Biomedical subjects

D Felix

Publications and source records attributed to D Felix.

At least 37 records · Page 2Linked to original sources

PubMed1996

Auditory fractal random signals: experimental data and clinical application.

In the mammalian primary cochlear afferents, fractals in the postsynaptic bursting behaviour triggered by a constant perisynaptic release of glutamatergic transmitter agonists have been demonstrated. In order to test the validity of fractally coded auditory signal transmission in man, frequency, intensity and temporal resolution tests were performed in cochlear implanted patients. All patients clearly recognized the fractally coded signals transmitted to the cochlear implants. These first results demonstrate evidence for fractally coded auditory signal transmission in man.

Adult↗

PubMed1996

Immunohistochemical and electrophysiological demonstration of substance P in human vestibular ganglion cells.

This study was performed in order to determine the immunohistochemical expression and distribution pattern as well as the electrophysiological actions of substance P in human vestibular ganglion cells. Substance P-like immunostaining was mainly found in the cytoplasm of small vestibular ganglion cells. In contrast, nerve fibers were not labeled. Using intracellular recording techniques, substance P produced a slow depolarization of membrane potentials accompanied by an increase in membrane resistance. Furthermore, an enhanced firing response to depolarization occurred.

Cell Culture Techniques↗

PubMed1995

A specific template-assembled peptidic agonist for the angiotensin II receptor subtype 2 (AT2) and its effect on inferior olivary neurones.

We synthesized a molecule composed of two angiotensin II 4-8 pentapeptide fragments attached to a carrier molecule (TA), according to the template-assembled synthetic proteins concept. This molecule was investigated for receptor binding on angiotensin type-1 and type-2 receptors (AT1 and AT2) and its biological activity was determined by iontophoretic experiments on neurones of the inferior olive (ION) that express only AT2 receptors. TA binds exclusively to the AT2 receptor and mediates an agonistic angiotensin-II effect on the ION. TA is the first agonist available to study the direct stimulation of AT2 receptors.

Amino Acid Sequence↗

PubMed1995

Origin of auditory fractal random signals in guinea pigs.

In guinea pigs, the constant iontophoretic release of transmitter agonists in the synaptic cleft of inner hair cells (IHC) triggers chemically an irregular and bursting mode of spiking discharge, subsynaptically recorded in the afferent dendrites. The tendency to form spike clusters appears to be independent of the quality and quantity of the used test substances, the excitatory amino acids N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4- isoxazole-propionic acid (AMPA). The recorded spike trains show a remarkable stability of the calculated individual box-counting dimension characterizing the bursting behaviour as a fractal random point process. The fractal kinetics seems to reflect molecular instabilities of cochlear afferent glutamate receptors, determining the mode of the signal transmission in the auditory periphery.

Action Potentials↗

PubMed1995

Avian Imc-tectal projection is mediated by acetylcholine and glutamate.

In the bird, biochemical and histochemical data suggest that the neurotransmitter between nucleus isthmi pars magnocellularis (Imc) and tectum is either acetylcholine or glutamate. There are, however, discrepancies regarding the functional role of acetylcholine. In the present study we investigated the action of acetylcholine and glutamate and their specific antagonists on excitatory isthmo-tectal synaptic transmission using electrophysiological and microiontophoretic techniques. The results show two different population of cells: (1) excitatory cholinergic input, blocked by atropine sulphate but not by glutamate antagonist; (2) excitatory glutamatergic input of NMDA or non-NMDA receptor type, which is blocked or reduced by CPP or CNQX but not by atropine sulphate.

Acetylcholine↗

PubMed1995

Water safety training as a potential means of reducing risk of young children's drowning.

