Clenbuterol increases stroke power and contractile speed of skeletal muscle for cardiac assist

BACKGROUND

Skeletal muscle assist (SMA) may be limited by loss of power, slowing of contraction and relaxation, and atrophy of the transformed latissimus dorsi muscle (LD). Clenbuterol (clen), a beta2-adrenergic receptor agonist, was used to improve the performance of trained skeletal muscle in sheep.

METHODS AND RESULTS

The following 4 groups were used: A (n=6), untrained controls; B (n=6), left LD progressively transformed toward a slow-twitch and fatigue-resistant phenotype by electrical stimulation over 12 weeks (2.5 to 5 V, 240- microsec pulse duration, 35 Hz, 3 to 6 pulses per burst, and up to 40 bursts per minute); C (n=6), clen-treated (0.5 mg/kg SC) for 12 weeks; and D (n=6), clen+trained. In a terminal experiment, the mobilized LD was wrapped around a rubber aorta of a mock circulation and stimulated to contract 40 times per minute. Group A had an initial mean pressure augmentation (DeltaP) of 24.6 mm Hg and stroke power of 2.28 W/kg, but both fell to <20% of their original values by 15 minutes because of fatigue (P<0.005). Group B was fatigue-resistant, with a DeltaP and stroke power at 60 minutes of 13 mm Hg (70% of initial) and 0.34 W/kg (39% of initial), respectively. The performance of group C was similar to that of controls. In group D, however, the muscles were stronger at all time points than in B, with a DeltaP of 23 mm Hg and stroke power of 2.66 W/kg at 60 minutes (P<0.01). The speeds of contraction (+dP/dt:DeltaP) and relaxation (-dP/dt:DeltaP) were significantly greater in group D than B. Protein analyses showed group D to have only a trend toward greater abundance of the fast isoforms of myosin heavy chain and sarcoplasmic reticulum Ca2+-ATPase (P>0.1). CONCLUSIOINS: ++Clen improves the performance of trained skeletal muscle in a model of aortomyoplasty by unknown mechanisms. These findings may have important implications in SMA.

S-Adenosylmethionine-dependent methylation in Saccharomyces cerevisiae. Identification of a novel protein arginine methyltransferase

We used sequence motifs conserved in S-adenosylmethionine-dependent methyltransferases to identify 26 putative methyltransferases from the complete genome of the yeast Saccharomyces cerevisiae. Seven sequences with the best matches to the methyltransferase consensus motifs were selected for further study. We prepared yeast disruption mutants of each of the genes encoding these sequences, and we found that disruption of the YJL125c gene is lethal, whereas disruptions of YCR047c and YDR140w lead to slow growth phenotypes. Normal growth was observed when the YDL201w, YDR465c, YHR209w, and YOR240w genes were disrupted. Initial analysis of protein methylation patterns of all mutants by amino acid analysis revealed that the YDR465c mutant has a defect in the methylation of the delta-nitrogen atom of arginine residues. We propose that YDR465c codes for the methyltransferase responsible for this recently characterized type of protein methylation, and we designate the enzyme as Rmt2 (protein arginine methyltransferase). In addition, we show that the methylation of susceptible residues in Rmt2 substrates is likely to take place on nascent polypeptide chains and that these substrates exist in the cell as fully methylated species. Interestingly, Rmt2 has 27% sequence identity over 138 amino acids to the mammalian guanidinoacetate N-methyltransferase, an enzyme responsible for methylating the delta-nitrogen of the small molecule guanidinoacetate.

Outcome of occlusion treatment for amblyopia

BACKGROUND

The purpose of this study was to determine the level of visual acuity following occlusion treatment for strabismic and anisometropic amblyopia and to analyze the factors that influence the outcome.

METHODS

In this observational study, we examined the medical records of 246 patients discharged between April 1991 and March 1996, including those who failed to complete treatment. Two groups were identified: Group 1 esotropia (n = 151); and Group 2 anisometropic amblyopia with or without microtropia (n = 79). Factors influencing outcome of treatment were analyzed, success being defined as 6/12 or better in the amblyopic eye.

RESULTS

In Group 1, 85% achieved 6/12 or better in the worst eye (linear acuity test), 15% achieved less than 6/12. (73% achieved 6/9 or better, 16% achieved 6/12 or 6/18, and 11% achieved less than 6/18). In group 2, 95% achieved 6/9 or better in the worst eye (linear acuity test); 5% achieved 6/12.

