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Biomedical subjects

R Chase

Publications and source records attributed to R Chase.

At least 19 recordsLinked to original sources
PubMed2000

Structure and function in the cerebral ganglion.

Evidence is reviewed to evaluate whether the term "brain is justified in referring to the snail's cerebral ganglion. The focus of the review is terrestrial species, with particular attention given to the genus Helix. In accordance with a standard definition of "brain, the cerebral ganglion is found to be differentiated both structurally and functionally. It receives convergent sensory inputs from a variety of anterior sensory organs plus the posterior body wall. Its outputs comprise motor commands directed towards anterior muscle systems, e.g., the tentacles and the penis, as well as premotor commands directed towards executory centers in other ganglia, e.g., the buccal, visceral, and pedal ganglia. Of the three major divisions in the ganglion, the procerebrum and the mesocerebrum are the most differentiated, whereas the metacerebrum is the least differentiated. The specializations of the procerebrum for olfactory functions, and the mesocerebrum for reproductive functions, reflect the importance of adaptations for feeding and mating in the evolution of the Gastropoda.

Animals↗
PubMed2000

Synapse distribution of olfactory interneurons in the procerebrum of the snail Helix aspersa.

The procerebrum is believed to be important for processing olfactory information and storing olfactory memories in terrestrial pulmonate molluscs. Previous results have demonstrated that the procerebral cell population is morphologically heterogeneous. In the present study, serial sections and electron microscopy were used to investigate differences in synapse distributions. The results demonstrate that procerebral neurons with different sites of arborization have distinct patterns of synapse distribution that probably reflect different functional contributions to the olfactory pathway. Cells that have all their arborizations in the procerebrum, but none in the internal mass, have multiple large varicosities that are specialized for output. On the other hand, cells that arborize in the internal mass or outside the procerebrum have mostly input synapses proximal to the soma and mostly output synapses in the terminal region of the neurites. These cells appear to transmit information from the procerebral cell body mass to other central nervous system regions, e.g., the internal mass and the mesocerebrum. The implications of these data are twofold. Firstly, the procerebrum directly participates in distributing processed olfactory information to more central regions of the nervous system. Secondly, the procerebral neuronal population may be divisible into two subgroups: 1) intrinsically arborizing interneurons; and 2) projection neurons. This is significant because the neural organization of the procerebrum may now be compared with that of olfactory systems in other organisms.

Animals↗
PubMed2000

A conserved location for the central nervous system control of mating behaviour in gastropod molluscs: evidence from a terrestrial snail.

We have investigated the role of the right mesocerebrum in the expression of mating behaviour in the garden snail Helix aspersa. Using an in vivo stimulation and recording technique, we provide evidence for both sensory and motor functions in the mesocerebral neuronal population. Some neurones were specifically sensitive to tactile stimuli delivered to the skin on the superior tentacles and around the genital pore. Electrical stimulation of the right mesocerebrum evoked genital eversion and, in combination with tactile stimulation, dart-shooting and penial eversion. Genital eversions were also elicited by injections of APGWamide. During courtship, one recorded unit increased its activity only in correlation with penial eversion, while six other units increased their activity only during dart-shooting. Three additional units increased their activity during both types of behaviour. In addition, most of the recorded units showed increased neuronal activity during times of contact with a partner. Comparison of our results with available data from other molluscs leads us to conclude that the right anteromedial region of the cerebral ganglion is an evolutionarily conserved region of the gastropod brain specialised for the control of male mating behaviour. It is striking to find such functional conservation in the central nervous system of phylogenetically distant gastropods given the large differences in behaviour during mating.

Animals↗
PubMed1999

Nucleoside triphosphatase and RNA helicase activities associated with GB virus B nonstructural protein 3.

