Lee F Schroeder

Stanford Medicine, Stanford, California, United States

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Publications (24)152.97 Total impact

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    Lee F Schroeder, Timothy Amukele
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    ABSTRACT: A recent survey of laboratories in Kampala, Uganda, demonstrated that only 0.3% of laboratories (3/954) met international quality standards. To benchmark laboratory quality throughout the rest of sub-Saharan Africa (SSA), we compiled a list of SSA laboratories meeting international quality standards.
    American Journal of Clinical Pathology 06/2014; 141(6):791-5. · 2.88 Impact Factor
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    ABSTRACT: Clostridium difficile infection (CDI) is the most common cause of infectious diarrhea in the healthcare setting, and presumptive patient isolation while awaiting laboratory results is costly. Newer rapid tests for CDI may reduce this burden, but the economic consequences of different testing algorithms remain unexplored. We used decision analysis from the hospital perspective to compare eight CDI testing algorithms for adult inpatients with suspected CDI, assuming treatment according to lab results. CDI testing strategies included combinations of on demand polymerase chain reaction (odPCR), batch PCR, lateral-flow diagnostics, plate-reader enzyme immunoassay, and direct tissue culture cytotoxicity. In the reference scenario, algorithms incorporating rapid testing were cost-effective relative to non-rapid algorithms. For every 10,000 symptomatic adults (relative to a strategy of treating nobody), lateral-flow GDH/odPCR generated 831 additional true-positive results and cost $1,600 per true-positive case treated. Stand-alone odPCR was more effective and more expensive, identifying 174 additional true-positive cases at $6,900 per case treated. All other strategies were dominated (i.e., more costly and less effective) compared to odPCR, either stand-alone or preceded by lateral-flow screening. Cost-benefit analysis (including cost savings from averted missed cases) favored stand-alone odPCR in many settings, but favored screening with lateral-flow diagnostics if a missed CDI case resulted in less than $5,000 of extended hospital stay costs and under 2 transmissions, if lateral-flow diagnostic sensitivity was over 93%, or if the symptomatic carrier proportion among toxigenic culture-positive cases was over 80%. These results can aid guideline developers and laboratory directors considering rapid testing algorithms for diagnosing CDI.
    Journal of clinical microbiology 11/2013; · 4.16 Impact Factor
  • Lee Schroeder, Niaz Banaei
    New England Journal of Medicine 03/2013; 368(12):e15. · 51.66 Impact Factor
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    ABSTRACT: We present a cell based system and experimental approach to characterize agonist and antagonist selectivity for ligand-gated ion channels (LGIC) by developing sensor cells stably expressing a Ca(2+) permeable LGIC and a genetically encoded Förster (or fluorescence) resonance energy transfer (FRET)-based calcium sensor. In particular, we describe separate lines with human α7 and human α4β2 nicotinic acetylcholine receptors, mouse 5-HT(3A) serotonin receptors and a chimera of human α7/mouse 5-HT(3A) receptors. Complete concentration-response curves for agonists and Schild plots of antagonists were generated from these sensors and the results validate known pharmacology of the receptors tested. Concentration-response relations can be generated from either the initial rate or maximal amplitudes of FRET-signal. Although assaying at a medium throughput level, this pharmacological fluorescence detection technique employs a clonal line for stability and has versatility for screening laboratory generated congeners as agonists or antagonists on multiple subtypes of ligand-gated ion channels. The clonal sensor lines are also compatible with in vivo usage to measure indirectly receptor activation by endogenous neurotransmitters.
    PLoS ONE 01/2011; 6(1):e16519. · 3.73 Impact Factor
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    ABSTRACT: Tools from molecular biology, combined with in vivo optical imaging techniques, provide new mechanisms for noninvasively observing brain processes. Current approaches primarily probe cell-based variables, such as cytosolic calcium or membrane potential, but not cell-to-cell signaling. We devised cell-based neurotransmitter fluorescent engineered reporters (CNiFERs) to address this challenge and monitor in situ neurotransmitter receptor activation. CNiFERs are cultured cells that are engineered to express a chosen metabotropic receptor, use the G(q) protein-coupled receptor cascade to transform receptor activity into a rise in cytosolic [Ca(2+)] and report [Ca(2+)] with a genetically encoded fluorescent Ca(2+) sensor. The initial realization of CNiFERs detected acetylcholine release via activation of M1 muscarinic receptors. We used chronic implantation of M1-CNiFERs in frontal cortex of the adult rat to elucidate the muscarinic action of the atypical neuroleptics clozapine and olanzapine. We found that these drugs potently inhibited in situ muscarinic receptor activity.
    Nature Neuroscience 12/2009; 13(1):127-32. · 15.25 Impact Factor
