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T H Le

Publications and source records attributed to T H Le.

43 records · Page 3Linked to original sources
PubMed1993

Transforming growth factor-beta is a renin secretagogue at picomolar concentrations.

Transforming growth factor-beta s (TGF-beta s), a family of peptides, have many actions including modulating cellular growth, differentiation, and influencing steroidogenesis. Because both TGF-beta and renin are present in renal juxtaglomerular cells, we have examined the effects of these peptides on renin secretion using static incubations of rat renal cortical slices. We report here an effect of both TGF-beta 1 and -beta 2 on renin secretion. At low concentrations, both TGF-beta 1 (4 x 10(-12) M) and -beta 2 (8 x 10(-12) M) stimulate basal renin secretion (control, 100 +/- 4%; TGF-beta 1, 123 +/- 4%; TGF-beta 2, 124 +/- 5%; both P < 0.02 compared with control). However, at higher concentrations (2 x 10(-10) M), both peptides do not alter basal renin release. Our previous studies show that both prostaglandins and lipoxygenase (LO) products of arachidonic acid play an important dual regulatory role in renin secretion; therefore, we have examined the effects of both cyclooxygenase (CO) and LO inhibition in TGF-beta action.(ABSTRACT TRUNCATED AT 250 WORDS)

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗
PubMed1989

Ia reflexes and EPSPs in human soleus motor neurones.

The reflex responses of single motor units in the soleus muscle to electrical stimulation of the tibial nerve were recorded in human volunteers. A feature of the experiments was the stimulation paradigm used. In order to control the peri-stimulus firing rate, a computer triggered the stimulus isolator only when 2 interspike intervals of specified duration occurred in succession. In addition, the timing of the stimulus in relation to the preceding action potential was controlled in a manner similar to a conditioning/testing paradigm. The general pattern of response was an initial, "H-reflex" excitation at monosynaptic latency, followed first by a silent period due to the refractoriness of the motor neurone, then by other phases of reduced activity. When the stimulus intensity was increased, the intensity of the excitation and the duration of the silent period increased in parallel. When the pre-stimulus firing rate of the motor unit was varied, the amplitude of the H-reflex response. normalized to the number of stimulus trials, was similar at 6, 8 and 10 Hz, but was greater at 4 Hz in most units tested. These findings were consistent with a simple model of the events occurring at the cell membrane in this reflex which was proposed by Ashby and Zilm (1982a), although some modification of the model was necessary to account for the different response at 4 Hz. The improved stimulation paradigm enabled a direct estimate to be made of the amplitude and shape of the rising phase of the Ia EPSP in human motor neurones.

Action Potentials↗
PubMed1989

Biphasic inhibitory responses and their IPSPs evoked by tibial nerve stimulation in human soleus motor neurones.

A novel stimulating protocol was used to demonstrate the existence of a biphasic inhibitory reflex in single soleus motor neurones in response to weak stimulation of the tibial nerve in human subjects. The stimulus intensity was sufficient to evoke a small M-response but was subthreshold for the H-reflex. Stronger stimulation caused the 2 phases of inhibition to fuse. The experimental protocol allowed excitatory and inhibitory responses to be recognized unambiguously. The criterion for excitation was stimulus-induced advance in the timing of the next action potential in certain trials: for inhibition, the criterion was stimulus-induced delay in the timing of the next action potential. The shorter-latency inhibitory response began at about 45-50 ms and lasted for about 20 ms. With the stimulus intensity used, only inhibitory responses were evoked at short latency in tibialis motor neurones, which suggests that the soleus inhibition resulted from recurrent inhibition via the Renshaw pathway rather than by activation of Ib afferents in the tibial nerve. A novel approach to the determination of the waveform of the IPSP underlying the shorter-latency (presumably Renshaw-mediated) inhibition revealed only part of the waveform owing to the sharp fall in the membrane potential at the onset of (presumably-Renshaw) IPSP. This approach was more successful when applied to the longer-latency, slower IPSP. The longer-latency inhibitory response in soleus motor neurones began at about 80-120 ms. Overall, the latency of this inhibition was less when it followed an M-response than when it followed an H-reflex.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

[Periungual capillaroscopic aspects in Behçet's disease. Apropos of 30 cases].

Nailed capillaroscopy was systematically performed in 30 patients with Behcet's disease to search capillary dystrophies with paradoxal normal number of capillary loops; some indirect signs of microvascular disease were noted: pallor of the background; petechiae; sludge; abnormal visibility of the venous plexus and of irregularly arranged venules. Eight patients had a normal capillaroscopy: thirteen had direct signs of microvalvular abnormalities (nine cases with two direct signs and at least two indirect signs; and four cases with two direct and one indirect, or one direct and three indirect signs). Nine patients had only sludge and/or petechiae. We never observed any abnormality in the number of the capillaries, in the sweat droplets nor in the circulatory speed. Two patients had megacapillaries resembling those seen in scleroderma. The petechiae were observed in 50 p. 100 of the cases. We found no correlation between the capillaroscopic abnormalities and the age, sex, duration of the disease, or ethnic background. However, the presence of aphthosis the day of the capillaroscopy seems to be correlated with the cutaneous microvascular abnormalities. Thus, there exist frequent capillaroscopic abnormalities in Behcet's disease. Although aspecific, they point out the vascular tropism of this disease, resembling that of the vascularite. The prognostic importance of the capillaroscopy in Behcet's disease is under study.

Adult↗
PubMedDate not supplied

Methods for assessing accuracy and reliability in functional MRI.

In this paper, methods for assessing the accuracy and the reliability of functional magnetic resonance imaging techniques are presented. First, a modified receiver operating characteristic analysis is described for evaluating the accuracy of fMRI studies. With this modified approach, the true positives or the activated pixels are estimated based on highly averaged experimental data acquired with the same stimulation/task. Unlike ROC analysis based on simulated activation data, the present approach can be applied to experimentally acquired data without simplifying the activation related changes. To assess the reliability of fMRI studies, the kappa statistic was adopted for evaluating the overall agreement of functional activation maps from repeated experiments in individual subjects. To demonstrate the utility of these techniques, both the ROC analysis and the reliability assessment were applied to quantitatively evaluate the improvement in accuracy and reliability of a retrospective technique for physiological noise reduction in fMRI.

Magnetic Resonance Imaging↗