GB virus B (GBV-B) is a positive-stranded RNA virus that belongs to the Flaviviridae family. This virus is closely related to hepatitis C virus (HCV) and causes acute hepatitis in tamarins (Saguinus species). Nonstructural protein 3 (NS3) of GBV-B contains sequence motifs predictive of three enzymatic activities: serine protease, nucleoside triphosphatase (NTPase), and RNA helicase. The N-terminal serine protease has been characterized and shown to share similar substrate specificity with the HCV NS3 protease. In this report, a full-length GBV-B NS3 protein was expressed in Escherichia coli and purified to homogeneity. This recombinant protein was shown to possess polynucleotide-stimulated NTPase and double-stranded RNA (dsRNA) unwinding activities. Both activities were abolished by a single amino acid substitution, from the Lys (K) residue in the conserved walker motif A (or Ia) "AXXXXGK(210)S" to an Ala (A), confirming that they are intrinsic to GBV-B NS3. Kinetic parameters (K(m) and k(cat)) for hydrolysis of various NTPs or dNTPs were obtained. The dsRNA unwinding activity depends on the presence of divalent metal ions and ATP and requires an RNA duplex substrate with 3' unpaired regions (RNAs with 5' unpaired regions only or with blunt ends are not suitable substrates for this enzyme). This indicates that GBV-B NS3 RNA helicase unwinds dsRNA in the 3' to 5' direction. Direct interaction of the GBV-B NS3 protein with a single-stranded RNA was established using a gel-based RNA bandshift assay. Finally, a homology model of GBV-B NS3 RNA helicase domain based on the 3-dimensional structure of the HCV NS3 helicase that shows a great similarity in overall structure and surface charge distribution between the two proteins was proposed.

Acid Anhydride Hydrolases↗
PubMed1999

A novel recombinant single-chain hepatitis C virus NS3-NS4A protein with improved helicase activity.

Hepatitis C virus (HCV) nonstructural protein 3 (NS3) has been shown to possess protease and helicase activities and has also been demonstrated to spontaneously associate with nonstructural protein NS4A (NS4A) to form a stable complex. Previous attempts to produce the NS3/NS4A complex in recombinant baculovirus resulted in a protein complex that aggregated and precipitated in the absence of nonionic detergent and high salt. A single-chain form of the NS3/NS4A complex (His-NS4A21-32-GSGS-NS3-631) was constructed in which the NS4A core peptide is fused to the N-terminus of the NS3 protease domain as previously described (Taremi et al., 1998). This protein contains a histidine tagged NS4A peptide (a.a. 21-32) fused to the full-length NS3 (a.a. 3-631) through a flexible tetra amino acid linker. The recombinant protein was expressed to high levels in Escherichia coli, purified to homogeneity, and examined for NTPase, nucleic acid unwinding, and proteolytic activities. The single-chain recombinant NS3-NS4A protein possesses physiological properties equivalent to those of the NS3/NS4A complex except that this novel construct is stable, soluble and sixfold to sevenfold more active in unwinding duplex RNA. Comparison of the helicase activity of the single-chain recombinant NS3-NS4A with that of the full-length NS3 (without NS4A) and that of the helicase domain alone suggested that the presence of the protease domain and at least the NS4A core peptide are required for optimal unwinding activity.

Amino Acid Sequence↗
PubMed1998

Serine protease of hepatitis C virus expressed in insect cells as the NS3/4A complex.

Hepatitis C virus (HCV) protease NS3 and its protein activator NS4A participate in the processing of the viral polyprotein into its constituent nonstructural proteins. The NS3/4A complex is thus an attractive target for antiviral therapy against HCV. We expressed the full-length NS3 and NS4A in insect cells as a soluble fusion protein with an N-terminal polyhistidine tag and purified the two proteins to homogeneity. Cleavage at the junction between HisNS3 and NS4A occurs during expression, producing a noncovalent complex between HisNS3 and NS4A with a subnanomolar dissociation constant. We purified the HisNS3/4A complex by detergent extraction of cell lysate and by metal chelate chromatography. We removed the His tag by thrombin cleavage and then further purified the complex by gel filtration. The purified NS3/4A complex is active in a protease assay using a synthetic peptide substrate derived from the NS5A-NS5B junction, with kcat/K(m) of 3700 (+/- 600) M-1 s-1, an order of magnitude above those previously reported for NS3 expressed by other strategies. This high protease activity implies that the full-length sequences of NS3 and NS4A are required for optimal activity of the NS3 protease domain. We examined the dependence of the NS3/4A protease activity on buffer conditions, temperature, and the presence of detergents. We find that, under most conditions, NS3 protease activity is dependent on the aggregation state of the NS3/4A complex. The monodisperse, soluble form of the NS3/4A complex is associated with the highest protease activity.

