frontal regions. Diabetes risk is particularly important for the integrity of cortical gray matter in APOE-∊4 and demonstrates a pattern of thinning that is expected in preclinical AD. However, in the absence of this genetic factor, age confers risk for reduced cortical thickness among regions of expected compromise. This study supports aggressive management of cerebrovascular factors and earlier preclinical detection of AD among individuals presenting with genetic and metabolic risks.

Anoikis-resistant subpopulations of human osteosarcoma display significant chemoresistance and are sensitive to targeted epigenetic therapies predicted by expression profiling

Background

Osteosarcoma (OS) is the most common type of solid bone cancer, with latent metastasis being a typical mode of disease progression and a major contributor to poor prognosis. For this to occur, cells must resist anoikis and be able to recapitulate tumorigenesis in a foreign microenvironment. Finding novel approaches to treat osteosarcoma and target those cell subpopulations that possess the ability to resist anoikis and contribute to metastatic disease is imperative. Here we investigate anchorage-independent (AI) cell growth as a model to better characterize anoikis resistance in human osteosarcoma while using an expression profiling approach to identify and test targetable signaling pathways.

Methods

Established human OS cell lines and patient-derived human OS cell isolates were subjected to growth in either adherent or AI conditions using Ultra-Low Attachment plates in identical media conditions. Growth rate was assessed using cell doubling times and chemoresistance was assessed by determining cell viability in response to a serial dilution of either doxorubicin or cisplatin. Gene expression differences were examined using quantitative reverse-transcription PCR and microarray with principal component and pathway analysis. In-vivo OS xenografts were generated by either subcutaneous or intratibial injection of adherent or AI human OS cells into athymic nude mice. Statistical significance was determined using student’s t-tests with significance set at α = 0.05.

Results

We show that AI growth results in a global gene expression profile change accompanied by significant chemoresistance (up to 75 fold, p < 0.05). AI cells demonstrate alteration of key mediators of mesenchymal differentiation (β-catenin, Runx2), stemness (Sox2), proliferation (c-myc, Akt), and epigenetic regulation (HDAC class 1). AI cells were equally tumorigenic as their adherent counterparts, but showed a significantly decreased rate of growth in-vitro and in-vivo (p < 0.05). Treatment with the pan-histone deacetylase inhibitor vorinostat and the DNA methyltransferase inhibitor 5-azacytidine mitigated AI growth, while 5-azacytidine sensitized anoikis-resistant cells to doxorubicin (p < 0.05).

Conclusions

These data demonstrate remarkable plasticity in anoikis-resistant human osteosarcoma subpopulations accompanied by a rapid development of chemoresistance and altered growth rates mirroring the early stages of latent metastasis. Targeting epigenetic regulation of this process may be a viable therapeutic strategy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0466-4) contains supplementary material, which is available to authorized users.

Abstract A70: Chemotherapy-resistant subpopulations in a tumor-initiating cell model of human osteosarcoma

Introduction: Tumor-initiating cells (TICs) are a subpopulation of therapy resistant cells in osteosarcoma. To date, TICs have been experimentally defined based on the chosen isolation technique. Common to all isolation methods, TICs demonstrate a high degree of the multi-drug resistance phenotype, are more invasive, metastasize readily, and have increased capacity for tumorigenesis. Given this phenotype TICs represent a viable therapeutic target. Cultivating cells in low-adherence, serum-deprived conditions results in spherical colony formation. Certain growth factors present in serum drive epithelial-to-mesenchymal transition, and typically confound TIC models of carcinoma. The effect of serum on mesenchymal-based sarcoma TIC models is less clear. Recent literature suggests that merely the presence of low-adherence conditions can enrich in TICs. We have shown that osteosarcoma cells cultured in low-adherence conditions in the presence of 10% fetal bovine serum (FBS) form spheres, exhibit an increased expression of genes implicated in developmental programs and stem cells, are more resistant to chemotherapy, and more readily initiate tumors than adherent cells when injected into mice.

Methods: The osteosarcoma cell lines 143B, mHOS, and MG-63 were cultured in low-adherence plates using DMEM or MEM media supplemented with 10% FBS. Spheres were routinely grown for 4-6 days between passages and dissociated using 0.05% trypsin. Relative mRNA expression levels of Nanog, Sox2, Oct4 and Axin2 was assessed using quantitative-PCR (SYBR Green). Resistance to chemotherapy (doxorubicin and cisplatin) was determined by comparing both adherent cells and spheres (in low adherence 96-well plates) grown to at least the second passage. After 72 hours IC50 values were calculated using the CellTitre Glo luminescence assay. To assess in vivo tumorgenicity, adherent and sphere cells were dissociated and injected into the flanks of nude mice at a density of 10,000 cells. Upon tumor formation the mice were euthanized and the tumors re-implanted into a second set of mice to test their ability to serially transplant.

Results: Sarcospheres can be successfully and reproducibly grown and passaged in low-adherent culture conditions in media supplemented with 10% FBS. Expression profiling demonstrates increased expression of Sox2, Oct4, Nanog, and Axin2, all genes that have been identified to be associated with developmental programs and stem cells. Sarcospheres also displayed increased chemoresistance compared to adherent cultures to both cisplatin (IC50 change of 1.9, 6.9, and 6.2-fold in 143B, mHOS and MG-63, respectively) and more so to doxorubicin (IC50 change of 12.7, 35 and greater than 74-fold in 143B, mHOS, and MG-63, respectively). Additionally, in a pilot subcutaneous xenograft study, using sphere and adherent cells, differential growth was observed within the TIC-enriched populations demonstrating (1) earlier tumor initiation and (2) a lower overall proliferation rate among the primary and serially transplanted tumors confirming a persistence of the TIC phenotype through in vivo passaging.