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    ABSTRACT: A highly interconnected network of arterioles overlies mammalian cortex to route blood to the cortical mantle. Here we test if this angioarchitecture can ensure that the supply of blood is redistributed after vascular occlusion. We use rodent parietal cortex as a model system and image the flow of red blood cells in individual microvessels. Changes in flow are quantified in response to photothrombotic occlusions to individual pial arterioles as well as to physical occlusions of the middle cerebral artery (MCA), the primary source of blood to this network. We observe that perfusion is rapidly reestablished at the first branch downstream from a photothrombotic occlusion through a reversal in flow in one vessel. More distal downstream arterioles also show reversals in flow. Further, occlusion of the MCA leads to reversals in flow through approximately half of the downstream but distant arterioles. Thus the cortical arteriolar network supports collateral flow that may mitigate the effects of vessel obstruction, as may occur secondary to neurovascular pathology.
    PLoS Biology 03/2006; 4(2):e22. · 12.69 Impact Factor
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    ABSTRACT: We tested the hypothesis that activation of nucleus basalis magnocellularis (NBM), which provides cholinergic input to cortex, facilitates motor control. Our measures of facilitation were changes in the direction and time-course of vibrissa movements that are elicited by microstimulation of vibrissa motor (M1) cortex. In particular, microstimulation led solely to a transient retraction of the vibrissae in the sessile animal but to a full motion sequence of protraction followed by retraction in the aroused animal. We observed that activation of NBM, as assayed by cortical desynchronization, induced a transition from microstimulation-evoked retraction to full sweep sequences. This dramatic change in the vibrissa response to microstimulation was blocked by systemic delivery of atropine and, in anesthetized animals, an analogous change was blocked by the topical administration of atropine to M1 cortex. We conclude that NBM significantly facilitates the ability of M1 cortex to control movements. Our results bear on the importance of cholinergic activation in schemes for neuroprosthetic control of movement.
    Journal of Neurophysiology 08/2005; 94(1):699-711. · 3.30 Impact Factor
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    ABSTRACT: Using two-photon microscopy, we quantify changes in blood flow after photothrombotic occlusion of individual blood vessels in rat neocortex, and find that flow reverses direction at the first branch that lies downstream from localized clots.
    Orthopaedics & Traumatology-surgery & Research - ORTHOP TRAUMATOL-SURG RES. 05/2004;
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    ABSTRACT: Functional magnetic resonance imaging (fMRI) based on blood-oxygen level dependent (BOLD) contrast today is an established brain research method and quickly gains acceptance for complementary clinical diagnosis. However, neither the basic mechanisms like coupling between neuronal activation and haemodynamic response are known exactly, nor can the various artifacts be predicted or controlled. Thus, modeling functional signal changes is non-trivial and exploratory data analysis (EDA) may be rather useful. In particular, identification and separation of artifacts as well as quantification of expected, i.e. stimulus correlated, and novel information on brain activity is important for both, new insights in neuroscience and future developments in functional MRI of the human brain. After an introduction on fuzzy clustering and very high-field fMRI we present several examples where fuzzy cluster analysis (FCA) of fMRI time series helps to identify and locally separate various artifacts. We also present and discuss applications and limitations of fuzzy cluster analysis in very high-field functional MRI: differentiate temporal patterns in MRI using (a) a test object with static and dynamic parts, (b) artifacts due to gross head motion artifacts. Using a synthetic fMRI data set we quantitatively examine the influences of relevant FCA parameters on clustering results in terms of receiver-operator characteristics (ROC) and compare them with a commonly used model-based correlation analysis (CA) approach. The application of FCA in analyzing in vivo fMRI data is shown for (a) a motor paradigm, (b) data from multi-echo imaging, and (c) a fMRI study using mental rotation of three-dimensional cubes. We found that differentiation of true "neural" from false "vascular" activation is possible based on echo time dependence and specific activation levels, as well as based on their signal time-course. Exploratory data analysis methods in general and fuzzy cluster analysis in particular may help to identify artifacts and add novel and unexpected information valuable for interpretation, classification and characterization of functional MRI data which can be used to design new data acquisition schemes, stimulus presentations, neuro(physio)logical paradigms, as well as to improve quantitative biophysical models.
    Artificial Intelligence in Medicine 12/2003; 29(3):203-23. · 1.36 Impact Factor
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    ABSTRACT: We use two-photon microscopy to observe changes in blood flow after localized photothrombotic clotting of individual blood vessels in rat neocortex. We find that flow reverses direction downstream from clotted arterioles, thereby maintaining tissue perfusion.
    Lasers and Electro-Optics Society, 2003. LEOS 2003. The 16th Annual Meeting of the IEEE; 11/2003