Adenosine Triphosphatases↗
PubMed1998

Heterogeneity of the hippocampus: effects of subfield lesions on locomotion elicited by dopaminergic agonists.

Structural abnormalities in the hippocampal formation and overactive dopamine neurotransmission in the ventral striatum are thought to be key pathologies in schizophrenia. This experiment examined the functional contribution of different hippocampal subfields to locomotion elicited by D-amphetamine (0.32-3.2 mg/kg) and the direct agonists quinpirole (0.025-0.5 mg/kg) and SKF 38393 (2.5-15.0 mg/kg). Male rats served as unoperated controls or received one of six different lesions (hippocampal formation, fimbria-fornix, subiculum, CA3-4, entorhinal cortex or dentate gyrus (DG)). The main results indicated that extensive ibotenic acid-induced lesions of the hippocampal formation, or colchicine-induced lesions of the DG enhanced locomotion elicited by the D2 agonist quinpirole. Electrolytic lesions of the fimbria-fornix, in comparison, had much larger effects and resulted in increases in the locomotor response to amphetamine and quinpirole. These results extend previous demonstrations of hippocampal modulation of the ventral striatum by showing that this modulatory influence is dependent on both the location and total extent of cell loss within the hippocampal formation. The results are discussed in relation to the causes of and neurophysiological mechanisms involved in enhanced drug-induced locomotion and in terms of their implications for mental diseases including schizophrenia.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1998

Changes in the reproductive system of the snail Helix aspersa caused by mucus from the love dart.

The function of the love dart in certain species of terrestrial snails is unknown. In Helix aspersa, the dart is a sharp calcareous structure that is used to pierce the partner's skin during courtship. When expelled, the dart is covered with a thick mucus. The hypothesis tested here is that the mucus contains a biologically active substance. Extracts of the digitiform glands that produce this mucus were applied to parts of the reproductive system in vitro. The extracts triggered an initial reconfiguration of the copulatory canal that caused the bursa tract diverticulum to become more accessible to the spermatophore. The reconfiguration of the copulatory canal also closed off the tract leading to the bursa copulatrix, a sperm-digesting organ. A few minutes after the initial contraction, the peristaltic contractions in the diverticulum became significantly more frequent. This latter effect continued for at least 1 h, provided that the mucus extract remained in the saline bath. The minimum effective dosage was less than the 2.2 mg of mucus transferred with the dart. Sperm competition is expected in Helix aspersa since multiple matings occur before eggs are laid. By influencing the female organs involved in the processing of foreign sperm, the dart shooter may increase the chance that his sperm will fertilise eggs.

Animals↗
PubMed1997

Morphology of interneurons in the procerebrum of the snail Helix aspersa.

Terrestrial snails have a highly developed sense of olfaction. Because the procerebrum has a large number of cells and is located at the entry site of the olfactory nerve into the brain, the structure is thought to have a significant role in the processing of olfactory stimuli. The morphology of the procerebral neurons in the snail Helix aspersa was investigated through intracellular injections of biocytin. No formal categorization of neuronal types was possible, but some cells were seen to have neurites entirely intrinsic to the procerebrum, whereas others had both intrinsic and extrinsic arborizations, and still others had only extrinsic arborizations. These interneurons were previously thought to have arborizations restricted to the procerebral lobe. We demonstrated the extent of the neurite projections outside of the procerebral lobe by making focal injections of biocytin or Neurobiotin into various regions of the cerebral ganglion. This technique revealed subsets of cells that send neurites not only in the ipsilateral ganglion but also through the cerebral commissure into the contralateral cerebral ganglion. Our results demonstrate not only that the procerebral cell population is heterogeneous but also that the procerebrum interacts more directly with the rest of the central nervous system than was formerly believed.

Animals↗
PubMed1997

SCH 43478 and analogs: in vitro activity and in vivo efficacy of novel agents for herpesvirus type 2.

