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Biomedical subjects

M Onofrj

Publications and source records attributed to M Onofrj.

At least 91 records · Page 5Linked to original sources
PubMed1986

Electrocerebral and behavioural analysis of systemic kainic acid-induced epilepsy in the rat.

A systematic study of the epileptic electrocerebral and behavioural effects of intraperitoneal kainic acid (KA) was carried out in 92 adult albino Wistar rats. The doses of KA ranged from 3 to 20 mg/kg. Chronic epidural and stereotaxically implanted cerebral electrodes (hippocampus, amygdala and thalamic reuniens nucleus) were used. All animals were studied for 5-12 after KA injection; in 20 animals the study was extended to 10 days. Sporadic spiking was the early EEG manifestation of epilepsy. Subsequently, ictal discharges were recorded. Both types of epileptic discharges were at first focal and then generalized. In the majority of animals, both types of electrographic events were first recorded from the limbic structures; in 7 to 35% of cases, however (depending on the dose of KA), they first appeared in the neocortex. Two groups of behavioural manifestations were observed: searching, staring spells, wet-dog shaking and gnawing: these could be independent of any recorded EEG epileptic event; and rearing, head nodding, forelimb clonus and tonic-clonic spells: these were always related to EEG epileptic activity, mostly generalized discharges. Spiking was still recorded from various structures 10 days after the KA injection.

Animals↗
PubMed1985

The hemispheric distribution of the transient rat VEP: a comparison of flash and pattern stimulation.

We investigated the hemispheric distribution of the rat visual evoked potential (VEP) to pattern reversal and flash stimuli, presented monocularly at a rate of 1 Hz. Pattern VEP components could be recorded only over an area bounded by the anatomical coordinates of area 17, while some flash VEP components were recordable outside the primary visual area. Monocular pattern stimulation, as expected, evoked dominant contralateral VEPs. Surprisingly, ipsilateral responses could be also recorded with the reference electrode near the nasal bone. These VEPs showed partial polarity inversion compared to the contralateral EPs. To assess the origin of the ipsilateral EPs, we also recorded EPs following surgical deafferentation of the ipsilateral cortex. Our data reveal that ipsilateral VEPs represent volume conducted potentials.

Animals↗
PubMed1984

The effect of contrast and spatial frequency on the visual evoked potential of the hooded rat.

Transient and steady-state visual evoked potentials, obtained with counterphase modulated grating patterns, were recorded through chronically implanted electrodes in lightly anesthetized and unanesthetized hooded rats. As a function of spatial frequency, the latency of the major positive wave (P1) of the transient VEP was minimal with a 0.1 cycles per degree (cpd) grating as stimulus. The amplitude of the P1-N2 component remained constant from 0.04 to 0.20 cpd and then decreased with higher spatial frequencies. The function relating amplitude of steady-state VEP to spatial frequency at high contrast depended on temporal frequency: It had a band-pass form at 5.0 Hz and a low-pass form at 8.4 Hz. As a function of contrast, the latency of the P1 wave linearly decreased and its amplitude increased with increments of contrast up to 55%. The contrast function of the amplitude of the second harmonic of the steady-state VEP (8.4 Hz) showed two linear segments: one for low contrasts with a shallow slope and one for high contrasts with a steep slope, suggesting two distinct contrast mechanisms.

Animals↗
PubMed1982

Dopaminergic deficiency causes delayed visual evoked potentials in rats.

Flash and pattern visual evoked potentials (VEPs) to two temporal frequencies of stimulation were studied in nineteen rats. The effect of a tyrosine hydroxylase inhibitor and of a dopamine receptor blocker on the VEP was explored in ten animals. Significant latency change occurred following injection of either drug, while only the hydroxylase inhibitor reduced the VEP amplitude. These changes were not caused by the anesthesia used in these experiments, although the same anesthetics in higher doses did depress VEP amplitudes. When dopamine blockade was followed by administration of apomorphine, a dopamine agonist, VEP delays could be partially reversed. Besides conduction defects of myelinated axons, synaptic malfunction may also cause delays in sensory evoked potentials.

Animals↗
PubMed1982

Pattern visual evoked potentials in the rat.

Pattern and flash visual evoked potentials (VEPs) were obtained in 25 adult male hooded rats. Different electrode placements were used to detect the origin of the VEPs. The spatial frequency and temporal modulation of the stimulating pattern and the refractive state of the eye were varied to investigate the specificity of these factors in pattern VEPs. Variations in latency, amplitude, and trace morphology were found which were consistent with the characteristics of the visual system of the rat.

Animals↗
PubMed1982

Visual evoked potential diagnosis of field defects in patients with chiasmatic and retrochiasmatic lesions.

Visual evoked potentials were studied in 18 patients with visual field defects assessed by perimetry. Stimuli were reversing checkerboard and grating patterns of 13', full field and hemifield. Two reversal rates were studied: 1 Hz (transient VEPs) and 8 Hz (steady-state VEPs). Using monocular hemifield stimulation the "paradoxical lateralisation" of transient but not of steady-state VEPs was confirmed. Diagnostic yield was 90% using transient, but less than 20% using steady-state stimuli.

Brain↗
PubMed1981

A follow-up electrophysiological study of rats with poor intrauterine fetal growth: the development of visual evoked responses (VERs).

The development of some electrophysiological activities of the visual system (VERs) was compared in control rats and in young rats with poor intrauterine fetal growth caused by an electrolytic lesion of the placenta. Treated rats showed a delayed development of the electrophysiological functions considered, thus confirming the postnatal effect of poor intrauterine fetal growth.

Animals↗
PubMedDate not supplied

Alterations in event-related potentials (ERPs) of MPTP-treated monkeys.

