Spatiotemporal modeling of cerebral evoked magnetic fields to median nerve stimulation.

We measured somatosensory evoked magnetic fields during median nerve stimulation in 6 normal subjects. We applied multiple dipole models to study the spatiotemporal structure of early somatosensory evoked magnetic fields (SEFs), as well as the number, 3-dimensional location and time activity of their underlying neuronal sources. Two dipole sources were necessary to model the first 40 msec of SEFs explaining 85% of the data variance. Source 1 was located deeper than source 2, showed primarily a tangential orientation, and accounted for a larger part of the variance; source 2 showed no consistent orientation across subjects. Both sources showed biphasic time activities corresponding to the previously described N20-P30 and P25-N35 components. Spatiotemporal modeling could identify sources which could not be modeled consistently above noise by single moving dipoles (P25 component), revealed small latency differences of the two sources in some subjects suggesting parallel activation of these sources, and allowed separation of sources overlapping considerably both in space and time. We conclude that spatiotemporal modeling of SEFs may be useful to study functional anatomy of human sensorimotor cortex non-invasively.     

Correlation between amount of retinal afferents to the pretectal nucleus of the optic tract and dorsal terminal accessory optic nucleus and performance of horizontal optokinetic reflex in rat.

Intraocular kainic acid injection in Long-Evans rats induces loss of retinal afferents to subcortical visual centers as assessed by the axoplasmic transport of [14C]valine. The optical terminal fields of the pretectal nucleus of the optic tract (NOT), superior colliculus and accessory optic system (AOS) nuclei appear particularly affected. Since NOT and the AOS dorsal terminal nucleus (DTN) represent the first relay station of the visuomotor pathway mediating horizontal optokinetic nystagmus (HOKR), we have studied the characteristics of HOKR after various degrees of retinal deafferentation of these nuclei induced by intraocular KA injection. Taking advantage of the arrangement of the primary optic projections to NOT-DTN, that in rats are almost entirely crossed, in each animal, monocular HOKR induced by stimulation of the injected eye was compared to monocular HOKR elicited by stimulation of the intact, ipsilateral eye. Following NOT-DTN optic denervation, HOKR gain always worsened, and in a way, that the greater the deficits of retinal afferents, the greater the HOKR inability to compensate for visual motion. Furthermore, for any given retinal denervation the higher the stimulus velocity, the greater the HOKR deficit. While the correlation between HOKR gain and the amount of retinal afferents to NOT-DTN would seem to indicate a functional homogeneity of the retinal ganglion cells sending axons to these nuclei, the finding that the extent of HOKR impairment also varied with velocity might not support the above view.     

The Effects of Zero Magnesium Dialysate and Magnesium Supplements on Ionised Calcium Concentration in Patients on Regular Dialysis Treatment

The effect of oral magnesium carbonate aluminium hydroxide onserum ionised calcium, total calcium, aluminium and magnesium,was assessed in 31 patients with chronic renal failure, duringand after one haemodialysis. The behaviour of ionised calcium and total calcium was the samein both groups. Each showed a slight fall during dialysis, whichwas not significant. Serum total calcium was 0.2–0.3 mmol/l(0.8–1.2 mg/dl) greater throughout the period of dialysisin the group taking aluminium hydroxide. Serum magnesium andaluminium were both lower in the group treated with magnesiumcarbonate. In the group taking magnesium carbonate, serum magnesium concentrationsfell markedly during dialysis, but otherwise were maintainedwithin the reference range by the use of a magnesium-free dialysate.These results show the effectiveness of magnesium carbonateoral phosphate-binding agents and zero magnesium dialysate inreducing serum aluminium without affecting the behaviour ofserum calcium fractions during dialysis.     

