A neurophysiologically-based mathematical model of flash visual evoked potentials

Evidence is presented that a neurophysiologically-inspired mathematical model, originally developed for the generation of spontaneous EEG (electroencephalogram) activity, can produce VEP (visual evoked potential)-like waveforms when pulse-like signals serve as input. It was found that the simulated VEP activity was mainly due to intracortical excitatory connections rather than direct thalamic input. Also, the model-generated VEPs exhibited similar relationships between prestimulus EEG characteristics and subsequent VEP morphology, as seen in human data. Specifically, the large correlation between the N1 amplitude and the prestimulus alpha phase angle, and the insensitivity of P2 to the latter feature, as observed in actual VEPs to low intensity flashes, was also found in the model-generated data. These findings provide support for the hypothesis that the spontaneous EEG and the VEP are generated by some of the same neural structures and that the VEP is due to distributed activity, rather than dipolar sources.

Inhibition of growth and appearance of estrogen-dependent rat mammary tumors by 10-propargylestr-4-ene-3,17-dione, an aromatase inhibitor

The aromatase inhibitor 10-propargylestr-4-ene-3,17-dione (PED) has been evaluated in vivo as an anticancer agent. Prolonged administration of PED to rats bearing dimethylbenzanthracene-induced mammary tumors resulted in significant regression of hormone-responsive tumors within several days. Greater than 50% regression was generally observed after 14 days of treatment, irrespective of dose (1, 5, or 50 mg/kg body weight/day). In addition to tumor regression, a significantly increased incidence in tumor stasis was observed over the course of PED treatment. While all doses of PED examined were equipotent for both tumor regression and stasis, a dose-dependent inhibition of new tumor formation was observed in PED-treated rats. In control animals an average of 1.2 new tumors was observed during the experimental period; in contrast, averages of 0.5 tumors appeared in animals receiving 1 mg PED/kg body weight/day, 0.1 tumors at 5 mg/kg, and at 50 mg of PED/kg body weight/day, no new tumors occurred during the time PED was administered. The effects of PED on both regression of existing tumors and appearance of new tumors were reversed by co-administration of estradiol. Thus, PED impairs estrogen-dependent mammary tumor growth, resulting in cessation of new growth and regression of responsive tumors.

Cerebral white matter and cognition in hydrocephalic children

Although children with hydrocephalus frequently show poor development of nonverbal cognitive skills relative to verbal skills, little is known about the neuropathologic correlates of these discrepancies. In this study, cerebral white-matter structures and lateral ventricles were measured from the magnetic resonance images of age-matched children with meningomyelocele, meningocele, and aqueductal stenosis and normal subjects. The volume of each lateral ventricle and the cross-sectional area of the corpus callosum and internal capsules were correlated with concurrent measures of verbal and nonverbal cognitive skills. The corpus callosum in the meningomyelocele and aqueductal stenosis groups was smaller. The lateral ventricles were larger, and the internal capsules were smaller, in all patient groups than in normal subjects. There were no differences in the size of the centra semiovale. Although verbal and nonverbal measures correlated positively with the size of the corpus callosum, the correlation was higher for nonverbal measures. Nonverbal measures correlated with the right, but not the left, lateral ventricle and with the area of the right and left internal capsules. Verbal measures correlated with the left, but not right, lateral ventricle and with the left, but not right, internal capsule. These results show a relationship between the corpus callosum and cognitive skills that is also influenced by hydrocephalus-related changes in the lateral ventricles and other cerebral white-matter tracts.

Topographic mapping of brain electromagnetic signals: a review of current technology

Topographic mapping of brain electromagnetic signals has become increasingly popular in recent years both as a clinical tool and as an area of research in its own right. The capabilities of existing computerized systems for displaying such maps and for performing localization of current sources in the brain have continued to expand. In this paper we review some of the methodological and technological issues concerning topographic mapping. These include issues of choice of interpolation algorithm, what to map, head geometry, EEG reference location, and scaling. We also discuss characteristics of clinical databases for patient comparison and the usefulness of quantitative EEG (which includes mapping) for the diagnosis of nervous system disorders. Finally, we compare five representative systems in terms of their topographic mapping capabilities. The overall conclusion is that future developments must make use of integrated data from other neuroimaging technologies such as MRI, PET, and SPECT, and determination of the normal limits of topographic parameters must be more carefully examined.