Using an auditory 'oddball' paradigm and classical conditioning, we have studied auditory evoked potentials (AEPs) and P300-like potentials in monkeys pre- and post-MPTP treatment. Free-field acoustic stimuli were 500 Hz and 4000 Hz tones, which were designated as the 'frequent' and 'rare' conditions, respectively. The 4000 Hz stimuli were reinforced with mild somatosensory electrical stimulation. During the first few weeks following 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) administration, all monkeys gradually developed a parkinsonian syndrome, which partially, but not completely improved within 30-40 days in 2 animals. The amplitudes of the AEP were initially significantly decreased, but progressively returned to pretreatment magnitudes in the 2 monkeys which partially recovered. P300-like potentials were initially abolished in all animals; however, 30-40 days later P300 spontaneously re-emerged in the same 2 monkeys. Latencies of both of these signals were unaffected by MPTP. Acute administration of dopamine precursor during the first phase of neurotoxicity partially and temporarily improved depressed AEP amplitudes, but did not restore absent P300-like potentials. The relevance of these results for Parkinson's disease is discussed.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMedDate not supplied

Maps of somatosensory evoked potentials (SEPs) to mechanical (tapping) stimuli: comparison with P14, N20, P22, N30 of electrically elicited SEPs.

Bit mapped color imaging of SEPs was recorded from 19 derivations in 11 healthy volunteers after electrical stimulation of the median nerve at the wrist, index finger digital nerve stimulation, and mechanical stimulation of the index fingertips by an electromechanically driven vibrating thin metallic plate. The latencies of SEP components increased for the various stimulation modalities, being shortest after median nerve stimulation at the wrist and longest after mechanical stimulation of the index fingertips. The scalp distribution of SEPs to mechanical stimuli was, however, the same as other SEPs, independently of the stimulation employed, and components corresponding to N20 and P22 were recorded only contralaterally to the stimulated side.

Adult↗
PubMedDate not supplied

Visual 'cognitive' evoked potentials in the behaving monkey.

Using a visual 'oddball' paradigm we studied ERPs in monkeys trained in a 'go' 'no-go' discrimination task. The stimuli were 2.5 cpd sinusoidal gratings differing only in orientation (0 degrees or 25 degrees). Monkeys released a lever during 1 of 2 response windows (RW), 480-1762 or 740-1672 msec, following target stimulus onset. Target stimulus presentation probabilities were 1.0, 0.5 and 0.3. The primary evoked potentials recorded to either the target or non-target stimulus were similar in all monkeys. P3 signals progressively emerged in the monkeys only to the target stimulus. P3 recorded at Cz, P3, and P4 had similar mean latencies and amplitudes. Eye movements showed no relationship to P3 potentials. Neither the primary visual potentials nor P3 changed significantly as a function of RW. P3 amplitude was inversely related to target probability. When the target stimulus was presented 100% of the time (P = 1.0) P3 disappeared over 4-5 blocks of trials, while the primary evoked potentials remained consistent.

Animals↗
PubMedDate not supplied

Mapped distribution of pattern reversal VEPs to central field and lateral half-field stimuli of different spatial frequencies.

Visual evoked potentials (VEPs) to pattern reversal vertical bar stimuli of 3 different sizes (1, 2, 4 c/deg) were recorded from 19 scalp derivations in 50 controls. The stimuli were presented on a full-field (FF) screen of 24 degrees visual angle, and on left and right half-fields (HF) of 12 degrees radius. In 15 controls partial HF stimuli were presented on the central 3 and 6 degrees and as hemiannular stimuli of 12 degrees with occlusion of the central 3 and 6 degrees. An antero-posterior polarity reversal of the N1-P1-N2 sequence was observed for FF VEPs. A tangential polarity reversal was observed for HF VEPs. Also with central or hemiannular stimuli polarity reversals of all VEP components were observed within the scalp. Variants of VEP distribution, absence or prominence of some of the ipsi- or contralateral VEP components were observed in 8-40% of controls. The FF and HF VEP distribution, and the variant VEP asymmetries were partly dependent on the pattern spatial frequency.

Adult↗
PubMedDate not supplied

Donepezil, rivastigmine, and vitamin E in Alzheimer disease: a combined P300 event-related potentials/neuropsychologic evaluation over 6 months.

The latency of P300 "cognitive" event-related potentials changes if cholinergic activities of the central nervous system are pharmacologically manipulated. We tested the hypothesis that the new cholinesterase inhibitors donepezil (DPZ) and rivastigmine (Riv) may have an effect on the frequently abnormal P300 component in patients with Alzheimer disease (AD), thereby allowing a significant evaluation of cholinesterase inhibitors. We evaluated 60 patients with mild to moderately severe probable AD, in comparison with 60 age-matched control subjects, with P300 recordings and neuropsychologic examinations. Forty patients were randomly assigned in a double-blinded trial to 5-10 mg/d DPZ versus 2,000 IU/d vitamin E, and 20 patients were instead treated in an open trial with 1.5 to 12 mg/d Riv. In patients treated with vitamin E, we observed latency increments (7.4 +/- 3.5 msec) correlated with worsening neuropsychologic test scores. In patients treated with DPZ and Riv, we found significant P300 latency reductions (15.3 +/- 3.2 msec and 22.0 +/- 3.3 msec). Shorter P300 latencies were associated with higher Wechsler Adult Intelligence Scale scores and with lower AD Assessment Scale-cognitive subscale (ADAS-cog) scores (R = 0.72). Correlations between ADAS-cog changes and P300 changes significantly separated patients treated with DPZ and Riv from those treated with vitamin E. Administration of DPZ and Riv reduced the latencies of P300 components proportionately to neuropsychologic test improvements. Combined P300 and neuropsychologic test evaluation significantly separated DPZ-treated patients and Riv-treated patients from vitamin E-treated patients.

Aged↗