Erythrocyte aging and malaria

The human malaria parasite, Plasmodium falciparum, ages the red blood cell during its intracellular development. During this process of erythrocyte senescence the parasitized cell becomes less dense and deformable, its biconcave disc shape becomes more spherical and is covered with microscopic protuberances (knobs); the amounts of membrane cholesterol and phospholipids are altered and phosphatidylserine (PS) is externalized. The malaria-infected cell is osmotically fragile, more permeable to a wide variety of molecules via new permeation pathways (NPP), and there is surface deposition of immunoglobulins and complement. There are declines in sialic acid, reduced glutathione, tocopherol and ATP. Hemichromes are deposited on the inner surface of the red cell membrane and there is clustering of the anion transporter, band 3 protein, as well as exposure of neoantigens which contribute to antigenic variation and adhesivity of the parasitized erythrocyte. These time-dependent changes result from oxidative assault and a combination of factors, including a decline in levels of anti-oxidants and ATP coupled with an enhanced flux of ions especially calcium. Despite these parasite-induced age effects P. falciparum is able to avoid destruction by splenic removal through microvessel sequestration in the deep tissues via PS, clustered band 3 protein and adhesive neoantigens.

Cytoadherence of the malaria-infected erythrocyte membrane to C32 melanoma cells after merozoites are released from parasitized infected cells

Infections with the human malaria parasite Plasmodium falciparum are characterized by cytoadherence of infected erythrocytes to the venular endothelium of several organs. Video microscopy studies have shown that at the end of the asexual life of P. falciparum, the residual body containing haemozoin is released to the extracellular environment along with merozoites, leaving behind an infected erythrocyte "ghost". It is possible that these infected erythrocyte "ghosts" could remain sequestered within the blood vessels of patients infected with P. falciparum even after merozoites have been released from infected erythrocytes. In this study an in vitro cytoadherence assay was developed to show that infected erythrocyte "ghosts" can interact with C32 melanoma cells. Adherent infected erythrocyte "ghosts" contain some of the subcellular compartments of the malaria-infected red blood cell such as the tubo-vesicular membrane network and remnants of the parasitophorous vacuolar membrane, but lack haemozoin.

Release of merozoites from Plasmodium falciparum-infected erythrocytes could be mediated by a non-explosive event

Little is known about the molecular mechanism underlying the release of merozoites from malaria-infected erythrocytes. In the present study, video microscopy was carried out, and images throughout the process of merozoite release from Plasmodium falciparum-infected erythrocytes were digitized and analyzed. Merozoites were shown to escape from the infected host cell in about 1 s through a single site of the infected erythrocyte membrane, whose dimension was estimated to be 2.5 microm. Merozoites were released together with the residual body containing hemozoin, leaving behind a membranous structure that persisted even after an extended period of observation. Densitometric measurements showed that the cytoplasmic content of the infected erythrocyte did not diffuse out as parasites were released, but was gradually lost thereafter. This would indicate that the release of merozoites from infected erythrocytes is not mediated by an explosive event.

Identification of two nonglycosylated polypeptides of Taenia solium recognized by immunoglobulins from patients with neurocysticercosis

An immunoprecipitation technique using biotin-labeled proteins of Taenia solium was developed to identify antigens recognized by immunoglobulins from patients with neurocysticercosis. Six major polypeptides of 100, 70, 50, 42, 35, and 24 kDa were recognized by cerebrospinal fluid from most serologically positive patients. All polypeptides except the 70- and 35-kDa antigens were retained on a lentil-lectin chromatography column and were recognized by lentil lectin in an overlay assay. The 70- and 35-kDa antigens were not labeled with biotin hydrazide, indicating that saccharide residues are not present in these two polypeptides. Furthermore, the 70- and 35-kDa antigens were recognized by antibodies of more than 86% of patients serologically positive for neurocysticercosis as opposed to none of the patients afflicted with other neuropathologies of the central nervous system. This finding indicates that immunodiagnosis of neurocysticercosis can be carried out with antigens different from those used in the standard enzyme-linked immunoelectrotransfer assay.

The mere exposure effect in patients with Alzheimer's disease

The mere exposure effect was examined in patients with mild to moderate Alzheimer's disease (AD). Twenty patients and 20 elderly controls judged the physical characteristics of faces. Implicit memory was tested later by presenting pairs of faces (old and new) and asking participants which faces they liked better. Patients and controls exhibited above chance preference for previously exposed faces. Experiment 2 evaluated whether the preserved implicit memory of patients was mediated by explicit memory. Patients and controls again judged faces but then later chose which faces they had seen before. Patients exhibited impaired recognition memory compared to controls. These findings suggest that a mere exposure effect for unfamiliar faces is present in mild to moderate AD. The results are discussed in terms of perceptual and conceptual priming and relatively spared occipital lobe functioning in early AD.

