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Biomedical subjects

T L Davis

Publications and source records attributed to T L Davis.

At least 55 records · Page 3Linked to original sources
PubMed1997

Morphometry of in vivo human white matter association pathways with diffusion-weighted magnetic resonance imaging.

The precise characterization of cortical connectivity is important for the understanding of brain morphological and functional organization. Such connectivity is conveyed by specific pathways or tracts in the white matter. Diffusion-weighted magnetic resonance imaging detects the diffusivity of water molecules in three dimensions. Diffusivity is anisotropic in oriented tissues such as fiber tracts. In the present study, we used this method to map (in terms of orientation, location, and size) the "stem" (compact portion) of the principal association, projection, and commissural white matter pathways of the human brain in vivo, in 3 normal subjects. In addition, its use in clinical neurology is illustrated in a patient with left inferior parietal lobule embolic infarction in whom a significant reduction in relative size of the stem of the left superior longitudinal fasciculus was observed. This represents an important method for the characterization of major association pathways in the living human that are not discernible by conventional magnetic resonance imaging. In the clinical domain, this method will have a potential impact on the understanding of the diseases that involve white matter such as stroke, multiple sclerosis, amyotrophic lateral sclerosis, head injury, and spinal cord injury.

Cerebral Cortex↗
PubMed1997

Pharmacological analysis of mast cell mediator and neurotransmitter receptors coupled to adenylate cyclase and phospholipase C on immunocytochemically-defined human conjunctival epithelial cells.

We sought to establish and immunocytochemically characterize primary cultures of human conjunctival epithelial (HCE) cells, and to determine the types of receptors coupled to adenylate cyclase (AC) and phospholipase C (PLC) present on them which may be stimulated following allergic or inflammatory provocation of the tissue. HCE cells possessed the key epithelial cell surface cytokeratins AE1, AE3 and AE5. Signal transduction studies (n > or = 3), using agonists and antagonists, revealed the presence of beta 2-adrenergic (isoproterenol EC50 = 5.2 nM), prostaglandin E2 (EC50 = 168 nM) and vasoactive intestinal peptide (EC50 = 0.69 nM) receptors positively coupled to AC in HCE cells. Bradykinin (EC50 = 0.83 nM), platelet activating factor (EC50 = 4.5 nM), leukotriene C4 (EC50 = 300 nM) and histamine1 (EC50 = 3.1 microM) receptors were coupled to PLC (n = 3 for each). These data suggest that HCE cells in vivo may represent target cells for mast cell mediators and certain neurotransmitters which are released into the tear-film upon allergic provocation of the conjunctiva.

Adenylyl Cyclases↗
PubMed1997

Tongue protrusion dystonia: treatment with botulinum toxin.

We report the treatment experience in a series of patients with involuntary tongue protrusion resulting from oromandibular dystonia (OMD) or Meige's syndrome. A retrospective analysis of clinical findings and results of treatment was conducted on patients treated at Vanderbilt University Medical Center between 1989 and 1995. After unsuccessful treatment with conventional oral medications, nine patients having involuntary tongue protrusion resulting from OMD or Meige's syndrome were treated with botulinum toxin type A (BTX-A) injected into the genioglossus muscle at four sites via a submandibular approach. A marked reduction in tongue protrusion was achieved in six patients (67%). Of 35 consecutive injections, 83% were successful at reducing tongue protrusion. Mild dysphagia complicated 14% of the injections. The average dose injected was 34 (+/- 3) units producing a 15 (+/- 2) week average duration of effect. Injection of the genioglossus with BTX-A may prove to be a valid treatment option for involuntary tongue protrusion related to OMD or Meige's syndrome. A double-blind, placebo-controlled trial is needed to better define efficacy and adverse events.

Aged↗
PubMed1997

Ropinirole for the treatment of early Parkinson's disease. The Ropinirole Study Group.

A prospective, randomized, placebo-controlled, double-blind, parallel-group, 6-month study assessed the efficacy and safety of ropinirole, a nonergoline D2-dopamine agonist, in patients with early Parkinson's disease (n = 241; Hoehn & Yahr stages I to III) with limited or no prior dopaminergic therapy. Patients (mean age, 62.8 years), stratified by concomitant use of selegiline, were randomized to ropinirole (n = 116) or placebo (n = 125). The starting dose of ropinirole was 0.25 mg tid with titration to at least 1.5 mg tid (maximum dose, 8 mg tid). Primary efficacy endpoint was the percentage improvement in Unified Parkinson's Disease Rating Scale (UPDRS) motor score. Ropinirole-treated patients had a significantly greater percentage improvement in UPDRS motor score than patients who received placebo (+24% vs -3%; p < 0.001). Ropinirole was well tolerated and patient withdrawals were infrequent. Most adverse experiences were related to peripheral dopaminergic activity. Ropinirole monotherapy is an effective and well-tolerated therapeutic option for treatment of early Parkinson's disease.