Conclusions: Osteosarcoma cells cultured in low-adherence conditions in the presence of serum display many of the characteristics of putative tumor-initiating cells including robust sphere formation, upregulation of key stemness mediators, enhanced chemoresistance, and in vivo tumor initiation and serial transplantability. Using this system, we aim to further evaluate these stem-like populations in order to elucidate potential therapies targeting this specialized, chemoresistant niche.

Citation Format: Jessica M. Foley, Noel R. Monks, Donald J. Scholten, II, David J. Monsma, Dawna Dylewski, Paula J. Davidson, Matthew R. Steensma. Chemotherapy-resistant subpopulations in a tumor-initiating cell model of human osteosarcoma. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr A70.

Interactive effects of apolipoprotein E4 and diabetes risk on later myelinating white matter regions in neurologically healthy older aged adults

Possession of the apolipoprotein E4 (APOE4) allele and diabetes risk are independently related to reduced white matter (WM) integrity that may contribute to the development of Alzheimer's disease (AD). The purpose of this study is to examine the interactive effects of APOE4 and diabetes risk on later myelinating WM regions among healthy elderly individuals at risk of AD. A sample of 107 healthy elderly (80 APOE4-/27 APOE4+) individuals underwent structural magnetic resonance imaging/diffusion tensor imaging (DTI). Data were prepared using Tract-Based Spatial Statistics, and a priori regions of interest (ROIs) were extracted from T1-based WM parcellations. Regions of interest included later myelinating frontal/temporal/parietal WM regions and control regions measured by fractional anisotropy (FA). There were no APOE group differences in DTI for any ROI. Within the APOE4 group, we found negative relationships between hemoglobin A1c/fasting glucose and APOE4 on FA for all later myelinating WM regions but not for early/middle myelinating control regions. Results also showed APOE4/diabetes risk interactions for WM underlying supramarginal, superior temporal, precuneus, superior parietal, and superior frontal regions. Results suggest interactive effects of APOE4 and diabetes risk on later myelinating WM regions, which supports preclinical detection of AD among this particularly susceptible subgroup.

Visuospatial and Attentional Abilities Predict Driving Simulator Performance Among Older HIV-infected Adults

OBJECTIVES

To examine the effects of aging and neuropsychological (NP) impairment on driving simulator performance within a human immunodeficiency virus (HIV)-infected cohort.

METHODS

Participants included 79 HIV-infected adults (n = 58 > age 50, n = 21 ≤ 40) who completed a NP battery and a personnel computer-based driving simulator task. Outcome variables included total completion time (time) and number of city blocks to complete the task (blocks).

RESULTS

Compared to the younger group, the older group was less efficient in their route finding (blocks over optimum: 25.9 [20.1] vs 14.4 [16.9]; P = .02) and took longer to complete the task (time: 1297.6 [577.6] vs 804.4 [458.5] seconds; P = .001). Regression models within the older adult group indicated that visuospatial abilities (blocks: b = -0.40, P <.001; time: b = -0.40, P = .001) and attention (blocks: b = -0.49, P = .001; time: b = -0.42, P = .006) independently predicted simulator performance. The NP-impaired group performed more poorly on both time and blocks, compared to the NP normal group.

CONCLUSIONS

Older HIV-infected adults may be at risk of driving-related functional compromise secondary to HIV-associated neurocognitive decline.

Cognitive reserve as a protective factor in older HIV-positive patients at risk for cognitive decline

The present study examined the impact of cognitive reserve in maintaining intact neuropsychological (NP) function among older HIV-positive individuals, a uniquely at-risk subgroup. Participants included 129 individuals classified by HIV serostatus, age group, and NP impairment. A three-way analysis of variance (ANOVA) followed by a series of within-group ANOVA and multiple regression analyses were conducted to investigate the pattern of cognitive reserve (vs. other protective) influence among groups with varying risks of NP impairment. Results indicated a significant age × HIV status interaction, with older HIV-positive individuals demonstrating higher cognitive reserve than subgroups with less risk for NP compromise (younger age and/or HIV-negative). Results demonstrated higher cognitive reserve specific to NP-intact older HIV-positive individuals. Within this group, the interaction of younger age and higher cognitive reserve independently contributed to cognitive status when controlling for psychiatric, immunological, and psychosocial protective mechanisms, suggesting the importance of cognitive reserve beyond other protective mechanisms in maintaining optimal NP functioning in those individuals most at risk. Alongside younger age, factors contributing to cognitive reserve (i.e., education and estimated premorbid intelligence) may provide substantial benefit for older HIV-positive adults who are at high risk for NP compromise.

Basal ganglia structures differentially contribute to verbal fluency: evidence from Human Immunodeficiency Virus (HIV)-infected adults

BACKGROUND

The basal ganglia (BG) are involved in executive language functions (i.e., verbal fluency) through their connections with cortical structures. The caudate and putamen receive separate inputs from prefrontal and premotor cortices, and may differentially contribute to verbal fluency performance. We examined BG integrity in relation to lexico-semantic verbal fluency performance among older HIV infected adults.

METHOD

20 older (50+ years) HIV+ adults underwent MRI and were administered measures of semantic and phonemic fluency. BG (caudate, putamen) regions of interest were extracted.

RESULTS

Performance on phonemic word generation significantly predicted caudate volume, whereas performance on phonemic switching predicted putamen volume.

CONCLUSIONS

These findings suggest a double dissociation of BG involvement in verbal fluency tasks with the caudate subserving word generation and the putamen associated with switching. As such, verbal fluency tasks appear to be selective to BG function.