The mere exposure effect in patients with Alzheimer's disease

The mere exposure effect was examined in patients with mild to moderate Alzheimer's disease (AD). Twenty patients and 20 elderly controls judged the physical characteristics of faces. Implicit memory was tested later by presenting pairs of faces (old and new) and asking participants which faces they liked better. Patients and controls exhibited above chance preference for previously exposed faces. Experiment 2 evaluated whether the preserved implicit memory of patients was mediated by explicit memory. Patients and controls again judged faces but then later chose which faces they had seen before. Patients exhibited impaired recognition memory compared to controls. These findings suggest that a mere exposure effect for unfamiliar faces is present in mild to moderate AD. The results are discussed in terms of perceptual and conceptual priming and relatively spared occipital lobe functioning in early AD.

Identification of peripheral membrane proteins associated with the tubo-vesicular network of Plasmodium falciparum infected erythrocytes

During intracellular development of the malarial parasite numerous membranous vesicles appear in the infected erythrocyte cytoplasm between the parasitophorous vacuolar membrane (PVM) and the erythrocyte plasma membrane. In this study we describe the characterization of a monoclonal antibody which recognizes two major parasite-encoded proteins of 50 and 41 kDa. Immunofluorescence and immunoelectron microscopy demonstrated that the monoclonal antibody reacts with cytoplasmic vesicles of Plasmodium falciparum infected erythrocyte referred to as Maurer's clefts. The antigens recognized by the monoclonal antibody were expressed very early during the erythrocytic life cycle of the parasite, and remained tightly associated within membrane vesicles even after merozoites are released from infected erythrocytes. The antigens were partially soluble in non-ionic detergents, and were released from the membrane by alkali treatment, indicating that the proteins recognized by the monoclonal antibody are peripheral membrane proteins. It is proposed that the 50 and 41 kDa antigens might be part of an underlying membrane skeletal network that provides structural support to vesicles and tubules present in the infected erythrocyte cytoplasm.

Identification of novel membrane structures in Plasmodium falciparum infected erythrocytes

Little is known about the molecular mechanisms underlying the release of merozoites from malaria infected erythrocytes. In this study membranous structures present in the culture medium at the time of merozoite release have been characterized. Biochemical and ultrastructural evidence indicate that membranous structures consist of the infected erythrocyte membrane, the parasitophorous vacuolar membrane and a residual body containing electron dense material. These are subcellular compartments expected in a structure that arises as a consequence of merozoite release from the infected cell. Ultrastructural studies show that a novel structure extends from the former parasite compartment to the surface membrane. Since these membrane modifications are detected only after merozoites have been released from the infected erythrocyte, it is proposed that they might play a role in the release of merozoites from the host cell.

Remembering the earthquake: direct experience vs. hearing the news

Three groups of informants--two in California, one in Atlanta--recalled their experiences of the 1989 Loma Prieta earthquake shortly after the event and again 11/2 years later. The Californians' recalls of their own earthquake experiences were virtually perfect. Even their recalls of hearing the news of an earthquake-related event were very good: much higher than Atlantan recalls of hearing about the quake itself. Atlantans who had relatives in the affected area remembered significantly more than those who did not. These data show that personal involvement in the quake led to greatly improved recall, but do not show why. Many Californian informants reported low levels of stress/arousal during the event; arousal ratings were not significantly correlated with recall. The authors suggest that repeated narrative rehearsals may have played an important role.

Therapeutic suggestion has not effect on postoperative morphine requirements

This study was designed to confirm the effect of therapeutic intraoperative auditory suggestion on recovery from anesthesia, to establish the effect of preoperative suggestion, and to assess implicit memory for intraoperative information using an indirect memory task. Sixty consenting unpremedicated patients scheduled for elective gynecologic surgery were randomly divided into three equal groups: Group 1 received a tape of therapeutic suggestions preoperatively, and the story of Robinson Crusoe intraoperatively; Group 2 heard the story of Peter Pan preoperatively and therapeutic suggestions intraoperatively; Group 3 heard the Crusoe story preoperatively and the Peter Pan story intraoperatively. A standardized anesthetic technique was used with fentanyl, propofol, isoflurane, and nitrous oxide. After surgery, all patients received patient-controlled analgesia (PCA) with a standardized regimen. In the 24 h postsurgery, morphine use was recorded every 6 h and at 24 h an indirect memory test (free association) was used to test for memory of the stories. Anxiety scores were measured before surgery and at 6 and 24 h postsurgery. There were no significant differences between groups for postoperative morphine use, pain or nausea scores, anxiety scores, or days spent in hospital after surgery. Seven of 20 patients who heard the Pan story intraoperative gave a positive association with the word "Hook," whereas 2 of 20 who did not hear the story gave such an association. Indirect memory for the Pan story was established using confidence interval (CI) analysis. (The 95% CI for difference in proportion did not include zero). No indirect memory for the Crusoe story could be demonstrated. This study did not confirm previous work which suggested that positive therapeutic auditory suggestions, played intraoperatively, reduced PCA morphine requirements. In contrast, a positive implicit memory effect was found for a story presented intraoperatively.