OBJECTIVES: To determine the effects of training in swimming and water safety on young preschool-children's ability to recover safely from a simulated episode of falling into a swimming pool. DESIGN: Randomized trial of 12 or eight weeks' duration water safety and swimming lessons for children 24 to 42 months old. OUTCOME MEASURES: Swimming ability, deck behavior, water recovery, and swimming to side after jumping into pool were measured before, during, and after the training program. RESULTS: 109 children completed the study (61 in the 12 week group, 48 in the eight week group). The average age was 34.2 months, 54% were male. Swimming ability, deck behavior, water recovery, and jump and swim skills improved over baseline levels in both groups. By the end of training, the 12 week group improved more than the eight week group only in swimming ability. Improvements in water recovery and jump and swim skills were associated positively with changes in swimming ability. CONCLUSIONS: Swimming ability and safety skills of young preschool children can be improved through training. Such programs may offer some protection for children at risk of drowning and there was no indication that this program increased the risk of drowning. However, pool fencing, other barriers around water, and parental supervision still remain the most important prevention strategies to reduce drowning in young children.

Accidental Falls↗

PubMed1995

Receptor pharmacological models for inner ear therapies with emphasis on glutamate receptors: a survey.

With the aid of microiontophoretic techniques we evaluated the action of different postsynaptic glutamate receptor subtypes that mediate neurotransmission between the inner hair cell and the afferent neuron. The sensory input is modulated by axodendritic efferents. In the central nervous system, excessive activation of glutamate receptors is thought to be responsible for a wide variety of neurotoxic actions, and calcium is involved in the etiology of glutamate-induced cell damage. Glutamatergic neurotoxicity may form an appropriate pathophysiological model to explain a variety of inner ear diseases characterized by acute or progressive hearing loss and tinnitus. In clinical trials, three sites of action are thought to attenuate glutamatergic otoneurotoxicity: presynaptically, via the reduction of excessive transmitter release; postsynaptically, via competitive or noncompetitive receptor antagonism; and intracellularly, via blockage of glutamate receptor-dependent calcium stores. The drugs discussed in this paper are currently available clinically and have only recently been found to attenuate glutamate toxicity. Magnesium and the quinoxaline derivative Caroverine, which have already been tested in humans, exhibit a statistically significant otoneuroprotective action in noise-induced hearing loss and tinnitus. The intensive search for further drugs that enhance the survival of cochlear afferents without disrupting acoustic signal processing is one of the main goals of research in clinical otoneuropharmacology in the near future.

Animals↗

PubMed1994

Effect of acetylcholine and NMDA on neurones of avian tectum and nucleus isthmi.

In the present study the effects of microiontophoretically applied acetylcholine and NMDA were investigated on neurones of the avian nucleus isthmi. Whereas acetylcholine affected equally cell firing in the two parts of the nucleus, the magnocellular (Imc) and the parvocellular (Ipc) division, the effect of NMDA was predominantly confined to Ipc. The NMDA induced firing was specifically blocked by the antagonist CPP, while having no effect on acetylcholine. Our results support earlier findings that isthmo-tectal feedback loops can be modulated by distinct mechanisms in separate divisions of nucleus isthmi.

Acetylcholine↗

PubMed1994

Multiple-channel fractal information coding of mammalian nerve signals.

As an average of minimal 3 to maximal 30 single auditory-nerve fibers converge in the auditory pathway, the fractal geometry of their signals is transformed to a different fractal geometry such that small variations of the primary discharge patterns correspond to large variations of the combined signal. The addition of white noise does not affect the fractal signal structure. The quality of the transsynaptic information transfer depends on the relation between the number of the convergent spike trains and the individual fractal geometries of the convergent spike trains.

Animals↗

PubMed1994

GABA as an inhibitory transmitter in the pigeon isthmo-tectal pathway.

In the present investigation, the effects of inhibitory amino acids and their antagonists were tested on isthmo-tectal projection in the pigeon. The majority of superficial tectal cells are inhibited following stimulation of the parvocellular division of nucleus isthmi. A smaller portion of tectal cells showed excitatory responses followed by an inhibitory period. Both inhibitory mechanisms are blocked by the specific gamma-aminobutyric acid (GABA)-antagonist bicuculline but not by strychnine. Our results support the idea that GABA acts as an inhibitory neurotransmitter in the pigeon isthmo-tectal pathways.