CONCLUSION

Outcome was better than other full population studies to date. A good visual outcome was achieved in all cases of pure anisometropic amblyopia. Significant factors influencing outcome in the esotropic group were compliance, anisometropia, and visual acuity at start of treatment. An occlusion protocol is suggested aimed at further improving compliance and outcome.

Clonally unrelated BCR-ABL-negative acute myeloblastic leukemia masquerading as blast crisis after busulphan and interferon therapy for BCR-ABL-positive chronic myeloid leukemia

We report a patient with Philadelphia (Ph)-positive, BCR-ABL rearrangement positive, chronic myeloid leukemia (CML) with a prolonged chronic phase of 24 years who was first prescribed alpha-2 interferon 22 years after initial diagnosis. This therapy was tolerated poorly on account of thrombocytopenia, but an eventual major cytogenetic response was followed soon afterwards by transformation to terminal acute myeloid leukemia (AML). Cytogenetic studies indicated that the transformed myeloblasts were karyotypically normal and Ph negative. Although polymerase chain reaction (PCR) analysis of total leukemic mRNA remained BCR-ABL positive, other molecular studies, including Southern blotting and fluorescent in situ hybridization (FISH) analyses, showed that myeloblasts were BCR-ABL rearrangement negative. PCR-based clonality studies using an X-chromosome-linked restriction fragment polymorphism within the phosphoglycerate kinase gene (PGK1) further showed that the Ph-negative blast cells had a different clonal origin from the Ph-positive clone of chronic phase. We suggest that cases of underlying Ph-negative leukemic transformation in Ph-positive CML warrant further study and should be considered for trial of intensive remission induction therapy as appropriate for acute leukemia.

Cortical regions contributing to the anterior commissure in man

The human anterior commissure is believed, by extrapolation from data obtained in macaque monkeys, to convey axons from the temporal and orbitofrontal cortex. Reports of interhemispheric transfer and sexual dimorphism related to the anterior commissure, however, make more precise data on the human anterior commissure desirable. We investigated the connectivity of the human anterior commissure in six adults (male and female) that had circumscribed hemispheric lesions in temporal, frontal, parietal or occipital cortices or in infrapallidal white matter using the Nauta for anterogradely degenerating axons. Axons originating in the inferior part of temporal or occipital lobes, occipital convexity and possibly central fissure and prefrontal convexity were found to cross the midsagittal plane in the anterior commissure. The largest contingent of commissural axons originated in the inferior part of the temporal lobe; it displayed a roughly topographic organization, preferentially running through the inferior part of the commissure. The inferior temporal contingent seemed to reach homotopic and heterotopic targets in the opposite hemisphere. Among the latter were the amygdala and possibly the orbitofrontal cortex. The present data suggest that the human anterior commissure conveys axons from much larger territories than expected from work on non-human primates. Similarly to the human and non-human primate corpus callosum, the anterior commissure is roughly topographically organized and participates in heterotopic connectivity.

delta-N-methylarginine is a novel posttranslational modification of arginine residues in yeast proteins

We have found a novel modification of protein arginine residues in the yeast Saccharomyces cerevisiae. Intact yeast cells lacking RMT1, the gene encoding the protein omega-NG-arginine methyltransferase, were labeled with the methyl donor S-adenosyl-L-[methyl-3H]methionine. The protein fraction was acid-hydrolyzed to free amino acids, which were then fractionated on a high resolution sulfonated polystyrene cation exchange column at pH 5.27 and 55 degreesC. In the absence of the omega-NG, NG-[3H]dimethylarginine product of the RMT1 methyltransferase, we were able to detect a previously obscured 3H-methylated species that migrated in the region of methylated arginine derivatives. The [3H]methyl group(s) of this unknown species were not volatilized by treatment with 2 M NaOH at 55 degreesC for up to 48 h, suggesting that they were not modifications of the terminal omega-guanidino nitrogen atoms. However, this base treatment did result in the formation of a new 3H-methylated derivative that co-chromatographed with delta-N-methylornithine on high resolution cation exchange chromatography, on reverse phase high pressure liquid chromatography, and on thin layer chromatography. From these data, we suggest that the identity of the original unknown methylated residue is delta-N-monomethylarginine. The presence of this methylated residue in yeast cells defines a novel type of protein modification reaction in eukaryotes.

