Biomedical subjects

F H Da Silva

Publications and source records attributed to F H Da Silva.

3 recordsLinked to original sources

PubMed1999

Medical technology assessment photic stimulation--standardization of screening methods.

RATIONALE: In many EEG laboratories in Europe, intermittent photic stimulation (IPS) is not performed routinely, and consequently, great variation exists in the type of photo stimulator used, the methodology employed, and the interpretation of the EEG curves, thus leading to different outcomes. METHODOLOGY: It was decided to hold a consensus meeting with experts in the field of photic stimulation from various European countries. This meeting was held at the Stichting Epilepsie Instellingen Nederland, Heemstede, the Netherlands. The consensus reached was presented and discussed at the 9th European Congress of Clinical Neurophysiology in Ljubjana in June 1998. RESULTS: Patients should be positioned at a distance of 30 cm from the photic stimulator (nasion to lamp) with dim surrounding lights, just enough to see the patient. Flashes should be delivered in separate trains of 10 s for each frequency, with intervals of 7 s minimum. First stimulation occurs with eyes open followed after 5 s by eye closure, while starting at 1 Hz progressing to 20 Hz, unless generalised epileptiform discharges are evoked at a lower frequency. Then, frequencies should start at 60 Hz decreasing to 25 Hz. The following frequencies should be used: 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 60, 50, 40, 30 and 25 Hz. The total duration is a maximum of 6 min (patients without a reaction to IPS). In interpreting the evoked responses, a clear distinction should be made between epileptiform responses confined to the occipital area (OSW), starting occipitally and spreading to frontal regions (OGSW), or generalised from the start (GSW). Other responses include generalised spikes (OR). CONCLUSION: This standard is safe, relatively quick, simple and reliable. Comparison of data within patients and between patients of various laboratories will also be possible. This will improve the quality of the care of the individual patient and make collaborative research possible.

Electroencephalography↗

PubMed1999

Activity-dependent neurotransmitter release kinetics: correlation with changes in morphological distributions of small and large vesicles in central nerve terminals.

In central nerve terminals transmitter release is tightly regulated and thought to occur in a number of steps. These steps include vesicle mobilization and docking prior to neurotransmitter release. Intrasynaptic changes in vesicle distribution were determined by electron microscopical analysis and neurotransmitter release was monitored by biochemical measurements. We correlated K + -induced changes in distribution of small and large vesicles with the release of their transmitters. For small synaptic vesicles, amino acid release as well as recruitment to and docking at the active zone were activated within 1 s of depolarization. In contrast, the disappearance of large dense-cored vesicles and the release of the neuropeptide cholecystokinin were much slower, and no docking was observed. Studies with diverse Ca2 + channel blockers indicated that mobilization and neurotransmitter release from both vesicle types were regulated by multiple Ca2 + channels, although in different ways. Neurotransmitter release from small synaptic vesicles was predominantly regulated by P-type Ca2 + channels, whereas primarily Q-type Ca2 + channels regulated neurotransmitter release from large dense-cored vesicles. The different Ca2 + channnel types directly regulated mobilization of and neurotransmitter release from small synaptic vesicles whereas, by their cooperativity in raising the intracellular Ca2 + concentration above release threshold, they more indirectly regulated large dense-cored vesicle exocytosis.

Animals↗

PubMed1983

Two types of interictal transients of reversed polarity in rat hippocampus during kindling.

Two different types of spontaneous interictal transients (SITs) have been found in the course of the development of an epileptogenic focus by Schaffer collateral kindling in the CA1 region of rat hippocampus. The first type has peak amplitudes of 250 microV up to 1 mV, a duration of about 80 msec and the same polarity as field potentials recorded from the same sites evoked by Schaffer collateral stimulation. These SITs occur early during kindling, but are also observed at later stages. The second type, which is dominant in later stages of kindling, has peak amplitudes of 2-3 mV, a duration of about 20 msec and the opposite polarity; in a later stage it may also contain a clear population spike. Both types can be considered as being caused by equivalent dipoles situated across the pyramidal cell layer of CA1 but with inverted polarities.

Animals↗