Immunomodulation by Candida albicans: crucial role of organ colonization and chronic infection with an attenuated agerminative strain of C. albicans for establishment of anti-infectious protection

Intravenous inoculation of an attenuated agerminative strain of Candida albicans (PCA-2) of low virulence, but not of two other species of Candida of low virulence (C. parapsilosis and C. viswanathii) into CD2F1 mice conferred protection against the highly virulent microbes C. albicans CA-6, Staphylococcus aureus and Aspergillus fumigatus. To provide protection, a definite inoculum size (10(6) cells per mouse) resulting in organ colonization and establishment of a long-lasting chronic infection with PCA-2 was needed. An inoculum of 10(5) cells gave rise to transient kidney colonization whereas inocula greater than 10(6) cells led to acute septicaemia and eventual death. Chronic infection of mice following inoculation of 10(6) PCA-2 cells was accompanied by detectable mannoprotein antigen levels in the serum (30-70 ng ml-1) while specific antibodies did not appear until 14 d after inoculation, at which time low antimannan antibody was present (ELISA titre 1:40-1:80). Chronic infection was characterized by the presence in the kidneys of 2-3 x 10(6) c.f.u. of PCA-2 for at least 40 d after inoculation. Pharmacological modulation of the host through administration of either an anti-Candida drug, amphotericin B, or an immunosuppressive agent, cyclophosphamide, strongly supported the premise that the anti-infectious state conferred by PCA-2 'immunization' correlated with the maintenance of a sufficient number of PCA-2 in vivo. Protection was 'switched on' when 2-3 x 10(5) cells were present in the kidneys. It was maximal at a kidney count of 2-3 x 10(6) c.f.u. of PCA-2, and promptly declined when the number of PCA-2 cells in the kidney fell below 2 x 10(5). Mice chronically infected with PCA-2 had splenic macrophages with pronounced candidacidal activity in vitro. Modulation of the growth of PCA-2 in vivo, which determined activation or deactivation of the protective state, was paralleled by a similar modulation in macrophage activation, showing that in all cases resistance to virulent organisms persisted as long as macrophage activation was present. The results demonstrate that a critical in vivo antigenic load is crucial for the occurrence of resistance to infection and suggests that macrophages could be involved in this protection.     

Pre-exposure to yeast protects larvae of Galleria mellonella from a subsequent lethal infection by Candida albicans and is mediated by the increased expression of antimicrobial peptides

Pre-exposure of the larvae of Galleria mellonella to Candida albicans or Saccharomyces cerevisiae protects against a subsequent infection with 10(6) C. albicans cells. This protection can also be induced by exposing larvae to glucan or laminarin prior to the administration of the potentially lethal inoculum. Analysis of the genes coding for galiomicin, a defensin in G. mellonella, a cysteine-rich antifungal peptide gallerimycin, an iron-binding protein transferrin and an inducible metalloproteinase inhibitor (IMPI) from G. mellonella demonstrated increased expression, which is at its highest after 24 h of the initial inoculum. Examination of the expression of proteins in the insect haemolymph using 2D electrophoresis and MALDI TOF analysis revealed an increased expression of a number of proteins associated with the insect immune response to infection 24 h after the initial exposure. This study demonstrates that the larvae of G. mellonella can withstand a lethal inoculum of C. albicans if pre-exposed to a non-lethal dose of yeast or polysaccharide 24 h previously which is mediated by increased expression of a number of antimicrobial peptides and the appearance of a number of peptides in the challenged larvae.     

Renal norepinephrine content decreases after chronic flow probe implantation.

Electromagnetic flow probes were chronically implanted around the left renal artery in 6 female beagle dogs. 3-10 months after implantation, renal cortex norepinephrine contents of right and left kidneys were compared (liquid chromatography). In 4 out of the 6 dogs investigated 3-6 months after implantation, the norepinephrine content of the left kidney was reduced by 27-72%. In 2 dogs investigated 7 and 10 months after implantation, the difference between left and right kidney was not significant. These findings should be taken into consideration when interpreting results from chronically instrumented kidneys.     