Colour constancy impairments in patients with lesions of the prestriate cortex

Colour matching and colour constancy were studied in seven patients and 46 control subjects. Subjects were required to match Munsell Colour Chips presented under either identical or different illumination. Three of the patients had deficits in colour constancy, i.e. failure to compensate for the change in the wavelength composition of the illumination. Two of the patients with defective constancy had suffered bilateral cortical damage to the posterior lingual and fusiform gyri, and one patient had a lesion restricted to the same regions of the right hemisphere. Our observations indicate that these cortical areas, which include part of putative human area V4, play an important role in colour constancy.

Distinct short-term memory systems for sound content and sound localization

Short-term memory for sound content and sound localization was investigated in normal subjects using the same/different comparison of two sound stimuli separated by an interval. Auditory or visual interference tasks requiring recognition or spatial judgements were introduced in the interval. Auditory interference tasks reduced memory for sound content and sound location in a specific way. Memory for sound content was significantly more reduced by auditory recognition than by auditory spatial interference task. Visual interference tasks reduced significantly memory for sound location but not for sound content. These results suggest that (i) short-term memory for sound content and that for sound location involve partially distinct processing; and (ii) auditory spatial functions are more closely linked to visual functions than auditory recognition.

A highly active protein repair enzyme from an extreme thermophile: the L-isoaspartyl methyltransferase from Thermotoga maritima

We show that the open reading frame in the Thermotoga maritima genome tentatively identified as the pcm gene (R. V. Swanson et al., J. Bacteriol. 178, 484-489, 1996) does indeed encode a protein L-isoaspartate (D-aspartate) O-methyltransferase (EC 2.1.1.77) and that this protein repair enzyme displays several novel features. We expressed the 317 amino acid pcm gene product of this thermophilic bacterium in Escherichia coli as a fusion protein with an N-terminal 20 residue hexa-histidine-containing sequence. This protein contains a C-terminal domain of approximately 100 residues not previously seen in this enzyme from various prokaryotic or eukaryotic species and which does not have sequence similarity to any other entry in the GenBank databases. The C-terminal region appears to be required for enzymatic function as no activity is detected in two recombinant constructs lacking this domain. Sedimentation equilibrium analysis indicated that the enzyme is monomeric in solution. The Km values for measured for peptide and protein substrates were found to be intermediate between those of the high-affinity human enzyme and those of the lower-affinity wheat, nematode, and E. coli enzymes. The enzyme was extremely heat stable, with no loss of activity after 60 min at 100 degreesC. Enzyme activity was observed at temperatures as high as 93 degreesC with an optimal activity of 164 nmol/min/mg protein at 85 degreesC. This activity is approximately 18-fold higher than the maximal activities of mesophilic homologs at 37 degreesC. These data suggest that the Thermotoga enzyme has unique features for initiating repair in damaged proteins containing L-isoaspartyl residues at elevated temperatures.

Mutations in the Escherichia coli surE gene increase isoaspartyl accumulation in a strain lacking the pcm repair methyltransferase but suppress stress-survival phenotypes

The Escherichia coli surE gene is co-transcribed with pcm, encoding the L-isoaspartyl protein repair methyltransferase, and is highly conserved among both the Eubacteria and the Archaea; however, no biochemical function has yet been identified for this gene. Isoaspartyl accumulation during stationary phase was much higher in a pcm surE double mutant than in either single mutant, suggesting that the two genes may represent two parallel pathways by which E. coli can respond to protein damage. A null mutation in surE also suppressed stress-survival defects previously observed in a pcm mutant strain, providing further evidence for an interaction between the two gene products.

RNA and protein interactions modulated by protein arginine methylation

This review summarizes the current status of protein arginine N-methylation reactions. These covalent modifications of proteins are now recognized in a number of eukaryotic proteins and their functional significance is beginning to be understood. Genes that encode those methyltransferases specific for catalyzing the formation of asymmetric dimethylarginine have been identified. The enzyme modifies a number of generally nuclear or nucleolar proteins that interact with nucleic acids, particularly RNA. Postulated roles for these reactions include signal transduction, nuclear transport, or a direct modulation of nucleic acid interactions. A second methyltransferase activity that symmetrically dimethylates an arginine residue in myelin basic protein, a major component of the axon sheath, has also been characterized. However, a gene encoding this activity has not been identified to date and the cellular function for this methylation reaction has not been clearly established. From the analysis of the sequences surrounding known arginine methylation sites, we have determined consensus methyl-accepting sequences that may be useful in identifying novel substrates for these enzymes and may shed further light on their physiological role.

