Modulation of corticomotor excitability by an I-wave intervention delivered during low-level voluntary contraction.

Transcranial magnetic stimulation (TMS) interventions that modulate cortical plasticity may achieve a more functional benefit if combined with neuro-rehabilitation therapies. With a TMS protocol targeting I-wave dynamics, it is possible to deliver stimuli while a subject performs a motor task, and this may more effectively target functional networks related to the task. However, the efficacy of this intervention during a simple task such as a low-level voluntary contraction is not known. We delivered paired-pulse TMS at an inter-pulse interval (IPI) of 1.5 ms for 15 min while subjects performed a 10 ± 2.5% voluntary contraction of the first dorsal interosseous (FDI) muscle and made motor evoked potential (MEP) amplitude and short-interval intracortical facilitation (SICF) curve measurements. Pre-intervention SICF curves showed only a single peak at 1.3-1.5 ms IPI. During the intervention, MEP amplitude steadily increased (P < 0.001) to 137 ± 13% of its initial value. After the intervention, SICF curves were increased in amplitude (P < 0.001) and later peaks emerged at 2.8 and 4.3 ms IPIs. A control experiment, replacing paired-pulse stimulation with single-pulse stimulation showed no effect on MEP amplitude (P = 0.951). We conclude that the I-wave intervention can be administered concurrently with a simple motor task and that it acts by increasing trans-synaptic efficacy across a number of I-waves. The ability to perform a motor task simultaneously with a TMS intervention could confer a degree of specificity to the induced excitability changes and may be beneficial for functional neuro-rehabilitation programs built around motor learning and retraining.

Effect of leaf position on levels of the chloroplast and cytosolic fructose bisphosphatase isozymes in the pea leaf nucleus.

Immunocytolocalization experiments indicate that nuclear levels of the pea leaf cytosolic fructose bisphosphatase are higher in leaves located near the base of the plant and lower in expanded leaves at the apex. It seems possible that the cytosolic isozyme in the nucleus has a role in tissue aging. In contrast, there is no indication that leaf position or tissue age affects levels of the chloroplastic enzyme in the nucleus. The density of the chloroplast fructose bisphosphatase is higher in the nucleolus than in the nucleoplasm. Conversely, the density of the cytosolic isozyme is slightly higher in the nucleoplasm. Analysis of double immunolabeling experiments indicates that both isozymes are distributed nonrandomly with respect to DNA, and therefore colocalized with DNA, in the nucleus, and that the chloroplast isozyme is also distributed nonrandomly with respect to DNA in the chloroplast.

Three enzymes of carbon metabolism or their antigenic analogs in pea leaf nuclei.

Antigens closely resembling or identical to the three glycolytic enzyme proteins phosphate-glycerate kinase, glyceraldehyde-3-phosphate dehydrogenase, and aldolase are found in situ in the nucleus of the leaf mesophyll cells of pea (Pisum sativum L.). These proteins have already been identified in vertebrate nuclei. Apparently, these enzymes are nuclear proteins with "secondary" roles not directly related to their enzymatic function in carbon metabolism in both animals and plants.

Nephritogenicity of antibodies to proteoglycans of the glomerular basement membrane--I.

We investigated nephritogenic potential of antibodies to heparan sulfate-proteoglycan of glomerular basement membrane. Glomeruli were isolated, basement membranes were prepared, proteoglycans extracted, and purified core protein was obtained. We immunized rabbits with the core protein, IgG fraction prepared from the antisera and specificity of the antibody determined. A single immunoprecipitin line in agar diffusion plate and a single band (approximately 18,000 mol wt) on the immunoblot autoradiograms were visualized. The antibody showed precise reactivity with the glomerular basement membranes. The clearance studies indicated that approximately 75% of the radioiodinated antibody disappeared from circulation within 1 h and 1-2% bound to the kidney. For nephritogenicity experiments, the antibody was intravenously administered into rats and we examined their kidneys at 1 h to 24 d later. A linear immunofluorescence of glomerular basement membranes was observed with rabbit IgG at all times while that of C3 until the 10th day. Early morphologic changes included glomerular infiltration of polymorphonuclear leukocytes with focal exfoliation of endothelium. The leukocytic infiltration subsided by the third day and was followed by progressive thickening of basement membranes, focal mesangial cell proliferation, increase in mesangial matrix, and accumulation of monocytes. Focal knob-like thickening of glomerular basement membrane was observed from the 15th day onward. Regularly-spaced electrondense deposits were seen in the lamina rara interna and externa of glomerular basement membranes and persisted throughout the investigatory period. No significant proteinuria was observed at any stage of the experiment. These findings suggest that the antibodies to the basement membrane heparan sulfate-proteoglycan are nephrotoxic but possess weak nephritogenic potential.

