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Biomedical subjects

R Flink

Publications and source records attributed to R Flink.

34 records · Page 2Linked to original sources
PubMed1990

Generator mechanisms of epileptic potentials analyzed by dipole tracing method.

A new dipole tracing method, based on a realistic head model, was used to determine dipole locations and vector moments of interictal convexity sharp waves recorded (with conventional EEG technique) from the right fronto-temporal region in a patient with partial complex seizures. When the dipole locations in the head model were compared to MRI scans, the majority of the sharp wave dipoles were found to be located in the right hippocampal area. For individual sharp waves, the hippocampal dipoles moved along tracks corresponding to the vector moment directions, suggesting that the electrical sources of the convexity sharp waves were somato-dendritic currents which spread rapidly from one neuron group to the next in the hippocampal area. Previous long-term subdural recording had shown seizure onset in this area. After right-sided anterior temporal lobectomy including the hippocampus the patient has been seizure-free for three months.

Adult↗
PubMed1988

Sensory thresholds in the male urethra measured by electrical stimulation.

The sensory pathways innervating the male urethra were investigated by recording the sensory thresholds with electrical stimulation. Twenty-six male subjects (age 16 to 73 years) were included in the study. Ring-electrodes mounted on a Foley catheter were used for stimulation in proximal and distal urethra. Square wave pulses (duration 0.5 ms) were delivered with a constant current stimulator at different frequencies and the lowest intensity felt by the subject was defined as the threshold. The sensory thresholds were in the order of 0.5 to 5 mA and decreased with increasing stimulation frequency. All patients described a qualitative difference in the experienced sensation when comparing proximal and distal urethral stimulation. The reason for this is discussed. The possible use of this method as an adjunct to the urodynamic investigation in diagnosing neurogenic lesions is proposed.

Adolescent↗
PubMed1987

Postnatal development of the feline lateral cervical nucleus: I. A quantitative light and electron microscopic study.

With the aim of obtaining some basic information for future developmental studies, the lateral cervical nucleus (LCN) was investigated in 32 kittens of different ages by electron microscopic and stereologic methods. Corresponding light microscopic measurements of neuronal and nuclear profiles and of the total LCN volume were also performed. The total LCN volume increased sixfold between the ages of 12 hours and 120 days, the most rapid increase occurring during the first month. The neuronal size was fairly constant up to the age of 9 days, whereafter it showed greater variation. The mean profile area increased rapidly during the second week and then more slowly. The relative volume of boutons increased significantly between birth and the age of 34 days and then decreased slightly up to 120 days postnatally. The total bouton volume showed a steady increase, which was most pronounced between the ages of 9 and 34 days. The relative dendritic volume decreased during the 120 days of observation, whereas the total volume of dendrites increased up to the age of 92 days and then decreased. The total volume of glial cells increased during the 120-day observation period, as did both the relative and total volumes of myelinated axons. The changes in the relative volumes of mitochondria in boutons and dendrites were very similar, with increases that were most marked between the ages of 9 and 34 days and between 92 and 120 days.

Animals↗
PubMed1986

Different neuron populations in the feline lateral cervical nucleus: a light and electron microscopic study with the retrograde axonal transport technique.

A comparative light and electron microscopic study was made of the two major neuron populations in the feline lateral cervical nucleus (LCN) that have an ascending projection--namely, the cervicothalamic and cervicomesencephalic neurons. The small population of neurons in the LCN that remained unlabelled after extensive injections into all known areas of LCN termination was also investigated. The intra-axonal retrograde tracing technique was employed and three different tracers were used: native horseradish peroxidase, horseradish peroxidase conjugated to wheat germ agglutinin, and cholera toxin subunit B (CTb). The diaminobenzidine and tetramethylbenzidine methods were used for the peroxidase reaction, and an immunocytochemical staining method with monoclonal antibodies was employed to localize CTb. The light microscopic cell count was performed on plastic-embedded semithin (2 micron) sections, and a section-embedding technique was used for sampling regions of interest for electron microscopy. The total number of neurons in the LCN was calculated to be 8,300, which is higher than numbers reported from other studies on frozen sections. It was concluded from control experiments that many neurons fail to counterstain in frozen sections. The average proportion of labelled cervicothalamic neurons was 94%, which accords with earlier reports. The frequency of labelled neurons projecting to the midbrain was 25-49%, depending on the method used. The highest number of labelled neurons was found with the immunocytochemical method with use of CTb as a tracer. In the electron microscopic study, the cell area, form factor, nuclear area, bouton covering ratio, mean appositional length of boutons, and bouton density were measured. There were no significant differences in these respects between the cervicothalamic and cervicomesencephalic neurons, but the unlabelled neurons differed significantly from the labelled ones, with a smaller somal area, a lower bouton covering ratio, and a larger relative nuclear area. The ascending neurons were scattered over the entire LCN, but the neurons that remained unlabelled after the extensive injections was found in its ventromedial part. It is suggested that these are interneurons. In the light microscopic study of the animals injected with CTb, the ventromedial part of the LCN displayed labelled structures resembling terminals. Electron microscopic examination of the sections revealed boutons synapsing on unlabelled neurons and dendrites. Occasionally labelled neurons and dendrites were also contacted.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1986

Fluorescent double-labelling study of ascending and descending neurones in the feline lateral cervical nucleus.