Depression, cognition, and self-appraisal of functional abilities in HIV: an examination of subjective appraisal versus objective performance

Depression frequently co-occurs with HIV infection and can result in self-reported overestimates of cognitive deficits. Conversely, genuine cognitive dysfunction can lead to an under-appreciation of cognitive deficits. The degree to which depression and cognition influence self-report of capacity for instrumental activities of daily living (IADLs) requires further investigation. This study examined the effects of depression and cognitive deficits on self-appraisal of functional competence among 107 HIV-infected adults. As hypothesized, higher levels of depression were found among those who over-reported problems in medication management, driving, and cognition when compared to those who under-reported or provided accurate self-assessments. In contrast, genuine cognitive dysfunction was predictive of under-reporting of functional deficits. Together, these results suggest that over-reliance on self-reported functional status poses risk for error when diagnoses require documentation of both cognitive impairment and associated functional disability in everyday life.

Medication and finance management among HIV-infected adults: the impact of age and cognition

This study examined the effects of aging and cognitive impairment on medication and finance management in an HIV sample. We observed main effects of age (older < younger) and neuropsychological impairment on functional task performance. Interactions between age and cognition demonstrated that older impaired individuals performed significantly more poorly than all other comparison groups. There were no relationships between laboratory performance and self-reported medication and finance management. The interaction of advancing age and cognitive impairment may confer significant functional limitations for HIV individuals that may be better detected by performance-based measures of functional abilities rather than patient self-report.

MRI evaluation of topical heat and static stretching as therapeutic modalities for the treatment of eccentric exercise-induced muscle damage

The aim of this study was to monitor the effects of topical heat and/or static stretch treatments on the recovery of muscle damage by eccentric exercise. For this purpose, 32 untrained male subjects performed intense eccentric knee extension exercise, followed by 2 weeks of treatment (heat, stretch, heat plus stretch) or no treatment (control, n=8/group). Isometric strength testing, pain ratings, and multi-echo magnetic resonance imaging of the thigh were performed before and at 2, 3, 4, 8, and 15 days following the exercise. Increased T2 relaxation time, muscle swelling, pain ratings, and strength loss confirmed significant muscle damage during the post-exercise period. Pain ratings and muscle volume recovered to baseline by 15 days, although muscle strength remained lower [77 (4) vs. 95 (3) kg pre-exercise, mean (SE)] and T2 values higher [32.2 (0.8) vs. 28.6 (0.2) ms pre-exercise]. Our results indicate that heat and/or static stretching does not consistently reduce soreness, swelling or muscle damage. The practical implication of our findings is that clinicians should be aware that prescribing heat and/or static stretching following intense eccentric or unaccustomed exercise will not enhance the recovery of damaged muscles.

In vitro propagation and transcriptional profiling of human mammary stem/progenitor cells

Although the existence of mammary stem cells has been suggested by serial transplantation studies in mice, their identification has been hindered by the lack of specific surface markers, and by the absence of suitable in vitro assays for testing stem cell properties: self-renewal and ability to generate differentiated progeny. We have developed an in vitro cultivation system that allows for propagation of human mammary epithelial cells (HMECs) in an undifferentiated state, based on their ability to proliferate in suspension, as nonadherent mammospheres. We demonstrate that nonadherent mammospheres are enriched in early progenitor/stem cells and able to differentiate along all three mammary epithelial lineages and to clonally generate complex functional structures in reconstituted 3D culture systems. Gene expression analysis of cells isolated from nonadherent mammospheres revealed overlapping genetic programs with other stem and progenitor cells and identified new markers that may be useful in the identification of mammary stem cells. The isolation and characterization of these stem cells should help elucidate the molecular pathways that govern normal mammary development and carcinogenesis.

Biarticular and monoarticular muscle activation and injury in human quadriceps muscle

We hypothesized that activation of the quadriceps femoris muscle group during eccentric exercise is related to the increase in magnitude of several markers of muscle injury that developed during the next week. Fourteen male subjects performed six to eight sets of five to ten repetitions of single-leg eccentric-only seated knee extension exercise. Magnetic resonance (MR) images were collected before and immediately after exercise and on days 2-4 and 6 after eccentric exercise. Changes in maximal voluntary contraction (MVC), perceived soreness, muscle volume and muscle transverse relaxation of water protons (T2) were determined for the quadriceps femoris muscle group each day. Changes in muscle volume and T2 were determined every day for each muscle [vastus lateralis (VL), vastus medialis (VM), vastus intermedius (VI), rectus femoris (RF)] of the quadriceps femoris group. Post-exercise T2 was greater than pre-exercise T2 (P < 0.05) for all muscles. The acute deltaT2 (Post-Pre) was similar (P>0.05) among VL, VM, VI, and RF [5.5 (0.3) ms], suggesting that the four muscles were equally activated during eccentric exercise. In the week after eccentric exercise, subjects experienced delayed-onset muscle soreness (DOMS) and all muscles demonstrated a delayed increase in T2 above pre-exercise values (P < 0.05), suggesting that muscle injury had occurred. For the quadriceps femoris muscle group, there was no correlation between acute deltaT2 and delayed (peak T2 during days 2, 3, 4, 6 minus pre-exercise T2) deltaT2 (r=0.04, P>0.05). Similar results were obtained when VL, VM, VI and RF were examined separately. Of the four muscles in quadriceps femoris, the biarticular RF experienced greater muscle injury [delayed deltaT2= 15.2 (2.0) ms] compared to the three monoarticular vasti muscles [delayed deltaT2 = 7.7 (1.3) ms; P< 0.05]. We propose that the disproportionate muscle injury to RF resulted from an ineffective transfer of torque from the knee to hip joint during seated eccentric knee extension exercise, thus causing RF to dissipate greater energy than normal. We conclude that in humans, muscle activation is not a unique determinant of muscle injury.

