The capacity of visual working memory for features and conjunctions

Short-term memory storage can be divided into separate subsystems for verbal information and visual information, and recent studies have begun to delineate the neural substrates of these working-memory systems. Although the verbal storage system has been well characterized, the storage capacity of visual working memory has not yet been established for simple, suprathreshold features or for conjunctions of features. Here we demonstrate that it is possible to retain information about only four colours or orientations in visual working memory at one time. However, it is also possible to retain both the colour and the orientation of four objects, indicating that visual working memory stores integrated objects rather than individual features. Indeed, objects defined by a conjunction of four features can be retained in working memory just as well as single-feature objects, allowing sixteen individual features to be retained when distributed across four objects. Thus, the capacity of visual working memory must be understood in terms of integrated objects rather than individual features, which places significant constraints on cognitive and neurobiological models of the temporary storage of visual information.     

In utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces genital dysmorphogenesis in the female rat

Recently, Gray and Ostby (Toxicol. Appl. Pharmacol. 133, 285-294, 1995) reported that in utero and lactational TCDD exposure causes striking abnormalities in the rat female reproductive system, including reduced fecundity and vaginal threads. The mechanism by which TCDD induces such abnormalities is unknown. Thus, we sought to determine: (1) whether TCDD reduced fecundity by destroying ovarian follicles and (2) whether the vaginal threads resulted from a TCDD-induced developmental defect during embryogenesis or abnormal vaginal opening at puberty. Pregnant Holtzman rats were treated with 1.0 microgram TCDD/kg or vehicle by a single oral dose on gestation day (GD) 11, 15, or 18. Female offspring were monitored for vaginal opening and terminated on postnatal days 2, 21, and 42. The reproductive tract was removed and evaluated for structural abnormalities. The number of primordial follicles also was determined for each ovary. TCDD exposure on GD 11, 15, or 18 did not change the day of vaginal opening, affect ovarian morphology, or reduce the number of primordial follicles. However, this exposure induced the cleft clitoris and vaginal thread originally described by Gray and Ostby (1995) in approximately 55-96% and 36-44% of the litters in our study, respectively. Histologically the thread presented as a thick cord of mesenchyme surrounded by epithelial cells. This defect was clearly visible in histological sections at birth and was noted in the closed vaginas of prepubertal animals. These data suggest that in utero and lactational exposure to TCDD does not reduce the size of the primordial follicle pool; however, it induces developmental abnormalities in the vaginal canal.     

Nicotinic and muscarinic cholinergic receptor binding in the human hippocampal formation during development and aging

High-affinity nicotine, alpha-bungarotoxin (alpha BT) and muscarinic receptor binding was measured in the human hippocampal formation in a series of 57 cases aged between 24 weeks gestation and 100 years. Changes in nicotine receptor binding during development and aging were more striking than differences in alpha BT and muscarinic binding. Nicotine binding was higher at the late foetal stage than at any other subsequent time in all areas investigated. In the hippocampus a fall in binding then occurred within the first six months of life, with little or no subsequent fall during aging, whereas in the entorhinal cortex and the presubiculum the major loss of nicotine binding occurred after the fourth decade. alpha BT binding was significantly elevated in the CA 1 region, but in no other region of the hippocampus, in the late foetus, and there was also a fall in alpha BT binding in the entorhinal cortex during aging from the second decade. The modest changes in total muscarinic binding, which appeared to reflect those in M1 and M3 + 4 rather than M2 binding, were a rise in the entorhinal cortex between the foetal stage and childhood and a tendency for receptors to fall with age in the hippocampus and subicular complex. These findings implicate mechanisms controlling the expression of nicotinic receptors to a greater extent than muscarinic receptors in postnatal development and aging in the human hippocampus.     

Comparative study of the recovery of silver(I) from aqueous solutions with different chelating resins derived from glycidyl methacrylate

Glycidyl methacrylate (GMA) was polymerized in the presence of divinylbenzene (DVB). The GMA/DVB resin was immobilized with different chelating moieties containing nitrogen or sulfur donor atoms. The resins obtained [an amino‐bearing resin (RI), an amino/thiocarbamate‐bearing resin (RII), a triazole‐bearing resin (RIII), and an amino/thiol‐bearing resin (RIV)] were tested toward the recovery of Ag(I) from its aqueous solutions. The adsorption behavior of Ag(I) and the resin regeneration were studied. The sulfur‐containing resins showed higher uptake and lower elution efficiency than those containing nitrogen. The maximum uptake values were 1.20, 1.33, 1.40, and 2.86 mmol/g for RI, RII, RIII, and RIV, respectively. The mechanism of interaction between Ag(I) and the resins is also suggested. Regeneration was achieved with a 0.5N thiourea solution, acidified thiourea, or 0.5N H₂SO₄, where the resins were stable over five cycles. Elution efficiencies of 94–96 and 90–93% were achieved for the nitrogen‐ and sulfur‐containing resins, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 806–812, 2005     