The organization of ascending and descending neurones of the lateral cervical nucleus (LCN) was investigated in 10 adult cats after injections of the fluorescent tracers Fast Blue and Nuclear Yellow. Injections into the thalamus and tectum resulted in up to 3000 labelled cell profiles within the contralateral LCN. This corresponded to a calculated number of 4500 labelled LCN neurones. The greatest diameter of the labelled cell profiles was about 30 micron. They were located throughout the nucleus, but were less numerous in its medial portion. Injections mainly into the dorsal horn of different pairs of cervical and lumbar segments of the spinal cord resulted in a calculated number of up to 305 labelled LCN cells. The diameter of these cell profiles was about 25 micron and they were mainly situated in the rostro-ventral and medial parts of the LCN. Double-labelled cells with ascending and descending projections were not encountered after injections into the thalamus-tectum and spinal segments C5-6. About 15% of the descending LCN cells were double-labelled by pairs of spinal injections separated by intervals of one segment. It is concluded that the neurones descending down the spinal cord and ascending to the thalamus-tectum constitute different subpopulations of cells within the LCN and that a minor proportion of the descending cells seem to project to at least three adjacent segments of the spinal cord.

Amidines↗
PubMed1986

The impact of pending technologies on a universal connector standard.

Standardization of pacemaker lead connectors promises to aid clinical practice. In the past, clinician concern for continued innovation has moderated calls for standardization. Today, connector standards are under consideration in the International Pacemaker Standards Working Group. Reliability, compatibility with existing implanted leads, and interchangeability between bipolar and unipolar leads are among the clinical concerns the standard process must address. Pending technologies will limit the future utility of the standard or be impeded by its regulatory imposition. Well-informed decision making in the standards process combined with a practical appraisal of the impact on future technology will help assure that, in balance, a net benefit to clinical practice results from connector standardization. The issues warrant broad review and discussion among individuals and groups interested in pacing.

Biomedical Engineering↗
PubMed1985

Convergence on the same neurons in the feline ventrobasal thalamus of terminals from the dorsal column and the lateral cervical nuclei: an ultrastructural study combining orthograde degeneration and anterograde axonal transport of lectin conjugated horseradish peroxidase.

After electrocoagulation of the dorsal column nuclei (DCN) and injections of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) into the lateral cervical nucleus (LCN), two kinds of changes in fibers and boutons were observed in the dorsolateral part of the thalamic ventroposterolateral nucleus (VPL). The axons and boutons from neurons in the DCN demonstrated dark degeneration, while the fibers and synaptic terminals from the LCN-neurons contained the characteristic needle-shaped peroxidase reaction products following incubation with tetramethylbenzidine (TMB). Occasionally dark degenerating boutons and boutons with TMB-positive reaction products showed synaptic contact with the same dendritic profiles. After consideration of the possibility of an axoaxonal transfer of the tracer it is concluded that the findings demonstrate convergence of synaptic input both from the DCN and from the LCN on the same postsynaptic VPL neurons. The present results are in accordance with earlier light microscopic and neurophysiological findings. It is also concluded that the ultrastructural technique employed in this study is well suited to reveal convergence of different afferent systems on the same postsynaptic neurons.

Afferent Pathways↗
PubMed1985

Synaptic terminals in the ventroposterolateral nucleus of the thalamus from neurons in the dorsal column and lateral cervical nuclei: an electron microscopic study in the cat.

The afferent fibres to the ventroposterolateral nucleus (VPL) of the contralateral thalamus from neurons in the dorsal column nuclei (DCN) and the lateral cervical nucleus (LCN) were labelled by anterograde transport of wheat germ agglutinin-horseradish peroxidase conjugate and subsequent histochemical processing with tetramethyl benzidine. In accordance with the results of previous light microscopical studies using the degeneration method or autoradiographic tracing technique, the distribution of the afferents from the DCN and LCN in the VPL differed considerably. Thus the DCN terminals, which were calculated to constitute about 7-8% of the total number of boutons in the VPL, were found throughout the entire VPL, whereas the LCN terminals were mainly located in its dorsal and dorsolateral parts, where they made up about 1% of the total number of boutons. However, the morphology and synaptic organization of the terminals from the DCN and LCN were virtually identical. Thus the synaptic terminals of the two afferent pathways seemed to be represented by large boutons of a similar type, which had large, slightly oval and loosely packed synaptic vesicles and contained numerous mitochondria. Both DCN and LCN terminals synapsed preferentially on medium-sized to large dendrites, but were also presynaptic to other vesicle-containing profiles, probably of internuncial origin, which in turn were in synaptic contact with the same dendrites as the labelled ones. It is suggested that the differences in physiological properties between the somatosensory information that is transmitted to the somatosensory cortex via the dorsal column-medial lemniscus pathway and the spino-cervico-thalamic tract do not seem to have a counterpart in differences in the synaptic organization of their relay in the VPL.