Trace analysis of SN-38 in human plasma by high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic method with fluorescence detection was developed and validated for the quantitation of SN-38, the active metabolite of irinotecan (CPT-11), a new anticancer drug. This method uses solid-phase extraction with a C18 column for sample clean-up and concentration following acidification of human plasma with two volumes of 0.1 M HCl. Using blank plasma spiked with SN-38, we found the assay to be linear over the concentration range of 10-500 pM (3.9-195 pg/ml) with acceptable total and within-day imprecision. The recovery of SN-38 ranged from 48.3% (10 pM) to 91.5% (500 pM) whereas that of the internal standard, 20-(S)-camptothecin, was 96.9% (500 pM). This method represents a sizeable increase in sensitivity over other published methods and is shown to be suitable for the measurement of 'trough' concentrations of SN-38 during the treatment of patients with a weekly regimen of irinotecan.

Simulating hospital patient flows

This case study development has benefited by the use of clear on-screen logic which has facilitated useful discussions between the analyst and end-users. The screen displays enable a realistic depiction of a system to be developed. A simple first model was gradually made more realistic in a step-by-step process involving both analyst and end-users. The investigation is continuing and the model is being further refined. Data collection is underway, and system data will be used to provide the model's input parameters of arrival and service rates. Times and lengths of queues of patients and total time in the system will be compared with their model equivalents. The resulting model is likely to be acceptable to the end-users because of their involvement in its development. This involvement has been facilitated by a simulation environment which enables on-screen iconic representations of system components to be created by analyst and end-user together.

PRMT 3, a type I protein arginine N-methyltransferase that differs from PRMT1 in its oligomerization, subcellular localization, substrate specificity, and regulation

Methylation is one of the many post-translational modifications that modulate protein function. Although asymmetric NG,NG-dimethylation of arginine residues in glycine-arginine-rich domains of eucaryotic proteins, catalyzed by type I protein arginine N-methyltransferases (PRMT), has been known for some time, members of this enzyme class have only recently been cloned. The first example of this type of enzyme, designated PRMT1, cloned because of its ability to interact with the mammalian TIS21 immediate-early protein, was then shown to have protein arginine methyltransferase activity. We have now isolated rat and human cDNA orthologues that encode proteins with substantial sequence similarity to PRMT1. A recombinant glutathione S-transferase (GST) fusion product of this new rat protein, named PRMT3, asymmetrically dimethylates arginine residues present both in the designed substrate GST-GAR and in substrate proteins present in hypomethylated extracts of a yeast rmt1 mutant that lacks type I arginine methyltransferase activity; PRMT3 is thus a functional type I protein arginine N-methyltransferase. However, rat PRMT1 and PRMT3 glutathione S-transferase fusion proteins have distinct enzyme specificities for substrates present in both hypomethylated rmt1 yeast extract and hypomethylated RAT1 embryo cell extract. TIS21 protein modulates the enzymatic activity of recombinant GST-PRMT1 fusion protein but not the activity of GST-PRMT3. Western blot analysis of gel filtration fractions suggests that PRMT3 is present as a monomer in RAT1 cell extracts. In contrast, PRMT1 is present in an oligomeric complex. Immunofluorescence analysis localized PRMT1 predominantly to the nucleus of RAT1 cells. In contrast, PRMT3 is predominantly cytoplasmic.

The L-isoaspartyl protein repair methyltransferase enhances survival of aging Escherichia coli subjected to secondary environmental stresses

Like its homologs throughout the biological world, the L-isoaspartyl protein repair methyltransferase of Escherichia coli, encoded by the pcm gene, can convert abnormal L-isoaspartyl residues in proteins (which form spontaneously from asparaginyl or aspartyl residues) to normal aspartyl residues. Mutations in pcm were reported to greatly reduce survival in stationary phase and when cells were subjected to heat or osmotic stresses (C. Li and S. Clarke, Proc. Natl. Acad. Sci. USA 89:9885-9889, 1992). However, we subsequently demonstrated that those strains had a secondary mutation in rpoS, which encodes a stationary-phase-specific sigma factor (J. E. Visick and S. Clarke, J. Bacteriol. 179:4158-4163, 1997). We now show that the rpoS mutation, resulting in a 90% decrease in HPII catalase activity, can account for the previously observed phenotypes. We further demonstrate that a new pcm mutant lacks these phenotypes. Interestingly, the newly constructed pcm mutant, when maintained in stationary phase for extended periods, is susceptible to environmental stresses, including exposure to methanol, oxygen radical generation by paraquat, high salt concentrations, and repeated heating to 42 degrees C. The pcm mutation also results in a competitive disadvantage in stationary-phase cells. All of these phenotypes can be complemented by a functional pcm gene integrated elsewhere in the chromosome. These data suggest that protein denaturation and isoaspartyl formation may act synergistically to the detriment of aging E. coli and that the repair methyltransferase can play a role in limiting the accumulation of the potentially disruptive isoaspartyl residues in vivo.