Identification of a novel annexin in Hydra vulgaris. Characterization, cDNA cloning, and protein kinase C phosphorylation of annexin XII

As a first step toward the elucidation of a simple animal model in which to investigate annexin function, we identified, isolated, and characterized a novel annexin from Hydra vulgaris, annexin XII. A hydra cDNA library was screened using a probe generated by polymerase chain reaction from primers based on the partial amino acid sequence of annexin XII. Annexin XII cDNA was cloned and the functional protein was expressed in high yields in Escherichia coli. The annexin XII cDNA sequence predicted a 316-amino acid protein that had between 44 and 54% sequence identity with the Ca2+-binding core domains of previously characterized vertebrate and Drosophila annexins. The amino-terminal domain of annexin XII did not have sequence similarity with other known annexins except at and around a site that resembled known protein kinase C (PKC) phosphorylation sites in other annexins. As anticipated from its sequence, annexin XII was a high affinity substrate for purified rat brain PKC; half-maximal phosphorylation occurred below 0.1 microM annexin XII, and incorporation of up to 0.8 mol of phosphate/mol of annexin XII was observed. A PKC-like activity in hydra extracts also phosphorylated annexin XII. In summary, hydra promises to be a valuable model system for investigating the biological function of annexins and for determining how this function is modulated by PKC phosphorylation.

Expression and characterization of human mitochondrial ferredoxin reductase in Escherichia coli

Ferredoxin reductase (Fd-reductase) supplies reducing equivalents obtained from NADPH to mitochondrial cytochrome P450 enzymes via the small iron-sulfur protein ferredoxin. Two cDNAs (differing by the presence or absence of an 18-bp insert in the coding region) for the human Fd-reductase were subcloned into a newly constructed general purpose expression vector, p delta blue; protein expression under control of the bacteriophage lambda pL promoter was then induced in Escherichia coli. Western blot analysis of subcellular fractions indicated that Fd-reductase protein expressed from both plasmids was present in both inclusion bodies and soluble fractions. However, only the form lacking the insert exhibited Fd-reductase activity. The active material was purified and was found to have electrophoretic, chromatographic, optical, and circular dichroism properties comparable to the bovine homologue. The apparent Km of the expressed protein for NADPH was determined to be 0.7 +/- 0.1 microM and the apparent Km for human ferredoxin was found to be 106 +/- 8 nM. While yields of active enzyme were relatively low (approximately 0.1 mg/liter of culture), the production of Fd-reductase in E. coli will allow structural and mechanistic studies of the enzyme and its interactions with ferredoxin.

Analysis of the N-terminal region of the 47-kilodalton integral membrane lipoprotein of Treponema pallidum

The 47-kDa lipoprotein is an abundant integral membrane protein and dominant immunogen of Treponema pallidum subsp. pallidum. Previous DNA sequencing of the 47-kDa-lipoprotein gene did not reveal consensus features representative of other bacterial lipoprotein genes; this prompted further analyses with emphasis on elucidation of the N terminus of the molecule. To assist in localizing start signals for the protein, the transcription initiation site for the 47-kDa-antigen gene was determined. RNA isolated from both T. pallidum and recombinant Escherichia coli expressing the 47-kDa antigen was used as a template in reverse transcriptase primer extension. Upon analysis of cDNA products, transcription initiation was localized to one nucleotide in T. pallidum and to two adjacent nucleotides in E. coli. When various primers were used in DNA sequencing reactions for these analyses, a previously undetected nucleotide (G) was found in the purported 5' untranslated region; this altered the upstream reading frame to reveal plausible sites for ribosome binding (GGAGG), translation initiation (GTG start codon), and signal peptidase II processing (Val-Val-Gly-Cys). Discounting acylation, the molecular weight of the mature polypeptide is 45,756 (approximately 46,600 with acylation). To derive nonacylated 47-kDa antigen for further structure-function studies, the 47-kDa-antigen gene was subcloned without acylation signals as a genetic construct encoding a glutathione S-transferase fusion protein; following cleavage with thrombin, the nonacylated 47-kDa protein was hydrophilic rather than amphiphilic but retained its antigenicity when tested against 116 human serum samples from patients with various stages of syphilis.