SCH 43478 and analogs are a class of non-nucleoside antiviral agents that have potent and selective activity against herpes simplex virus type 2 (HSV-2). The IC50 for these compounds in plaque reduction analysis using Vero cells ranges from 0.8 to 2.0 microg/ml. All compounds have a LC50 > 100 microg/ml in cytotoxicity analysis. Mechanism of action studies suggest that these molecules have an effect on the transactivation of viral immediate early (alpha) gene expression. Time of addition studies indicate that antiviral activity of these analogs is limited to the initial 2-3 h after infection and is not due to inhibition of viral adsorption or penetration. Analysis of HSV protein expression demonstrates that SCH 49286 inhibits the accumulation of viral immediate early (alpha) gene products. SCH 43478 demonstrates statistically significant efficacy (P < 0.05) in the guinea pig genital model of HSV infection. Following subcutaneous administration in a therapeutic treatment regimen, SCH 43478 (90 mg/kg/day) is efficacious in reducing the number and severity of lesions and the neurological complications of acute HSV infection. Thus, SCH 43478 and analogs are anti-herpesvirus agents with a unique mechanism of action.

Adsorption↗
PubMed1997

Neural circuit mediating tentacle withdrawal in Helix aspersa, with specific reference to the competence of the motor neuron C3.

The tentacle withdrawal reflex in the terrestrial snail Helix aspersa involves bending and retraction of the tentacles. When elicited by mechanical stimulation of the tentacle, the reflex is mediated by the conjoint action of the central and peripheral nervous systems. The neural circuit underlying the stimulus-response pathways was studied in vitro using a combination of morphological and physiological techniques. Sensory input caused by stimulation of the nose (situated at the superior tentacle's tip) first passes into the tentacle ganglion. Motor fibers are likely excited in the tentacle ganglion to form a peripheral stimulus-response pathway. While still in the tentacle ganglion, the excitation caused by a brief stimulus is transformed into a prolonged neuronal discharge. This modified signal travels, via the olfactory nerve, to the cerebral ganglion where it excites the giant motor neuron C3 along with numerous smaller motor neurons. Afferent input to C3 also arrives from several other sources. The afferent convergence is followed by a marked divergence of C3's output. C3 innervates the muscles mediating both tentacle retraction and tentacle bending through multiple cerebral nerves. Thus C3's pattern of effector innervation allows this single cell to elicit and coordinate both components of the tentacle withdrawal reflex. Lesion experiments indicate that C3 is responsible for 85% of the central contribution to tentacle retraction, though C3 is actually sufficient to mediate maximal muscle contraction as evidenced by intracellular stimulation. In addition to C3, three groups of putative central motor neurons were identified through nerve backfills and nerve recordings. The additional motor neurons mediating tentacle retraction are important for maximizing the rate of muscle contraction, whereas those mediating tentacle bending are likely more important for nondefensive behaviors. These neurons are arranged in parallel with C3, but unlike C3, each of these neurons innervates only a single effector or portion thereof. Given C3's direct innervation of multiple effectors and its sufficiency to evoke strong responses in those effectors, we conclude that C3 is paramount in eliciting and coordinating tentacle withdrawal.

Animals↗
PubMed1996

Comparative morphology of three types of projection-identified pyramidal neurons in the superficial layers of cat visual cortex.

The morphology and dendritic organization of corticocortical neurons in the superficial layers of area 18 that project to area 17 were studied by intracellular injection of lucifer yellow in the fixed-slice preparation. This corticocortical population contains primarily standard pyramidal cells, but occasional nonpyramidal, modified, fusiform, star, and inverted pyramidal cells were also seen. All cell types were present throughout layer 2 and in the upper and middle parts of layer 3. Standard pyramidal cells were found exclusively in lower layer 3. The mean somatic area of the area 17 projecting neurons was 251 microns 2. The width of basal dendritic fields was correlated to cell size for standard pyramidal cells but not for the other cell types. Next, the morphology and dendritic organization of the area 17 projecting neurons were compared to the pyramidal cells of the local horizontal patch networks and of the callosal system. The depth profile of the area 17 projecting and callosal pyramidal groups was virtually identical, peaking at 400 microns from the pial surface, whereas the local patch pyramidal group peaked at 281 microns. The local patch, area 17 projecting, and callosal pyramidal cells displayed increasingly larger mean somatic areas and basilar dendritic field width measurements. The number of basal dendritic branch points was greatest for callosal cells, and it was indistinguishable between local patch and area 17 projecting neurons. In the tangential plane, circular dendritic fields were observed on all callosal cells, but they were found on only approximately half of the local patch and area 17 projecting neurons. The remaining local patch and area 17 projecting neurons displayed mediolaterally and anteroposteriorly elongated basal dendritic fields, respectively.