Myeloid-specific gene expression

The mononuclear phagocytes are recruited from bone marrow precursors to most tissues of the body, particularly during inflammation or immune stimulation. This combination of accessibility as stem cells and heterogenity of tissue locations makes the myeloid cell potentially important as a carrier of therapeutic agents. Understanding the regulation of transcription in myeloid cells is necessary for any future design of tissue-specific gene targeting vectors, particularly if there are inherent size limitations. Identified members of the C/EBP, Runt/PEBP2/CBF, and Ets families of transcription factors are critical for myeloid-specific gene expression and may have myeloid-restricted expression or myeloid-specific regulation in the hematopoietic system. AP-1, Sp1, and Myb appear to be important for myeloid-restricted expression in some cases. In addition, factors involved in the up-regulation of the level of gene expression when macrophages are activated by agents such as interferon-gamma and bacterial products have been identified. Some of the sequences to which these transcription factors bind in myeloid-restricted genes have been tested in cell lines and in transgenic mice and it is now possible to make an attempt to describe the characteristics of a myeloid-specific promoter.

Compartments within human primary auditory cortex: evidence from cytochrome oxidase and acetylcholinesterase staining

The human primary auditory area (AI) corresponds to granular cortex located on Heschl's gyrus. We studied its pattern of cytochrome oxidase and acetylcholinesterase activity in 10 normal human hemispheres. In cytochrome-oxidase-stained coronal sections layer IV was prominent by its dark staining. The overall staining intensity varied along the medio-lateral extent of Al; a 2.0-2.5-mm-wide antero-posterior dark band was present at mid-AI. In acetylcholinesterase-stained coronal sections a dark antero-posterior band appeared at the same location, corresponding to the highly granular part of Al. In cytochrome-oxidase-stained tangential sections of flattened Al, approximately 500-microm thick alternating dark and light cytochrome oxidase stripes were present in layers III and IV. These stripes were perpendicular to the dark band. Comparison with tonotopic maps of human Al obtained by activation studies suggests that the cytochrome oxidase and acetylcholinesterase dark band is most likely parallel to isofrequency lines and may correspond to the representation of frequencies critical for speech comprehension. The narrow stripes may be related to particular binaural or ampliotopic domains, whose presence is suggested by evidence from electrophysiological recordings in cat Al and from magnetoencephalographic studies in humans.

Quantified EEG activity in adolescent attention deficit hyperactivity disorder

The aim of this study was to explore elements of the maturational and cortical hypoarousal models in adolescent ADHD, by examining EEG activity in a rest eyes open condition, in 26 adolescent unmedicated ADHD males and 26 age and sex matched normal controls. ADHD adolescents were found to have increased anterior EEG absolute theta activity and reduced posterior relative beta activity compared with controls. These results lend some support to the continuation of a maturational lag and reduced cortical arousal in adolescent ADHD. These measures need to be further explored using concomitant EEG with electrodermal measures of arousal.

Targeted gene disruption of the Caenorhabditis elegans L-isoaspartyl protein repair methyltransferase impairs survival of dauer stage nematodes

