Search PubMed⌕ Search

Biomedical subjects

C Koch

Publications and source records attributed to C Koch.

At least 415 records · Page 23Linked to original sources
PubMed1985

Effects of phenytoin, phenobarbital, and valproic acid, alone and in selected combinations, on schedule-controlled behavior of rats.

The present study examined the effects of phenytoin (20, 30, 40, and 50 mg/kg), phenobarbital (10, 20, 30, and 40 mg/kg), and valproic acid (80, 120, 160, and 240 mg/kg), and those of phenobarbital (10 and 30 mg/kg) combined with phenytoin (20, 30, and 40 mg/kg) or valproic acid (80, 120, and 160 mg/kg), on the lever pressing of rats maintained under fixed-ratio and interresponse-time-greater-than-t schedules of food delivery. High doses of each individual drug significantly decreased mean group response (and reinforcement) rate under the fixed-ratio schedule. No dose of an individual agent significantly affected mean group response rate under the interresponse-time-greater-than-t schedule, although high doses of phenobarbital and valproic acid significantly reduced the mean group reinforcement rate under this schedule. When given in combination, phenobarbital and phenytoin and phenobarbital and valproic acid significantly reduced response (and reinforcement) rate under the fixed-ratio schedule and reinforcement rate under the interresponse-time-greater-than-t schedule. These reductions did not significantly differ in magnitude from those predicted by an additive model of drug interaction.

Animals↗
PubMed1985

A simple algorithm for solving the cable equation in dendritic trees of arbitrary geometry.

We present an efficient algorithm for solving the one-dimensional cable equation in the Laplace (frequency) domain for an arbitrary linear membrane. This method, a reformulation and extension of the geometrical calculus developed by Butz and Cowan (1974), solves for the transfer impedance between any two points in a branched cable structure of arbitrary geometry (but without loops) by the repetitive application of four simple equations. Such an algorithm is used to analyze the electrical behaviour of nerve cells with highly branched dendritic trees. The algorithm can be implemented using a language such as C, PASCAL or LISP and runs on small machines.

Cell Membrane↗
PubMed1985

G inversion in bacteriophage Mu DNA is stimulated by a site within the invertase gene and a host factor.

The Gin function of bacteriophage Mu catalyzes inversion of the G DNA segment, thus switching the host range of Mu phage particles. This site-specific recombination event takes place between inverted repeat sequences (IR) that border the G segment. Sequences in the Mu beta region extending approximately from position 118 to 178 are essential for efficient inversion. In cis this region, termed sis, stimulates inversion about 15-fold. Neither the relative orientation of sis with respect to the IR sequences nor the distance to IR substantially influences the stimulatory effect. For full activity purified Gin protein must be supplemented with crude host factor from E. coli K12. We suggest that, in addition to Gin, a DNA-binding host protein is required for efficient G inversion.

Bacterial Proteins↗
PubMed1985

Imipenem/cilastatin treatment of multiresistant Pseudomonas aeruginosa lung infection in cystic fibrosis.

Ten patients with cystic fibrosis and chronic broncho-pulmonary Pseudomonas aeruginosa infection received 45 mg imipenem/cilastatin per kg body weight/day, intravenously for two weeks. The treatment was safe with only minor side effects and clinical parameters improved considerably during therapy. In all patients resistance of Ps. aeruginosa to imipenem developed in the second week of treatment; in seven patients the therapy selected for a resistant strain and in three resistance developed in the original strain. The resistance persisted after cessation of treatment and thus the clinical usefulness of imipenem/cilastatin as monotherapy in CF-patients with Ps. aeruginosa seems to be limited.

Adolescent↗
PubMed1985

Analysis of chickens for recombination within the MHC (B-complex).

In an attempt to further map the chicken MHC (the B complex), a systematic search for genetic recombinants within the B complex was performed by serotyping the progeny from F2 crosses of chickens by means of specific anti-class I, anti-class II, and anti-class IV alloantisera. Two recombinant B-haplotypes (B21r and B15r) were found by analysing 2,656 F2 chickens representing 5,312 informative typings. In either case, the B-G (class IV) allele was recombined with both the B-F and B-L alleles of the opposite haplotype. MLC typings, tests for direct compatibility by GVH reactions, and absorption analyses confirmed the original serological typing of the two recombinant B haplotypes. No recombination between B-F (class I) and B-L (class II) loci was found. This very low frequency of recombination within the B complex as compared with recombination frequencies found in mammalian MHC's is discussed.

Animals↗
PubMed1985

Frequency of Aspergillus fumigatus isolates and antibodies to aspergillus antigens in cystic fibrosis.