Animals↗
PubMed1996

Enzymatic characterization of hepatitis C virus NS3/4A complexes expressed in mammalian cells by using the herpes simplex virus amplicon system.

The hepatitis C virus (HCV) NS3 protein possesses three enzymatic activities: an N-terminal serine protease activity, a C-terminal RNA-stimulated NTPase activity, and an RNA helicase activity. To characterize them, the full-length NS3(631)/4A and three C-terminal truncated proteases (NS3(201)/4A, NS3(181)/4A, and NS3(155)/4A were expressed in mammalian cells with HSV amplicon-defective viruses. Our results revealed that all of the NS3/4A proteins produced in mammalian cells (except NS3(155)/4A) are active in processing both cis and trans cleavage sites. Temperature optimization studies revealed that the protease is more active at temperatures ranging from 4 to 25 degrees C and is completely inactive at 42 degrees C. The RNA-stimulated ATPase activity was characterized with a partially purified NS3(631)/4A fraction and has a higher optimal temperature at 37 to 42 degrees C. The effects of detergents on both NS3 protease and RNA-stimulated ATPase were similar. Nonionic detergents such as Triton X-100, Nonidet P-40 and Tween 20 did not affect the activities, while anionic detergents such as sodium dodecyl sulfate and deoxycholic acid were inhibitory. Zwitterionic detergent such as 3-[(3-cholamidopropyl)- dimethyl-ammoniol-1-propanesulfonate (CHAPS) inhibited protease activity at a concentration of 0.5% (8 mM), which had no effect on ATPase activity. Finally, RNA-unwinding activity was demonstrated in the NS3(631)/4A fraction but not in the similarly purified NS3(181)/4A and NS3(201)/4A fractions. NS(363)/4A unwinds RNA duplexes with 3' but not 5' single-stranded overhangs, suggesting that the NS3 RNA helicase functions in a 3'-to-5' direction.

Adenosine Triphosphatases↗
PubMed1995

Correlation of axon projections and peptide immunoreactivity in mesocerebral neurons of the snail Helix aspersa.

The purpose of this investigation was to elucidate the organization of efferent neurons in the mesocerebrum of a terrestrial snail. The mesocerebrum is one of three regions, or lobes, that can be identified by gross inspection. Previous studies have indicated a possible function for the mesocerebrum in the control of mating behavior. We used both anterograde and retrograde tracing methods to determine the axon projections of mesocerebral neurons. Virtually all the neurons (96%) send an axon into the cerebropedal connective nerve, and about 25% of these fibers continue into the nervus cutaneous pedalis primus dexter, which innervates the dart sac. Many neurons have additional axon branches in other nerves, especially the penial nerve, which receives projections from about 25% of mesocerebral cells. Neurons that are backfilled from the nervus cutaneus pedalis primus dexter are predominantly immunoreactive for FMRF amide, whereas neurons that are backfilled from the penial nerve are predominately immunoreactive for APGWamide. These results suggest a functional association between FMRFamide and dart shooting on the one hand, and between APGWamide and penial eversion on the other. Some cells contain both APGWamide and FMRFamide; these cells may have dual projections in both the penial nerve and the nervus cutaneous pedalis primus dexter.

Animals↗
PubMed1993

Tracing neural pathways in snail olfaction: from the tip of the tentacles to the brain and beyond.

