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Biomedical subjects

L A Cooper

Publications and source records attributed to L A Cooper.

At least 19 recordsLinked to original sources
PubMed1996

Male reproductive success of Schistosoma mansoni-infected Biomphalaria glabrata snails.

Infection of Biomphalaria glabrata by Schistosoma mansoni results in a dramatic reduction in the snail's ability to produce eggs. We studied the ability of such parasitically castrated snails to fertilize the eggs of uninfected snails. Pigmented B. glabrata snails (13141 stock) were infected with S. mansoni miracidia and reared individually until they ceased laying eggs. These infected snails were then given the opportunity to mate with uninfected albino (NMRI) snails. Each of the infected snails was paired with a different albino partner each subsequent week. Sperm transfer by the infected snails was evident from the production of pigmented progeny by the uninfected albino snails. Infected snails successfully acted as males for up to 6 wk after parasitic castration had occurred. The duration of allosperm use by uninfected recipients was lengthy, regardless of the infection status of the pigmented sperm donor.

Animals↗
PubMed1995

Brain regions associated with retrieval of structurally coherent visual information.

An object's global, three-dimensional structure may be represented by a specialized brain system involving regions of inferior temporal cortex. This system's role in object representation can be understood by experiments in which people study drawings of novel objects with possible or impossible three-dimensional structures, and later make either possible/impossible object decisions or old/new recognition decisions about briefly flashed studied and non-studied objects. Although object decisions about possible objects are facilitated by prior study, there is no corresponding facilitation for impossible objects, thereby implicating a system that is specifically involved in the representation of structurally coherent visual objects. Here we show, by positron emission tomography (PET), that increases in blood flow in inferior temporal regions are associated with object decisions about possible but not impossible objects, and that there are increases in the vicinity of the hippocampal formation associated with episodic recognition of possible objects.

Brain Mapping↗
PubMed1995

Varieties of visual representation: how are we to analyze the concept of mental image?

This paper presents a selective account of imagery research during the 1970s and 80s, whose chief objective was to establish the functional equivalence of imaginal and perceptual representations. More recent attention to imagery by cognitive neuroscience has extended and solidified this idea of functional equivalence, but it has also introduced conceptual complexities by demonstrating that imagery, like perception and object recognition, may consist of distinguishable subsystems whose representational properties become activated in response to the demands of particular cognitive tasks.

Cognition↗
PubMed1995

Bias in the priming of object decisions: logic, assumption, and data.

R. Ratcliff and G. McKoon (1995) describe 7 experiments that led them to conclude that priming of possible but not impossible objects on the object decision task introduced by D.L. Schacter, L.A. Cooper, & S.M. Delaney (1990) is attributable to explicit memory processes that offset a bias to call studied objects "possible." On the basis of this point, Ratcliff and McKoon (1995) claim to have undermined our hypothesis that a structural description system plays an important role in object decision priming. Ratcliff and McKoon (1995) also offer a general critique of multiple memory systems accounts of priming and explicit memory. Ratcliff and McKoon's (1995) arguments are based on an inaccurate characterization of Schacter et al.'s theoretical position; the evidence for Ratcliff and McKoon's (1995) idea that explicit memory offsets bias is weak, and the central assumptions that underlie both Ratcliff and McKoon's (1995) specific experimental manipulations and their general conclusions are questionable.

Decision Making↗
PubMed1994

Schistosoma mansoni: relationship between low fecundity and reduced susceptibility to parasite infection in the snail Biomphalaria glabrata.

Biomphalaria glabrata snails which were not susceptible as juveniles to infection by Schistosoma mansoni were selectively bred (by self-fertilization) from the highly susceptible NMRI laboratory snail stock. The susceptibility rate among juvenile snails derived from interbreeding NMRI parents was initially 85-95%, but after several generations of selection, less than 5% of exposed snails became infected by the parasite. Selection for low susceptibility also resulted in a large proportion of snails that displayed low fecundity and produced abnormal egg masses. Individual adult snails which were isolated from an interbreeding population of nonselected NMRI snails usually produced well-developed egg masses each containing 15-30 embryos. However, when juvenile snails from this same population were reared in isolation and not allowed to cross-fertilize, many displayed a pattern of low fecundity and abnormal egg production similar to that observed in the selected low susceptible line. Furthermore, it was found that many of the isolated snails which exhibited low egg production were also not susceptible to parasitic infection.

Animals↗
PubMed1993

Schistosoma mansoni: analysis of an unusual infection phenotype in the intermediate host snail Biomphalaria glabrata.