Sequential addition of temperature-sensitive missense mutations into the PB2 gene of influenza A transfectant viruses can effect an increase in temperature sensitivity and attenuation and permits the rational design of a genetically engineered live influenza A virus vaccine

We have previously described a strategy for the recovery of a synthetic influenza A virus wild-type (wt) PB2 gene (derived from influenza A/Ann Arbor/6/60 [AA] virus) into an infectious virus. It was possible to introduce an attenuating temperature-sensitive (ts) mutation at amino acid residue 265 of the AA wt PB2 gene and to rescue this mutant gene into infectious virus. Application of this new technology to influenza A virus vaccine development requires that multiple attenuating mutations be introduced to achieve a satisfactorily attenuated virus that retains the attenuation (att) phenotype following replication in vivo. In this report, we demonstrate that putative ts mutations at amino acids 112, 556, and 658 each indeed specify the ts and att phenotypes. Each of these mutations was introduced into a cDNA copy of the AA mutant mt265 PB2 gene to produce three double-mutant PB2 genes, each of which was rescued into an infectious virus. In general, the double-mutant PB2 transfectant viruses were more ts and attenuated in the lower respiratory tracts of hamsters than the single-mutant transfectant viruses, and the ts phenotype of two of three double-mutant PB2 transfectant viruses was stable even after prolonged replication in the upper respiratory tracts of immunocompromised mice. Two triple-mutant PB2 transfectant viruses with three predicted amino acid substitutions resulting from five nucleotide substitutions in the cDNA were then generated. The triple-mutant PB2 transfectant viruses were more ts and more attenuated than the double-mutant PB2 transfectant viruses. These results indicate that sequential introduction of additional ts mutations into the PB2 gene can yield mutants that exhibit a stepwise increase in temperature sensitivity and attenuation compared with the preceding mutant(s) in the series. Furthermore, the level of temperature sensitivity of the transfectant viruses correlated significantly with the level of attenuation of these viruses in hamsters. Although the triple-mutant PB2 transfectant viruses were attenuated in hamsters, intranasal administration of these viruses elicited a vigorous serum hemagglutination-inhibiting antibody response, and this was associated with resistance of the lower respiratory tract to subsequent wt virus challenge. These observations suggest the feasibility of using PB2 reverse genetics to generate a live influenza A virus vaccine donor strain that contains three attenuating mutations in one gene. It is predicted that reassortant viruses derived from such a donor virus would have the properties of attenuation, genetic stability, immunogenicity, and protective efficacy against challenge with wt virus.     

Intratumoral chemotherapy with a sustained-release drug delivery system inhibits growth of human pancreatic cancer xenografts

This study provides the first evidence that treatment of human pancreatic adenocarcinoma is markedly improved by the intratumoral administration of chemotherapeutic agents in a novel drug delivery system. The effect of chemotherapeutic agents delivered in a sustained-release, protein-based, injectable gel was evaluated on the growth of human pancreatic adenocarcinoma cell line, BxPC-3. In vitro chemosensitivity of BxPC-3 cells exposed for 24 or 72 h to fluorouracil (0.01-5 mM), cisplatin or doxorubicin (0.1-50 microM) and floxuridine, vinblastine, mitomycin or paclitaxel (1.0-100 microM) was compared with that of untreated cells. In vitro chemosensitivity was also studied with fluorouracil and mitomycin in the poorly differentiated PANC-1, human pancreatic cancer cell line. Survival was determined after 7-10 days. All drugs decreased cell growth in a dose-dependent fashion. The efficacy of fluorouracil, cisplatin and doxorubicin increased with prolonged exposure, rendering these drugs most appropriate for a sustained-release preparation. For in vivo studies, athymic nude mice bearing BxPC-3 xenografts were treated either with fluorouracil, cisplatin or doxorubicin in the therapeutic injectable gel containing epinephrine or with vehicle alone administered intratumorally on days 1 and 4. After 28 days, the mice were sacrificed and tumors dissected and weighed. Tumors in mice treated with the injectable gel decreased in size by 72-79% compared with tumors in untreated controls and tumors treated with vehicle alone. Intratumoral injection of drug solution and intraperitoneal injection of drug in the injectable gel did not change tumor size compared with controls. In a drug-retention study, mice were injected intratumorally with [3H]fluorouracil either in the injectable gel or in solution. Sustained radioactivity was observed in tumors injected with the gel, and, conversely, greater radioactivity was detected in the liver and kidneys in mice receiving the radiolabeled solution. These results suggest that the therapeutic injectable gel chemotherapy, when given intratumorally, may improve tumor response with less systemic toxicity in comparison with conventional systemic chemotherapy.     

