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Biomedical subjects

S Knapp

Publications and source records attributed to S Knapp.

At least 19 recordsLinked to original sources
PubMed1991

Identification of a virulence-associated antigen of Toxoplasma gondii by use of a mouse monoclonal antibody.

A monoclonal antibody generated against the mouse-lethal RH strain of Toxoplasma gondii was developed. Tachyzoites of virulent and avirulent T. gondii isolates grown in permanent macrophage cell cultures were examined for differences in reactivity with this antibody. Virulence of these Toxoplasma isolates was quantified by injecting different numbers of tachyzoites into NMRI mice and observing the animals for signs of infection or death. The monoclonal antibody identified a 23-kDa antigen expressed by the mouse-lethal strains BK and RH, whereas this antigen was not detected in low-mouse-virulent strains, which were all clinical isolates from Europe. Using Western blot (immunoblot), immunofluorescence, and immunoelectron microscopy, we localized the 23-kDa antigen to the membrane compartment. From these results, we suggest that this 23-kDa antigen is a marker of strain virulence upon which a virulence classification of T. gondii may be based.

Animals↗
PubMed1990

Structures of a spiro[3.3]heptane and a related dispiro[3.1.3.1]decane derivtive.

2,2,6,6-Tetrakis(mesyloxymethyl)spiro[3.3]heptane (1), C15H28O12S4, Mr = 528.64, triclinic, P1, a = 10.319 (1), b = 14.233 (2), c = 8.5187 (9) A, alpha = 97.87 (1), beta = 104.08 (1), gamma = 98.86 (1) degrees, V = 1179.0 (6) A3, Z = 2, Dm = 1.46 (1), Dx = 1.489 Mg m-3, lambda(Mo K alpha) = 0.71073 A, mu = 0.44 mm-1, F(000) = 556, T = 298 (1) K, R = 0.036 for 2411 reflections. Diethyl 8,8-bis(mesyloxymethyl)dispiro[3.1.3.1]decane-2,2-dicarboxyl ate (2) C20H32O10S2, Mr = 496.60, triclinic, P1, a = 12.168 (1), b = 16.789 (2), c = 5.9411 (6) A, alpha = 90.416 (8), beta = 94.294 (9), gamma = 87.590 (9) degrees, V = 1209.2 (4) A3, Z = 2, Dm = 1.35 (1), Dx = 1.364 Mg m-3, lambda(Mo K alpha) = 0.71073 A, mu = 0.26 mm-1, F(000) = 528, T = 292 (1) K, R = 0.037 for 2530 reflections. The cyclobutane rings in both structures are puckered. Dihedral angles of these rings in the spiroheptane derivative (1) [12.9 (7) and 21.2 (5) degrees], and in the end rings of the dispirodecane derivative (2) [18.9 (5) and -18.5 (4) degrees], are significantly smaller than that for the central cyclobutane ring in (2) [29.0 (3) degrees]. Ring puckering in (2) gives the molecule a decided bow shape when viewed normal to the best plane of the central four-membered ring.

Models, Molecular↗
PubMed1990

Sensitive analysis of plasma physostigmine levels using dual-cell electrochemistry in the redox mode.

A column liquid chromatographic method using dual-electrode, redox electrochemical detection has been developed for measuring plasma and cerebrospinal fluid physostigmine levels. The method is suitable for detecting drug levels in a geriatric population following oral ingestion of sustained-release physostigmine preparations and for determining the pharmacokinetics of these preparations in biological fluids.

Administration, Oral↗
PubMed1990

A new assay for invasion of HeLa 229 cells by Bordetella pertussis: effects of inhibitors, phenotypic modulation, and genetic alterations.

Invasion and intracellular survival of Bordetella pertussis in HeLa 229 cells was studied by a new assay that utilizes polymyxin B instead of gentamicin to rapidly kill extracellular organisms. Invasion measured by this assay was time and temperature dependent and was inhibited by the microfilament drug cytochalasin D. The invasion process was also dependent on a functional vir locus (also known as bvg), the positive regulator of virulence gene expression in B. pertussis. Four spontaneous Vir- phase variants of B. pertussis and a mutant with a transposon insertion mutation in the vir locus did not invade. Cells that were environmentally modulated and thus did not express virulence determinants also did not invade. Two Vir- mutants, a vir-directed plasmid insertion mutant and a UV-light-induced mutant, were capable of invasion, although they did not produce other known virulence factors such as pertussis toxin and hemolysin but did produce small amounts of filamentous hemagglutinin (FHA) and the 69-kilodalton outer membrane protein. None of 70 Tn5 IS50L::phoA (TnphoA) insertion mutants of strain Bp18323 (including three mutants defective in FHA) tested showed any reproducible defect in invasion. A mutant carrying a site-directed deletion mutation in FHA was also capable of invasion in our assay. These data suggest that there is redundancy in the invasion functions of B. pertussis and that one or more of these are coordinately regulated with FHA and the 69-kilodalton outer membrane protein more tightly than with other vir-activated gene products.

Bacterial Proteins↗
PubMed1990

Evidence that modulation requires sequences downstream of the promoters of two vir-repressed genes of Bordetella pertussis.

