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Biomedical subjects

K Jordan

Publications and source records attributed to K Jordan.

At least 19 recordsLinked to original sources
PubMed1992

Effects of the nootropic AWD 52-39 on the blood-brain transfer of leucine, choline and glucose in rats after 14-d exposure to ethanol.

The transport of the neutral amino acid L-leucine as well as of choline and D-glucose across the blood-brain barrier (BBB) of male Wistar rats was studied after 14-day exposure to ethanol and treatment with the nootropic drug AWD 52-39 (1). After ethanol exposure the half-saturation constant (Km) and the maximum velocity of transport (Vmax) declined in the majority of the investigated brain regions. Also, the treatment elicited a regionally different increase of the permeability-surface area (PS) product of choline (between 10% and 33%) and glucose (between 12% and 27%). The changes in the blood-brain transfer of the three compounds were diminished or prevented by additional application of 1. The cerebral blood flow was increased by the exposure to ethanol by maximally 44%. After additional administration of 1 the changes were reversed and the blood flow reached control values. In addition, the activity of the enzyme acetylcholine esterase was determined in the striatum and the hippocampus. After ethanol exposure the enzyme activity declined by 32%. It was less diminished after treatment with 1. The latter effects let assume that the changes of the BBB permeability elicited by ethanol and 1 are related to alterations of brain metabolism.

Acetylcholinesterase↗
PubMed1991

Spatial resolution in SPECT: influence of measurement set-up and reconstruction parameters.

The ability of a tomographic system to detect small lesions and to assess them quantitatively is affected by several performance parameters, among them spatial resolution in the transverse slice and in the axial direction. This study was done to determine reconstructed resolution under clinical conditions for various parameters, i.e. radius of rotation, radial position within the transverse field of view, and amount of smoothing in the reconstruction process (various reconstruction filters and a Metz prefilter). The axial resolution is independent of the reconstruction filter but depends on the prefilter, the radius of rotation (ROR), and the source position. The transaxial resolution is dependent on the reconstruction filter, the prefilter, the ROR, and the source position. The reconstructed resolution and the system resolution were compared and differences between both are discussed.

Humans↗
PubMed1990

Canine IAPP cDNA sequence provides important clues regarding diabetogenesis and amyloidogenesis in type 2 diabetes.

Islet amyloid polypeptide (IAPP) is a recently discovered pancreatic islet hormone which is stored with insulin in beta cell granules. IAPP may have a significant role in the development of Type 2 diabetes mellitus due to its propensity to form islet cell-disrupting amyloid deposits, and by opposing the action of insulin in peripheral tissues. Most evidence to-date suggests that an intrinsic structural motif of IAPP is linked to the amyloidogenicity of IAPP, and that this motif occurs only in those species (e.g., humans and cats) that also develop age-associated or Type 2 diabetes We utilized polymerase chain reaction methodology in this study to obtain the IAPP nucleotide and protein sequences of the dog, a species not known to develop islet amyloid. We show that dog IAPP contains the same putative amyloidogenic sequence (GAILS) at residues 24-28 as human and cat IAPP, and that although dogs do not develop islet amyloid they do develop IAPP-derived amyloid in association with neoplastic beta cells (i.e., insulinomas). These results provide strong evidence that the amyloidogenicity of IAPP is linked to at least two prerequisites: a species-specific amyloidogenic structural motif, and aberrations in the synthesis (or processing) of IAPP which leads to increased concentration of IAPP in the local milieau.

Amino Acid Sequence↗
PubMed1990

The putative hormone islet amyloid polypeptide (IAPP) induces impaired glucose tolerance in cats.

Islet amyloid polypeptide (IAPP) has been implicated by in vitro studies as an inhibitor of insulin-stimulated glucose utilization by skeletal muscle cells and also as an inhibitor of insulin-stimulated insulin secretion by beta cells. Increased expression and production of IAPP by beta cells, as has been suggested to occur in cats with impaired glucose tolerance, could thus contribute substantially to the development of the insulin resistance and impaired insulin release which are the hallmarks of Type 2 diabetes mellitus. The effects of IAPP with respect to glucose metabolism in living animals, however, have not been previously reported. In the present in vivo study we show that synthetic amidated IAPP induced impaired glucose tolerance in each of the 3 cats studied, with dramatic impairment (increases in glucose to T1/2 values of 124% and 234%) in 2 of the 3 cats. Impaired insulin responses were also evident in the 2 cats with the most dramatic states of glucose intolerance. These results provide the most direct evidence to-date that IAPP may have an important role in the development of Type 2 diabetes mellitus.

Amyloid↗
PubMed1990

Pharmacokinetics of two alternative dosage forms for cyclosporine: liposomes and intralipid.