Source memory in mild to moderate Alzheimer's disease

This research examined whether source memory is preserved in patients with mild to moderate Alzheimer's disease (AD). In Experiment 1, AD patients and normal elderly controls recalled true facts (information acquired outside of the experimental setting) and made-up facts (information acquired in the experiment), and they determined the source of these memories. Relative to controls, AD patients recalled fewer facts, but when they remembered this information, they attributed their learning to the correct source. In Experiment 2, memory of made-up facts was equated between groups by incorporating a 1-week recall delay for the controls. Again, AD patients accurately determined whether facts were learned inside or outside of the experiment. However, both groups performed at chance in terms of their memory for whether a made-up fact was read on a card or told by the examiner. The findings indicate relative preservation of source memory in the earliest stages of AD and are discussed in terms of methodological problems in testing source memory in impaired groups and in terms of frontal-lobe functioning.

Crystal structure of the repetitive segments of spectrin

The elongated proteins of the spectrin family (dystrophin, alpha-actinin, and spectrin) contain tandemly repeated segments and form resilient cellular meshworks by cross-linking actin filaments. The structure of one of the repetitive segments of alpha-spectrin was determined at a 1.8 angstrom resolution. A segment consists of a three-helix bundle. A model of the interface between two tandem segments suggests that hydrophobic interactions between segments may constrain intersegment flexibility. The helix side chain interactions explain how mutations that are known to produce hemolytic anemias disrupt spectrin associations that sustain the integrity of the erythrocyte membrane.

Indirect memory during anesthesia. The effect of midazolam

BACKGROUND

The preservation of implicit memory function during anesthesia is controversial, with conflicting results appearing in the literature. This study was designed to elucidate the effect of midazolam as part of an anesthetic technique on implicit memory function during anesthesia. Using a prospective randomized, double-blind study design, performance in three tasks (category generation, free association, and homophone spelling) was assessed.

METHODS

Forty-eight consenting patients were assigned to two equal groups, to receive 2 mg intravenous midazolam or normal saline before induction of anesthesia. Anesthesia was induced with fentanyl and propofol and maintained with isoflurane 1.3 MAC until incision and isoflurane 1.0 MAC in 70% nitrous oxide thereafter. Fentanyl was used for supplementation of anesthesia. During anesthesia, one of two 50-min tapes containing the test material was played to each patient on a portable cassette player. In the postanesthesia care unit and 48 h after surgery, patients were engaged in three tasks by an observer unaware of the treatment group or tape.

RESULTS

No significant main effect of priming or midazolam was observed in any of the tasks. In the word-association task, an interaction was observed between priming and treatment group (F = 9.62, P < .01) due to negative priming in the placebo group.

CONCLUSIONS

The lack of a main effect of priming in any of the three tasks is consistent with the conclusion that indirect memory was not demonstrated for events occurring during the standard anesthetic conditions of this study. Further, midazolam appeared to have no effect.

The complete sequence of Drosophila beta-spectrin reveals supra-motifs comprising eight 106-residue segments

The alpha and beta chains of spectrin are homologous, yet they have acquired different structural features that work in synergy to give the multimer its overall properties. The primary amino acid sequence of each spectrin subunit is dominated by tandemly repeated 106-residue motifs. By comparing the complete Drosophila beta-spectrin sequence with other spectrins we have discovered evidence that a higher-order, 848-amino acid supra-motif is tandemly repeated in both alpha- and beta-spectrin. These data argue that alpha- and beta-spectrin, rather than evolving independently from sequences encoding the ancestral 106-residue motifs, must have arisen after the establishment of a large supra-motif composed of eight of the 106-residue motifs. Our data suggest the segment structure of a progenitor gene that gave rise to both alpha- and beta-spectrin as well as dystrophin. The structural differences that evolved after the split between the alpha- and beta-spectrin genes confer the independent functions that exist in their products today.