The anatomical organization of the olfactory system of terrestrial snails and slugs is described in this paper, primarily on the basis of experiments using the African snail Achatina fulica. Behavioral studies demonstrate the functional competence of olfaction in mediating food finding, conspecific attraction, and homing. The neural substrate for olfaction is characterized by an extraordinarily large number of neurons relative to the rest of the nervous system, and by the fact that many of them are unusually small. There exist multiple serial and parallel pathways connecting the olfactory organ, located at the tip of the tentacle, with integrative centers in the central nervous system. Our methods of studying these pathways have relied on the selective neural labels horseradish peroxidase and hexamminecobaltous chloride. One afferent pathway contains synaptic glomeruli whose ultrastructure is similar to that of the glomeruli seen in the mammalian olfactory bulb and the insect olfactory lobe. All of the olfactory neuropils, but especially the tentacle ganglion, contain large numbers of morphologically symmetrical chemical synapses. The procerebrum is a unique region of the snail brain that possesses further features analogous with olfactory areas in other animal groups. Olfactory axons from the tentacle terminate in the procerebrum, but the intrinsic neurons do not project outside of it. An output pathway from the procerebrum to the pedal ganglion has been identified and found to consist of inter-ganglionic dendrites. The major challenge for future studies is to elucidate the pattern of connectivity within, rather than between, the various olfactory neuropils.

Animals↗
PubMed1992

Effect of the Gulf War on infant and child mortality in Iraq.

BACKGROUND: Increased malnutrition and morbidity among Iraqi children after the onset of the Persian Gulf war have been reported by several fact-finding missions. The magnitude of the effect of the war and the economic embargo on child mortality remains uncertain, however. METHODS: We conducted a survey of 271 clusters of 25 to 30 households each, chosen as a representative sample of the Iraqi population. The households were selected and the interviews conducted by an international team of public health professionals independent of Iraqi authorities. In each household all women 15 to 49 years of age were interviewed, and the dates of birth and death of all children born on or after January 1, 1985, were recorded. RESULTS: The study population included 16,076 children, 768 of whom died during the period surveyed (January 1, 1985, to August 31, 1991). The age-adjusted relative mortality for the period after the war began, as compared with the period before the war, was 3.2 (95 percent confidence interval, 2.8 to 3.7). No material change in the relative risk was observed after adjustment for region of residence, maternal education, and maternal age. The increase in mortality after the onset of the war was higher among children 1 to less than 12 months old (relative risk, 4.1; 95 percent confidence interval, 3.3 to 5.2) and among those 12 to less than 60 months old (relative risk, 3.8; 95 percent confidence interval, 2.6 to 5.4) than among those less than 1 month old (relative risk, 1.8; 95 percent confidence interval, 1.4 to 2.4). The association between the war and mortality was stronger in northern Iraq (relative risk, 5.3) and southern Iraq (relative risk, 3.4) than in the central areas (relative risk, 1.9) or in Baghdad (relative risk, 1.7). CONCLUSIONS: These results provide strong evidence that the Gulf war and trade sanctions caused a threefold increase in mortality among Iraqi children under five years of age. We estimate that more than 46,900 children died between January and August 1991.

Child, Preschool↗
PubMed1992

Synaptic innervation of the giant cerebral neuron in sated and hungry snails.

The giant cerebral neuron (GCN) is a serotoninergic cell that facilitates feeding behaviour in gastropod molluscs. We have examined the morphology of its cerebral arborizations after labelling them by intracellular injection of hexamminecobalt. Observations in the light microscope reveal extensive arborizations, with similar overall distributions, in the terrestrial snails Achatina fulica and Rumina decollata. All the major peripheral nerves terminate within the zone covered by the GCN arbor. In a sample of 370 synapses in which the GCN participated, the GCN was identified as the postsynaptic element in every case, thereby establishing the dendritic nature of the cerebral arborizations. A total of approximately 1,000 synapses contacts the GCN, with no evident regional differences in innervation density. The synaptic membrane of the presynaptic profile is characterized by an agglomeration of small clear vesicles and small dense vesicles. At nonsynaptic membranes there are agglomerations of larger dense and dense core vesicles, suggestive of nonsynaptic release. The dendrites of the GCN also contain vesicles. Starvation for five days (Rumina decollata) caused a significant increase in the proportion of curved synapses relative to flat synapses. This might be a plastic change allowing for a greater efficiency of transmission between sensory afferents and the GCN.

Animals↗