Afferent Pathways↗
PubMed1983

The termination in the mesencephalon of fibres from the lateral cervical nucleus. An anatomical study in the cat.

The termination in the dorsal mesencephalon of fibres from the lateral cervical nucleus (LCN), recently discovered with the retrograde tracing technique, was investigated by both the degeneration method and anterograde transport of lectin-conjugated horseradish peroxidase. Both strategies gave similar results. The termination area was found to be situated at the level of transition between the superior and inferior colliculi and comprises mainly the intercollicular nucleus and the deep and intermediate layers of the posterolateral pole of the superior colliculus. The functional implication of the demonstrated projection from LCN is discussed in relation to somatosensory activity in the mesencephalic tectum.

Afferent Pathways↗
PubMed1980

Differences in the collateralization of neuronal projections from the dorsal column nuclei and lateral cervical nucleus to the thalamus and tectum in the cat: an anatomical study using two different double-labeling techniques.

The dorsal column nuclei (DCN) and the lateral cervical nucleus (LCN) project to the diencephalon and tectum. In order to determine which neurons project to these targets and whether any of them have collateral projections, the double-retrograde labeling techniques developed by Hayes and Rustioni and Kuypers et al. were used. Both strategies produced similar results. Within DCN, neurons which projected to the diencephalon were located differently and had a different morphology than those which projected to the tectum. The diencephalic-projecting neurons, which were preferentially located within the middle part of the DCN complex were mainly large (> 15 micrometer diameter) and round. The tectal-projecting neurons, often located along the edges of the gracile and cuneate nuclei or between them, were most often found outside of the middle parts of the DCN complex (i.e. predominantly rostrally and frequently also caudally). These tectal-projecting neurons varied in size and were usually oval or fusiform in shape. In contrast to DCN, neurons in LCN which projected either to the tectum or diencephalon did not differ morphologically and in both groups were of various sizes and shapes. They were intermixed haphazardly, predominantly within the lateral two-thirds of the nucleus. In addition, another class of neurons, constituting more than 40% of the labeled population in some experiments, had collateral projections to both terminal targets. These double-labeled neurons were haphazardly mixed with other labeled neurons.

Animals↗
PubMed1979

HLA antigens and schizophrenia.

We typed 45 schizophrenic patients for 35 HLA antigens and compared their frequencies with 1,263 population controls. No significant differences between schizophrenics and controls were found. When the schizophrenics were subtyped, a significant (P less than .05) excess of Aw26 was found among the hebephrenics, compared with the population controls. When the published literature on schizophrenia-HLA associations was surveyed, none of the reported associations were found to be consistent across studies. Some possible explanations for the heterogeneity among studies are discussed and it is concluded that an association between schizophrenia and any of the HLA antigens has not yet been demonstrated.

Adult↗
PubMed1976

Heterogeneity of antibody response to human platelet transfusion.

To study the antibody response to human platelet transfusions, nine thrombocytopenia patients with bone marrow failure were given 6 U (3X10(11)) of random platelet concentrates twice a week. Before transfusion, none of the patients had preexisting antibodies detectable with lymphocytotoxicity, platelet aggregation, or capillary leukoagglutination techniques. After receiving 18-78 U of platelets, they became refractory to further transfusions of random platelets and alloantibodies were detectable. Two patterns of antibody response could be identified. In three patients, the sera were not lymphocytotoxic with a panel of standard cells in which all the known HLA antigens in the first and second series were represented at least once. Yet, they caused platelet aggregation with 30, 24, and 60%, respectively, of a donor population studied. The aggregating activities were inhibited by antihuman IgG but not by antihuman IgA or antihuman IgM antiserum. The aggregating antibodies could be absorbed out with donor platelets but not lymphocytes or granulocytes. Antibodies from two of these patients aggregated platelets of their respective siblings matched for both HLA haplotypes. Transfusion of platelets from these two siblings did not increase the platelet count while platelets obtained from aggregation-negative donors did. The sera from the remaining six patients were lymphocytotoxic with 15-100% of the panel of standard cells. They also had aggregating antibodies, which could be absorbed out by both platelets and lymphocytes, suggesting that they were HLA antibodies. These data suggest that the development of platelet-specific antibodies may play an important role in the immunological rejection of isologous platelets, and should be considered in the selection of donors for patients who are refractory to platelets from random donors.

Adult↗