Pathogenicity of various species of Candida in an experimental murine system

The systemic infection induced by Candida albicans, Candida krusei and Candida viswanathii was studied in an experimental murine system. Candida albicans is able to kill outbred CD1 mice within a few days and at a very low concentration; C. krusei is not pathogenic not even when inoculated at a higher concentration; C. viswanathii is able to kill animals only a a higher concentration. The different resistances do not seem to be under genic control, in as much as the different strains of mice used (hybrid CD2F1 and B6C3HF1, inbred Balb/c) show the same degree of resistance as the CD1 mice to the three species of Candida. The colony forming units (CFU) in the kidneys of CD1 mice inoculated intravenously with 10(5) cells of the three species of Candida, collected at various intervals showed a good correlation with the median survival times: a rapid moltiplication of the C. albicans is evident in the kidneys of the animals 24 hours after the inoculation, while the C. krusei and the C. viswanathii do not moltiply.     

Inoculum size effect in dimorphic fungi: extracellular control of yeast-mycelium dimorphism in Ceratocystis ulmi

We studied the inoculum size effect in Ceratocystis ulmi, the dimorphic fungus that causes Dutch elm disease. In a defined glucose-proline-salts medium, cells develop as budding yeasts when inoculated at > or = 10(6) spores per ml and as mycelia when inoculated at <10(6) spores per ml. The inoculum size effect was not influenced by inoculum spore type, age of the spores, temperature, pH, oxygen availability, trace metals, sulfur source, phosphorous source, or the concentration of glucose or proline. Similarly, it was not influenced by added adenosine, reducing agents, methyl donors, amino sugars, fatty acids, or carbon dioxide. Instead, growing cells excreted an unknown quorum-sensing factor that caused a morphological shift from mycelia to budding yeasts. This yeast-promoting effect is abolished if it is extracted with an organic solvent such as ethyl acetate. The quorum-sensing activity acquired by the organic solvent could be added back to fresh medium in a dose-dependent fashion. The quorum-sensing activity in C. ulmi spent medium was specific for C. ulmi and had no effect on the dimorphic fungus Candida albicans or the photomorphogenic fungus Penicillium isariaeforme. In addition, farnesol, the quorum-sensing molecule produced by C. albicans, did not inhibit mycelial development of C. ulmi when present at concentrations of up to 100 microM. We conclude that the inoculum size effect is a manifestation of a quorum-sensing system that is mediated by an excreted extracellular molecule, and we suggest that quorum sensing is a general phenomenon in dimorphic fungi.     

Inequality in function of the right and left ovaries and uterine horns of the mouse

Inequality in function of the left and right ovaries and uterine horns of mice was evaluated in three separate experiments. In Exp. 1, the effect of position in the reproductive tract on various reproductive characteristics was evaluated in 158 pregnant hybrid mice. Ovulation rate, number of fetuses, total fetal weight and total placental weight were higher (P less than 0.05) on the right than the left on Day 18 of pregnancy (vaginal plug = Day 1). In Exp. 2, the effect of previous sham or unilateral ovariectomy (right or left) in mated Swiss-Webster mice was compared with unoperated mated controls (N = 17-24/treatment). In control mice, ovulation rate, total fetal weight and ovarian weight were higher (P less than 0.05) on the right than left side. Surgery (sham or unilateral, ovariectomy) decreased (P less than 0.005) ovulation rates, number of fetuses, ovarian weights, total fetal weight and total placental weight on Day 18 of pregnancy. Unilateral ovariectomy decreased (P less than 0.05) ovulation rates and ovarian weights more than did sham operation. Ovulation rates were higher (P less than 0.01) when the left ovary was manipulated or removed rather than the right ovary. For Exp. 3, pairs of 8 hybrid mouse embryos each (morulae and blastocysts) were surgically transferred to the left and right uterine horns of the same (bilateral, N = 15) or different (unilateral, N = 28) Swiss-Webster recipients. In almost all incidences, embryo survival (to Day 18 of pregnancy) was twice as high (P less than 0.05) in right than left uterine horns. We conclude that the left and right ovaries and uterine horns are not equal in function in Swiss-Webster and a hybrid strain of mice.     