Effect of aerobic capacity on the T(2) increase in exercised skeletal muscle

The increase in nuclear magnetic resonance transverse relaxation time (T(2)) of muscle water measured by magnetic resonance imaging after exercise has been correlated with work rate in human subjects. This study compared the T(2) increase in thigh muscles of trained (cycling VO(2 max) = 54.4 +/- 2.7 ml O(2). kg(-1). min(-1), mean +/- SE, n = 8, 4 female) vs. sedentary (31.7 +/- 0.9 ml O(2). kg(-1). min(-1), n = 8, 4 female) subjects after cycling exercise for 6 min at 50 and 90% of the subjects' individually determined VO(2 max). There was no significant difference between groups in the T(2) increase measured in quadriceps muscles within 3 min after the exercises, despite the fact that the absolute work rates were 60% higher in the trained group (253 +/- 15 vs. 159 +/- 21 W for the 90% exercise). In both groups, the increase in T(2) of vastus muscles was twofold greater after the 90% exercise than after the 50% exercise. The recovery of T(2) after the 90% exercise was significantly faster in vastus muscles of the trained compared with the sedentary group (mean recovery half-time 11.9 +/- 1.2 vs. 23.3 +/- 3.7 min). The results show that the increase in muscle T(2) varies with work rate relative to muscle maximum aerobic power, not with absolute work rate.

Detection of chromoluminance patterns on chromoluminance pedestals II: model

A model for chromoluminance pattern detection and pedestal effects is described. This model has five stages. The stimulus is first processed by the cone array and then by color-spatial linear operators. The outputs of the linear operators may be expressed as weighted sums of cone contrasts over space. There are three opposite sign pairs of linear spatial operators in the model. Their spectral tuning at each point in space is similar to the luminance, green/red and blue/yellow mechanisms in color opponent models, but their sensitivity to cone inputs varies as a function of space. The operators in each pair are the same except that the signs of the cone inputs in one are the opposite of those in the other. A non-linear response operator follows each linear operator. It receives two inputs, one excitatory and the other divisive inhibitory. The excitatory input is the half-wave rectified output of one of the linear operators. The inhibitory input is a non-linear sum of all linear operator outputs. The non-linear response operator raises the excitatory input to a power, and divides it by the inhibitory input plus a constant to produce the response. The detection variable is computed by combining the difference in response to target-plus-pedestal and pedestal alone across the three non-linear operators. The model accounts well for the large data set presented in the companion paper and is generally consistent with other results in the literature. The spectral sensitivities of the inferred chromoluminance pattern mechanisms are similar to those obtained with different methods. The data set is shown to be inconsistent with several other models.

Detection of chromoluminance patterns on chromoluminance pedestals I: threshold measurements

Measurement of the detection thresholds of patterns on pedestals of various kinds has the potential of providing insight into the mechanisms that mediate pattern vision. This study is concerned with chromoluminance patterns, that is, patterns that vary over space in luminance, chromaticity, or both. Contrast thresholds for 1 c/deg Gabor patterns (targets) were measured as a function of the contrast of Gabor pedestal patterns (TvC functions), where the pedestals paired with each target were modulated in a wide range of directions in color space. For most target-pedestal pairs, the TvC function decreased (facilitation) and then increased as pedestal contrast increased. The increase went above the absolute contrast threshold (masking) for all target-pedestal pairs except in cases where facilitation occurred at the upper end of the pedestal contrast range. The specific form of the TvC function varied greatly with the target and pedestal, consistent with a general model of pedestal effects proposed by Foley [Journal of the Optical Society of America A, 1994, 11(6)]. There were two sets of target-pedestal pairs for which facilitation did not occur, but masking did occur: pairs in which the target was a luminance modulation and the pedestals were individually isoluminant and pairs in which the pedestal was blue/yellow and the target was in any of our directions except blue/yellow.

MR measurements of muscle damage and adaptation after eccentric exercise

The purposes of this study were, first, to clarify the long-term pattern of T2 relaxation times and muscle volume changes in human skeletal muscle after intense eccentric exercise and, second, to determine whether the T2 response exhibits an adaptation to repeated bouts. Six young adult men performed two bouts of eccentric biceps curls (5 sets of 10 at 110% of the 1-repetition concentric maximum) separated by 8 wk. Blood samples, soreness ratings, and T2-weighted axial fast spin-echo magnetic resonance images of the upper arm were obtained immediately before and after each bout; at 1, 2, 4, 7, 14, 21, and 56 days after bout 1; and at 2, 4, 7 and 14 days after bout 2. Resting muscle T2 [27.6 +/- 0.2 (SE) ms] increased immediately postexercise by 8 +/- 1 ms after both bouts. T2 peaked 7 days after bout 1 at 47 +/- 4 ms and remained elevated by 2.5 ms at 56 days. T2 peaked lower (37 +/- 4 ms) and earlier (2-4 days) after bout 2, suggesting an adaptation of the T2 response. Peak serum creatine kinase values, pain ratings, and flexor muscle swelling were also significantly lower after the second bout (P < 0.05). Total volume of the imaged arm region increased transiently after bout 1 but returned to preexercise values within 2 wk. The exercised flexor compartment swelled by over 40%, but after 2 wk it reverted to a volume 10% smaller than that before exercise and maintained this volume loss through 8 wk, consistent with partial or total destruction of a small subpopulation of muscle fibers.

