Biomedical subjects

I Winkler

Publications and source records attributed to I Winkler.

At least 19 recordsLinked to original sources

PubMed1999

Pre-attentive detection of vowel contrasts utilizes both phonetic and auditory memory representations.

Event-related brain potentials (ERP) were recorded to infrequent changes of a synthesized vowel (standard) to another vowel (deviant) in speakers of Hungarian and Finnish language, which are remotely related to each other with rather similar vowel systems. Both language groups were presented with identical stimuli. One standard-deviant pair represented an across-vowel category contrast in Hungarian, but a within-category contrast in Finnish, with the other pair having the reversed role in the two languages. Both within- and across-category contrasts elicited the mismatch negativity (MMN) ERP component in the native speakers of either language. The MMN amplitude was larger in across- than within-category contrasts in both language groups. These results suggest that the pre-attentive change-detection process generating the MMN utilized both auditory (sensory) and phonetic (categorical) representations of the test vowels.

Acoustic Stimulation↗

PubMed1998

Structures of Tyr188Leu mutant and wild-type HIV-1 reverse transcriptase complexed with the non-nucleoside inhibitor HBY 097: inhibitor flexibility is a useful design feature for reducing drug resistance.

The second generation Hoechst-Bayer non-nucleoside inhibitor, HBY 097 (S-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3, 4-dihydroqui noxalin-2(1H)-thione), is an extremely potent inhibitor of HIV-1 reverse transcriptase (RT) and of HIV-1 infection in cell culture. HBY 097 selects for unusual drug-resistance mutations in HIV-1 RT (e.g. Gly190Glu) when compared with other non-nucleoside RT inhibitors (NNRTIs), such as nevirapine, alpha-APA and TIBO. We have determined the structure of HBY 097 complexed with wild-type HIV-1 RT at 3.1 A resolution. The HIV-1 RT/HBY 097 structure reveals an overall inhibitor geometry and binding mode differing significantly from RT/NNRTI structures reported earlier, in that HBY 097 does not adopt the usual butterfly-like shape. We have determined the structure of the Tyr188Leu HIV-1 RT drug-resistant mutant in complex with HBY 097 at 3.3 A resolution. HBY 097 binds to the mutant RT in a manner similar to that seen in the wild-type RT/HBY 097 complex, although there are some repositioning and conformational alterations of the inhibitor. Conformational changes of the structural elements forming the inhibitor-binding pocket, including the orientation of some side-chains, are observed. Reduction in the size of the 188 side-chain and repositioning of the Phe227 side-chain increases the volume of the binding cavity in the Tyr188Leu HIV-1 RT/HBY 097 complex. Loss of important protein-inhibitor interactions may account for the reduced potency of HBY 097 against the Tyr188Leu HIV-1 RT mutant. The loss of binding energy may be partially offset by additional contacts resulting from conformational changes of the inhibitor and nearby amino acid residues. This would suggest that inhibitor flexibility can help to minimize drug resistance.

Antiviral Agents↗

PubMed1998

Retention of marked sensitivity to (S)-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3,4-di hydroquin oxaline-2(1H)-thione (HBY 097) by an azidothymidine (AZT)-resistant human immunodeficiency virus type 1 (HIV-1) strain subcultured in the combined presence of quinoxaline HBY 097 and 2',3'-dideoxy-3'-thiacytidine (lamivudine).

An azidothymidine (AZT)-resistant virus strain (HIV-1/AZT) (containing the 67 Asp --> Asn, 70 Lys --> Arg, 215 Thr --> Phe and 219 Lys --> Gln mutations into its reverse transcriptase) was grown in the combined presence of 2',3'-dideoxy-3'-thiacytidine (3TC, lamivudine) and the nonnucleoside reverse transcriptase inhibitor (S)-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3,4-dih ydroquinoxaine-2(1H)-thione (quinoxaline HBY 097). Replication of HIV-1/AZT was inhibited to a significantly greater extent by the combination of 3TC and quinoxaline HBY 097 than by either drug alone. Virus breakthrough was markedly delayed in the combined presence of 3TC and HBY 097 at drug concentrations as low as 0.05 microg/mL and 0.0025 microg/mL, respectively. The virus that was recovered after exposure to the compounds (3TC and HBY 097) individually had acquired, in the genetic AZT-resistance background of HIV-1/AZT, 103 Lys --> Glu and 106 Val --> Ala mutations. The 103 Lys --> Glu mutation had not been observed before. However, both virus mutants retained marked sensitivity to HBY 097. In all cases, the genotypic AZT-resistance mutations were maintained in the mutant virus RT genomes, and the viruses also remained phenotypically resistant to AZT. Given the exquisite potency of a concomitant combination of 3TC and HBY 097 in suppressing virus replication, this drug combination should be further pursued in clinical trials in HIV-1-infected individuals.