The relationship between prestimulus-alpha amplitude and visual evoked potential amplitude

Root-mean-square (RMS) amplitude derived from power spectral measures in the alpha band of the 1 s prestimulus EEG were related to the peak-to-peak amplitude of the N1 and P2 components (N1P2PP) of the visual evoked potential (VEP) in 7 male subjects. Stimuli were low intensity flashes delivered randomly between 2 and 6 whole seconds. Trials were rank ordered according to the levels of prestimulus alpha amplitude and were partitioned into groups of 40 trials each (25 groups per data set). Averaged VEPs were computed from these groups and scattergrams of N1P2PP and enhancement factor (following the approach by Başar, 1980) vs. prestimulus alpha amplitude were produced. There was a correlation of 0.74 (p less than .0001) between prestimulus alpha amplitude and N1P2PP, and all seven subjects displayed a general inverse relationship between VEP enhancement and prestimulus alpha amplitude, replicating the results of Başar. However, we observed an exponential relationship, rather than the linear relationship reported by Başar.

Lipoproteins of Borrelia burgdorferi and Treponema pallidum activate cachectin/tumor necrosis factor synthesis. Analysis using a CAT reporter construct

Lipoproteins from two pathogenic spirochetes (Borrelia burgdorferi and Treponema pallidum) induced the biosynthesis of TNF in murine macrophages and in permanently transformed macrophages of the cell line RAW 264.7. Induction was studied by measuring the secretion of biologically active TNF and by measuring the activity of the reporter enzyme chloramphenicol acetyltransferase (CAT) produced within macrophages transfected with an endotoxin-responsive CAT construct. Several lines of evidence indicated that the induction of TNF and CAT was attributable to the spirochete lipoproteins rather than to contaminating or endogenous LPS: 1) the dose response curves observed for the lipoproteins were markedly different from those obtained with LPS; 2) lipoprotein-mediated activation was unaffected by amounts of polymyxin B that completely neutralized the induction of TNF and CAT by LPS, 3) low concentrations of the lipoproteins induced TNF in macrophages from endotoxin-unresponsive C3H/HeJ mice as effectively as in macrophages from normal C3H/HeN mice, and 4) isolated spirochete lipoproteins, but not a non-lipoprotein immunogen, were potent inducers of CAT in the transformed macrophages. Moreover, LPS was not detected in the B. burgdorferi lipoprotein mixtures by Limulus amebocyte lysate assay. Proteolytic digestion of the intact bacterial protein preparations only modestly diminished their ability to activate the cells, suggesting that small lipopeptides comprise the biologically active portions of the molecules, as is the case with the murein lipoprotein of Escherichia coli. Through their ability to induce TNF production by macrophages, spirochete lipoproteins may play important roles in the development of the local inflammatory changes and the systemic manifestations that characterize syphilis and Lyme disease.

Lipoproteins of Borrelia burgdorferi and Treponema pallidum activate cachectin/tumor necrosis factor synthesis. Analysis using a CAT reporter construct