Pixel T2 distribution in functional magnetic resonance images of muscle

Increases in skeletal muscle (1)H-NMR transverse relaxation time (T2) observed by magnetic resonance imaging have been used to map whole muscle activity during exercise. Some studies further suggest that intramuscular variations in T2 after exercise can be used to map activity on a pixel-by-pixel basis by defining an active T2 threshold and counting pixels that exceed the threshold as "active muscle." This implies that motor units are nonrandomly distributed across the muscle and, therefore, that the distribution of pixel T2 values ought to be substantially broader after moderate exercise than at rest or after more intense exercise, since moderate-intensity exercise should recruit some motor units, and hence some pixels, but not others. This study examined the distribution of pixel T2 values in three muscles (quadriceps, anterior tibialis, and biceps/brachialis) of healthy subjects (5 men and 2 women, 18-46 yr old) at rest, after exercise to fatigue (50% 1 repetition maximum at 20/min to failure = Max), and at 1/2Max (25% 1 repetition maximum, same number of repetitions as Max). Although for each muscle there was a linear relationship between exercise intensity and mean pixel T2, there was no significant difference in the variance of pixel T2 between 1/2Max and Max exercise. There was a modest (10-43%) increase in variance of pixel T2 after both exercises compared with rest, but this was consistent with a Monte Carlo simulation of muscle activity that assumed a random distribution of motor unit territories across the muscle and a random distribution of muscle cells within each motor unit's territory. In addition, 40% of the pixel-to-pixel muscle T2 variations were shown to be due to imaging noise. The results indicate that magnetic resonance imaging T2 cannot reliably map active muscle on a pixel-by-pixel basis in normal subjects.

Pattern detection in the presence of maskers that differ in spatial phase and temporal offset: threshold measurements and a model

Four experiments are described in which brief Gabor patterns are detected in the presence of full-field gratings or Gabor patterns that are superimposed in space, but vary in spatial phase and temporal offset (SOA). E1: Threshold versus masker contrast (TvC) functions were determined for relative phases of 0, 90, 180 and 270 degrees at SOA = 0. For 0 degree relative phase, TvC functions decrease (facilitation) and then increase (masking) as contrast increases. For 90 degrees, there is little or no facilitation and thresholds increase with masker contrast. For 180 degrees, the form of the TvC function varies with observer and conditions. E2: Like E1, except that maskers are Gabor patterns. TvC functions are similar in form to those for full-field maskers, but there is less masking. E3: Forward masking. TvC functions were determined for relative phases of 0, 90, and 180 degrees at SOA = -33 ms. The forms of the TvC functions for 0 and 180 degrees are reversed relative to those at SOA = 0. E4: TvP (threshold versus phase) functions were determined for SOA's of -100, -67, -33, 0 and 33 ms at a constant masker contrast of 0.063. Masking occurs at all relative phases. For simultaneous and backward masking, the threshold is minimum for a relative phase of 0 and maximum at 180 degrees. For forward masking, the form of the function is inverted. A model of pattern masking and facilitation (Foley, J. M. (1994a) Journal of the Optical Society of America A, 11, 1710-1719) is extended to account for masker phase and SOA effects. The model assumes four mechanisms tuned to phases 90 degrees apart, and divisively inhibited by stimuli of all phases. Performance depends on the detection strategy of the observer.

An integrated model of discharge planning for acutely-ill elderly patients

Prior research has demonstrated that current discharge-related practices present resource-related and ethical problems for all those involved. The purpose of this 9-month qualitative study was to develop a more resource efficient and compassionate discharge planning model for acutely-ill, elderly patients. The focus group interviewing method was used to elicit 99 participants' perceptions of an ideal approach to discharge planning. Focus group participants included professionals from acute-care hospitals and community organizations. Telephone interviews were also completed with 25 patients and 6 family members. Themes identified in the analysis revealed that an ideal approach to discharge planning would incorporate seven elements. According to participants, the approach is ideal because it potentially addresses both resource utilization and ethical issues. Program evaluation of the model is underway in order to determine its effectiveness.

Reliability and validity of body composition measures in female athletes

The purpose of this investigation was to determine the reliability and validity of bioelectrical impedance (BIA) and near-infrared interactance (NIR) for estimating body composition in female athletes. Dual-energy X-ray absorptiometry was used as the criterion measure for fat-free mass (FFM). Studies were performed in 132 athletes [age = 20.4 +/- 1.5 (SD) yr]. Intraclass reliabilities (repeat and single trial) were 0.987-0.997 for BIA (resistance and reactance) and 0.957-0.980 for NIR (optical densities). Validity of BIA and NIR was assessed by double cross-validation. Because correlations were high (r = 0.969-0.983) and prediction errors low, a single equation was developed by using all 132 subjects for both BIA and NIR. Also, an equation was developed for all subjects by using height and weight only. Results from dual-energy X-ray absorptiometry analysis showed FFM = 49.5 +/- 6.0 kg, which corresponded to %body fat (%BF) of 20.4 +/- 3.1%. BIA predicted FFM at 49.4 +/- 5.9 kg (r = 0.981, SEE = 1.1), and NIR prediction was 49. 5 +/- 5.8 kg (r = 0.975, SEE = 1.2). Height and weight alone predicted FFM at 49.4 +/- 5.7 kg (r = 0.961, SEE = 1.6). When converted to %BF, prediction errors were approximately 1.8% for BIA and NIR and 2.9% for height and weight. Results showed BIA and NIR to be extremely reliable and valid techniques for estimating body composition in college-age female athletes.

Temporal sensitivity of human luminance pattern mechanisms determined by masking with temporally modulated stimuli

Target contrast thresholds were measured using vertical spatial Gabor targets in the presence of full field maskers of the same spatial frequency and orientation. In the first experiment both target and masker were 2 cpd. The target was modulated at a frequency of 1 or 10 Hz and the maskers varied in temporal frequency from 1 to 30 Hz and in contrast from 0.03 to 0.50. In the second experiment both target and masker had a spatial frequency of 1, 5 or 8 cpd. The target was modulated at 7.5 Hz and the same set of maskers was used as in the first experiment. The results are not consistent with a widely used model that is based on mechanisms in which excitation is summed linearly and the sum is transformed by an S-shaped nonlinear excitation-response function. A new model of human pattern vision mechanisms, which has excitatory and divisive inhibitory inputs, describes the results well. Parameters from the best fit of the new model to the results of the first experiment show that the 1 Hz and 10 Hz targets were detected by mechanisms with temporal low-pass and band-pass excitatory sensitivity, respectively. Fits to the second experiment suggest that at 1 cpd, the excitatory tuning of the detecting mechanism is band-pass. At 5 and 8 cpd, the mechanisms are excited by a broad range of temporal frequencies. Mechanism sensitivity to divisive inhibition depends on temporal frequency in the same general way as sensitivity to excitation. Mechanisms are more broadly tuned to divisive inhibition than to excitation, except when the target temporal frequency is high.