Aged↗
PubMed1997

SDC-3 coordinates the assembly of a dosage compensation complex on the nematode X chromosome.

X chromosome expression in C. elegans is controlled by a chromosome-wide regulatory process called dosage compensation that specifically reduces by half the level of transcripts made from each hermaphrodite X chromosome. This process equalizes X expression between the sexes (XX hermaphrodites and XO males), despite their two-fold difference in X chromosome dose, and thereby prevents sex-specific lethality. Dosage compensation is achieved by a protein complex that associates with X in a sex-specific fashion to modulate gene expression. SDC-3, a protein that coordinately controls both sex determination and dosage compensation, activates dosage compensation by directing the dosage compensation protein complex to the hermaphrodite X chromosomes. We show that SDC-3 coordinates this assembly through its own sex-specific association with X. SDC-3 in turn requires other members of the dosage compensation gene hierarchy for its stability and its X localization. In addition, SDC-3 requires its own zinc finger motifs and an amino-terminal region for its X association. Our experiments suggest the possible involvement of zinc finger motifs in X chromosome recognition and the amino-terminal region in interactions with other dosage compensation proteins.

Animals↗
PubMed1997

Characterization of cerebral blood oxygenation and flow changes during prolonged brain activation.

The behavior of cerebral blood flow and oxygenation during prolonged brain activation was studied using magnetic resonance imaging (MRI) sensitized to flow and oxygenation changes, as well as positron emission tomography sensitized to flow. Neuronal habituation effects and hemodynamic changes were evaluated across tasks and cortical regions. Nine types of activation stimuli or tasks, including motor activation, vibrotactile stimulation, and several types of visual stimulation, were used. Both flow and oxygenation were evaluated in separate time course series as well as simultaneously using two different MRI methods. In most cases, the activation-induced increase in flow and oxygenation remained elevated for the entire stimulation duration. These results suggest that both flow rate and oxygenation consumption rate remain constant during the entire time that primary cortical neurons are activated by a task or a stimulus.

Blood Flow Velocity↗
PubMed1997

Adult-onset focal dystonias: presentation and treatment options.

Adult-onset focal dystonias (AFD) are common disorders that are often misdiagnosed and incorrectly treated. Their presentation is readily recognized, and botulinum toxin has become the agent of choice for treating these disorders. Most of the focal dystonias include cervical dystonia, blepharospasm, oromandibular dystonia, spasmodic dysphonia, and limb dystonia, specifically writer's cramp. Their onset is either idiopathic, familial, or post-traumatic, and the pathophysiology of the focal dystonias is not currently known. Local injections of botulinum toxin into the affected area result in chemical denervation of the muscle, resulting in a weakness of the muscles that are involved in the sustained contractions. This weakness alleviates the painful contraction of the dystonia. In this paper we present a case study of the most common type of focal dystonia, cervical dystonia. The etiology in this case was post-traumatic, and significant improvement resulted after treatment with botulinum toxin type A.

Botulinum Toxins, Type A↗
PubMed1996

Functional magnetic resonance imaging shows localized brain activation during serial transcranial stimulation in man.

Area and depth penetration of transcranial stimulation methods such as transcranial electrical stimulation (TES) are poorly defined. We investigated the feasibility of a simultaneous TES and fMRI measurement. The aim was to compare the signal intensity changes measured using BOLD fMRI during sequential finger movement with the signal response during artificial transcranial stimulation. Tes induced contralateral finger contractions and in T2* weighted images a transient signal increase was observed in the area underlying the electrodes. Compared with the signal obtained during sequential finger movements, the area activated by TES was more localized, signal amplitude, was smaller and there was no post-stimulus undershoot. These data indicate that TES induces a local blood flow increase associated with a drop in the concentration of deoxyhaemoglobin.

Brain↗
PubMed1996

Functional magnetic resonance imaging of symptom provocation in obsessive-compulsive disorder.