Anti-HIV Agents↗

PubMed1998

Temporal constraints of auditory event synthesis: evidence from ERPs.

The temporal constraints of auditory event synthesis were investigated using event-related potentials. Standard stimuli consisted of an initial constant-frequency segment followed by a frequency glide. Occasionally, stimuli deviating from this standard both in intensity and within the direction of the glide were presented in the otherwise repetitive sound sequence. Previous results suggested that such 'double' deviants elicit only a single mismatch negativity (MMN) if the two temporally separate deviant elements were integrated within a common unit. Two successive MMNs were elicited by double deviants when the initial constant-frequency segment of the sound was 250 ms long, but only one when this segment was 150 ms in duration. The results support the hypothesis that the auditory input is processed in approximately 200 ms long temporal integration windows.

Acoustic Stimulation↗

PubMed1998

Preattentive processing of auditory spatial information in humans.

Auditory event-related potentials were recorded from reading subjects to frequent and infrequent tones. Frequent tones presented by a loudspeaker in front of the subject were interspersed with infrequent tones delivered either by one of the symmetrically-placed lateral loudspeakers, or by both lateral loudspeakers simultaneously. This latter sound was perceived as originating from a spacious source in the direction of the central loudspeaker. A sizable mismatch negativity (MMN) and P3a were elicited by all three infrequent stimuli, suggesting that infrequent changes in the direction or perceived spaciousness of the sound source were preattentively detected. In addition, a dissociation between the MMN and P3a amplitudes was found: whereas lateral deviants elicited a larger P3a than the simultaneous left + right deviant, the MMN amplitude was approximately equal for all three deviants.

Acoustic Stimulation↗

PubMed1998

Combined mapping of human auditory EEG and MEG responses.

Auditory electric and magnetic P50(m), N1(m) and MMN(m) responses to standard, deviant and novel sounds were studied by recording brain electrical activity with 25 EEG electrodes simultaneously with the corresponding magnetic signals measured with 122 MEG gradiometer coils. The sources of these responses were located on the basis of the MEG responses; all were found to be in the supratemporal plane. The goal of the present paper was to investigate to what degree the source locations and orientations determined from the magnetic data account for the measured EEG signals. It was found that the electric P50, N1 and MMN responses can to a considerable degree be explained by the sources of the corresponding magnetic responses. In addition, source-current components not detectable by MEG were shown to contribute to the measured EEG signals.

Acoustic Stimulation↗

PubMed1998

Neural mechanisms of involuntary attention to acoustic novelty and change.

Behavioral and event-related brain potential (ERP) measures were used to elucidate the neural mechanisms of involuntary engagement of attention by novelty and change in the acoustic environment. The behavioral measures consisted of the reaction time (RT) and performance accuracy (hit rate) in a forced-choice visual RT task where subjects were to discriminate between odd and even numbers. Each visual stimulus was preceded by an irrelevant auditory stimulus, which was randomly either a "standard" tone (80%), a slightly higher "deviant" tone (10%), or a natural, "novel" sound (10%). Novel sounds prolonged the RT to successive visual stimuli by 17 msec as compared with the RT to visual stimuli that followed standard tones. Deviant tones, in turn, decreased the hit rate but did not significantly affect the RT. In the ERPs to deviant tones, the mismatch negativity (MMN), peaking at 150 msec, and a second negativity, peaking at 400 msec, could be observed. Novel sounds elicited an enhanced N1, with a probable overlap by the MMN, and a large positive P3a response with two different subcomponents: an early centrally dominant P3a, peaking at 230 msec, and a late P3a, peaking at 315 msec with a right-frontal scalp maximum. The present results suggest the involvement of two different neural mechanisms in triggering involuntary attention to acoustic novelty and change: a transient-detector mechanism activated by novel sounds and reflected in the N1 and a stimulus-change detector mechanism activated by deviant tones and novel sounds and reflected in the MMN. The observed differential distracting effects by slightly deviant tones and widely deviant novel sounds support the notion of two separate mechanisms of involuntary attention.