De novo cellular synthesis of sulfated proteoglycans of the developing renal glomerulus in vivo.

The site of cellular synthesis of glomerular proteoglycans was investigated in developing glomeruli of 4- to 5-day-old rats. [35S]Sulfate was administered intravenously and animals were sacrificed 15 min to 12 hr later. The outermost layers of the kidney cortices were utilized for characterization of proteoglycans and electron microscopic autoradiography. Sepharose CL-6B chromatography and cellulose acetate electrophoresis revealed that most (approximately equal to 96%) of the radioactivity was associated with heparan sulfate-proteoglycan synthesized during maturation of glomerular capillaries. Tissue autoradiography revealed the following: (i) during the S-shaped body stage, there is rapid incorporation of [35S]sulfate by mesenchymal cells into the cleft region (site for development of future glomerular extracellular matrices); (ii) during the precapillary stage, mesenchyme-derived cells showed higher incorporation of radioisotope than did epithelial cells; and (iii) during the mature capillary stage, all glomerular cell types (mesangial, endothelial, and epithelial) incorporated [35S]sulfate, incorporation by mesangial cells being the greatest. Radiolabeling was also higher in the mesangial matrix than in the glomerular basement membrane of peripheral capillary loops. Synthesis of a single major species of sulfated glycosaminoglycan by cells of different embryologic origin may be unique to glomerular capillaries.

Effect of beta-D-xyloside on the glomerular proteoglycans. I. Biochemical studies.

The effect of p-nitrophenyl-beta-D-xylopyranoside on glomerular extracellular matrices (glomerular basement membrane and mesangial matrix) proteoglycans was studied. The proteoglycans of rat kidneys were labeled with [35S]sulfate in the presence or absence of beta-xyloside (2.5 mM) by using an isolated organ perfusion system. The proteoglycans from the glomeruli and perfusion medium were isolated and characterized by Sepharose CL-6B chromatography and by their behavior in CsCl density gradients. With xyloside treatment there was a twofold decrease in 35S-labeled macromolecules in the tissues but a twofold increase in those recovered in the medium as compared with the control. The labeled proteoglycans extracted from control kidneys eluted as a single peak with Kav = 0.25 (Mr = approximately 130,000), and approximately 95% of the radioactivity was associated with heparan sulfate proteoglycan (HS-PG), the remainder with chondroitin (or dermatan) sulfate proteoglycan (CS-PG). In the xyloside-treated kidneys, the proteoglycans extracted from the tissue eluted as two peaks, Kav = 0.25 (Mr = approximately 130,000) and 0.41 (Mr = approximately 46,000), which contained approximately 40 and approximately 60% of the total radioactivity, respectively. The first peak contained mostly the HS-PG (approximately 90%) while the second peak had a mixture of HS-PG (approximately 70%) and CS-PG (approximately 30%). In controls, approximately 90% of the radioactivity, mostly HS-PG, was confined to high density fractions of a CsCl density gradient. In contrast, in xyloside experiments, both HS-PG and CS-PG were distributed in variable proportions throughout the gradient. The incorporated 35S activity in the medium of xyloside-treated kidneys was twice that of the controls and had three to four times the amount of free chondroitin (or dermatan) sulfate glycosaminoglycan chains. The data suggest that beta-xyloside inhibits the addition of de novo synthesized glycosaminoglycan chains onto the core protein of proteoglycans and at the same time stimulates the synthesis of chondroitin or dermatan sulfate chains which are mainly discharged into the perfusion medium.