The frequency of Aspergillus fumigatus isolates from sputum was assessed prospectively during a 22-month period in 156 patients with cystic fibrosis (CF) from one center, and findings were compared to a cross-sectional evaluation of specific IgG and IgA antibodies, occurrence of chronic Pseudomonas aeruginosa infection, and pulmonary function. The prevalence rate for the 22-month period was 40%. Positive A. fumigatus cultures appeared to be independent of the presence or duration of chronic bronchopulmonary Ps. aeruginosa infection, but isolation of A. fumigatus in patients with pseudomonas infection for more than 5 years was associated with notably decreased pulmonary function. Levels of IgG antibodies to a 470,000 daltons A. fumigatus antigen fraction were higher in patients with positive cultures in the observation period than in those without. IgG antibodies to a 25,000-50,000 daltons antigen fraction were directly correlated to A. fumigatus frequency in patients with positive cultures both prior to and during the survey. On the other hand, levels of IgA antibodies to the 470,000 daltons fraction were inversely related to A. fumigatus frequency, suggesting a role of IgA antibodies in the bronchial clearance of aspergilli. Decreased pulmonary function was found to be associated with elevated levels of A. fumigatus antibodies. It is concluded that immune reactions elicited by A. fumigatus may play a role in clearance of the fungus from the airways but also may contribute to lung morbidity in some patients.

Adolescent↗
PubMed1985

Shifts in selective visual attention: towards the underlying neural circuitry.

Psychophysical and physiological evidence indicates that the visual system of primates and humans has evolved a specialized processing focus moving across the visual scene. This study addresses the question of how simple networks of neuron-like elements can account for a variety of phenomena associated with this shift of selective visual attention. Specifically, we propose the following: (1) A number of elementary features, such as color, orientation, direction of movement, disparity etc. are represented in parallel in different topographical maps, called the early representation. (2) There exists a selective mapping from the early topographic representation into a more central non-topographic representation, such that at any instant the central representation contains the properties of only a single location in the visual scene, the selected location. We suggest that this mapping is the principal expression of early selective visual attention. One function of selective attention is to fuse information from different maps into one coherent whole. (3) Certain selection rules determine which locations will be mapped into the central representation. The major rule, using the conspicuity of locations in the early representation, is implemented using a so-called Winner-Take-All network. Inhibiting the selected location in this network causes an automatic shift towards the next most conspicious location. Additional rules are proximity and similarity preferences. We discuss how these rules can be implemented in neuron-like networks and suggest a possible role for the extensive back-projection from the visual cortex to the LGN.

Attention↗
PubMed1984

Assay for the specificity of monoclonal antibodies in crossed immunoelectrophoresis.

A method is described based on crossed immunoelectrophoresis of a complex antigen mixture in agarose gel followed by incubation of the gel with the monoclonal antibody. The bound monoclonal antibody is detected by the use of a secondary enzyme-labelled antibody. Using this technique we have been able to identify the precipitate arc in crossed immunoelectrophoresis of major histocompatibility complex (MHC) class I molecules in a mixture of all detergent solubilized cell membrane molecules by means of a monoclonal antibody, the specificity of which was known independently to be against MHC class I molecules. In other experiments using the same technique we demonstrated the reaction of a monoclonal antibody specific for chicken Ig light chains.

Animals↗
PubMed1984

Cable theory in neurons with active, linearized membranes.

This investigation aims at exploring some of the functional consequences of single neurons containing active, voltage dependent channels for information processing. Assuming that the voltage change in the dendritic tree of these neurons does not exceed a few millivolts, it is possible to linearize the non-linear channel conductance. The membrane can then be described in terms of resistances, capacitances and inductances, as for instance in the small-signal analysis of the squid giant axon. Depending on the channel kinetics and the associated ionic battery the linearization yields two basic types of membrane: a membrane modeled by a collection of resistances and capacitances and membranes containing in addition to these components inductances. Under certain specified conditions the latter type of membrane gives rise to a membrane impedance that displays a prominent maximum at some nonzero resonant frequency fmax. We call this type of membrane quasi-active, setting it apart from the usual passive membrane. We study the linearized behaviour of active channels giving rise to quasi-active membranes in extended neuronal structures and consider several instances where such membranes may subserve neuronal function: 1. The resonant frequency of a quasi-active membrane increases with increasing density of active channels. This might be one of the biophysical mechanisms generating the large range over which hair cells in the vertebrate cochlea display frequency tuning. 2. The voltage recorded from a cable with a quasi-active membrane can be proportional to the temporal derivative of the injected current. 3. We modeled a highly branched dendritic tree (delta-ganglion cell of the cat retina) using a quasi-active membrane. The voltage attenuation from a given synaptic site to the soma decreases with increasing frequency up to the resonant frequency, in sharp contrast to the behaviour of passive membranes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

B-L antigens (class II) of the chicken major histocompatibility complex control T-B cell interaction.