Lipoproteins from two pathogenic spirochetes (Borrelia burgdorferi and Treponema pallidum) induced the biosynthesis of TNF in murine macrophages and in permanently transformed macrophages of the cell line RAW 264.7. Induction was studied by measuring the secretion of biologically active TNF and by measuring the activity of the reporter enzyme chloramphenicol acetyltransferase (CAT) produced within macrophages transfected with an endotoxin-responsive CAT construct. Several lines of evidence indicated that the induction of TNF and CAT was attributable to the spirochete lipoproteins rather than to contaminating or endogenous LPS: 1) the dose response curves observed for the lipoproteins were markedly different from those obtained with LPS; 2) lipoprotein-mediated activation was unaffected by amounts of polymyxin B that completely neutralized the induction of TNF and CAT by LPS, 3) low concentrations of the lipoproteins induced TNF in macrophages from endotoxin-unresponsive C3H/HeJ mice as effectively as in macrophages from normal C3H/HeN mice, and 4) isolated spirochete lipoproteins, but not a non-lipoprotein immunogen, were potent inducers of CAT in the transformed macrophages. Moreover, LPS was not detected in the B. burgdorferi lipoprotein mixtures by Limulus amebocyte lysate assay. Proteolytic digestion of the intact bacterial protein preparations only modestly diminished their ability to activate the cells, suggesting that small lipopeptides comprise the biologically active portions of the molecules, as is the case with the murein lipoprotein of Escherichia coli. Through their ability to induce TNF production by macrophages, spirochete lipoproteins may play important roles in the development of the local inflammatory changes and the systemic manifestations that characterize syphilis and Lyme disease.

Effect of 4-hydroxyandrostenedione on murine Leydig tumor cell steroidogenesis

The murine Leydig cell tumor (M5480A) possesses high levels of estrogen receptor and is known to produce estrogens. In these studies we examined the effects of the potent aromatase inhibitor 4-hydroxyandrostenedione (4-OHA) on Leydig tumor cell steroidogenesis both in vitro and in vivo. The addition of 4-OHA to Leydig tumor cells in primary culture resulted in a dose- and a time-dependent decrease in media progesterone levels. The observed decrease was most likely due to impaired synthesis of progesterone, inasmuch as no alteration in progesterone metabolism was seen when progesterone levels were diminishing. However, 4-OHA inhibited progesterone conversion to testosterone following 1 h of incubation, but this effect disappeared coincident with 4-OHA metabolism. Analysis of pregnenolone production revealed a biphasic dose-dependent effect of 4-OHA. At low doses (0.01-0.1 microM), 4-OHA was found to decrease pregnenolone concentrations, while at higher doses (1-10 microM) pregnenolone levels were elevated. Therefore, the actions of 4-OHA on Leydig cell steroidogenesis in vitro appear to be multifocal. Other experiments were performed to evaluate the effects of 4-OHA on tumor-bearing male mice in vivo. In these studies, the predominant effects of 4-OHA were to act as an aromatase inhibitor and to inhibit progesterone production. Thus, while 4-OHA is a potent aromatase inhibitor, we have found that this compound may alter steroidogenesis in Leydig tumor cells at several sites prior to aromatization.

The effect of the phase of prestimulus alpha activity on the averaged visual evoked response

The relationship between the latencies and amplitudes of the N1 and P2 components of the averaged visual evoked potential (EP) and the phase of the alpha activity immediately preceding the time of the stimulus, has been investigated in 7 male subjects. Low intensity flashes, delivered randomly between 2 and 6 whole seconds, were used as the stimuli. The phase angle of the EEG at the moment of stimulation was computed for all trials containing more than 100 microV2 of prestimulus alpha power. The single trials were grouped into 8 classes on the basis of the phase angle value, and averaged EPs for each individual were computed from these groups. In addition, averaged EPs were computed in 3 ways: (1) a grand average consisting of all artifact-free trials, (2) an 'alpha average' consisting of all trials containing more than 100 microV2 of prestimulus alpha power, and (3) a 'non-alpha average' consisting of all trials with less than 100 microV2 of prestimulus alpha power. Each of these 3 averages were cross-correlated with the phase-selective averages. It was found that the particular N1 component assessed in this experiment may possibly be entrained alpha activity, and that the measured P2 component is not an alpha process, yet it is influenced by the amount of prestimulus alpha activity.