Cyclosporine (CsA), commercially available as iv or oral Sandimmune, is a potent immunosuppressant which can induce dose-related nephrotoxocity. In addition, the iv product contains a solubilizing agent, Cremophore EL, which in itself is reported to be nephrotoxic and can induce, in sensitized patients, anaphylactic reactions. Solubilization of CsA with liposomes or lipid emulsions could provide a suitable alternative dosage form for iv administration. With this in mind, male New Zealand white rabbits were given iv CsA (10 mg/kg) in three different dosage forms: (1) CsA:liposomes; (2) CsA:Intralipid (soybean oil and phospholipids); and (3) the commercially available Sandimmune (cyclosporine). The CsA concentration in whole blood samples was analyzed by HPLC. The terminal disposition half-life of CsA (t1/2 beta) ranged from 400 to 475 min and was not statistically different among the three groups. However, the distribution characteristics of CsA changed dramatically depending on the dosage form. The volume of distribution of CsA at steady state (Vdss) in Sandimmune was 2.7 +/- 0.2 L/kg and was significantly lower than that of either Intralipid (10.6 +/- 2.7 L/kg) or liposomes (7.4 +/- 2.3 L/kg). A significantly lower total body clearance (TBC) of CsA also was seen for Sandimmune (12.7 +/- 0.3 mL/min/kg) as compared with that of either Intralipid (24.4 +/- 8.2 mL/min/kg) or liposomes (18.9 +/- 3.9 mL/min/kg). Since CsA is extensively bound to lipoproteins, it is surprising that both test vehicles showed a different distribution pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Behavioural and EEG responses to auditory stimuli during sleep in newborn infants and in infants aged 3 months.

Two studies were conducted in order to assess EEG and behavioural responsiveness to auditory stimuli as a function of sleep state in infants. The subjects in the first experiment were 11 infants aged 3 months, and in the second study the responsiveness of 8 infants aged 3 months was compared with that of 8 newborn infants. The stimuli ranged in intensity from 36 to 90 dB and were presented using a modification of the method of constant stimuli. The occurrence and intensity of behavioural responses were recorded by a trained observer. Electroencephalogram (EEG) responses were defined as EEG desynchronization and were identified by a Fast Fourier Transform algorithm. The results of the two studies showed that infants were more responsive during active sleep (AS) than during quiet sleep (QS) and gave behavioural responses at lower stimulus intensities than EEG responses. Behavioural responsiveness and EEG responsiveness during AS increased as a function of age, while EEG responsiveness during QS decreased. The marked suppression of EEG responsiveness during QS at 3 months of age is thought to be a consequence of developmental changes in sleep mechanisms--an effect which may have clinical implications.

Age Factors↗
PubMed1990

Cataract surgery with intraocular lens implantation in Fuchs' heterochromic cyclitis.

The results of cataract extraction with posterior chamber lens implantation in twenty eyes with Fuchs' Heterochromic Cyclitis are reported. No serious operative complications were experienced. The visual outcome has been excellent in all but those eyes with coexistent glaucoma. The postoperative complications seem no more frequent than would be expected for the underlying condition.

Adult↗
PubMed1990

Mueller-Lyer decrement: practice or prolonged inspection?

Noting the similarity between the illusion decrement and selective adaptation paradigms, Long has challenged the view that illusion decrement effects reflect a strategic--as opposed to a structural--underlying mechanism, and has called for further research on this issue. To investigate the confound between prolonged free inspection and repeated trials in the standard decrement procedure, the effects of three inspection conditions (continuous, intermittent, and immediate) on the magnitude of the overestimation Mueller-Lyer illusion have been assessed under two levels of trials (a total of two or six judgments). Significant illusion decline was found only under conditions of repeated trials, with either continuous or intermittent inspection. These findings do not support the predictions of purely structural theories (including neural adaptation and efferent readiness theories), according to which degree of decrement should be determined solely by viewing time. Instead, the data demonstrate that illusion decrement is a product of practice, providing converging evidence for the view of decrement as involving a cognitive 'recalibration' or learning process.

Adult↗
PubMed1990

Structure of cat islet amyloid polypeptide and identification of amino acid residues of potential significance for islet amyloid formation.

Cats and humans, unlike most rodent species, develop amyloid in the islets of Langerhans in conjunction with non-insulin-dependent diabetes mellitus. The amyloid consists of a 37-amino acid polypeptide referred to as islet amyloid polypeptide (IAPP). The primary structures of IAPP from human and three rodent species have previously been determined. Sequence divergence was seen in the region corresponding to amino acid residues 20-29, which in human IAPP has been suggested to confer the amyloidogenic properties to the molecule. Using polymerase chain-reaction methodology, we determined the primary sequence of cat IAPP. Amino acid region 20-29 shows specific similarities and differences compared with human and rodent IAPP, respectively. A synthetic cat IAPP20-29 decapeptide formed amyloid fibrils spontaneously in vitro. Comparison between the structure and amyloid fibril-forming activity of various synthetic peptides suggests that the amino acid residues at positions 25-26 in mature IAPP are important for the amyloidogenic properties of the molecule.