Snails from a B. glabrata stock, selected for nonsusceptibility to the NMRI strain of S. mansoni, exhibited unusual schistosome infections, with multiple sporocysts prominent in the head-foot (foot-sporocysts). When F1 progeny from numerous crosses between well-defined susceptible (S) and resistant (R) parental snails were exposed, 60% of the infected snails also exhibited this unusual phenotype. F1 progeny from S x S snail crosses developed normal infections. Foot-sporocysts usually developed much later than secondary sporocysts of normal infections and before 12 weeks postexposure the tissue reaction surrounding foot-sporocysts was less intense than reactions to sporocysts in other tissues of the body. Cercariae were seen emerging directly from foot-sporocysts. Infection of S x R hybrid progeny by three other strains of S. mansoni also resulted in the production of foot-sporocysts. Development of the foot-sporocyst infection phenotype in progeny from many snail crosses suggests that this phenotype is more common than previously recognized. Over 50% of the F1 progeny from S x R parental crosses developed patent infections, a fact relevant to the possible biological control of schistosomiasis by the introduction of refractory snails into endemic areas.

Animals↗
PubMed1993

Implicit and explicit memory for novel visual objects: structure and function.

Six experiments compared the effects of structural and functional encoding tasks on implicit and explicit memory for novel objects. Implicit memory was assessed with a possible-impossible object decision test, and explicit memory was assessed with a yes-no recognition test. Results revealed that recognition memory was higher after functional than after structural encoding tasks, whereas priming effects on the object decision test were unaffected by the same manipulations. The priming effects that were observed after functional encoding tasks could be attributed to structural analyses that are carried out in the course of making judgments about functional properties of novel objects. Results are consistent with the hypothesis that implicit memory for novel objects depends on a presemantic structural description system that can operate independently of episodic memory.

Adult↗
PubMed1992

Priming and recognition of transformed three-dimensional objects: effects of size and reflection.

In 2 experiments exploring memory for unfamiliar 3-dimensional objects, Ss studied drawings under conditions that encouraged encoding of global object structure. Implicit memory for objects was assessed by a judgment of structural possibility; explicit memory was assessed by recognition. The principal manipulation was the relationship between the sizes or the left-right parities of the studied and tested objects. Priming was observed on the possible-impossible object decision task despite transformations of size or reflection. Recognition, by contrast, was significantly impaired by the transformations. These results suggest that a structural description system constructs representations of objects invariant over size and reflection, whereas a separable episodic system encodes these transformations as properties of an object's distinctive representation in memory.

Adult↗
PubMed1992

Implicit and explicit memory for novel visual objects in older and younger adults.

Two experiments examined effects of aging on implicit and explicit memory for novel visual objects. Implicit memory was assessed with an object decision task in which subjects indicated whether briefly exposed drawings represented structurally possible or impossible objects. Explicit memory was assessed with a yes-no recognition task. On the object decision task, old and young subjects both showed priming for previously studied possible objects and no priming for impossible objects; the magnitude of the priming effect did not differ as a function of age. By contrast, the elderly were impaired on the recognition task. Results suggest that the ability to form and retain structural descriptions of novel objects may be spared in older adults.

Adolescent↗
PubMed1992

Schistosoma mansoni infection in diapausing Biomphalaria glabrata snails: studies of temperature and genetic influences on diapausing behavior.

Snails that are capable of undergoing diapause can circumvent unfavorable environmental conditions, including long periods of drought. Studies were performed to investigate possible temperature and/or genetic factors that may trigger lamella formation and diapausing behavior. The influence of diapause in Biomphalaria glabrata snails on susceptibility to Schistosoma mansoni infection and levels of cercarial production was also investigated. Rearing temperatures of 23 degrees C or higher did not induce lamella formation or diapause, regardless of the parental phenotype. However, substantial percentages of progeny from lamellated or lamellated/diapausing parental snails developed lamellae at 18 degrees C and underwent diapause. Only a small percentage of offspring from nonlamellated parents formed lamellae at this temperature. Juvenile snails exposed just prior to diapause, or immediately following a diapause period of three weeks, were highly susceptible to infection by S. mansoni miracidia. Snails that underwent diapause produced comparable or only slightly fewer cercariae than did nondiapausing snails. These studies indicate that diapause in B. glabrata does little to decrease a snail's ability to act as an intermediate host for S. mansoni or to interrupt the development of the parasite. For these reasons, we believe that greater attention should be given to diapausing snail populations when planning field surveys or mollusciciding programs.

Animals↗
PubMed1992

Schistosoma mansoni infections in neonatal Biomphalaria glabrata snails.

In areas endemic for schistosomiasis, the population dynamics of the snail intermediate hosts have a direct effect on parasite transmission. The present study focused on the potential for neonatal Biomphalaria glabrata snails to become infected with Schistosoma mansoni and to produce cercariae under various conditions. It was found that snails as small as 0.74 mm in shell diameter could survive miracidial penetration and could release cercariae when as small as 1.6 mm in diameter. Cercariae produced by small snails were equally infectious for mice when compared with those shed by larger snails. Likewise, histological examination of neonatally exposed snails revealed normally developing parasites at all stages of infection. It was found that in 2 snail populations expressing either high or low susceptibility to the parasite, peak susceptibility occurred at 25 days of age in both groups. Daily cercarial production for neonatally exposed snails was initially low but increased dramatically as the snails grew, eventually reaching values as high as 2,100 cercariae/snail/day. A moderate to high percentage of snails infected as neonates was eventually capable of simultaneously producing both eggs and cercariae. These studies emphasize the potential importance of neonatal and preadult snails in helping to maintain foci of S. mansoni infection in endemic areas.