Contrast detection, discrimination and adaptation in patients with Parkinson's disease and multiple system atrophy

Visual spatial contrast thresholds and suprathreshold contrast matches were measured before and after adaptation to high-contrast sinewave gratings in patients with Parkinson's disease (n = 27), patients with multiple system atrophy (n = 6) and a group of age-matched control patients without CNS disease (n = 27). Contrast thresholds were higher in the Parkinson's disease patients than in either the multiple system atrophy patients or control patients. The effect of contrast adaptation on both contrast thresholds and matches was approximately equal in the three groups. This suggests that contrast adaptation is not affected by these CNS disorders and is consistent with the hypothesis that the loss in contrast sensitivity in Parkinson's disease is mediated by retinal effects. The results are discussed in terms of the underlying pathology of the visual deficits in Parkinson's disease and the possible diagnostic implications for differentiating Parkinson's disease and multiple system atrophy.

Analysis of the effect of pattern adaptation on pattern pedestal effects: a two-process model

Pattern contrast thresholds for vertical Gabor patterns were measured on pattern pedestals that were vertical or horizontal. Contrast of the pedestal was varied to measure the function relating target contrast threshold to pedestal contrast (TvC function). TvC functions were measured without an adaptor and after adaptation to vertical, horizontal and plaid patterns. For a pedestal with the same orientation as the target, the vertical and plaid adapters increased thresholds at low pedestal contrasts, but not high. For the pedestal orthogonal to the target, the same two adaptors increased thresholds over the whole range of pedestal contrasts. These asymmetric effects are described by a model of adaptation and masking derived from a model of masking (Foley, 1994a) by allowing two parameters to vary with the adapt state; one of them is an additive parameter in the denominator of the response function, which can be interpreted as adaptor-produced divisive inhibition that persists after adaptor offset; the other is the sensitivity to pedestal-produced divisive inhibition, which is changed by adaptation for the pedestal orthogonal to the target. Other models do not account for both effects.

Linear dependence of muscle phosphocreatine kinetics on oxidative capacity

The influence of muscle oxidative capacity on phosphocreatine (PCr) changes during and after stimulation was examined in the superficial (fast-twitch) section of rat gastrocnemius muscles. Muscle mitochondrial enzymes were increased in one group of rats by 8-10 wk of training on a running wheel (to a final regimen of 50 min/day at 38 m/min, 5 days/wk) and decreased in another group by chemical thyroidectomy [0.025% methimazole (MMI) in drinking water for 8 wk]. After these treatments, muscle citrate synthase activity was 179 and 29%, respectively, of that in corresponding control groups. Muscle PCr and pH were measured by 31P-nuclear magnetic resonance spectroscopy before, during, and after 8 min of isometric twitch stimulation at 0.33 Hz (MMI) or 0.75 Hz (trained) and 2 Hz. There was a significant linear correlation (r = 0.84, P < 0.01) between the rate constant for PCr recovery after submaximal stimulation (0.33 or 0.75 Hz) and citrate synthase activity. Within the control groups, there was a significant correlation (r = 0.72, P < 0.01) between the rate constant for PCr recovery and intracellular pH at the end of stimulation. The results are quantitatively consistent with linear/quasilinear models of respiratory control by the cytoplasmic free energy of ATP hydrolysis but not with respiratory control by cytoplasmic ADP.

Effect of acute head-down tilt on skeletal muscle cross-sectional area and proton transverse relaxation time

This study investigated changes in skeletal muscle cross-sectional area (CSA) evoked by fluid shifts that accompany short-term 6 degrees head-down tilt (HDT) or horizontal bed rest, the time course of the resolution of these changes after resumption of upright posture, and the effect of altered muscle CSA, in the absence of increased contractile activity, on proton transverse relaxation time (T2). Average muscle (CSA and T2 were determined by standard spin-echo magnetic resonance imaging. Analyses were performed on contiguous transaxial images of the neck and calf. After a day of normal activity, 24 h of HDT increased neck muscle CSA 19 +/- 4(SE)% (P < 0.05) while calf muscle CSA decreased 14 +/- 3% (P < 0.05). The horizontal posture (12 h) induced about one-half of these responses: an 11 +/- 2% (P < 0.05) in the neck muscle CSA and an 8 +/- 2% decrease (P < 0.05) in the calf. Within 2 h after resumption of upright posture, neck and calf muscle CSA returned to within 0.5% (P > 0.05) of the values assessed after a day of normal activity, with most of the change occurring within the first 30 min. No further change in muscle CSA was observed through 6 h of upright posture. Despite these large alterations in muscle CSA, T2 was not altered by more than 1.1 +/- 0.6% (P > 0.05) and did not relate to muscle size. These results suggest that postural manipulations and subsequent fluid shifts modeling micro-gravity elicit marked changes in muscle size. Because these responses were not associated with alterations in muscle T2, it does not appear that simple movement of water into muscle can explain the contrast shift observed after exercise.