Phasing the conformational unit of spectrin

Many proteins contain a repetitive sequence motif, which implies that they contain a repetitive structural motif. Spectrin and the related proteins dystrophin and alpha-actinin consist largely of repeated motifs of 100-120 residues. But the repeating motif is degenerate and it has been difficult to define the boundaries of the repeating sequence unit or its corresponding structural unit. We have determined at which residues the structural units that correspond to spectrin's repeating 106-amino acid motifs begin and end. Drosophila alpha-spectrin cDNAs were expressed in bacteria to show that single segments (106 amino acids) and pairs of segments encoded by selected regions of spectrin cDNA can fold into stable conformations whose biophysical and biochemical properties are similar to those of native spectrin. Because such folding was critically dependent on the phasing of the expressed sequence with respect to the apparent boundaries of the repeating motifs, our data provide experimental evidence that relates the boundaries of the folded, conformational unit to the chemical sequence of repeating motifs.

Indirect assessment of memory for music during anesthesia

STUDY OBJECTIVE

To obtain evidence for intraoperative registration of auditory information in patients undergoing elective surgery.

DESIGN

Within-subject design with three levels of frequency of exposure to music.

SETTING

A university hospital and a university language laboratory.

PATIENTS

Thirty-four patients scheduled for elective surgery and 20 healthy undergraduate psychology students.

INTERVENTIONS

Selections of instrumental ethnic music were played to patients for 0, 3, or 12 exposures in one experiment and for 0, 6, or 24 exposures in another study. The undergraduates heard 0, 3, or 12 exposures of the music while awake.

MEASUREMENTS AND MAIN RESULTS

Forty-eight hours after hearing the music, all subjects were tested on their preference for the selections they had heard as well as selections they had not heard. For the patients, the mean preference ratings (in millimeters, mm) on a visual analog scale following 0, 3, and 12 exposures were 73.3 mm, 74.0 mm, and 65.1 mm, respectively, a nonsignificant difference. For the patients who were exposed to the music 0, 6, and 24 times, the mean preference ratings were 64.4 mm, 66.1 mm, and 70.6 mm, respectively, a nonsignificant difference. For the waking participants, the mean preference ratings following 0, 3, and 12 exposures were 55 mm, 66.2 mm, and 62.5 mm, respectively, a significant difference (p less than 0.05).

CONCLUSIONS

The anesthetized patients did not exhibit indirect memory for music played intraoperatively, at least to the extent required to demonstrate an exposure effect.

Antigens on the Plasmodium falciparum infected erythrocyte surface are not parasite derived

After invasion by Plasmodium falciparum a red blood cell undergoes marked alterations to its morphology and physiological properties. There are two schools of thought on the origin of these modifications: in the first of this pair of articles, Irwin Sherman and Enrique Winograd put the case for the changes to the surface proteins of the red cell being parasite-induced modifications to host proteins. They suggest that changes to naturally occurring host red cell proteins, especially band 3, result in subtle changes to the antigenicity, cytoadherence and to some extent to the morphology of infected red cells.

Naturally occurring anti-band 3 autoantibodies recognize a high molecular weight protein on the surface of Plasmodium falciparum infected erythrocytes

Naturally occurring anti-band 3 autoantibodies bind to erythrocytes infected with a knobby variant of the human malaria Plasmodium falciparum (FCR-3 strain). The autoantibodies recognized a greater than 240 kDa protein in SDS extracts made from surface iodinated infected erythrocytes. The antigen was associated only with erythrocytes infected with a knobby variant, and was removed by trypsin treatment of intact infected cells. By two-dimensional peptide map analysis the antigen was shown to be structurally related to the human erythrocyte anion transporter, band 3.

Characterization of a modified red cell membrane protein expressed on erythrocytes infected with the human malaria parasite Plasmodium falciparum: possible role as a cytoadherent mediating protein