Acoustic Stimulation↗

PubMed1998

Processing of novel sounds and frequency changes in the human auditory cortex: magnetoencephalographic recordings.

Whole-head magnetoencephalographic (MEG) responses to repeating standard tones and to infrequent slightly higher deviant tones and complex novel sounds were recorded together with event-related brain potentials (ERPs). Deviant tones and novel sounds elicited the mismatch negativity (MMN) component of the ERP and its MEG counterpart (MMNm) both when the auditory stimuli were attended to and when they were ignored. MMNm generators were located bilateral to the superior planes of the temporal lobes where preattentive auditory discrimination appears to occur. A subsequent positive P3a component was elicited by deviant tones and with a larger amplitude by novel sounds even when the sounds were to be ignored. Source localization for the MEG counterpart of P3a (P3am) suggested that the auditory cortex in the superior temporal plane is involved in the neural network of involuntary attention switching to changes in the acoustic environment.

Acoustic Stimulation↗

PubMed1997

Pre-attentive categorization of sounds by timbre as revealed by event-related potentials.

Infrequent (10%) pure tones were randomly presented among nine different missing-fundamental tones having the same pitch (10% each) to subjects playing a computer game. MMN (an index of pre-attentive change detection) was elicited by timbre-deviant pure tones with 150 and 500 ms stimulus duration. This suggests that the spectral component of timbre is pre-attentively determined from relatively short (150 ms) acoustic samples. Previous research established that resolving the pitch of the same missing-fundamental tones requires longer (> 150 ms) sounds. Consequently, timbre and pitch are probably determined by separate neural processes. The present results also demonstrate pre-attentive categorization of sounds based on timbre as MMN could only be elicited by the pure tones if their timbre was contrasted with the combined group of the nine standard sounds of qualitatively similar rich timbre.

Acoustic Stimulation↗

PubMed1997

In vitro selection for different mutational patterns in the HIV-1 reverse transcriptase using high and low selective pressure of the nonnucleoside reverse transcriptase inhibitor HBY 097.

In vitro resistance of HIV-1 against high levels of HBY 097 ((S)-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3, 4-dihydro-quinoxaline-2(1H)-thione) and other quinoxaline nonnucleoside reverse transcriptase inhibitors (NNRTIs) is characterized by a specific amino acid substitution in the reverse transcriptase (RT), Gly 190Glu. This change results in decreased RT polymerase activity and in reduced growth properties of the corresponding viral variant. Here we show that the appearance of the crippling mutation at codon 190 can be prevented by lowering the selective pressure exerted by HBY 097. Under low selective pressure an accumulation of other NNRTI-specific mutations is observed. Up to five NNRTI-specific substitutions were detected in some of these virus lineages. In addition, we report novel RT amino acid changes which were not observed previously, including Val106lle, Val106Leu, and Gly190Thr. HBY 097 selects for different mutational patterns under high and low selective pressure conditions, respectively. Thus, the type of mutations which appear in HIV-infected patients undergoing therapy may be determined by the levels of the selecting drug.

Antiviral Agents↗

PubMed1997

Zidovudine-resistant human immunodeficiency virus type 1 strains subcultured in the presence of both lamivudine and quinoxaline HBY 097 retain marked sensitivity to HBY 097 but not to lamivudine.

Replication of zidovudine-resistant human immunodeficiency virus type 1 (HIV-1) strains (containing the 41 Met-->Leu and 215 Thr-->Tyr mutations in reverse transcriptase [RT]) was inhibited to a significantly greater extent by the combination of lamivudine and quinoxaline HBY 097 than by either drug alone or even fully suppressed by concomitant HBY 097 and lamivudine administration at relatively low concentrations. The virus recovered after exposure to the drug combinations individually had acquired the 103 Lys-->Arg, 138 Glu-->Lys, 184 Met-->Ile, and 189 Val-->Ile mutations in the genetic zidovudine-resistance background of zidovudine-resistant HIV-1. These mutants retained marked sensitivity to HBY 097. The genotypic zidovudine-resistance mutations were maintained in the mutant virus RT genomes, and the viruses also remained phenotypically resistant to zidovudine. Given the exquisite potency of the combination of lamivudine and HBY 097 in suppressing viral replication, this combination should be further pursued in clinical trials examining treatment of HIV-1-infected persons.