Comparison of loop diuretics in patients with chronic renal insufficiency

Furosemide and bumetanide share a number of characteristics including reduced natriuretic effects in azotemic patients. It has been presumed that this condition affects each drug equally. Previous studies, however, suggest dissimilar pathways of delivery to their sites of action. Though not rigorously tested, this potential disparity might cause them to differ when used in azotemia. We, therefore, assessed the pharmacokinetic and pharmacodynamic characteristics of intravenously administered furosemide and bumetanide in ten adult patients with stable, chronic renal insufficiency (mean creatinine clearance = 14.1 +/- 2.0 ml/min/1.73 m2) in a randomized, cross-over study during controlled sodium intake. Our goals were to assess differences in diuretic effectiveness and in so doing to determine the dose required to produce a maximal response. The mean diuretic doses of 172 and 4.3 mg for furosemide and bumetanide, respectively (ratio = 40:1) were sufficient to produce a maximum response. Despite similarities in maximal fractional excretion of sodium (18.2 +/- 2.6% with furosemide vs. 19.4 +/- 4.5% with bumetanide, P = 0.687) demonstrating an equal tubular responsiveness to both drugs, overall response as quantified by cumulative natriuresis in the initial eight hour period was 52% greater with furosemide (108 +/- 17 vs. 71 +/- 7 mEq; P = 0.042). The difference in total excreted sodium was accounted for by a preserved nonrenal clearance of bumetanide (113 +/- 12 compared to 53 +/- 5 ml/min for furosemide, P = 0.001) which resulted in relatively less bumetanide in serum available to be delivered into the urine.(ABSTRACT TRUNCATED AT 250 WORDS)     

The management of preexcitation syndromes

The introduction of new techniques such as epicardial mapping and programmed stimulation of the heart has made it possible to unravel most of the mysteries surrounding ventricular preexcitation. They helped us to understand the mechanisms of the arrhythmias that frequently are found in these patients and led to better-directed therapeutic interventions. The purpose of this article is to review this information and to indicate how it can be used in the treatment of the patient with preexcitation.     

Differential ontogeny of divalent cation effects on rat brain delta-, mu-, and kappa-opioid receptor binding

The effect of the divalent cations, Mn2+, Mg2+ and Ca2+ on rat forebrain delta-, mu- and kappa-receptor binding was examined during postnatal development. It was found that delta-receptor binding, assessed with [3H]D-Ala2-D-Leu5-enkephalin ([3H]DADLE) (+ 10 nM D-Ala2- MePhe4-Gly-ol5-enkephalin (DAMGE)), was stimulated by the 3 cations in a dose- and developmental time-dependent manner. delta-Binding was most sensitive to the cations during the first week postnatal, prior to the appearance of high-affinity delta-binding. In contrast, inhibition of mu-receptor binding ([3H]DAMGE) by divalent cations appeared early in development and remained constant throughout the postnatal period. Divalent cation inhibition of kappa-binding ([3H]ethylketocyclazocine ([3H]EKC) + 100 nM DAMGE and 100 nM DADLE) appeared after the second week postnatal. These results demonstrate that the characteristics and postnatal development of divalent cation modulation of mu-, delta- and kappa-binding is distinctly different. Thus, the neonate may be a good model system to examine the binding properties and functions of delta- and kappa-receptor subtypes.     

Acute effects of nitroglycerin on the energetics of the human left ventricular myocardium

We analyzed performance and efficiency of the left ventricular myocardium on the basis of two new energetic parameters. The myocardial energy consumed during one cardiac cycle is related to performed work on the one hand (E1) and to the stress-time-integral on the other (E2). E1 was obtained by analysis of the pressure-volume integral divided by left ventricular muscle mass. E2 was obtained as follows: the stress-time integral was analyzed from pressure-volume data and wall thickness using an ellipsoidal calculation model. In order to transfer the stress-time integral into energy units, the value was multiplied by a constant factor which was obtained in experimental myothermal studies. In ten patients with coronary heart disease undergoing diagnostic heart catheterization, angiocardiography was performed before and after oral administration of nitroglycerin (1.6 mg). Total energy consumption (2E1 + E2) per gram myocardium per beat decreased from 6.1 +/- 1.3 mcal/g to 4.7 +/- 1.4 mcal/g (P less than 0.01), and myocardial efficiency (E1/[2E1 + E2]) increased from 27.0 +/- 3.1% to 28.4 +/- 4.3% (N.S.) on the average. This analysis explains quantitatively the beneficial effect of nitro-preparations on myocardial function and energetics.     

Marked hypodiploidy in blast phase chronic myelogenous leukemia: report of a case and review of the literature

The emergence of a near-haploid clone of cells in blast phase chronic myelogenous leukemia is an unusual event. We report such a case and review eight other cases described in the English literature. The significance of the substantial loss of genetic material is discussed as is the phenotypic and genotypic heterogeneity observed in this group of patients.