Infections with the human malaria Plasmodium falciparum are characterized by the retention of parasitized erythrocytes in tissue capillaries and venules. Erythrocytes containing trophozoites and schizonts attach to the endothelial cells that line these vessels by means of structurally identifiable excrescences present on the surface of the infected cell. Such excrescences, commonly called knobs, are visible by means of scanning or transmission electron microscopy. The biochemical mechanisms responsible for erythrocyte adherence to the endothelial cell are still undefined. In an attempt to identify the cytoadhesive molecule on the surface of the infected cell, we have prepared monoclonal antibodies to knob-bearing erythrocytes infected with the FCR-3 strain of P. falciparum. One of these monoclonal antibodies, designed 4A3, is an IgM that reacts (by means of immunofluorescence) with the surface of unfixed erythrocytes bearing mature parasites of the knobby line; it does not react with knobless lines or uninfected erythrocytes. By immunoelectron microscopy the monoclonal antibody 4A3 was localized to the knob region. In an in vitro cytoadherence assay, the monoclonal antibody partially blocked the binding of knob-bearing cells (FCR-3 strain) to formalin-fixed amelanotic melanoma cells. The monoclonal antibody was used to immunoprecipitate a protein from extracts of knobby erythrocytes that had been previously surface iodinated. By a two-dimensional peptide mapping technique, the antigen recognized by the monoclonal antibody was found to be structurally related to band 3 protein, the human erythrocyte anion transporter.

Expression of senescent antigen on erythrocytes infected with a knobby variant of the human malaria parasite Plasmodium falciparum

Erythrocytes infected with a knobby variant of Plasmodium falciparum selectively bind IgG autoantibodies in normal human serum. Quantification of membrane-bound IgG, by use of 125I-labeled protein A, revealed that erythrocytes infected with the knobby variant bound 30 times more protein A than did noninfected erythrocytes; infection with a knobless variant resulted in less than a 2-fold difference compared with noninfected erythrocytes. IgG binding to knobby erythrocytes appeared to be related to parasite development, since binding of 125I-labeled protein A to cells bearing young trophozoites (less than 20 hr after parasite invasion) was similar to binding to uninfected erythrocytes. By immunoelectron microscopy, the membrane-bound IgG on erythrocytes infected with the knobby variant was found to be preferentially associated with the protuberances (knobs) of the plasma membrane. The removal of aged or senescent erythrocytes from the peripheral circulation is reported to involve the binding of specific antibodies to an antigen (senescent antigen) related to the major erythrocyte membrane protein band 3. Since affinity-purified autoantibodies against band 3 specifically bound to the plasma membrane of erythrocytes infected with the knobby variant of P. falciparum, it is clear that the malaria parasite induces expression of senescent antigen.

Reminding as a basis for temporal judgments

In the normal course of events, some events bring to mind earlier events. This reminding or, in the context of list learning experiments, study-phase retrieval can serve as a basis for the accurate judgment of the relative recencies of the two events in question. In this article, evidence for this position is presented in three experiments. By manipulations of encoding using visual imagery instructions and word associations, appropriate conditions were arranged for reminding to occur. The results of all three studies support the position that reminding provides a direct basis for later judgments of the relative recency of events.

Reminding as a basis for temporal judgments

In the normal course of events, some events bring to mind earlier events. This reminding or, in the context of list learning experiments, study-phase retrieval can serve as a basis for the accurate judgment of the relative recencies of the two events in question. In this article, evidence for this position is presented in three experiments. By manipulations of encoding using visual imagery instructions and word associations, appropriate conditions were arranged for reminding to occur. The results of all three studies support the position that reminding provides a direct basis for later judgments of the relative recency of events.

Aging and the picture superiority effect in recall

One recurrent theme in the literature on aging and memory is that the decline of memory for nonverbal information is steeper than for verbal information. This research compares verbal and visual encoding using the picture superiority effect, the finding that pictures are remembered better than words. In the first experiment, an interaction was found between age and type of material; younger subjects recalled more pictures than words while older subjects did not. However, the overall effect was small and two further experiments were conducted. In both of these experiments, the picture superiority effect was found in both age groups with no interaction. In addition, performing a semantic orienting task had no effect on recall. The finding of a picture superiority effect in older subjects indicates that nonverbal codes can be effectively used by subjects in all age groups to facilitate memory performance.

Elaboration and distinctiveness in memory for faces

This research attempts to account for the finding that faces that have been judged with reference to traits such as honesty or friendliness are better remembered than faces judged with respect to a physical feature. Four experiments are reported in which the orienting task engaged in by the subjects was controlled. The first two experiments support an elaboration hypothesis that it is the amount rather than the type of information encoded that accounts for the observed effect. Experiments 3 and 4 provide evidence that elaborative encoding is effective because the likelihood of a distinctive feature being encoded increases with the degree of elaboration. The role of distinctiveness is emphasized.

List differentiation with varied trials on both lists

Differentiation, defined as the discrimination of list membership, was studied with a recognition procedure. In each of the two studies, the number of learning trials was varied for one list and the trials on the other list were held constant. Differentiation was a U-shaped function of trials, passing through a minimum when both lists were shown equally often.