Immunocytochemical localization and enzymatic distribution of rat ovarian aromatase

A rabbit antiserum directed against purified human placental aromatase was used for immunohistochemical localization of the enzyme in rat ovaries. Immunostaining was conducted on tissue from animals at various ages and in different reproductive states: immature; immature, eCG-treated; immature pseudopregnant; adult cycling; and adult pregnant. Various labeling protocols were employed (e.g. horseradish peroxidase-conjugated secondary antibody, peroxidase-antiperoxidase, and avidin-biotin-peroxidase on fresh frozen and Bouin's fixed paraffin-embedded sections), but the avidin-biotin-peroxidase method on paraffin sections proved to be superior to the others. In immature rats, most of the immunostaining, which was quite weak, was limited to the stroma. After stimulation with eCG, some of the granulosa cells of antral follicles exhibited immunostaining; in pseudopregnant rats, most staining occurred in the luteal cells. In mature animals, the corpora lutea of pregnant and cycling rats demonstrated the greatest degree of immunostaining. No significant immunoreactivity was detected in pre-antral follicles, but in early antral follicles and preovulatory follicles, both theca and granulosa cells exhibited immunostaining. Aromatase enzymatic activity was also determined on ovarian microsomal fractions of eCG-treated immature animals, pregnant animals at term, and cycling animals. Furthermore, enzyme activity and estradiol concentrations were examined after ovaries from proestrous rats were dissected into follicular, luteal, and residual components. Activity was found in all regions and correlated with immunostaining and estrogen production. These results argue against a model in which all the immunoreactive/enzymatically active protein is localized in granulosa cells of Graafian follicles and suggest that corpora lutea may be involved in estrogen synthesis during the rat estrous cycle as well as during pregnancy.

A vector for directional cloning and expression of polymerase chain reaction products in Escherichia coli

This paper describes the construction of a modified vector for the cloning and expression of protein-encoding genes in Escherichia coli. The vector, pfXblue, is derived from the system originally developed by Nagai and Thøgerson [Nature 309 (1984) 810-812], but contains a modified multiple cloning site (MCS) from M13mp18 to allow directional insertion of foreign coding sequences. The MCS is located within the M13mp18 lacZ' gene and thus allows blue/white screening of colonies for inserts. The inserted gene is expressed as a fusion protein, which, when cleaved by the coagulation factor Xa protease, yields the mature product. This vector was successfully used for the production of a mitochondrial [2Fe-2S]ferredoxin using polymerase chain reaction products generated from a chick kidney cDNA library.

Pre-stimulus spectral EEG patterns and the visual evoked response

The relationship between the latencies and amplitudes of the N1 and P2 components of the visual evoked potential (VEP) and the psychophysiological state of the brain immediately preceding the time of the stimulus has been investigated in 7 male subjects. Power spectral measures in the delta, theta, alpha and beta bands of the 1 sec pre-stimulus EEG were used to assess the brain state, and low intensity flashes, delivered randomly between 2 and 6 whole seconds, were used as the stimuli. Trials were ranked separately according to the relative amounts of pre-stimulus power in each EEG band and were partitioned into groups by an equal pre-stimulus spectral power criterion. Averaged EPs were computed from these groups and multiple regression analysis was used to relate pre-stimulus spectral power values to EP features. Five of the 7 subjects displayed consistent increases in N1-P2 amplitude as a function of increasing pre-stimulus relative alpha power. The between-subjects effect of pre-stimulus EEG on N1 latency was small, but was moderate for P2 latency (both significant). Both N1 and P2 latency were found to decrease with increasing amounts of pre-stimulus relative delta and theta power.

Immunogenic integral membrane proteins of Borrelia burgdorferi are lipoproteins

The pathogenic spirochete Borrelia burgdorferi contains a set of integral membrane proteins which were selectively extracted into the detergent phase upon solubilization of intact B. burgdorferi with the nonionic detergent Triton X-114. Virtually all of these hydrophobic proteins were recognized by antibodies in pooled sera from patients with chronic Lyme arthritis, demonstrating that proteins partitioning into the detergent phase of Triton X-114 encompass the major B. burgdorferi immunogens. Furthermore, most of these immunogenic proteins, including the previously characterized OspA and OspB membrane antigens, could be biosynthetically labeled when B. burgdorferi was incubated in vitro with [3H]palmitate. The OspA and OspB antigens were radioimmunoprecipitated from [3H]palmitate-labeled detergent-phase proteins with monoclonal antibodies, and [3H]palmitate was recovered unaltered from these proteins after sequential alkaline and acid hydrolyses. The combined results provide formal confirmation that the major B. burgdorferi immunogens extracted by Triton X-114 are lipoproteins. The demonstration that B. burgdorferi integral membrane antigens are lipoproteins may explain the basis of their immunogenicity and may help to improve our understanding of the surface topology of B. burgdorferi.