BACKGROUND: The new technique of functional magnetic resonance imaging was used to investigate the mediating neuroanatomy of obsessive-compulsive disorder symptoms. METHODS: Ten patients with obsessive-compulsive disorder and 5 normal subjects were studied via functional magnetic resonance imaging during control and provoked conditions. Data analysis entailed parametric and nonparametric statistical mapping. RESULTS: Statistical maps (nonparametric; P < 10(-3)) showed activation for 70% or more of patients with obsessive-compulsive disorder in medial orbitofrontal, lateral frontal, anterior temporal, anterior cingulate, and insular cortex, as well as caudate, lenticulate, and amygdala. No normal subjects exhibited activation in any brain region. CONCLUSIONS: Results of functional magnetic resonance imaging were consistent with past studies of obsessive-compulsive disorder that used other functional neuroimaging modalities. However, paralimbic and limbic activations were more prominent in the present study.

Adult↗
PubMed1996

Drug therapy for Parkinson's disease.

Parkinson's disease (PD) is a common neurodegenerative disease characterized by tremor, rigidity, bradykinesia, and loss of postural reflexes. Although the agents available for symptomatic treatment now allow most parkinsonian patients to live a normal life-span, these patients become progressively unable to participate in social functions, perform activities of daily living, and work. Therapy for PD may be associated with many complications that contribute to these disabilities. For this reason, education is helpful for the patient newly diagnosed with PD. Over the past 6 years, three new medications (selegiline, pergolide, and controlled-release levodopa) have been approved for use in Parkinson's disease. Other agents now available for the treatment of psychiatric illness may also be helpful in selected cases of PD. With this in mind, we review the commonly prescribed drugs and outline a rational plan for treatment of parkinsonism.

Activities of Daily Living↗
PubMed1996

Intradermal nodular fasciitis presenting as an eyelid mass.

BACKGROUND: Nodular fasciitis is a fibroblastic proliferation in which nodules, most commonly appearing on the extremities, develop suddenly and rapidly. Although excisional biopsy is curative, the nodules will often resolve spontaneously; however, the histologic appearance of a pleomorphic spindle cell neoplasm with frequent mitotic figures may raise concern of a more malignant neoplasm and lead to unnecessary and overly aggressive therapy. METHODS: A case of nodular fasciitis presenting in an unusual location, intradermally at the lateral canthus, is discussed. RESULTS: Review of the recent literature from other disciplines reveals new insights into the etiology and diagnostic options (fine needle aspiration, tomography, other imaging techniques) for this puzzling disease. CONCLUSIONS: When nodular fasciitis occurs in an unusual location, such as on the head and neck or at an intradermal location, it will not present as the deep, mobile, nontender nodule described in the dermatologic literature. Fine-needle aspiration and modern imaging techniques may help in the diagnosis and prevent unnecessary surgery for a self-limited condition.

Adult↗
PubMed1996

Hyperacute stroke: evaluation with combined multisection diffusion-weighted and hemodynamically weighted echo-planar MR imaging.

PURPOSE: To evaluate acute stroke with conventional, multisection diffusion-weighted (DW), and hemodynamically weighted (HW) magnetic resonance (MR) imaging. MATERIALS AND METHODS: The three MR imaging techniques were performed in 11 patients within 10 hours of the onset of acute hemiparesis. The volume of DW and HW abnormalities were compared with infarct volumes depicted at initial and/or follow-up MR or computed tomography (CT). RESULTS: Findings at DW and HW imaging were abnormal in nine of the 11 patients, despite normal findings at initial CT and/or MR. In all nine patients, infarcts were depicted at follow-up CT or MR. The DW abnormality was generally smaller and the HW abnormality was generally larger than the infarct volume determined at subsequent imaging. In the two patients with normal findings at DW and HW imaging, symptoms resolved completely within 1-48 hours. CONCLUSION: Different aspects of hyperacute cerebral ischemia are depicted at DW and HW imaging before infarction is depicted at conventional MR or CT. These techniques may improve stroke diagnosis and may contribute to advances in treatment.

Acute Disease↗
PubMed1995

Dystonia and unique muscle features. A 23-year follow-up and correction of diagnosis in two brothers.

