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Biomedical subjects

G Avanzini

Publications and source records attributed to G Avanzini.

At least 109 records · Page 6Linked to original sources
PubMed1992

F response and somatosensory and brainstem auditory evoked potential studies in HMSN type I and II.

To evaluate conduction along the proximal and distal segments of motor and sensory long limb nerves, as well as along the very short acoustic nerve, F response and somatosensory and brainstem auditory evoked potential were studied in a series of patients with hereditary motor and sensory neuropathy (HMSN) types I and II. A diffuse and comparable slowing of conduction in proximal and distal nerve segments, as well as along the acoustic nerve, seems to favour a primary myelin defect in HMSN I. F response and motor conduction velocity showed a similar derangement in both proximal and distal motor segments. Latencies of somatosensory evoked potentials were symmetrically prolonged and correlated with motor nerve impairment. Central conduction times were normal. Studies of brainstem auditory evoked potentials showed a high incidence of acoustic nerve involvement, the most evident abnormality being a statistically significant increase in the latency of the I wave. Our data seem to support the presence of primary myelinopathic damage in HMSN I.

Adolescent↗
PubMed1991

Physiologic properties of human dentate granule cells in slices prepared from epileptic patients.

The neurophysiological properties of human dentate granule cells were studied in hippocampal slices prepared from patients undergoing surgical treatment for medically intractable temporal lobe epilepsy. In 24 neurons which were morphologically identified as dentate granule cells by intracellular staining with biocytin, there were 2 types of synaptic responses to perforant path stimulation: one showed an EPSP-IPSP sequence (n = 10) and the other showed prolonged EPSPs without accompanying hyperpolarizing IPSPs (n = 14). The prolonged EPSPs were markedly retarded by the application of an NMDA receptor antagonist, APV. Membrane properties of neurons showing the different classes of synaptic responses were similar in resting membrane potential (pooled average: -56.2 mV +/- 0.94 SEM) and spike amplitude (pooled average: 65.2 mV +/- 1.69 SEM). However, membrane resistance tended to be lower in neurons with prolonged EPSPs (31.8 M omega +/- 2.63 SEM) than in neurons that showed EPSP-IPSP responses (40.2 +/- 4.33) (P less than 0.05, Fisher). No spontaneous and/or evoked burst firing was observed. These data provide fuller information on the neurophysiological properties of human dentate granule cells in surgically resected epileptogenic hippocampus, implicating a role of NMDA receptor activation in human temporal lobe epilepsy.

Action Potentials↗
PubMed1991

Desferrioxamine infusion can modify EEG tracing in haemodialysed patients.

Neurological derangement has been reported in haemodialysed patients receiving intravenous desferrioxamine (DFO) for aluminium-related disorders. The possible direct effects of desferrioxamine on EEG recordings were investigated in ten haemodialysed patients who underwent a DFO test 2 h after the end of dialysis. According to a commonly accepted protocol, 40 mg/kg body-weight of desferrioxamine was infused in 60 min. EEG recording was continuously performed, starting 30 min before and stopping 30 min after the desferrioxamine infusion. Besides visual inspection, EEG records were digitised, tapered, and spectrally analysed with Digital PDP 11/73 microcomputer. Basal EEG recording was normal in all patients. In three patients a progressive EEG slowing was detected by visual inspection during desferrioxamine infusion; in these cases automatic analysis revealed a 50% increase in power of slower frequencies 30 min after starting the infusion, when no changes in plasma aluminium concentrations are detected; a complete recovery was observed 30 min after desferrioxamine withdrawal. In one patient bilateral paroxysms of slow waves appeared, so we stopped desferrioxamine infusion. Two of the three patients who developed EEG abnormalities also had an increased aluminium body burden (positive DFO test). Results indicated that desferrioxamine per se can modify EEG in haemodialysis patients and that its effect is not mediated by acute increases of plasma aluminium concentrations. The finding of a positive DFO test in two of three patients with EEG changes may suggest that an aluminium-induced blood-brain barrier derangement could have played a role. However, prompt recovery after ceasing desferrioxamine infusion strongly suggests a direct role of desferrioxamine in the induction of EEG changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum↗
PubMed1990

Influence of surgery and antiepileptic drugs on seizures symptomatic of cerebral tumours.