Animals↗

PubMed1994

[7-D-ALA]-angiotensin-(1-7): selective antagonism of angiotensin-(1-7) in the rat paraventricular nucleus.

Microiontophoretic application of both, the octapeptide angiotensin II (Ang II) and its N-terminal heptapeptide angiotensin-(1-7), [Ang-(1-7)], has been shown to increase the firing rate of rat hypothalamic paraventricular neurones. In the present microiontophoretic study, the effect of the angiotensin analogue [7-D-Ala]-Ang-(1-7) on Ang II- and Ang-(1-7)-induced firing rate increase of paraventricular neurones has been tested. While the response to Ang II was unchanged, the response to Ang-(1-7) was effectively blocked by [7-D-Ala]-Ang-(1-7). The results indicate that the Ang-(1-7)-induced excitation of paraventricular neurones may be mediated by a distinct Ang-(1-7)-receptor and that [7-D-Ala]-Ang-(1-7) is a selective antagonist of this receptor.

Action Potentials↗

PubMed1994

The Seattle children's bicycle helmet campaign: changes in helmet use and head injury admissions.

OBJECTIVE: To describe the impact of a community bicycle helmet campaign on helmet use and the incidence of bicycle-related head injuries. SETTING: Metropolitan community and a large health maintenance organization. INTERVENTIONS: Communitywide bicycle helmet campaign. OUTCOMES: Rate of observed bicycle helmet use in the community and incidence of bicycle-related injuries in an health maintenance organization population. RESULTS: Helmet use among school-aged children increased from 5.5% in 1987 to 40.2% in 1992. Bicycle-related head injuries decreased by 66.6% in 5- to 9-year-old and 67.6% in 10- to 14-year-old members of an health maintenance organization. CONCLUSIONS: Educational campaigns can increase helmet use and decrease the incidence of bicycle-related head injury.

Adolescent↗

PubMed1993

Healthy People 2000. The rationale and potential efficacy of preventive nutrition in heart disease: the Framingham Offspring-Spouse Study.

BACKGROUND: To examine the rationale for preventive nutrition intervention and the potential efficacy of nutrition-related risk factor modification on heart disease incidence, the cardiovascular disease risk and dietary profiles of Framingham (Mass) men and women, 30 to 79 years old (n = 1798 and 1845, respectively), were compared with the Healthy People 2000: National Health Promotion and Disease Prevention Objectives for the Nation and used to project the 10-year incidence of coronary heart disease with and without lowering serum cholesterol levels. METHODS: Data for this report are derived from the 1984 to 1988 cycle III examinations of the Framingham offspring-spouse cohort. Estimates of the reduction in coronary heart disease risk associated with modifications in serum cholesterol levels and other cardiovascular disease risk factors are projected using Framingham models. RESULTS: About 40% met guidelines for desirable total cholesterol levels (< 5.17 mmol/L [< 200 mg/dL]); 20% were hypertensive; one quarter smoked; and 10% of women and 20% of men were obese. Twenty-four-hour dietary data, adjusted for estimates of usual intake, indicated that about 50% to 80% met dietary cholesterol (< 300 mg) and 55% to 94% met sodium (< 3 g/d) objectives. In contrast, mean total fat intakes were high (38% of total energy), and only 6% to 9% of subjects met total fat, 9% to 14% met saturated fat, and fewer than 3% met dietary fiber guidelines. Ten-year cumulative incidence for coronary heart disease was projected to be up to 25% lower with reduction in serum cholesterol level. CONCLUSION: Risk factor lowering, emphasizing preventive nutrition measures, is an important element of health care reform, particularly strategies to reduce cardiovascular disease rates and to promote population health.

Adult↗

PubMed1993

Immunohistochemical demonstration of angiotensin II receptors in rat brain by use of an anti-idiotypic antibody.