Divergence between ovarian aromatase activity, estrogen, and androgen levels in the cycling rat

Serum estrogen levels vary in a cyclic fashion during the rat estrous cycle, reaching peak values on proestrus and then rapidly declining. Daily measurements of ovarian aromatase activity appear to follow a similar pattern, suggesting a potential regulatory role for the enzyme. To examine this hypothesis, mature rats were killed at various times, and ovarian microsomes were assayed for aromatase activity, while androstenedione, testosterone, estradiol, and estrone levels were measured in ovarian cytosol by RIA. The ovarian aromatase activity reached a peak about 9 h after the onset of the light period on the day of proestrus, and then began to decrease gradually to 75% lower levels by the morning of estrus. Similarly, the estradiol levels also peaked at about 9 h, but then dropped sharply; at 18 h the estradiol levels were reduced 90-95%, while aromatase activity was still close to its peak value. In contrast, the androstenedione and testosterone levels remained high for 3-4 h after the estradiol levels began to decrease. Estrone levels varied considerably less than those of estradiol, reaching lower peak values, but then decreasing only 50-75%. The dissociation between product levels and enzyme activity cannot be explained by a change in the Km of aromatase, which was about 20 nM for androstenedione throughout this period. Therefore, it appears that the decrease in estradiol levels from the peak of the surge may in part be a consequence of a shift in the ratio of the estrogen products synthesized by the ovary, rather than a decrease in the ovarian capacity for estrogen production, although other factors appear to be involved as well.

The effects of in vivo administration of 10-propargylestr-4-ene-3,17-dione on rat ovarian aromatase and estrogen levels

We have previously demonstrated that 10-propargylestr-4-ene-3,17-dione (PED) functioned as an irreversible inhibitor of rat ovarian aromatase in vitro. These studies were undertaken to examine the in vivo effects of PED on rat ovarian aromatase activity and estrogen production. In the current experiments, a single injection of PED (0.5 or 2.5 mg/kg) was found to maximally inhibit aromatase at 3 h regardless of dose. Significant inhibition of enzyme activity by PED was observed beyond 18 h, although some recovery was noted at the lower dose (0.5 mg/kg). Concomitantly, ovarian estrogen levels were also maximally reduced at 3 h, however ovarian estrogen levels returned toward control values prior to the recovery in enzyme activity. Even though significant inhibition of enzyme activity was observed at 12 h following a single injection of PED, the effect of double injections of the inhibitor at 12 h intervals was surprisingly not cumulative. Similarly, continued multiple injections of PED revealed significant inhibition of enzyme activity and estrogen production several hours after the injection, but variations in effectiveness were observed by 12 h which changed in accordance with a circannual cycle in aromatase. Apparently other factors are involved with maintaining aromatase levels and compensating for reduced enzyme activity. These mechanisms are evidenced by a continuation of the rat reproductive cycle with prolonged PED administration and a reduced influence of PED in regard to enzyme inhibition at certain times of the year. Despite these variations in the duration of action of PED, no comparable changes were observed in effectiveness as an anti-tumor agent. These results suggest that complex mechanisms exist which regulate the activity of aromatase in order to maintain estrogen production. Further research using compounds such as PED may assist in elucidating the factors that modulate ovarian estrogen production.