Anti-HIV Agents↗

PubMed1997

Two separate codes for missing-fundamental pitch in the human auditory cortex.

Two auditory event-related potential components, the supratemporal N1 and the mismatch negativity (MMN), index traces encoding the missing-fundamental pitch. The present results suggest that these two codes derive from separate pitch extraction processes. Frequent 300-Hz and infrequent 600-Hz missing-fundamental tones were presented, in some stimulus blocks with short (150 ms), in others, with long (500 ms) stimulus durations. MMN, reflecting a preattentive change detection process, was elicited by infrequent missing-fundamental tones only in the long-duration condition. Correspondingly, subjects were able to detect these high-pitch missing-fundamental tones amongst similar low-pitch ones only when the stimulus duration was long. In addition, the MMN response peaked ca. 120 ms later for missing-fundamental tones than for pure tones of the fundamental frequency suggesting that missing-fundamental pitch resolving took substantially longer than extracting the spectral pitch. In contrast, a differential N1 response to the missing-fundamental pitch was found for both stimulus durations, with no substantial difference in peak latency between the pure and missing-fundamental tones. The contrasting features found for the two auditory cortical missing-fundamental pitch codes support the notion of two separate missing-fundamental pitch resolving mechanisms.

Adolescent↗

PubMed1997

Characterization of the genome of feline foamy virus and its proteins shows distinct features different from those of primate spumaviruses.

The genome of the feline foamy virus (FeFV) isolate FUV was characterized by molecular cloning and nucleotide sequence analysis of subgenomic proviral DNA. The overall genetic organization of FeFV and protein sequence comparisons of different FeFV genes with their counterparts from other known foamy viruses confirm that FeFV is a complex foamy virus. However, significant differences exist when FeFV is compared with primate foamy viruses. The FeFV Gag protein is smaller than that of the primate spumaviruses, mainly due to additional MA/CA sequences characteristic of the primate viruses only. Gag protein sequence motifs of the NC domain of primate foamy viruses assumed to be involved in genome encapsidation are not conserved in FeFV. FeFV Gag and Pol proteins were detected with monospecific antisera directed against Gag and Pol domains of the human foamy virus and with antisera from naturally infected cats. Proteolytic processing of the FeFV Gag precursor was incomplete, whereas more efficient proteolytic cleavage of the pre125Pro-Pol protein was observed. The active center of the FeFV protease contains a Gln that replaces an invariant Gly residue at this position in other retroviral proteases. Functional studies on FeFV gene expression directed by the promoter of the long terminal repeat showed that FeFV gene expression was strongly activated by the Bell/Tas transactivator protein. The FeFV Bell/Tas transactivator is about one-third smaller than its counterpart of primate spumaviruses. This difference is also reflected by a limited sequence similarity and only a moderate conservation of structural motifs of the different foamy virus transactivators analyzed.

Amino Acid Sequence↗

PubMed1996

Adaptive modeling of the unattended acoustic environment reflected in the mismatch negativity event-related potential.

The mismatch negativity (MMN) event-related potential is elicited by changes in repetitive auditory stimuli. The present paper suggests that: (1) an acoustic model of the auditory environment is maintained even in the absence of attention focussed on auditory stimuli, preattentively detecting repetitive features of the acoustic stimulation; and (2) the MMN reflects modifications to existing parts of this model during incorporation of a new stimulus into the model. MMN responses were investigated during the period when a repetitive stimulus (standard) was replaced by a new standard sound. It was found that whereas the new standard stimulus stopped eliciting an MMN after its third presentation with respect to the old standard, a probe stimulus, differing from both standards, elicited an MMN with respect to the old standard, even when following four presentations of the new standard. The probe stimulus also elicited an MMN with respect to the new standard after four or more presentations of this new standard stimulus, thus eliciting two consecutive MMNs. The comparison (conducted on the basis of the present and some previous findings) of the present hypothesis with alternative explanations of MMN based on the presence and strength of auditory transient memory traces supported the model adjustment hypothesis.