Contractile and metabolic effects of increased creatine kinase activity in mouse skeletal muscle

The effects of increased expression of creatine kinase (CK) in skeletal muscle were studied in control and transgenic animals homozygous for expression of the B subunit of CK. CK activity was 47% higher in transgenic gastrocnemius muscle. The CK activity was distributed as follows: 45 +/- 1% MM dinner, 31 +/- 4% MB dimer, and 22 +/- 5% BB dimer. No significant differences in metabolic or contractile proteins were detected except for a 22% decrease in lactate dehydrogenase activity and a 9% decrease in adenylate kinase activity. The only significant effect in contractile activity was that the rise time of a 5-s isometric contraction was 28% faster in the transgenic muscle. 31P nuclear magnetic resonance (NMR) spectra were obtained from control and transgenic muscles during mechanical activation, and there were no NMR measurable differences detected. These results indicate that a 50% increase in CK activity due to expression of the B subunit does not have large effects on skeletal muscle metabolism or contractile function. Therefore, control muscle has sufficient CK activity to keep up with changes in cellular high-energy phosphates except during the early phase of intense contractile activity.

Different effects of gradual vs. acute adenine nucleotide depletion on ATP cost of muscle contraction

ATP and phosphocreatine (PCr) levels were chronically reduced in rat fast-twitch muscle by 40 and 87%, respectively, after rats were fed a diet containing 1% beta-guanidinopropionate (beta-GPA) for 9 wk. Myosin heavy chain distribution of superficial gastrocnemius muscle changed from 22:78% type IIA/type IIB in control to 39:61% in GPA-treated muscles. ATP cost of contractions was estimated from the PCr changes measured by gated 31P-nuclear magnetic resonance after brief (< 6 s) bursts of contractions. There was no significant change in the ATP cost of either twitch (0.3 mumol.g-1.twitch-1) or tetanic (2.5 mumol.g-1.100 ms tetanus-1) contractions in gastrocnemius muscle after chronic phosphagen depletion due to beta-GPA feeding. In two other groups of rats, ATP of gastrocnemius muscles was acutely depleted to inosine 5'-monophosphate (IMP) by tetanic stimulation. IMP reanimation was inhibited during a subsequent 75-min recovery period in one group by hadacidin treatment (100 mg/kg), resulting in 46% ATP depletion compared with the similarly stimulated and recovered control group. In contrast to gradual ATP depletion due to beta-GPA feeding, this acute ATP depletion treatment was associated with a 39% decrease in ATP cost of twitch contractions.

Human luminance pattern-vision mechanisms: masking experiments require a new model

A widely used model of simultaneous luminance pattern masking is based on mechanisms that sum inputs linearly and produce a response that is an S-shaped function of that sum. This model makes two predictions about masking: (1) Changing the masker spatial waveform will shift the threshold-versus-masker contrast function horizontally by a multiplicative constant. (2) Adding a second fixed-contrast masker will shift this function horizontally by an additive constant. Experimental tests do not support these predictions. The results can be explained by a new model that incorporates broadband divisive inhibition, consistent with physiology.

Changes in magnetic resonance images of muscle depend on exercise intensity and duration, not work

Echo-planar magnetic resonance imaging was used to study the effect of exercise rate and duration on magnetic resonance imaging signal intensity (SI) of anterior tibialis muscle in normal human subjects (mean age 35 yr, n = 6). Axial midcalf echo-planar images (repetition time/echo time = 6,000/45, acquisition time = 80 ms) were acquired every 6 s for 1 min before and during 15 min of dynamic ankle dorsiflexion exercise (peak force 36% of 1 repetition maximum) at 10, 20, and 30 contractions/min. At each rate, muscle SI rose along an approximately exponential time course (mean time constant 1.8 min) toward a plateau that was linearly dependent on force times contraction rate (r = 0.64, P < 0.01) but varied significantly among subjects. The results confirm previous reports that changes in muscle SI correlate with exercise intensity, but not with total work performed, over a submaximal range of exercise intensities.

Testing models of respiratory control in skeletal muscle

We examined the relationships between PCr and Pi vs oxygen consumption or twitch rate during stimulation of rat muscle in situ and of perfused cat biceps and soleus muscles. In fast-twitch muscles such as rat gastrocnemius and cat biceps, we found a linear relationship between PCr and oxygen consumption. This result favors thermodynamic regulation of oxygen consumption by cytoplasmic phosphorylation potential rather than kinetic regulation by ADP. PCr changes during stimulation of rat muscle depleted of total creatine or adenine nucleotide were also not consistent with simple kinetic regulation by ADP. In cat soleus (slow-twitch) muscle, the observation of nonexponential PCr changes during stimulation suggested more complicated regulation, possibly involving changes in mitochondrial redox potential.

Forward pattern masking and adaptation: effects of duration, interstimulus interval, contrast, and spatial and temporal frequency

Eight experiments are described that compare pattern adaptation and forward pattern masking by examining the effects of five variables on the contrast threshold of a target presented after an adapter or masker. The target is a Gabor pattern with a center frequency of 2 c/deg and a duration of 33 msec. Thresholds are determined using an adaptive spatial forced-choice method. Principal results are as follows. (1) An adapt-refresh regime with a 2 sec refresh and a 2 sec recovery period on each trial is shown to maintain constant performance. (2) Desensitization is very rapid, reaching near maximum in < 200 msec. (3) Recovery is very rapid during the first 100-200 msec and then very slow with the rate of slow recovery decreasing as adapter/masker duration increases. (4) Threshold vs contrast functions are step-like for certain frequency pairs. (5) Sensitivity vs frequency functions derived from adapting and masking are similar in form. (6) Masker temporal frequency (0-15 Hz) has very little effect. These results are described by a theory that postulates that the target is detected by a few mechanisms that are differentially tuned to spatial frequency. The effect of both a forward masker and an adapter is to desensitize the mechanisms that respond to it. Recovery is a weighted sum of two decay processes, one fast and one slow. The theory fits the data from both paradigms well with some differences in parameters.