Major integral membrane protein immunogens of Treponema pallidum are proteolipids

A number of the major pathogen-specific immunogens of Treponema pallidum were characterized recently as amphiphilic, integral membrane proteins by phase partitioning with Triton X-114 (J. D. Radolf, N. R. Chamberlain, A. Clausell, and M. V. Norgard. Infect. Immun. 56:490-498, 1988). In the present study, we demonstrated that the same membrane immunogens (designated as detergent phase proteins [DPPs]) become radiolabeled upon in vitro incubation of T. pallidum with various 3H-labeled fatty acids. Radioimmunoprecipitation with a monoclonal antibody confirmed that the 3H-labeled 47-kilodalton protein corresponded to the well-characterized treponemal antigen with the identical apparent molecular mass. Failure to detect 3H-labeled DPPs following incubation with erythromycin confirmed that protein acylation required de novo protein synthesis by the bacteria. When treponemes were incubated with [3H]myristate, [3H]palmitate, or [3H]oleate, radiolabeled proteins corresponding to the DPPs were detected upon autoradiography. Demonstration that a number of the abundant membrane immunogens of T. pallidum are proteolipids provides information to help clarify their membrane association(s) and may serve to explain their extraordinary immunogenicity.

Characterization of pregnant mare's serum gonadotropin-stimulated rat ovarian aromatase and its inhibition by 10-propargylestr-4-ene-3,17-dione

Aromatase, the important regulatory enzyme that converts androgens to estrogens, is found in relatively high levels in the human placenta. However, since the ovary is the major source of the estrogens in females, we undertook studies to compare the rodent ovarian enzyme with that from human placenta. Pregnant mare's serum gonadotropin (PMSG) markedly increases aromatase activity in the ovaries of immature rats, and this model was used in order to reproducibly obtain high enzyme levels. An injection of PMSG resulted in a specific stimulation of aromatase activity 12 times the increase in ovarian weight in 48 h. Kinetic studies demonstrated that, although the PMSG-stimulated ovarian microsomes had one-tenth the specific activity of the human placenta, the Km values were similar (about 33 and 44 nM, respectively). The potent inhibitor of placenta aromatase, 10-propargylestr-4-ene-3,17-dione, was used to further characterize the enzyme. It inhibited the rat aromatase with an I50 of 36 nM and exhibited time-dependent inhibition with a half-life of inactivation of 16 min and a Ki of 15 nM. These values are similar to those we obtained with the human enzyme (10 nM, 12 min, and 5 nM, respectively). The enzyme parameters in the presence and absence of the inhibitor suggest that the enzymes from the two sources are kinetically quite similar.

Inhibition of aromatase activity and of endocrine-responsive tumor growth by 10-propargylestr-4-ene-3, 17-dione and its 17-propionate derivative

Two androstenedione derivatives, 10-propargylestr-4-ene-3,17-dione and its 17-propionated form, were administered to normal cycling rats, and both compounds led to an inhibition of ovarian aromatase. Under in vitro conditions, only the former compound exhibited high potency as an inhibitor of rat ovarian and human placental microsomal aromatase. At 1 mg/kg/day both compounds were effective in promoting regression of 9,10-dimethyl-1,2-benzanthracene-induced mammary tumors in rats without terminating their estrous cycle. PED also inhibited growth of a human ovarian carcinoma in athymic mice. The results with the 17-propionated compound testify to the necessity of in vivo assays in screening antitumor agents. In summary, PED and its propionated derivative inhibited ovarian aromatase in vivo and inhibited the growth of hormone-responsive tumors.

No decrement in visual P300 amplitude during extended performance of the oddball task

Research indicates that in visual sustained attention paradigms, the amplitude of the P300 component of the event-related potential invoked by target (critical) stimuli shows a decrement in amplitude. This amplitude decrement parallels decrements in vigilance performance that result from the difficult discrimination that is typically required between the infrequent targets and the frequent nontargets (neutral stimuli). In contrast, target stimulus P300 does not appear to show a decrement across large numbers of trials during performance of the "oddball" paradigm, in which targets and nontargets are highly discriminable. The present study measured target and nontarget P300 amplitude during performance of a visual oddball paradigm extended over an interval of some 3 1/2 hours, a period well in excess of the 3/4 hour intervals employed in previous research. The results indicated no decrement in P300 amplitude as a function of time for either targets or nontargets. The only significant relationship between P300 and behavioral data was an inverse correlation across oddball runs between average nontarget P300 amplitude and total number of targets missed.