Decreased capacity for type-specific-antigen synthesis accounts for high prevalence of nontypeable strains of group B streptococci in Mexico

The low incidence of group B streptococcal (GBS) invasive neonatal disease in Mexico has been attributed to the low prevalence of serotype III strains, a major serotype in developed countries. In addition, nontypeable strains account for 12% of the isolates in Mexico and < 1% of the isolates in the United States. In this study, 57 GBS isolates (28 nontypeable by the Lancefield procedure) from carrier and infected neonates and women from Mexico were also examined for the presence of type-specific antigen by an enzymatic procedure using N-acetylmuramidase digestion of the cell wall to release soluble type-specific antigen. Of the 28 nontypeable strains from Mexico, 23 were typeable by the enzyme extraction procedure, with serotype III being the predominant serotype in invasive disease. These results suggest that nontypeable isolates of GBS should be further examined by the enzymatic extraction procedure to determine the presence of type-specific antigen. Furthermore, these limited results suggest that serotype III is likely a major serotype in invasive disease also in Mexico.     

Novel high-performance liquid chromatographic assay using fluorescence detection for the quantitation of plasma gamma-methylene-10-deazaaminopterin and its major metabolite, 7-hydroxy-gamma-methylene-10-deazaaminopterin, in patients with solid cancers in a phase I trial

Gamma-methylene-10-deazaaminopterin (MDAM), a unique dihydrofolate reductase inhibitor, has demonstrated antitumor activity against a broad spectrum of human solid tumors in preclinical studies. A novel reversed-phase, ion-pair high-performance liquid chromatography (HPLC) assay that uses fluorescence detection has been developed to quantitate levels of MDAM and its major metabolite, 7-hydroxy-gamma-methylene-10-deazaaminopterin (7-OH-MDAM), in human plasma. The recovery of MDAM and 7-OH-MDAM from plasma was >97% by a simple one-step deproteinization process using tetrabutylammonium bromide (TBABr) and methanol. MDAM and 7-OH-MDAM remained stable in plasma over a 28-day test period at ambient temperatures, and neither compound was light-sensitive. The limit of quantitation was 0.005 microM for both MDAM and 7-OH-MDAM. This assay has been found to be simple, sensitive and reproducible in determining plasma concentrations of MDAM and 7-OH-MDAM in patients with solid cancers in a phase I trial.     

Effect of reduced myristoylated alanine-rich C kinase substrate expression on hippocampal mossy fiber development and spatial learning in mutant mice: transgenic rescue and interactions with gene background

The myristoylated alanine-rich C kinase substrate (MARCKS) is a prominent protein kinase C (PKC) substrate in brain that is expressed highly in hippocampal granule cells and their axons, the mossy fibers. Here, we examined hippocampal infrapyramidal mossy fiber (IP-MF) limb length and spatial learning in heterozygous Macs mutant mice that exhibit an approximately 50% reduction in MARCKS expression relative to wild-type controls. On a 129B6(N3) background, the Macs mutation produced IP-MF hyperplasia, a significant increase in hippocampal PKCepsilon expression, and proficient spatial learning relative to wild-type controls. However, wild-type 129B6(N3) mice exhibited phenotypic characteristics resembling inbred 129Sv mice, including IP-MF hypoplasia relative to inbred C57BL/6J mice and impaired spatial-reversal learning, suggesting a significant contribution of 129Sv background genes to wild-type and possibly mutant phenotypes. Indeed, when these mice were backcrossed with inbred C57BL/6J mice for nine generations to reduce 129Sv background genes, the Macs mutation did not effect IP-MF length or hippocampal PKCepsilon expression and impaired spatial learning relative to wild-type controls, which now showed proficient spatial learning. Moreover, in a different strain (B6SJL(N1), the Macs mutation also produced a significant impairment in spatial learning that was reversed by transgenic expression of MARCKS. Collectively, these data indicate that the heterozygous Macs mutation modifies the expression of linked 129Sv gene(s), affecting hippocampal mossy fiber development and spatial learning performance, and that MARCKS plays a significant role in spatial learning processes.