Animals↗
PubMed1991

Implicit memory for possible and impossible objects: constraints on the construction of structural descriptions.

Four experiments examined implicit memory or priming effects on an object decision task in which subjects decided whether structurally possible or impossible novel objects could exist in three-dimensional form. Results revealed equivalent levels of priming for possible objects after 1 vs. 4 5-s exposures to the same structural encoding task (Experiment 1) and when objects were studied with a single structural encoding task or 2 different structural encoding tasks (Experiment 3). Explicit memory, by contrast, was greatly affected by both manipulations. However, priming of possible objects was not observed when Ss were given only a single 1-s exposure to perform a structural encoding task (Experiment 2). No evidence for priming of impossible objects was observed in any of the 4 experiments. The data suggest that object decision priming depends on a presemantic structural description system that is distinct from episodic memory.

Attention↗
PubMed1990

Mental representation of three-dimensional objects in visual problem solving and recognition.

Subjects inspected sets of flat, separated orthographic projections of surfaces of potential three-dimensional objects. After solving problems based on these orthographic views, subjects discriminated between isometric views of the same objects and drawings of distractor structures. Recognition of the isometrics, which had never been shown during the problem solving phase of the experiment, was excellent. In addition, recognition of isometrics corresponding to problems that had been solved correctly when presented in orthographic form was significantly superior to recognition of isometrics based on problems solved incorrectly. In Experiment 2, conditions were included in which either orthographic or isometric views functioned as problem solving or recognition displays. Only in the case of orthographic problem solving followed by isometric recognition (Experiment 1) was the superiority of recognition for correctly-solved problems over incorrectly-solved problems obtained. The pattern of results suggests that viewers construct mental representations embodying structural information about integrated, three-dimensional objects when asked to reason about flat, disconnected projections.

Depth Perception↗
PubMed1990

Implicit memory for unfamiliar objects depends on access to structural descriptions.

We investigated implicit memory for unfamiliar objects with a task in which subjects decided whether structurally possible and impossible line drawings could exist in three-dimensional space. In Experiment 1, significant priming effects on object decision performance were observed after encoding of global, three-dimensional object structure but not local, two-dimensional object features. Explicit memory did not differ significantly as a function of global vs. local study processing. In Experiments 2 and 3, elaborative encoding had different effects on object decision and recognition performance, thus providing evidence for functional dissociation between implicit and explicit memory. Stochastic independence between object decision and recognition performance was also observed. Results were consistent with the hypothesis that implicit memory, as indexed by priming on the object decision task, depends on encoding of and access to structural descriptions of objects.

Attention↗
PubMed1989

Re-establishing a life cycle of Schistosoma mansoni from cryopreserved larvae.

To study the feasibility of re-establishing a life cycle of Schistosoma mansoni (NMRI strain) from cryopreserved larvae, schistosomules were suspended in the cryoprotectant 1,2-ethanediol and cryopreserved in liquid nitrogen. Mice were injected intramuscularly with samples thawed after 3 days, 3 wk, or 6 mo in liquid nitrogen storage. Two to 5% of the cryopreserved larvae and approximately 18% of corresponding unfrozen control larvae developed into adult worms. Infectivity did not decrease as a function of storage time. The adult worms showed no structural damage or changes in overall size and morphology when examined by light and transmission electron microscopy. Female worms derived from cryopreserved larvae had the same or slightly elevated egg production as controls, but tissue egg distributions were comparable. Subsequent passages through Biomphalaria glabrata snails and mice revealed no difference in snail prepatent death rate, percentage of snails infected, cercarial production per snail, or cercarial infectivity.

Animals↗
PubMed1984

Differentiation and melanin production in hyaline and pigmented strains of Microdochium bolleyi.

The effect of various compounds on growth, melanin biosynthesis and cell differentiation was studied in a hyaline (SH25) and a pigmented (SH25B) strain of Microdochium bolleyi. Dark pigment production by the hyaline strain was induced by the presence of DOPA and indole in the medium, both of which are intermediates in the tyrosine pathway of melanin biosynthesis. These substrates also induced conidia and chlamydospore production, structures which were not normally seen in the hyaline strain. The systemic fungicide, tricyclazole, inhibited melanin synthesis in the pigmented strain but not the development of chlamydospore-like cell structures.

Aminobenzoates↗
PubMed1984

The induction of mycelial development in Aureobasidium pullulans (IMI 45533) by yeast extract.

Germ tube and subsequent mycelial development from yeast-like and swollen cells of Aureobasidium pullulans (IMI 45533) was induced by yeast extract in defined liquid medium. This morphogenetic transition was dependent on inoculum size; pH effects were not involved and once mycelial development was induced in the cells it continued even in the absence of yeast extract. The progeny of mycelium and future generations were unaffected by yeast extract. Cessation of germination was not due to any obvious medium changes but appeared to be partly due to the production of a germination inhibitor, which could also be produced by control cells grown in the absence of yeast extract.

Culture Media↗