Energy cost of twitch and tetanic contractions of rat muscle estimated in situ by gated 31P NMR

The phosphagen cost of maximal isometric twitch and tetanic contractions in rat gastrocnemius muscle was measured in situ by 31P NMR with acquisitions gated to precise time points after a brief (< 10 s) burst of contractions. Alteration of twitch stimulation frequency did not affect the energy cost per contraction. Pooled results of four twitch rates from 1 to 8 Hz produced an average cost of 0.257 +/- 0.012 mumol ATP/g/twitch. This value was compared with the initial twitch cost estimated from the time zero derivative of an exponential fit of averaged scan phosphocreatine (PCr) data from a previous study of 8 min of contraction in situ at 0.75 Hz. Agreement of the two estimates validates the use of the fitting/derivative method to assess energy cost and confirms the monoexponential character of the PCr time course. Evaluation of muscle pH changes demonstrated that all ATP use during the brief twitch contraction bouts could be accounted for by PCr hydrolysis. Results also showed a brief delay in onset of PCr recovery, consistent with the response time of oxidative systems. Tetanic contractions of 100 ms duration at 100 Hz required 2.17 +/- 0.07 mumol ATP/g muscle/contraction, in general agreement with estimates reported using a variety of other methods.

Magnetic resonance measurement of blood flow in peripheral vessels after acute exercise

Velocity-encoded Cine magnetic resonance imaging (MRI) was used to measure blood flow in the anterior tibial artery (AT), posterior tibial artery (PT), and popliteal artery of adult human subjects (mean age 29 yr) before and after 90 s of ankle dorsiflexion exercise. Before exercise, mean flow, peak systolic velocity, and end-diastolic velocity in AT were 8.1 +/- 1.6 (SE, n = 6) ml/min, 26.9 +/- 2.6 cm/s, and -0.6 +/- 0.4 cm/s, respectively. After exercise, mean flow and peak systolic velocity in AT increased by 19-fold and 3-fold, respectively, and end-diastolic velocity increased to 8.7 +/- 1.1 cm/s. Flow in popliteal artery above its bifurcation was similar to the sum of flows in AT and PT, both before and after exercise. Flow in AT declined exponentially after exercise with a mean half-time of 4 min. The results demonstrate the utility of MR phase-encoded flow-velocity measurements for physiological studies of peripheral vascular dynamics after exercise.

Decreased ATP cost of isometric contractions in ATP-depleted rat fast-twitch muscle

ATP was depleted to inosine 5'-monophosphate (IMP) in gastrocnemius muscles of anesthetized rats during two consecutive bouts of intermittent tetanic stimulation (each 1 Hz at 100 Hz, 100-ms duration, for 3 min) separated by 5 min. During a subsequent 75-min recovery period, resynthesis of adenine nucleotide from IMP was inhibited in one group of muscles with hadacidin (N-formyl-N-hydroxyaminoacetate, total dose 300 mg/kg ip), an inhibitor of adenylosuccinate synthase. In vivo 31P-nuclear magnetic resonance spectra and analysis of muscle extracts confirmed that ATP was reduced by over 30% in hadacidin-treated muscles compared both with nonstimulated muscles and with identically stimulated and rested control muscles in saline-injected rats. After the recovery period, calculated [ADP] in ATP-depleted muscles was half that in controls, while phosphorylation potential [PP = ln([ATP]/[ADP] [Pi]), where Pi is inorganic phosphate] and twitch force were similar. During a final 8 min of 0.75-Hz twitch stimulation, [ADP] and the initial rate of phosphocreatine (PCr) hydrolysis were less in ATP-depleted compared with control muscles, while changes in PP and twitch force were similar in the two groups. During a final 3 min of tetanic stimulation, ATP, PCr, and pH decreased less in ATP-depleted compared with control muscles. The results indicate that the ATP cost of isometric contraction is decreased by acute ATP depletion.

Ethical issues in the management of cerebrovascular disease

Medical ethics, as a scholarly and applied discipline, is concerned with the morality of behavior in medical matters. The field of cerebrovascular disease is a worthy paradigm of medical ethical issue. Victims, whether they be patients or their families, are vulnerable, and the ethical virtues of kindness, understanding, compassion, mercy, and justice are badly needed. A variety of hypothetical ethical scenarios faced by the physician are discussed in this article in addition to four actual patient studies with commentary.

Muscle buffer capacity estimated from pH changes during rest-to-work transitions

Gated phosphorus nuclear magnetic resonance (31P-NMR) spectra were acquired after 5 or 9 s of 5-Hz stimulation in rat and cat skeletal muscles, respectively. Net phosphocreatine (PCr) hydrolysis was associated with an intracellular alkalinization of 0.08 +/- 0.01 and 0.05 +/- 0.003 pH units in isolated perfused cat biceps and soleus, respectively, and 0.12 +/- 0.02 in the superficial predominantly fast-twitch white portion of gastrocnemius of anesthetized rats. The net change in [H+] expected from PCr hydrolysis was calculated, and apparent buffer capacity (beta) in intact muscles was calculated from beta = delta [H+]/delta pH. The beta of the same muscle types was also estimated from titration of muscle homogenates between pH 6.0 and 8.0. The contribution of Pi to total beta of the homogenates was subtracted to ascertain the non-Pi beta for each muscle. The non-Pi beta values were added to the actual amount of Pi present in the stimulated muscles to calculate a predicted beta at pH 7. The apparent beta calculated from PCr and pH changes in intact muscles and the predicted beta from homogenate titrations were in good agreement (38 +/- 9 vs. 38 slykes in cat biceps, 21 +/- 7 vs. 30 in cat soleus, and 30 +/- 6 vs. 27 in rat gastrocnemius). The results indicate that changes in pH during the first few seconds of contraction can be entirely accounted for by proton consumption via net PCr hydrolysis.