The methylation of abnormal L-isoaspartyl residues by protein L-isoaspartate (D-aspartate) O-methyltransferase (EC 2.1.1.77) can lead to their conversion to L-aspartyl residues. For polypeptides damaged by spontaneous reactions that generate L-isoaspartyl residues, these steps represent a protein repair pathway that can limit the accumulation of potentially detrimental proteins in the aging process. We report here the construction and the characterization of an animal model deficient in this methyltransferase. We utilized Tc1-transposon-mediated mutagenesis in the nematode Caenorhabditis elegans to construct a homozygous excision mutant lacking exons 2-5 of the pcm-1 gene encoding this enzyme. Nematodes carrying this deletion exhibited no detectable L-isoaspartyl methyltransferase activity. These worms demonstrated normal morphology and behavior and adult mutant nematodes exhibited a normal lifespan. However, the survival of dauer-phase mutants was diminished by 3.5-fold relative to wild-type dauers after 50 days in the dauer phase. The fitness of the pcm-1 deletion nematodes was reduced by about 16% relative to that of wild-type nematodes as measured by the ability of these mutants to compete reproductively against a wild-type population. We found that the absence of the functional methyltransferase gene leads to a modest accumulation of altered protein substrates in aged dauer worms. However, in the viable fraction of these dauer worms, no differences were seen in the levels of altered substrate proteins in the parent and methyltransferase-deficient worms, suggesting that the enzyme in wild-type cells does not efficiently catalyze the repair of spontaneously damaged proteins.

Face recognition and postero-inferior hemispheric lesions

Two patients with severe and lasting prosopagnosia were studied for visuo-cognitive functions and anatomo-clinical correlations. Both patients were deficient in recognizing familiar faces and items of previously well known categories (plants and fish for patient 1, mountains for patient 2). Patient 2, but not patient 1, was also deficient for matching of unknown faces. Patient 1, but not patient 2, was achromatopsic. Both patients had bilateral symmetrical lesions. Patient 1 had a lesion of the inferior occipito-temporal cortex, including inferior parts of early stage visual areas. Patient 2 had a lesion of the inferior temporal and fusiform gyri anterior to the early stage visual areas. When compared in Talairach space, the lesions of both patients had minimal overlap. Thus, severe and lasting prosopagnosia was associated with two almost exclusive lesion sites in the postero-inferior part of the hemispheres. Comparison between activation studies of face processing (by others) and our lesion study uncovered several paradoxes. Lesions of regions involved in a given task in normal subjects do not produce a deficit in this task, as shown here for gender discrimination and partially for face matching. Conversely, lesions of a region not specifically involved in a given task in normal subjects can produce a deficit in the task, as shown here for face identification.

Protein repair L-isoaspartyl methyltransferase in plants. Phylogenetic distribution and the accumulation of substrate proteins in aged barley seeds

Protein L-isoaspartate (D-aspartate) O-methyltransferases (MTs; EC 2.1.1.77) can initiate the conversion of detrimental L-isoaspartyl residues in spontaneously damaged proteins to normal L-aspartyl residues. We detected this enzyme in 45 species from 23 families representing most of the divisions of the plant kingdom. MT activity is often localized in seeds, suggesting that it has a role in their maturation, quiescence, and germination. The relationship among MT activity, the accumulation of abnormal protein L-isoaspartyl residues, and seed viability was explored in barley (Hordeum vulgare cultivar Himalaya) seeds, which contain high levels of MT. Natural aging of barley seeds for 17 years resulted in a significant reduction in MT activity and in seed viability, coupled with increased levels of "unrepaired" L-isoaspartyl residues. In seeds heated to accelerate aging, we found no reduction of MT activity, but we did observe decreased seed viability and the accumulation of isoaspartyl residues. Among populations of accelerated aged seed, those possessing the highest levels of L-isoaspartyl-containing proteins had the lowest germination percentages. These results suggest that the MT present in seeds cannot efficiently repair all spontaneously damaged proteins containing altered aspartyl residues, and their accumulation during aging may contribute to the loss of seed viability.

Single trial variability within the P300 (250-500 ms) processing window in adolescents with attention deficit hyperactivity disorder

The traditional averaging process used to derive event related potential components (ERPs) is a soundly based method of determining the underlying ERP. Averaging, however, ignores the variability due to the single-trial ERPs that constitute the traditional average ERP. This variability may reflect complementary functional information to the average measure. Our group applied a simple procedure, the response variance curve (RVC), which measures single-trial ERP variability relative to their average. In this study, the average ERP and RVC measures (generated from the same single-trial task-relevant target ERPs) were assessed in an auditory oddball paradigm, in 17 unmedicated male adolescents with attention deficit hyperactivity disorder (ADHD) and in 17 age- and sex-matched normal controls. P300 amplitude, latency and point of maximum variability of the RVC were measured within the P300 processing window (250-500 ms post-stimulus). There were no significant differences in P300 amplitude or latency between the groups. Unmedicated ADHD patients, however, showed significantly increased single-trial variability within the P300 window compared with controls. This variability was significantly reduced with stimulant medication.