Proteinase production and pathogenicity of Candida albicans. II. Virulence for mice of C. albicans strains of different proteinase activity

We have studied the virulence for mice of Candida albicans strains with different proteinase activity in the culture. The mortality rates for mice infected with the type Ia strains, which secrete proteinase whose activity porsisted for a week in vitro, were higher than those infected with the type Ib strains, which secrete proteinase whose activity declined at 2 or 3 days in vitro and the type II proteinase-deficient strains. This was substantiated by the number of colony-forming units (CFU) recovered from kidneys of mice infected with C. albicans. In the kidney tissues of mice infected with the type Ia strains, extensive invasion by fungal cells and the secretion of proteinase were histologically demonstrated, while in those infected with the type Ib and II strains fungal cells were rarely found. However, the mice infected with the type Ib strain NUM 978 were an exception; the recovery of CFU from the kidney was high, but the animals survived longer. Histologically, Candida cells were not colonized but interspersed in the tissue. Type II strain NUM 584 was found to be moderately virulent when infected at a high dose. These observations indicate that the proteinase plays a role in type Ia strains but that other factors are involved in the type Ib or II strains for the establishment of pathogenicity of C. albicans.     

Sex and age differences of relationships among stepping parameters for evaluating dynamic balance in the elderly

This study aimed to examine the relationships among various stepping parameters, sex, and age in the elderly. Healthy elderly Japanese individuals 60-85 years old (50 males and 61 females) performed 4 types of stepping motions for 20 s. Stepping motions included bilateral stepping (back/forth and right/left) and unilateral stepping (back/forth and right/left). The number of steps, the average connecting time of a foot during one step, and the average time of both feet touching the floor at the same time (bilateral connecting time) were measured with a foot switch sheet. The trial-to-trial reliability was very high (above 0.86) except for the bilateral connecting time in the bilateral stepping back/forth test for 70-85 year olds (males: 0.67, females: 0.68). With age, the number of steps was significantly smaller, and the average connecting time and the bilateral connecting time were shorter in all stepping tests. There were significant sex differences in bilateral connecting time for bilateral stepping right and left and the number of steps for the bilateral stepping back and forth and the unilateral stepping right and left tests. The number of steps and average connecting time showed high correlations between bilateral stepping right/left and back/forth (r=0.71-0.94) and between unilateral stepping back/forth and right/left (r=0.87-0.99). There were significant correlations of the average connecting time between bilateral and unilateral stepping motions (r=0.51-0.83), but both stepping motions are considered to have different motion properties from the viewpoint of center of gravity sway. The correlations between the bilateral connecting time and the number of steps in bilateral stepping were relatively low (males: /r/<0.70, females: /r/<0.57). The bilateral connecting time was near 0 s in many males; thus, it may depend greatly on individual or sex differences in stepping strategy. These results suggest that the stepping motions used in this study can evaluate dynamic balance ability, and that the unilateral test may be useful for the elderly who cannot walk independently with ease.     

Augmentation of host resistance to Candida albicans infection in ascites tumor-bearing mice.

We found that the number of peripheral blood polymorphonuclear leukocytes (PMN) dramatically increased in both sarcoma 180 (S-180) and MM-46 mammary carcinoma (MM-46) ascites tumor-bearing mice, and mice required a remarkable resistance to Candida albicans infection via intravenous route. When the resistance was determined by number of cells of C. albicans in the kidney, a significant decrease in the number of fungal cells was observed in the kidneys of infected ascites tumor-bearing mice. An increase of active oxygen levels of PMN from ascites tumor-bearing mice was observed, suggesting that this factor is important in developing of resistance in ascites tumor-bearing mice. Additionally, a culture supernatant of tumor cells co-cultivated with bone-marrow cells in vitro increased the number of granulocytes and macrophages differentiated from the bone-marrow cells.     

Loss of poly(ADP-ribose) polymerase 1 attenuates renal fibrosis and inflammation during unilateral ureteral obstruction

Poly(ADP-ribose) polymerase 1 (PARP1) contributes to necrotic cell death and inflammation in several disease models; however, the role of PARP1 in fibrogenesis remains to be defined. Here, we tested whether PARP1 was involved in the pathogenesis of renal fibrosis using the unilateral ureteral obstruction (UUO) mouse model. UUO was performed by ligation of the left ureter near the renal pelvis in Parp1-knockout (KO) and wild-type (WT) male mice. After 10 days of UUO, renal PARP1 expression and activation were strongly increased by 6- and 13-fold, respectively. Interstitial fibrosis induced by UUO was significantly attenuated in Parp1-KO kidneys compared with that in WT kidneys at 10 days, but not at 3 days, based on collagen deposition, α-smooth muscle actin (α-SMA), and fibronectin expression. Intriguingly, the UUO kidneys in Parp1-KO mice showed a dramatic decrease in infiltration of neutrophil and reduction in expression of proinflammatory proteins including intercellular adhesion molecule-1, tumor necrosis factor-α, inducible nitric oxide synthase, and toll-like receptor 4 as well as phosphorylation of nuclear factor-κB p65, but not transforming growth factor-β1 (TGF-β1) at both 3 and 10 days. Pharmacological inhibition of PARP1 in rat renal interstitial fibroblast (NRK-49F) cell line or genetic ablation in primary mouse embryonic fibroblast cells did not affect TGF-β1-induced de novo α-SMA expression. Parp1 deficiency significantly attenuated UUO-induced histological damage in the kidney tubular cells, but not apoptosis. These data suggest that PARP1 induces necrotic cell death and contributes to inflammatory signaling pathways that trigger fibrogenesis in obstructive nephropathy.     