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    ABSTRACT: Photothrombotic microstrokes are produced in rat cortex by 532-nm single-photon optical excitation of an intravenously injected photosensitizer, rose bengal. The dynamics of blood flow and clot formation in the cortical vasculature are observed using two-photon laser scanning microscopy of an intravenously injected fluorescent dye. Flowing and clotted vessels are clearly distinguishable in both large and small vessels, down to individual capillaries, using this technique. We find that by tightly focusing the laser light used to excite the photosensitizer, clots can be formed in individual blood vessels without affecting neighboring vessels tens of micrometers away. We observe many changes in blood flow as a result of localized clot formation, including upstream vascular dilation, clot clearing, i.e. recanalization, and complete reversal of blood flow direction downstream.
    Proc SPIE 06/2003;
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    ABSTRACT: Emotion processing deficits are notable in schizophrenia. The authors evaluated cerebral blood flow response in schizophrenia patients during facial emotion processing to test the hypothesis of diminished limbic activation related to emotional relevance of facial stimuli. Fourteen patients with schizophrenia and 14 matched comparison subjects viewed facial displays of happiness, sadness, anger, fear, and disgust as well as neutral faces. Functional magnetic resonance imaging was used to measure blood-oxygen-level-dependent signal changes as the subjects alternated between tasks of discriminating emotional valence (positive versus negative) and age (over 30 versus under 30) of the faces with an interleaved crosshair reference condition. The groups did not differ in performance on either task. For both tasks, healthy participants showed activation in the fusiform gyrus, occipital lobe, and inferior frontal cortex relative to the resting baseline condition. The increase was greater in the amygdala and hippocampus during the emotional valence discrimination task than during the age discrimination task. In the patients with schizophrenia, minimal focal response was observed for all tasks relative to the resting baseline condition. Contrasting patients and comparison subjects on the emotional valence discrimination task revealed voxels in the left amygdala and bilateral hippocampus in which the comparison subjects had significantly greater activation. Failure to activate limbic regions during emotional valence discrimination may explain emotion processing deficits in patients with schizophrenia. While the lack of limbic recruitment did not significantly impair simple valence discrimination performance in this clinically stable group, it may impact performance of more demanding tasks.
    American Journal of Psychiatry 01/2003; 159(12):1992-9. · 14.72 Impact Factor
  • Schizophrenia Research - SCHIZOPHR RES. 01/2003; 60(1):219-219.
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    ABSTRACT: Functional neuroimaging studies have helped identify neural systems involved in cognitive processing and more recently have indicated limbic activation to emotional stimuli. Some functional magnetic resonance imaging (fMRI) studies have reported increased amygdala response during exposure to emotional stimuli while others have not shown such activation. The present study was designed to test the hypothesis that activation of the amygdala is related to the relevance of the emotional valence of stimuli. Healthy young participants (7 men, 7 women) were studied in a high-field (4 tesla) scanner using blood oxygenation-level dependent (BOLD) signal changes in a blocked "box car" design. They viewed facial displays of happiness, sadness, anger, fear, and disgust as well as neutral faces obtained from professional actors and actresses of diverse ethnicity and age. Their task alternated between emotion discrimination (indicating whether the emotion was positive or negative) and age discrimination (indicating whether the poser was older or younger than 30). Blocks contained the same proportion of emotional and neutral faces. Limbic response was greater during the emotion than during the age discrimination conditions. The response was most pronounced in the amygdala, but was also present in the hippocampus and circumscribed voxels in other limbic regions. These results support the central role of the amygdala in emotion processing, and indicate its sensitivity to the task relevance of the emotional display.
    NeuroImage 08/2002; 16(3 Pt 1):651-62. · 6.25 Impact Factor
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    ABSTRACT: n-back letter and fractal tasks were administered to 11 participants during functional magnetic resonance imaging to test process specificity theories of prefrontal cortex (PFC) function and assess task validity. Tasks were matched on accuracy, but fractal n-back responses were slower and more conservative. Maintenance (1-back minus 0-back) activated inferior parietal and dorsolateral PFC, with additional activation in right ventrolateral PFC during letter n-back and left lingual gyrus during fractal n-back. Maintenance plus manipulation (2-back minus 0-back) activated inferior parietal, Broca's area, insula, and dorsolateral and ventral PFC, with greater right dorsolateral PFC activation for letter n-back. Manipulation only (2-back minus 1-back) produced additional and equivalent dorsolateral PFC and anterior cingulate activation in both tasks. Results support fractal n-back validity and indicate substantial overlap in working memory functions of dorsal and ventral PFC.
    Neuropsychology 08/2002; 16(3):370-9. · 3.58 Impact Factor
