Effects of phenytoin on N100 augmenting/reducing and the late positive complex of the event-related potential: a topographic analysis

The effects of 100 mg of phenytoin on the topographic distribution of augmenting/reducing (amplitude response/nonresponse to increases in stimulus intensity) of the visual N100 component of the event-related potential (ERP) were examined. In normal subjects, visual N100 augmenting is associated with impulsivity and attentional distraction. Effects of phenytoin on the topographic distributions of the P300 and slow-wave cognitive ERP components were also examined. Subjects counted the total number of light flashes presented at two highly discriminable but equiprobable intensities. Results indicated that phenytoin had a significant reducing effect on the intensity response of N100 at the vertex and anterior temporal electrode sites, and approached significance at the frontal pole. That is, at these loci N100 showed less of an increase in amplitude (or, in some subjects, more of a decrease) in going from baseline to drug than in going from baseline to placebo. Results also indicated that phenytoin significantly enhanced the amplitude of the frontal, negative portion of slow wave, but not the posterior, positive portion or the P300 component. These findings are consistent with behavioral evidence that phenytoin reduces impulsivity and improves concentration.

Inhibition of Leydig tumor cell steroidogenesis by 10-propargylestr-4-ene-3,17-dione, an irreversible aromatase inhibitor

The murine Leydig cell tumor (M5480A) was assayed for the presence of aromatase activity and for the effects of 10-propargylestr-4-ene-3,17-dione (PED), an aromatase inhibitor, on steroidogenesis. Microsomal preparations from these tumors contained low levels of aromatase activity which was PED sensitive. In addition, these Leydig tumor cells were maintained in primary culture and incubated under basal and gonadotropin-stimulated conditions with various doses of PED. Medium levels of progesterone, a major product of these cells, were found to decrease in a dose- and time-dependent manner upon addition of PED. To determine whether the observed effect was due to reduced synthesis or to increased metabolism of progesterone, tritiated progesterone was added to these cell cultures. Analysis of culture medium by high-performance liquid chromatography suggested that PED dramatically reduced the conversion of labeled progesterone to testosterone. Furthermore, examination of medium pregnenolone levels revealed diminished amounts of this steroid as well. Taken together, these results suggest that PED or its metabolites inhibit Leydig tumor cell steroidogenesis at several sites. Thus, in addition to its role as an aromatase inhibitor, this agent also has effects prior to pregnenolone production, as well as other effects in the pathway between progesterone and testosterone.

Individual differences in visual event-related potentials: P300 cognitive augmenting/reducing parallels N100 sensory augmenting/reducing

In a visual event-related potential experiment, both N100 augmenting/reducing data and oddball paradigm P300 data were collected from the same subjects. A significant correlation was obtained between augmenting/reducing and the degree to which stimulus probability affected P300 amplitude. Subjects who augment/reduce in response to increased stimulus brightness in the sensory domain also appear to augment/reduce in response to low probability in the cognitive domain.

Inhibitors of glyoxalase I in vitro

Inhibition in vitro of human red blood cell glyoxalase I activity was measured by the decrease in the rate of formation of S-D-lactoyl-glutathione as determined by the change in absorbance at 240 nm. The percentage activity remaining was determined after addition of various potential inhibitor compounds and the concentration for 50% activity was obtained by graphical interpolation. The inhibitors were selected on the basis of their similarity to a possible transition-state enediol intermediate of methylglyoxal. The most effective inhibitors were dihydroxycoumarins with a 50% inhibition of 0.03 mM. Inhibition of methylglyoxal catabolism suggests possible application as chemotherapeutic agents based on the inhibitor characteristics of methylglyoxal.