Integrin αXβ2 Is a Leukocyte Receptor for Candida albicans and Is Essential for Protection against Fungal Infections

The opportunistic fungus Candida albicans is one of the leading causes of infections in immunocompromised patients, and innate immunity provides a principal mechanism for protection from the pathogen. In the present work, the role of integrin α(X)β(2) in the pathogenesis of fungal infection was assessed. Both purified α(X)β(2) and α(X)β(2)-expressing human epithelial kidney 293 cells recognized and bound to the fungal hyphae of SC5314 strain of C. albicans but not to the yeast form or to hyphae of a strain deficient in the fungal mannoprotein, Pra1. The binding of the integrin to the fungus was inhibited by β-glucans but not by mannans, implicating a lectin-like activity in recognition but distinct in specificity from that of α(M)β(2). Mice deficient in α(X)β(2) were more prone to systemic infection with the LD(50) fungal inoculum decreasing 3-fold in α(X)β(2)-deficient mice compared with wild-type mice. After challenging i.v. with 1.5 × 10(4) cell/g, 60% of control C57BL/6 mice died within 14 d compared with 100% mortality of α(X)β(2)-deficient mice within 9 d. Organs taken from α(X)β(2)-deficient mice 16 h postinfection revealed a 10-fold increase in fungal invasion into the brain and a 2-fold increase into the liver. These data indicate that α(X)β(2) is important for protection against systemic C. albicans infections and macrophage subsets in the liver, Kupffer cells, and in the brain, microglial cells use α(X)β(2) to control fungal invasion.     

The Computerized Table Setting Test for Detecting Unilateral Neglect

Background

Patients with unilateral neglect fail to respond normally to stimuli on the left side. To facilitate the evaluation of unilateral spatial neglect, we developed a new application that runs on a tablet device and investigated its feasibility in stroke patients.

Methods

We made the computerized table setting test (CTST) to run on the tablet computer. Forty acute ischemic stroke patients (20 patients with right hemispheric infarction with neglect, 10 patients with right hemispheric infarction without neglect, and 10 patients with left hemispheric infarction) and 10 healthy controls were prospectively enrolled to validate the CTST. The test requires subjects to set a table by dragging 12 dishes located below the table on the tablet screen. The horizontal deviation of the 12 dishes from the midline of the table, the selection tendency measured by the sequence of the dish selection, and the elapsed time for table setting were calculated automatically.

Results

Parameters measured by the CTST were correlated with the results of conventional neglect tests. The horizontal deviation was significantly higher in patients with right hemispheric infarction with neglect compared with the other groups. The selection tendency and elapsed time also were significantly different in patients with right hemispheric infarction with neglect compared with the left hemispheric infarction and control groups, but were similar to those with right hemispheric infarction without neglect.

Conclusions

The CTST is feasible to administer and comparable with conventional neglect tests. This new application may be useful for the initial diagnosis and follow-up of neglect patients.     

Cytology of the interstitial tissue in scrotal and abdominal testes of post-puberal boars