The detailed study of the genetic control of T-B cell interactions in the chicken has been hampered by the lack of defined major histocompatibility complex (MHC) recombinant chicken lines. In the present study we have used some recently described MHC recombinant chicken lines separating regions encoding antigens that are homologous to class I and class II antigens of mammals in adoptive bursa cell transfer experiments, in which bursa cells from newly hatched chicks were transplanted into cyclophosphamide (Cy)-treated chicks. Subsequent immunizations of the recipients with a thymus-dependent antigen (SRBC) and a thymus-independent antigen (Brucella abortus) showed that the generation of germinal centers in the spleen and the production of antibodies to SRBC required identity between donor and recipient class II antigens (B-L antigens), whereas response to Brucella antigen did not require identity at any of the known MHC loci of the chicken. The results thus reveal that also in the chicken class II (B-L) region genes encode cell-surface glycoproteins that serve as restriction elements in T-B cell cooperation.

Animals↗
PubMed1984

Activation of vertebrate complement by Helix pomatia haemolymph.

Haemolymph plasma from the pulmonate snail Helix pomatia contains a constituent, not yet identified, which causes activation of vertebrate complement via the alternative complement pathway in fluid phase. The activation of vertebrate complement by snail plasma is closely analogous to the activation caused by cobra venom factor (CVF), the snake's C3b, with one notable exception; the snail factor requires vertebrate C3 for the formation of C3 convertase which cobra venom factor does not. Our results do not allow any definite conclusion on the exact mechanism but we favour the idea that the haemolymph contains a complement-like protein which functions as an opsonin in the snail, and which can interact with vertebrate alternative complement pathway components.

Animals↗
PubMed1984

A clinical comparison of aerosol and powder administration of beclomethasone dipropionate in childhood asthma.

Forty children with childhood asthma were conducted through a double-blind cross-over study to compare the effect of 400 micrograms beclomethasone dipropionate administered as aerosol and powder (Rotacaps). Children with severe asthma derived more benefit from the steroid administered as aerosol judged from their peak flow performance in the morning, although neither evening peak flow nor symptom scores revealed any difference. It is concluded that the Rotacaps are an advantageous supplement to available medication for the treatment of asthmatic children, although it should be observed that, using equal amounts of BDP, powder administration seems less effective than aerosol.

Adolescent↗
PubMed1984

Bacterial histamine release by immunological and non-immunological lectin-mediated reactions.

The mechanisms of bacteria-induced histamine release were examined in vitro in human leukocytes and rat mast cells. Three types of bacterial responders were found. In persons with IgE-bearing basophilocytes bacterial histamine release could be triggered by two different mechanisms, an IgE-dependent mechanism where removal of IgE abolished the release and a non-immunological mechanism where this was not the case. In responders with no IgE-bearing cells bacterial histamine release was caused by a non-immunological mechanism. The non-immunological mechanism was further substantiated by release in isolated mast cells from germ-free rats. These experiments suggest a direct interaction between bacteria and target cell, and experiments with multi-washed bacteria and bacteria cell wall preparations indicate the possibility of the bacteria wall interacting with the target cell. It is probable that the non-immunological mechanism depends on lectin-mediated reactions, since bacteria-induced histamine release was inhibited by lectin-binding sugars as is release caused by plant lectins.

Basophils↗
PubMed1984

Interaction of human IgG preparations with polymorphonuclear leukocytes in vitro.

The effect of purified human immunoglobulin G, prepared for intravenous administration by polyethylene glycol precipitation and ion exchange chromatography, on polymorphonuclear leukocytes (PMN) in vitro was studied. IgG induced a dose-dependent stimulation of the oxidative metabolism of the cells, as measured by release of superoxide anion and by chemiluminescence. The lowest concentration giving a detectable effect was 0.001 mg/ml. Two commercially available preparations of IgG for clinical intravenous use caused similar stimulation of the PMN although they differ in methods of isolation and purification. The addition of 10% maltose markedly reduced the stimulation by all three preparations of IgG. We suggest that i.v. infusion of purified IgG may lead to activation in vivo of host phagocytic cells without participation of complement, and that this interaction may be responsible for the hitherto unexplained side-effects caused by i.v. infusion of such preparations.

Energy Metabolism↗
PubMed1984

Methylprednisolone resistance of cystic fibrosis lymphocytes.

In the current study, the in vitro viability and resistance to methylprednisolone (MP) was investigated in lymphocytes from patients with cystic fibrosis (CF) and normal controls. The addition of MP to phytohemagglutinin-stimulated lymphocyte cultures inhibits the proliferative response in a dose-dependent way. The dose response curves to MP were similar in CF cultures and controls (P greater than 0.05). Neither preincubation nor pulse exposure to MP revealed any difference between normal and CF lymphocytes. Skin fibroblasts from patients with CF have been reported to show increased resistance to the toxic effect of dexamethasone (1-3, 5-6). This study was undertaken to investigate the suppressive effect of glucocorticoids on another cell culture system using MP on phytohemagglutinin-stimulated lymphocytes.

Adolescent↗