rRNA chemical groups required for aminoglycoside binding.

Through an affinity chromatography based modification-interference assay, we have identified chemical groups within Escherichia coli 16S ribosomal RNA sequence that are required for binding the aminoglycoside antibiotic paromomycin. Paromomycin was covalently linked to solid support via a nine atom spacer from the 6"'-amine of ring IV, and chemical modifications to an A-site oligonucleotide that disrupted binding were identified. Positions in the RNA oligonucleotide that correspond to G1405(N7), G1491(N7), G1494(N7), A1408(N7), A1493(N7), A1408(N1), A1492(N1), and A1493(N1), as well as the pro-R phosphate oxygens of A1492 and A1493 in 16S rRNA are chemical groups that are essential for a high-affinity RNA-paromomycin interaction. These data are consistent with genetic, biochemical, and structural studies related to neomycin-class antibiotics and provide additional information for establishing an exact model for their interaction with the ribosome.

Synthesis and characterization of 8-methoxy-2'- deoxyadenosine-containing oligonucleotides to probe the syn glycosidic conformation of 2'-deoxyadenosine within DNA.

The synthesis of 8-methoxy-2'-deoxyadenosine (moA) protected at N6 as an N,N-dimethylformamidine derivative and incorporation of the modified nucleoside into oligodeoxynucleotides via the phosphoramidite method are described. UV thermal denaturation studies were conducted on duplexes containing moA:G, moA:C and moA:T base pairs to determine the thermodynamic stability of duplexes containing moA relative to their adenosine (A)-containing counterparts. In the case of moA:G base pairs the effect of moA substitution is sequence dependent. In A:G mismatch-containing sequences, which have been shown by structural characterization to have a syn conformational preference at the glycosidic bond of A, moA substitution results in stabilization of the duplex. In contrast, in sequences where the A in the A:G mismatch has been shown to prefer the anti conformation moA substitution is destabilizing to the duplex. Thus moA may be a useful probe for investigating the conformational preferences of the N-glycosidic bond of adenosine within DNA. In addition, moA nucleoside is more resistant to acid-catalyzed depurination than previously described 8-bromo-2'-deoxyadenosine, allowing for facile incorporation into oligonucleotides via automated solid phase DNA synthesis.

Ferrioxamine B derivatives as hepatobiliary contrast agents for magnetic resonance imaging.

Succinyl (SDF), phenylsuccinyl (PSDF), glutaryl (GDF), and phenylglutaryl (PGDF) derivatives of desferrioxamine B (DF) have been synthesized. In rats given the 59Fe(III) chelates of each these ligands at tracer levels, 82-94% of the 59Fe was eliminated within 1-2 days. 59Fe given as DF, SDF, and GDF chelates was excreted primarily in the urine, while nearly 50% of that given as PSDF and PGDF was excreted in the feces. Correspondingly, Fe-DF, Fe-SDF, and Fe-GDF (0.2 mmol/kg) produced early, marked renal, but no gastrointestinal magnetic resonance imaging (MRI) enhancement. Fe-PSDF and Fe-PGDF (0.2 mmol/kg) produced marked and rapid MRI enhancement of the upper small intestine. In animals with cannulated bile ducts, 59Fe from 59Fe-PGDF (carrier added, 0.1 mmol/kg) appeared rapidly in the collected bile, but not in the intestinal contents, proving that the contrast agent reaches the bowel via the bile. These changes in the excretion and MRI enhancement patterns brought about by the presence of a phenyl substituent apparently were not related to changes in lipophilicity or protein binding.

Subcortical gating in the human visual system during spatial selective attention.

The question of whether subcortical gating occurs as a function of spatial selective attention remains unsettled. This issue was investigated, using the paradigm of Eason et al. (1969) wherein subjects are instructed to attend to a specified location in a given visual field while attempting to ignore stimuli presented in the opposite field. Visual evoked responses falling within the 40-70 ms range were found to be significantly more negative when the location at which the evoking stimulus appeared was being attended to than when it was not. Also, later deflections (100-200 ms) were enhanced in amplitude and negatively biased. The very early effect provides further evidence for spatial attention-induced precortical gating. The later effects provide additional evidence for the amplitude enhancement of 'exogenous' components, along with the possible involvement of glial cell activity in the generation of slow wave negativity.

The conjoint influence of spatial selective attention and motor set on very short latency VERs.

This study investigated whether motor set, in conjunction with spatial selective attention (sensory set), influences the transmission of incoming visual information at a precortical level in humans. Stimuli were presented concomitantly in both the right and left visual fields while subjects attended to the relevant visual field (either left or right) on a given trial, and was prepared to make one of three kinds of responses (an eye movement, foot-lift, or counting) to target stimuli appearing in that field. VERs were obtained from frontal and parietal sites. A deflection falling within a 40-70 msec range was more negative under the attend than under the unattend condition for the eye movement task, the opposite being the case for the counting task. No attention effect was found for the foot-lift task. The findings were interpreted as providing support for the precortical hypothesis.

Voluntary alpha control, visually evoked potentials, and peripheral physiological indicants of activation.

To test the hypothesis that voluntary alpha control is mediated in part through self-induced changes in cortical activation level and bodily arousal, changes in several physiological indicants of such activity were systematically examined as a function of the voluntary enhancement and suppression of scalp-recorded alpha activity. Following per-training, 6 subjects attempted to either produce or suppress alpha with eyes closed while receiving continuous anditory feedback of their alpha levels. The results were interpreted as offering tentative support for the hypothesis.

Evoked cortical potentials: relation to visual field and handedness.

The amplitiude of evoked responses of occipital cortex in man depends on the visual field in which the stimulus appears. Greater responses occurred repeatedly for two of three subjects, both left-handed. when the stimululs appeared in the left field than in the right. Subsequent tests of 13 right- and 13 left-handed males indicted that the magnitude of the response of the right lobe, relative to that of the left, was greater for left-handed individuals. We conclude that the difference in amplitude between the two lobes is related to handedness.