The interstitial tissue of the testes from healthy boars, and unilateral and bilateral abdominal cryptorchid boars was examined by light and transmission electron microscopy. The left and right testes of healthy boars, and the left (scrotal) testis of unilateral cryptorchid boars had abundant mature Leydig cells, few fibroblasts and mast cells, scarce and small blood vessels, and little lymphatic areas. The right (abdominal) testis of unilateral cryptorchid boars contained abundant Leydig cells, fibroblasts and erythrocytes, scarce mast cells, and frequent blood vessels; Leydig cells exhibited either a mature but degenerative appearance or an immature appearance, and fibroblasts displayed immaturity signs. The interstitial tissue of the left (abdominal) testes of bilateral cryptorchid boars had small blood vessels surrounded by erythrocytes, lymphocytes, and few plasma cells, and abundant mature and immature Leydig cells, immature fibroblasts, and mast cells. Mature Leydig cells showed mid or advanced degeneration, and immature Leydig cells displayed either non-degenerative or degenerative patterns. The right (abdominal) testes of bilateral cryptorchid boars contained scarce immature Leydig cells in advanced degeneration, large fibrous and adipose areas, and blood vessels. These results indicated that unilateral abdominal cryptorchidism affect neither the structural nor the cytologic features of the interstitial tissue in scrotal testes. Unilateral and bilateral cryptorchidism induced abnormal differentiation of Leydig cells and fibroblasts leading to decreased steroid production and increased collagenization in abdominal testes.     

Apoptosis of phagocytic cells induced by Candida albicans and production of IL-10

Macrophages co-incubated with Candida albicans strain CR1 in vitro showed early signs of apoptosis, but evolved to necrosis after 2 h. In this study, we investigated whether strain CR1 caused apoptosis or necrosis of macrophages after its inoculation into mice peritoneal cavity, and whether this correlated with the secretion of IL-10. Peritoneal macrophages from mice that received an inoculum of C. albicans CR1 showed signs of apoptosis and necrosis from 30 min to 2 h afterwards, whereas heat-killed C. albicans did not cause those effects. IL-10 production was low during the first 6 h post-infection, when macrophages predominated in the peritoneal exudate, whereas its higher production after 24 h correlated with an increase of neutrophils in the exudate. Treatment of CR1 with pepstatin (an inhibitor of proteinases) prevented the process of apoptosis and significantly reduced IL-10 production, suggesting that the increased production of IL-10 was caused by processes occurring during the initial phase of infection, such as apoptosis, necrosis and uptake of death cells.     

Lateralization and unilateral transfer of spatial memory in marsh tits: are two eyes better than one?

Two previous experiments on food storing and one-trial associative learning in marsh tits (Clayton 1992a; Clayton and Krebs 1992) demonstrate that information coming into the brain from the left eye disappears from the left eye system between 3 and 24 h after memory formation, whereas that coming into the brain from the right eye remains stable within the right eye system for at least 51 h after memory formation. Performance after a 7 h retention interval appears to represent an intermediate stage in which the information is no longer accessible to the left eye system but is not yet available to the right eye system, suggesting a unilateral transfer of memory. The experiments reported here further investigated lateralization and unilateral transfer of memory in food-storing marsh tits, Parus palustris, using the technique of monocular occlusion. Birds were tested for their ability to retrieve stored seeds after retention intervals of 3, 7 and 24 h under 4 different occlusion treatments. Two predictions were tested: (a) with right eye occlusion during storage, birds should show better memory performance after 3 and 24 h than after 7 h and (b) memory should be more accurate when both eyes are used during storage than with monocular occlusion. The first prediction, which arises from the fact that memory is transferred from the left to the right eye system at about 7 h and is inaccessible during the transfer, was supported by the data. The second prediction, however, was not supported. Previous work has shown that in marsh tits the two eye systems remember preferentially different aspects of the stimulus: the left eye system responds to spatial position and the right eye system to object-specific cues. It is possible that the failure to find superior performance in binocular tests was because the task could be solved by either spatial or object-specific memory.     

Mental representations of movements. Brain potentials associated with imagination of hand movements

The present study was designed in order to contribute towards the understanding of the physiology of motor imagery. DC potentials were recorded when subjects either imagined or executed a sequence of unilateral or bilateral hand movements. The sequence consisted of hand movements in 4 directions, forwards, backwards, to the right and to the left, and varied from trial to trial. The sequence had been cued by visual targets on a computer screen and had to be memorized before the trial was initiated. Changes of DC potentials between task execution and imagination were localized in central recordings (C3, Cz, C4) with larger amplitudes when executing the task than when imagining to do so. Stimulation of peripheral receptors associated with task execution or a different level of activation of the cortico-motoneural system could account for this finding. The main result of the present study was that with unilateral performance, the side of the performing hand (right, left) had localized effects in recordings over the sensorimotor hand area (C3, C4) which were qualitatively the same with imagination and execution and quantitatively similar (i.e., without significant difference). Performance of the right hand augmented negative DC potentials in C3, performance of the left hand augmented amplitudes in C4. This result is consistent with the assumption that the primary motor cortex is active with motor imagery. Finally, the question has been addressed whether motor imagery may involve the left hemisphere to a larger extent than the execution of the movement. It is shown that a particular contribution of the left hemisphere associated with motor imagery may only show up under strictly controlled conditions.     