In the present study we investigated the ability of an anti-idiotypic antibody which recognizes angiotensin II (AII) receptors to demonstrate the presence of such receptors under immunohistochemical conditions. The experiments revealed punctate immunoreactive granules on neurons of the nucleus supraopticus and of the nucleus paraventricularis of the hypothalamus. This localization of AII receptors is consistent with the findings obtained using other experimental approaches to the brain renin-angiotensin system. The conclusion of this study is that the applied anti-idiotypic antibody seems to be a reliable tool for mapping AII receptor distribution. The established experimental approaches to AII receptors are thus now supplemented with the possibility of immunohistochemical investigation. Moreover, the possible microscopic analysis of AII receptors on distinct cells will allow studies at an ultrastructural level.

Animals↗

PubMed1993

Enkephalin suppresses afferent cochlear neurotransmission.

The effects of enkephalin and naloxone, applied iontophoretically, were tested on induced firing activity of the afferent dendrites on inner hair cells in the guinea pig. Enkephalin strongly depresses the depolarizing effect of N-methyl-D-aspartate (NMDA), quisqualate and kainate. Enkephalin exerted a stronger inhibitory effect on non-NMDA-induced fibre activity than on NMDA-induced activity. It was possible to block this inhibitory effect by applying the opiate antagonist naloxone, which suggests a specific enkephalin action. Our results appear to demonstrate that enkephalin acts as a neurotransmitter or a neuromodulator in the efferent neurones of inner hair cells which have synaptic contact to the afferents of the inner hair cells.

Animals↗

PubMed1993

Sialectasis and HIV infection.

The sialographic findings of the parotid gland of an HIV-positive patient are presented. Multiple areas of sialectasia were noted and their similarity to Sjögren's syndrome is discussed.

Constriction↗

PubMed1992

Effects of angiotensin II and its selective antagonists on inferior olivary neurones.

On the basis of biochemical and autoradiographic studies it has been shown that the inferior olivary nucleus (ION) contains predominantly angiotensin II (Ang II) receptors of the subtype 2 (AT2). In the present investigation we used microiontophoretic techniques to test the effect of Ang II on the spontaneous firing rate of rat neurones in the ION in vivo. Ang II excited the majority of histologically identified ION neurones. Furthermore, the antagonism of this angiotensin-induced excitation by selective angiotensin receptor blockers of subtype 1 and 2 (AT1 and AT2) was examined. The excitation could be blocked by low doses of the AT2-antagonists PD 123177 and CGP 42112A, whereas the AT1-antagonist DuP 753 was ineffective even at high doses. On a few occasions, however, ejection of the AT1-antagonist resulted in a potentiation of angiotensin-induced excitation. The results suggest that Ang II has an excitatory effect on a considerable number of ION neurones and that this effect is mediated by AT2-receptors.

Angiotensin II↗

PubMed1992

Effects of angiotensin analogues and angiotensin receptor antagonists on paraventricular neurones.

In a previous study we observed that most neurones in the paraventricular nucleus are excited by angiotensin-(1-7). In comparison with angiotensin III this excitatory action was significantly delayed. The aim of the present microiontophoretic study of angiotensin II-sensitive rat paraventricular neurones was to compare the effect of the angiotensin-analogues angiotensin-(1-7), angiotensin-(2-7), angiotensin II and angiotensin III on the spontaneous activity of these neurones and to test angiotensin receptor subtype 1 antagonists (CGP 46027 or DuP 753) and subtype 2 selective antagonists (CGP 42112A and PD 123177) in order to acquire more evidence of the receptor subtype present. As previously observed angiotensin II, angiotensin III and angiotensin-(1-7) excited most neurones. The effect of angiotensin-(1-7) was usually weaker than that of angiotensin II, and in contrast to angiotensin III the latencies were not significantly different. Angiotensin-(1-7) seemed to be active by itself, because its effect was antagonised by angiotensin receptor antagonists. Angiotensin-(2-7) was mostly inactive, although a few cells were excited. Whereas the excitatory effects of angiotensin-(1-7), angiotensin II and angiotensin III could always be inhibited with both angiotensin receptor subtype antagonists 1 and 2, that produced by angiotensin-(2-7) was only weakly antagonised, if at all. Subtype 1 selective antagonists were effective at lower concentrations than selective subtype 2 antagonists.

Angiotensin II↗