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    ABSTRACT: TheGuilty Knowledge Test (GKT) has been used extensively to model deception. An association between the brain evoked response potentials and lying on the GKT suggests that deception may be associated with changes in other measures of brain activity such as regional blood flow that could be anatomically localized with event-related functional magnetic resonance imaging (fMRI). Blood oxygenation level-dependent fMRI contrasts between deceptive and truthful responses were measured with a 4 Tesla scanner in 18 participants performing the GKT and analyzed using statistical parametric mapping. Increased activity in the anterior cingulate cortex (ACC), the superior frontal gyrus (SFG), and the left premotor, motor, and anterior parietal cortex was specifically associated with deceptive responses. The results indicate that: (a) cognitive differences between deception and truth have neural correlates detectable by fMRI, (b) inhibition of the truthful response may be a basic component of intentional deception, and (c) ACC and SFG are components of the basic neural circuitry for deception.
    NeuroImage 04/2002; 15(3):727-32. · 6.25 Impact Factor
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    ABSTRACT: Neuropsychological studies have shown that deficits in verbal episodic memory in schizophrenia occur primarily during encoding and retrieval stages of information processing. The current study used positron emission tomography to examine the effect of schizophrenia on change in cerebral blood flow (CBF) during these memory stages. CBF was measured in 23 healthy comparison subjects and 23 patients with schizophrenia during four conditions: resting baseline, motor baseline, word encoding, and word recognition. The motor baseline was used as a reference that was subtracted from encoding and recognition conditions by using statistical parametric mapping. Patients' performance was similar to that of healthy comparison subjects. During word encoding, patients showed reduced activation of left prefrontal and superior temporal regions. Reduced left prefrontal activation in patients was also seen during word recognition, and additional differences were found in the left anterior cingulate, left mesial temporal lobe, and right thalamus. Although patients' performance was similar to that of healthy comparison subjects, left inferior prefrontal activation was associated with better performance only in the comparison subjects. Left frontotemporal activation during episodic encoding and retrieval, which is associated with better recognition in healthy people, is disrupted in schizophrenia despite relatively intact recognition performance and right prefrontal function. This may reflect impaired strategic use of semantic information to organize encoding and facilitate retrieval.
    American Journal of Psychiatry 08/2001; 158(7):1114-25. · 14.72 Impact Factor
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    ABSTRACT: Evidence of bilateral prefrontal activation during memory encoding and retrieval has increased attention given to anatomical subdivisions within the prefrontal cortex. The current study examined anterior and inferior aspects of the prefrontal cortex to determine their degree of functional and hemispheric overlap during encoding and recognition. Cerebral blood flow of 25 healthy volunteers was measured using PET (15)O-water methods during four conditions: resting baseline, sequential finger movement, word encoding, and word recognition. Resting and motor images were averaged to provide a single reference that was subtracted from encoding and recognition using statistical parametric mapping (SPM96). Memory conditions were also subtracted from each other to identify differences in regional activity. Subjects performed well (86% correct) and had a slightly conservative response bias. Baseline subtraction from encoding revealed focal activation of left inferior prefrontal cortex (area 45) without significant contralateral activation. Recognition minus baseline subtraction produced a focal right anterior prefrontal activation (areas 9 and 10) that was not present in the left hemisphere. Bilateral effects were seen in area 45 during recognition. Subtraction of memory tasks from each other did not reveal any areas of greater activity during encoding. However, the recognition task produced greater activation in right area 9 extending into the anterior cingulate. Greater activity during recognition was also observed in left insula and bilateral visual integration areas. These results are discussed in relation to the prevailing model of prefrontal hemispheric asymmetry during episodic memory.
    NeuroImage 07/2000; 11(6 Pt 1):624-33. · 6.25 Impact Factor
  • Biological Psychiatry - BIOL PSYCHIAT. 01/2000; 47(8).
  • International Journal of Psychophysiology. 41(3):204-204.

Publication Stats

1k Citations
152.97 Total Impact Points

Institutions

  • 2013
    • Stanford Medicine
      • Department of Pathology
      Stanford, California, United States
  • 2003–2009
    • University of California, San Diego
      • • Department of Physics
      • • Department of Medicine
      San Diego, CA, United States
    • Vanderbilt University
      • Department of Psychology
      Nashville, MI, United States
  • 2002–2003
    • Hospital of the University of Pennsylvania
      • Department of Psychiatry
      Philadelphia, Pennsylvania, United States
  • 2000–2002
    • University of Pennsylvania
      • Department of Psychiatry
      Philadelphia, PA, United States
    • Pennsylvania Department of Health
      Harrisburg, Pennsylvania, United States