Gene expression in Bordetella pertussis is altered by environmental signals in a process called antigenic modulation. In the presence of modulating signals, expression of several known virulence factors and outer membrane proteins is coordinately reduced. From a bank of TnphoA fusions, we have identified five genes whose expression profiles are reciprocal of those of the major virulence determinants; that is, alkaline phosphatase activity is maximal during growth in the presence of the modulators nicotinic acid and MgSO4 (S. Knapp and J. J. Mekalanos, J. Bacteriol. 170:5059-5066, 1988). We have called these loci vir-repressed genes (vrg). Two of these gene fusions (vrg-6 and vrg-18) have been cloned in Escherichia coli, returned on low-copy-number plasmids to several strains of B. pertussis, and found to be regulated similarly to the fusions harbored on the chromosome. Deletions of the two vrg promoters were constructed and returned to B. pertussis. Regulation was maintained even when all but 24 nucleotides upstream of the vrg-18 initiation codon and 60 nucleotides upstream of the vrg-6 initiation codon were deleted, suggesting that cis-acting regulatory elements of these genes lie very near or within the coding region. We observed a 21-base palindromic sequence overlapping an 8-base direct repeat within the signal sequence coding region of vrg-6; insertion of a 6-bp linker in this region abolished regulation. These repetitive sequences are also at the site of greatest primary sequence identify between vrg-6 and vrg-18 and correspond to the signal sequence coding region. We propose models that involve recognition of this region by a vir-regulated gene product.

Alkaline Phosphatase↗
PubMed1990

[Sterility therapy of women in the course of time].

In all eras and cultures infertility has been regarded as one of the worst female diseases. Consequently, infertility investigation has always been one of the central diagnostic and therapeutic problems in medicine. We have attempted a summary of the tremendous evolution of infertility investigation and therapy, culminating in the modern concept of investigation and therapy of the infertile couple as a unit.

Female↗
PubMed1979

Conformational influences on brain tryptophan hydroxylase by submicromolar calcium: opposite effects of equimolar lithium.

Tryptophan hydroxylase from rat midbrain, EGTA-pretreated and dialyzed, manifested allosteric properties with respect to its substrate tryptophan, cofactor tetrahydrobiopterin, and the calcium ion. Kinetic studies suggest two preferred enzyme conformations in the presence of low concentrations of the cosubstrates: a higher affinity form manifesting hyperbolic substrate kinetics, induced by submicromolar (0.4--0.8 microM) calcium in vitro and cocaine in vivo, and a lower affinity form exaggerating cooperativity with respect to substrate, induced by submicromolar (0.4 to 0.8 microM) lithium in vitro and lithium in vivo. Lithium's effect on serotonin biosynthesis may be due to its antagonism of the positive effector influence of calcium on tryptophan hydroxylase, either as a negative effector or by blocking the calcium site.

Animals↗
PubMed1976

Histologic and enzymatic studies of the mesolimbic and mesostriatal serotonergic pathways.

Selective lesions of the dorsal (B7), median (B8), or lateral (B9) raphe nuclei were made stereotaxically in male rats 4 weeks before sacrifice. The extent of damage to each raphe nucleus was quantified histologically by means of a simplified formaldehyde histochemical method for visualization of serotonin in cryostat sections. A detailed mapping of the distribution of the yellow-fluorescent raphe perikarya provided the basis for quantification. Tryptophan hydroxylase activity was measured in 6 forebrain regions from each animal, and the results were correlated with the per cent damage to each raphe nucleus. Tyrosine hydroxylase was also assayed in 5 of these regions; it was not significantly affected by any of the raphe lesions. Dorsal raphe lesions reduced tryptophan hydroxylase activity in the striatum, thalamus, cortex, and hypothalamus, but not in the septal nuclei or hippocampus. Damage to B8 resulted in decrements in this serotonergic enzyme in the septal nuclei, hippocampus, cortex, and hypothalamus, but not in the striatum or thalamus. Lesions of the scattered B9 cells had no significant effect on enzyme activity in any region examined. These data suggest that the dorsal and median raphe nuclei provide two distinct though perhaps overlapping serotonergic systems innervating different parts of the forebrain: a mesostriatal pathway originating in B7 and a mesolimbic system derived from B8. Behavioral studies on the animals, which are presented in a companion paper, indicated that damage to the median nucleus is responsible for many of the behavioral effects previously reported after combined lesions of both major raphe nuclei.

Animals↗
PubMed1976

A neurobiological model for the symmetrical prophylactic action of lithium in bipolar affective disorder.

By treating rats with lithium chloride or cocaine hydrochloride, or lithium chloride followed by cocaine hydrochloride, we have shown the antagonistic effects of these drugs on two mechanisms that may be involved in regulating serotonin 5-HT) synthesis in the striate cortex. Lithium chloride (5 to 10 meq/kg/day) stimulates the relative velocity of the active uptake of labelled tryptophan and proportionally enhances the conversion of labelled tryptophan to 5-HT in synaptosomally enriched preparations. With continued administration of lithium chloride, the activity of tryptophan hydroxylase from the median raphe and subsequently in lysed synaptosomal preparations from striate cortex is reduced; the substrate uptake remains enhanced, but the conversion of substrate to transmitter returns to control levels. In contrast, an injection of cocaine hydrochloride inhibits the high affinity uptake of tryptophan, reducing the conversion of the amino acid to 5-HT and resulting in an increase in the biosynthetic enzyme activity. However, administration of cocaine hydrochter three daily lithium chloride injections (10 meq/kg) results in no apparent effects on substrate uptake, conversion, or enzyme activity. We theorize that the effect of lithium was to push two regulatory parameters (the uptake of substrate and the enzyme activity) to their respective functional upper and lower limits, leaving the serotonergic neurons "buffered" against the "usual" effects of the stimulant drug, and offer this neurobiological model for consideration in relation to the clinical effects of lithium in the prophylaxis of both mania and depression in some patients.

Animals↗