One hundred and twenty-eight adult patients presenting with and operated on for supratentorial neoplasms were studied. Sixty-five had preoperative seizures and were treated with antiepileptic drugs (AEDs). Among the 63 patients without preoperative epileptic fits, 41 were given AEDs (either phenobarbital or phenytoin) as prophylactic treatment and 22 were not treated. The preoperative epilepsy course was considered with respect to tumour site and histological type. Early and late postoperative seizure occurrence was considered in the different groups of patients. The results suggest the usefulness of a short term preventive treatment with AEDs after surgery in patients without preoperative seizures. In patients with preoperative epilepsy, AEDs should be continued after surgery. However long-term AEDs treatment should not be recommended in patients without preoperative epilepsy. In fact, no significant difference in late seizure occurrence was found between preventively treated and untreated patients.

Adult↗
PubMed1989

Epilepsy course in cerebral gangliogliomas: a study of 16 cases.

From November 1979 to March 1988, 16 patients with cerebral gangliogliomas were investigated and underwent surgery at the Institute Neurologico "C. Besta" of Milan. Their age varied from 11 to 48 years. 15 of these patients presented with a seizure as the first and often the only neurological symptom. This report deals with the epileptologic and neuroradiologic features of these patients before and after surgical treatment.

Adolescent↗
PubMed1989

Excitatory amino acids mediate responses elicited in vitro by stimulation of cortical afferents to reticularis thalami neurons of the rat.

The effects of the excitatory amino acids on the nucleus reticularis thalami were examined by intracellular recordings from rat thalamic slices. Non-N-methyl-D-aspartate receptor agonists and glutamate induced a membrane depolarization and a reduction in input resistance, while N-methyl-D-aspartate and aspartate induced a prolonged discharge, which in some neurons took the form of a burst firing associated with an apparent increase in membrane input resistance. Both the N-methyl-D-aspartate and the aspartate effects were blocked by D-2-amino-5-phosphonovalerate, while the effects of glutamate, kainate and quisqualate were not. The excitatory postsynaptic potential evoked by corticothalamic fiber stimulation shows two components: an early, short-lasting, 2-amino-5-phosphonovalerate-insensitive portion, and a late, 2-amino-5-phosphonovalerate-sensitive decay phase. It is suggested that glutamate acts in nucleus reticularis thalami cells preferentially on the non-N-methyl-D-aspartate receptors, while aspartate shows an N-methyl-D-aspartate-like effect. The two excitatory amino acids glutamate and aspartate play a determinant role in the modulation of thalamic activity driven by corticothalamic projection.

2-Amino-5-phosphonovalerate↗
PubMed1989

Intrinsic properties of nucleus reticularis thalami neurones of the rat studied in vitro.

1. Neurones of the nucleus reticularis thalami of the rat were studied by intracellular recordings from in vitro slices. The resting membrane potential was -56.28 +/- 5.86 mV (mean value +/- S.D.); input resistance was 43.09 +/- 9.74 M omega; the time constant tau was 16.51 +/- 3.99 ms. At the resting membrane potential tonic firing is present, while at membrane potentials more negative than -60 mV a burst firing mode gradually prevails. 2. Prolonged depolarizing current pulses superimposed on a steady hyperpolarization consistently activated sequences of burst-after-hyperpolarization complexes. The all-or-none burst response consisted of Na+-mediated, TTX-sensitive fast action potentials superimposed on a low threshold spike (LTS). The burst was followed by a stereotyped after-hyperpolarization lasting 100-120 ms (BAHP), with a maxima -85 mV. The BAHP was blocked by Cd2+ and apamine but not by 8-Br cyclic AMP. The early component of BAHP was significantly attenuated by TEA. The oscillatory rhythmic discharges were abolished by agents which blocked the BAHP. 3. The presence of strong after-hyperpolarizing potentials (SAHP and BAHP) in RTN neurones plays a significant role in determining two different functional states, defined as tonic and oscillatory burst firing modes, respectively.

Action Potentials↗
PubMed1989

Brainstem auditory evoked potential abnormalities and magnetic resonance imaging in posterior fossa lesions.