Bilateral field advantage in visual enumeration

A number of recent studies have demonstrated superior visual processing when the information is distributed across the left and right visual fields than if the information is presented in a single hemifield (the bilateral field advantage). This effect is thought to reflect independent attentional resources in the two hemifields and the capacity of the neural responses to the left and right hemifields to process visual information in parallel. Here, we examined whether a bilateral field advantage can also be observed in a high-level visual task that requires the information from both hemifields to be combined. To this end, we used a visual enumeration task--a task that requires the assimilation of separate visual items into a single quantity--where the to-be-enumerated items were either presented in one hemifield or distributed between the two visual fields. We found that enumerating large number (>4 items), but not small number (<4 items), exhibited the bilateral field advantage: enumeration was more accurate when the visual items were split between the left and right hemifields than when they were all presented within the same hemifield. Control experiments further showed that this effect could not be attributed to a horizontal alignment advantage of the items in the visual field, or to a retinal stimulation difference between the unilateral and bilateral displays. These results suggest that a bilateral field advantage can arise when the visual task involves inter-hemispheric integration. This is in line with previous research and theory indicating that, when the visual task is attentionally demanding, parallel processing by the neural responses to the left and right hemifields can expand the capacity of visual information processing.     

Equilibrium analysis of binding of Candida albicans to human buccal epithelial cells

The effect of growth temperature on the binding of Candida albicans to human buccal epithelial cells (BECs) was examined using an equilibrium of binding analysis. Candida albicans was cultured in M9 medium either for 12 h at 25 degrees C or for 9 h at 25 degrees C and then shifted to 37 degrees C for 3 h. The temperature shift did not result in germ tube formation; however, the adherence of C. albicans to BECs was altered. Shifting temperature increased the yeast's ability to bind to BECs. A Langmuir adsorption isotherm was used to calculate the maximum number of available binding sites (N) and the apparent association constants of binding (Ka) for all resolvable adhesin-receptor interactions. Three classes of adhesin-receptor interactions were resolved when the yeast was cultured at 25 degrees C and included a low copy number site (N = 3.0 cfu/BEC; Ka = 2.11 X 10(-6) mL/cfu), a medium copy number site (N = 23.6 cfu/BEC, Ka = 8.21 X 10(-7) mL/cfu), and a high copy number site (N = 91.7 cfu/BEC, Ka = 3.35 X 10(-8) mL/cfu). Two classes of adhesin-receptor interactions were resolved when the incubation temperature was shifted to 37 degrees C: a low copy number site (N = 4.5 cfu/BEC, Ka = 3.98 X 10(-6) mL/cfu) and a high copy number site (N = 150.5 cfu/BEC, Ka = 8.47 X 10(-8) mL/cfu). Augmented C. albicans adherence to BECs due to the elevated growth temperatures appears to result from a temperature-regulated alteration in the C. albicans adhesin that recognizes a high copy number receptor site with relatively low affinity.     

Motor cortex excitability during unilateral muscle activity.

The effect of unilateral tonic muscle activity with and without co-activation of the antagonists on motor cortex excitability has been studied. Motor evoked potentials (MEPs) were recorded from the first dorsal interosseus muscles of both hands in response to transcranial magnetic stimulation (TMS) during relax, isometric index finger abduction and antagonistic co-activation. The intracortical inhibition (ICI) and intracortical facilitation (ICF) were investigated by paired-pulse TMS with interstimulus intervals of 3 and 13 ms. The unilateral tonic activation of the right hand facilitated contralateral and ipsilateral responses (cMEP and iMEP) recorded from both hands with an exception of iMEPs recorded from the left hand. During paired-pulse TMS ICI for cMEPs was not influenced by the unilateral tonic activity in both hands, while ICF was suppressed when MEPs were recorded from the active right hand. The effect of unilateral tonic activity on iMEP in response to paired-pulse TMS was essentially different: generally, ICI was greater for iMEPs and ICF was completely abolished with an exception of iMEPs recorded from the left hand during right finger isometric abduction when a strong ICF was evident. The decreased ICF and/or increased ICI are assumed to reflect mechanisms underlying the co-activation of antagonists.