OBJECTIVE: To provide follow-up information and a corrected diagnosis on two brothers who were primarily described in the ARCHIVES in 1971 as having had a genetic dystonia with unusual muscle biopsy features. MEASURES: Clinical observation of response to treatment and muscle histologic findings. RESULTS: These brothers are an unusual example of dopa-responsive dystonia that was present since birth. The muscle histopathologic features were caused by an abnormal cerebral influence on the developing motor unit and were not a primary abnormality. A repeated muscle biopsy performed 1 year after treatment continued to show the same pattern of fiber-type abnormalities. CONCLUSIONS: Dopa-responsive dystonia can be present from birth or early infancy. The response to levodopa is excellent even after a delay in treatment of more than 20 years. Intrauterine dystonia can cause a predominance of small type 2 fibers. A trial of levodopa/carbidopa is indicated in all patients with a childhood-onset dystonia or gait disturbance.

Adult↗
PubMed1995

Effects of tolcapone in Parkinson's patients taking L-dihydroxyphenylalanine/carbidopa and selegiline.

A double-blind, placebo-controlled, crossover trial of tolcapone (RO 40-7592), a potent reversible inhibitor of catechol-O-methyltransferase (COMT), was performed in 10 Parkinson's disease (PD) patients to determine single-dose safety and efficacy. All subjects were chronically treated with stable doses of selegiline and L-dihydroxyphenylalanine (L-DOPA)/carbidopa. Tolcapone was administered in four single ascending doses (50-800 mg) randomly paired with placebo. Motor ratings were performed every 30 min for 6 h. At higher doses (400 mg and 800 mg), tolcapone prolonged the antiparkinson response of L-DOPA. Nausea was the most common adverse effect of the tolcapone-L-DOPA/carbidopa-selegiline combination. Adverse cardiovascular effects were not seen. The acute inhibition of amino acid decarboxylase, monoamine oxidase-B, and COMT is well tolerated and prolongs the L-DOPA response in PD patients. Tolcapone may be a safe and useful adjunct to L-DOPA/carbidopa in PD patients taking selegiline.

Aged↗
PubMed1995

EPI imaging of global increase of brain MR signal with breath-hold preceded by breathing O2.

Brain MR signal has been observed to decrease during cessation of breathing due to the increase of deoxyhemoglobin in the blood. However, for both animal and human studies, we have demonstrated that if the subjects breathed 100% oxygen in advance of apnea for a short time, T2*-weighted MR brain signal increased when breathing was stopped for a period of 30-60 s. This demonstrates the possibility of measuring responses to hemodynamic change throughout the entire brain with a single respiratory perturbation in a rapid, reliable, and robust manner.

Animals↗
PubMed1995

The intravascular contribution to fMRI signal change: Monte Carlo modeling and diffusion-weighted studies in vivo.

Understanding the relationship between fMRI signal changes and activated cortex is paramount to successful mapping of neuronal activity. To this end, the relative extravascular and intravascular contribution to fMRI signal change from capillaries (localized), venules (less localized) and macrovessels (remote, draining veins) must be determined. In this work, the authors assessed both the extravascular and intravascular contribution to blood oxygenation level-dependent gradient echo signal change at 1.5 T by using a Monte Carlo model for susceptibility-based contrast in conjunction with a physiological model for neuronal activation-induced changes in oxygenation and vascular volume fraction. The authors compared our Model results with experimental fMRI signal changes with and without velocity sensitization via bipolar gradients to null the intravascular signal. The model and experimental results are in agreement and suggest that the intravascular spins account for the majority of fMRI signal change on T2*-weighted images at 1.5 T.

Blood Flow Velocity↗
PubMed1995

MR perfusion studies with T1-weighted echo planar imaging.

The T1 perfusion model has worked well in brain functional studies where flow changes are measured. Using selective and nonselective inversion pulses, a new method has been developed to study steady-state brain blood flow. The authors obtained flow-sensitive images using selective inversion and flow-insensitive images using nonselective inversion. Subtraction of flow-insensitive images from flow-sensitive images gave us flow-weighted images with good gray-white flow contrast in cortical gray matter as well as in the thalamus and basal ganglia. Fitting T1s of flow-insensitive and flow-sensitive images allowed us to obtain preliminary results of brain blood flow maps. Two specific problems can seriously affect the accuracy of the brain blood flow values and the gray-white flow contrast of brain blood flow maps. These are the problems of the partial volume effect of CSF and gray matter, and the difference between blood T1 and white matter T1. The authors discuss in detail the character of these problems and present a number of approaches to manage such problems.

Artifacts↗