Brainstem auditory evoked potentials (BAEPs) were evaluated in a series of 15 patients with extra-axial cerebello-pontine angle tumors (3 cases), demyelinating plaques (11 cases), and intra-axial tumor (1 case), verified by magnetic resonance imaging (MRI). A satisfactory correlation between the location of the lesions and the type of BAEP abnormalities was found in 11 cases. In 2 other cases, definite MRI brainstem lesions located outside the acoustic pathways were associated with normal BAEPs. In the opposite situation (2 cases of BAEP abnormalities with normal MRI), the inability of MRI to detect demyelinating lesions may be due to the temporal evolution of the lesions themselves. The results of this BAEP-MRI comparative study confirm that BAEP is a sensitive diagnostic tool in revealing brainstem dysfunction, although its localizing power appears to be debatable. The most satisfactory MRI/BAEP topodiagnostic correlation was found with lesions involving the acoustic nerve in its intracranial tract or the caudal pons and bulbopontine junctions.

Adolescent↗
PubMed1988

Electrophysiological characteristics of morphologically identified reticular thalamic neurons from rat slices.

This study is aimed at the investigation of the morphological and electrophysiological characteristics of neurons from the nucleus reticularis thalami in rat thalamic slices incubated in vitro. Ten neurons were recorded in the ventrobasal complex, four of which were successfully injected following horseradish peroxidase injection. Two main types of reticular thalamic neurons were morphologically identified: (1) the small fusiform 'f' cells characterized by a very elongated perikaryon, dendritic arborization prevalent in the rostrocaudal and dorsoventral planes, and an axon without any collaterals branching within the nucleus reticularis thalami; and (2) the large fusiform 'F' neurons with dendrites arborizing mainly in the horizontal plane and with axonal branches within the nucleus reticularis thalami. The electrophysiological properties of the neurons were similar in F and f cells. The reticular neurons showed, in resting conditions, a single spike response followed by a postexcitatory hyperpolarizing potential. The hyperpolarization of these neurons transformed the single spike response into a burst discharge similar to that observed in thalamic relay neurons at resting membrane potential. The same phenomenon was observed when bicuculline was administered by perfusion to the slices and, in this case, a recovery to a single spike response was obtained by a depolarizing d.c. current injection. By contrast, the local administration of GABA induced a depolarization with a pronounced decrease in input resistance. The present data demonstrate the presence of at least two neuronal subtypes within the nucleus reticularis thalami, suggesting that only one is responsible for the phenomenon of auto-inhibition by means of intrinsic axon collaterals. Moreover, it is hypothesized that intranuclear GABAergic collaterals could control neuronal excitability of reticular thalamic cells by both shunting the membrane and shifting the burst firing to a single spike firing mode.

Action Potentials↗
PubMed1986

Classification of the EEG during neurosurgery. Parametric identification and Kalman filtering compared.

A procedure is described which aims to classify an EEG recorded during neurosurgery, for example intracerebral aneurysm clipping. A parametric approach is used; it employs auto-regressive (AR) modelling and Kalman filtering to quantify directly the dynamics of the EEG generating mechanism, supposing it to be a linear, time-invariant system driven by white noise. The results of this EEG processing are analysed together with simultaneous values of arterial blood pressure (ABP) as surgery of this kind is carried out under conditions of controlled hypotension. The object is to compare the sensitivity of ABP data with that obtained from the EEG and so provide an early warning of a potentially dangerous non-physiological state induced by the hypotensive drug (in this case sodium nitroprusside). Some methodological comments on the correct implementation of these algorithms are given and the procedure is compared with similar approaches which have appeared in the literature during the last few years. Particular emphasis is placed on the power spectral analysis of the signal by pointing out a method for spectral decomposition, related to AR power density estimation, which permits the separation of single spectral components in terms of central frequencies and their associated power. Other potential applications of this method are in long term EEG monitoring for the detection of changes due for example to drug infusion, to fast transient events, or to changes in the stationary condition.

Anesthesia↗
PubMed1983

Oculomotor disorders in cortical lesions in man: the role of unilateral neglect.