Acoustic Stimulation↗

PubMed1996

Preattentive auditory change detection relies on unitary sensory memory representations.

Event-Related potentials (ERPs) were recorded to series of frequent (standard) and three types of rare (deviant) tones differing from the standard in frequency, duration, or in both features. All deviants elicited the mismatch negativity (MMN) ERP component, indexing the deviation of a sound from the transient auditory memory trace of the standard. Duration deviance could be detected only after the offset of the duration deviant delaying the MMN to this deviant by 70 ms compared with the MMN of the frequency deviant. The MMN to the double deviant extended only to the latency range of the frequency MMN, revealing that feature-MMNs were coordinated by a memory trace integrating the outcome of the various feature analysers.

Acoustic Stimulation↗

PubMed1996

Selective pressure of a quinoxaline nonnucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) on HIV-1 replication results in the emergence of nucleoside RT-inhibitor-specific (RT Leu-74-->Val or Ile and Val-75-->Leu or Ile) HIV-1 mutants.

The quinoxaline nonnucleoside RT inhibitor (NNRTI) (S)-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3,4- dihydroquinoxaline-2(1H)-thione (HBY 097) was used to select for drug-resistant HIV-1 variants in vitro. The viruses first developed mutations affecting the NNRTI-binding pocket, and five of six strains displayed the RT G190-->E substitution, which is characteristic for HIV-1 resistance against quinoxalines. In one variant, a new mutant (G190-->Q) most likely evolved from preexisting G190-->E mutants. The negative charge introduced by the G190-->E substitution was maintained at that site of the pocket by simultaneous selection for V179-->D together with G190-->Q. After continued exposure to the drug, mutations at positions so far known to be specific for resistance against nucleoside RT inhibitors (NRTIs) (L74-->V/I and V75-->L/I) were consistently detected in all cultures. The inhibitory activities of the cellular conversion product of 2',3'-dideoxyinosine (ddI, didanosine), 2',3'-dideoxyadenosine (ddA) and of 2',3'-didehydro-3'-deoxythymidine (d4T, stavudine) against these late-passage viruses were shown to be enhanced with the L74-->V/I RT mutant virus as compared with the wild-type (wt) HIV-1MN isolate. Clonal analysis proved linkage of the codon 74 and codon 75 mutations to the NNRTI-specific mutations in all RT gene fragments. The nonnucleoside- and nucleoside-resistance mutation sites are separated by approximately 35 A. We propose that the two sites "communicate" through the template-primer which is situated in the DNA-binding cleft between these two sites. Quinoxalines cause high selective pressure on HIV-1 replication in vitro; however, the implication of these findings for the treatment of HIV-1 infection has yet to be determined.

Antiviral Agents↗

PubMed1996

Characterization of the spliced pol transcript of feline foamy virus: the splice acceptor site of the pol transcript is located in gag of foamy viruses.

Foamy viruses, or spumaviruses, are distinct members of the Retroviridae. Here we have characterized the long terminal repeat of the feline, or cat, foamy virus by determining the locations of the transcriptional start site and the poly(A) addition site. The splice donor and splice acceptor sites of the subgenomic mRNA responsible for Pro-Pol protein expression were identified by nucleotide sequencing of the corresponding cDNAs. The leader exon of the feline foamy virus is 57 nucleotides long. The splice acceptor of the subgenomic pol mRNA was found to be located in gag. The location of the splice acceptor of the human foamy virus pol mRNA was confirmed to map in gag. The pol splice acceptor site in gag of the cat foamy virus is located further downstream than that of human foamy virus.

Animals↗

PubMed1995

From objective to subjective: pitch representation in the human auditory cortex.

Magnetic brain responses to infrequent changes in the pitch of complex sounds were recorded. The composition of the test sounds required that pitch-deviant stimuli elicited the mismatch response only if perceived pitch was represented in auditory sensory memory. Results revealed that subjective features, such as pitch, are formed from objective stimulus parameters (i.e. the spectral contents of a sound) before storing acoustic information in memory. The origin of the magnetic response to pitch change showed that pitch deviation was detected in the auditory cortex. Pitch memory might also be located in the auditory cortex, as previous evidence suggests that storage for an auditory feature lies in the vicinity of the neuronal elements activated by deviations in that feature.

Acoustic Stimulation↗