Amino Acid Sequence↗
PubMed1990

A new approach to cerebral asymmetry: RT differences in simultaneous bimanual finger movement during verbal and nonverbal tasks.

This study was aimed at testing a new approach for examination of functional laterality based on hemispheric specialization. The subjects had to perform verbal (words/nonwords) and nonverbal (similar/different patterns) discrimination. The separation of the two hemispheres during information processing was realized by requiring a simultaneous response of both index fingers. The obtained over-all reaction times (RT) were faster for verbal than for pattern tasks. Considering the RTs for solely the particular, faster response of one or the other index finger, the right index finger turned out to be faster on verbal tasks whereas the left one dominated on pattern tasks. According to the hypothesis that the faster hand indicates the more active (contralateral) hemisphere, it can be assumed that words are responded to more quickly when processed in the left hemisphere. On the other hand, patterns are responded to more quickly when the right hemisphere is active. These results suggest that each hemisphere may be capable of processing verbal and nonverbal material; the speed of information processing, however, is faster in the more adept one.

Adult↗
PubMed1990

Image rotation of misoriented letter strings: effects of orientation cuing and repetition.

Three experiments were designed to investigate whether the characteristic function relating response time to stimulus orientation reflects the observer imagining the rotation of the stimulus to upright (the "image rotation" hypothesis) or rotation of an internal reference frame in response to the misoriented stimulus (the "frame rotation" hypothesis). Identification times in response to misoriented words were measured in Experiment 1, whereas in Experiments 2 and 3, lexical decision times in response to misoriented letter strings were measured. Trials occurred in blocks; words within a block were presented at the same orientation. It was argued that this mode of presentation would facilitate the use of a frame rotation strategy by allowing for a gradual readjustment of an internal reference frame. The characteristic "mental rotation" function was observed in all three experiments. However, the data indicated that observers continued to imagine the rotation of the word to upright in each trial; there was no evidence of readjustment of an internal reference frame. An additional finding of interest occurred in Experiment 1, in which observers identified the same set of misoriented words across two sessions. The identification times were faster, and the slope of the mental rotation function was lower, in the second session. These results are discussed as in relation to the image rotation hypothesis of mental rotation and to "instance-based skill acquisition" (Masson, 1986) in word recognition.

Adult↗
PubMed1989

Evaluation of PET count rate performance.

A proposal is made for the test conditions to evaluate PET count rate performance. This performance depends in a complex manner on the spatial distribution of activity and scattering material. Therefore, a combined body phantom is proposed, which is as simple as possible but which adequately simulates the range of clinical application of a whole body tomograph. Taking into account the special properties of the new block detector design, a comprehensive test procedure is developed. This includes not only the common count rate characteristic, but also checks for the accuracy of randoms estimation and count loss correction schemes, and for the occurrence of pulse pile up. This is done for different source and scatter configurations, simulating brain, cardiac, and abdominal imaging, respectively. Examples are given, based on measurements of the latest generation PET scanners, namely the CT1 PT 931/08-12 and the Scanditronix PC 2048-07WB.

Models, Structural↗
PubMed1989

The surgical management of dysthyroid related eyelid retraction using Mersilene mesh.

The use of Mersilene mesh as a spacer material in the surgical management of seven patients with dysthyroid-related eyelid retraction is presented. To date, fourteen eyelids have been operated on using this material with an average follow-up of nine months. It appears that Mersilene mesh is a realistic alternative to preserved sclera in the surgical management of such cases.

Adult↗
PubMed1989

Combined extracapsular cataract extraction and trabeculectomy using a separated corneal section.

A retrospective study of 35 cases of extracapsular cataract extraction with posterior chamber lens implant combined with trabeculectomy was undertaken. The cataract extractions were performed through a corneal section to separate the cataract wound from the trabeculectomy. Control of intraocular pressure was achieved without medication in 77% of cases. Median improvement in visual acuity was 3.5 lines at one year. This technique provided improved trabeculectomy drainage compared with previous reports for corneoscleral incisions. Improvement in visual acuity was poorer for a group of patients with severe preoperative field loss.

Cataract Extraction↗
PubMed1989

Simultaneous sampling and length contrast.

The illusion of perceived line length produced by the parallel lines configuration reverses from assimilation to contrast with large spatial separation of the contextual and test lines (Jordan & Schiano, 1986). In the present experiment, we tested whether length contrast is produced by the sequential sampling of contextual and test lines or by the simultaneous sampling of the stimuli from a spatially distributed attentive field. Scanning instructions were manipulated such that one group of observers was encouraged to sample the lines sequentially, and a third group was given no specific scanning instructions. The data indicated that the reversal to length contrast is produced by simultaneous sampling of contextual and test lines. Implications for attentional descriptions of visual illusions are discussed.

Adult↗