The saccades of 22 patients with lesions of the left (6) and right (16) hemisphere were analysed. Seven patients with a right hemispheric lesion presented a left unilateral neglect (UN) syndrome. In the first test session the saccades were performed in response to a predicted sequence of targets; in the second session the luminous stimuli were unpredicted and randomized. In patients with UN we observed the absence of saccadic response to 25% of the targets a lengthening of the reaction time and a staircase pattern in the left hemifield. In the predicted stimulus sequence the oculomotor performance was not significantly better. Hemianopia, a defect of arousal and an altered visuospatial orientation are the most important elements that account for the alterations of oculomotor strategy in the UN syndrome.

Brain Damage, Chronic↗
PubMed1983

Plasma levels of primidone and its metabolite phenobarbital: effect of age and associated therapy.

The effects of age and associated therapy on plasma primidone (PRM) and derived phenobarbital (PB) concentrations, and on plasma concentrations-to-PRM dose ratios (L/D ratio) were evaluated retrospectively from 408 consecutive PRM and derived PB determinations in 238 chronically treated epileptic patients (153 children and adolescents between 5 months and 15 years of age and 85 adults between 16 and 55 years of age). The correlation between PRM administered and both plasma PRM and derived PB levels was significant; the correlation between PRM and PB plasma levels was also significant, but the scatter of values for the linear regressions was such that the relationship had no predictive value. Significant differences in mean plasma PRM and PB L/D ratios were found between patients aged 0-3 years, 4-9 years, 10-15 years, and adults (16-55 years), with higher values in the older groups. The PB/PRM concentration ratios were significantly lower in children than in adolescents and adults. Concomitant treatment with carbamazepine affected PRM disposition and led to increased L/D ratios for PB and decreased L/D ratios for PRM, whereas phenytoin increased the L/D ratios for PB without any significant change in the L/D ratios for PRM. The variability in the results indicates the need for routine monitoring of PRM and derived PB plasma levels, particularly in pediatric populations, in order to tailor the dose to each patient.

Adolescent↗
PubMed1983

Change of seizure frequency in pregnant epileptic women.

The effect of pregnancy on seizure frequency was monitored prospectively in 136 pregnancies of 122 epileptic women. Pregnancy did not influence the seizure frequency in 68 pregnancies (50%). In 50 pregnancies (37%) the number of seizures increased during pregnancy or puerperium. The seizure frequency decreased in 18 pregnancies (13%). In 34 out of 50 pregnancies (68%) the increase was associated with non-compliance with the drug regimen or sleep deprivation. In seven out of 18 pregnancies (39%) improvement was related to correction of non-compliance or sleep deprivation during the pregestational nine months. Insufficiently low plasma concentrations of antiepileptic drugs were found in 47% of the women with uncontrolled epilepsy during pregnancy. The course of epilepsy during pregnancy is primarily influenced by non-compliance, sleep deprivation during pregnancy, and inadequate therapy before and during pregnancy. With good medical attention pregnancy itself seems to have only a minimal influence on the course of epilepsy.

Adult↗
PubMed1982

Comparison of the effectiveness of several formulations of sodium valproate: tablets, enteric-coated capsules, solutions and rectal capsules.

The effects of an oral enteric-coated preparation (VAL 579 capsules) of sodium valproate (VPA) were compared with those of conventional oral and rectal preparations in 24 epileptic patients. Enteric-coated capsules are useful for avoiding gastric intolerance to VPA. Plasma VPA level peaks after the enteric- coated form were later than after other forms. The bioavailability appeared to be the same for all the forms.

Adolescent↗
PubMed1982

Oculomotor disturbances in Balint's syndrome: anatomoclinical findings and electrooculographic analysis in a case.

A 67-year-old man had repeated cerebral ischemic attacks, which resulted in a clinical picture combining paralysis of visual fixation, optic ataxia and impairment of visuospatial orientation, consistent with the definition of Balint's syndrome. Postmortem examination showed multiple lesions involving the occipital cortex of both sides and the white matter underlying the right insular cortex. EOG recording demonstrated a marked impairment of refixation saccades and saccades on verbal command. Smooth pursuit movements were completely abolished. Visual fixation was randomly achieved after many erratic exploratory movements and steadily maintained on the target (spasmodic fixation). During spasmodic fixation, EOG recording detected an ocular flicker resulting in a continuous instability of eye position. It is suggested that these findings may all be accounted for by the loss of panoramic vision due to a bilateral impairment of cortical areas 18 and 19.

Aged↗