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Biomedical subjects

M G Marciani

Publications and source records attributed to M G Marciani.

At least 73 records · Page 4Linked to original sources
PubMed1986

Clinical evaluation of biofiltration in uremic patients undergoing chronic hemodialysis.

The clinical efficiency of biofiltration (BF) was evaluated in six hemodialysis patients with poor clinical tolerance for standard hemodialysis. Three were adults (mean age 34 years, mean body weight 67 kg) and three adolescents (mean age 17 years, mean body weight 38 kg). Mean maintenance hemodialysis time was 90.5 months (range 49-132). BF treatments lasted three hours in all cases, for a total of nine hours weekly, with AN69 S membranes and infusion of 3 liters of HCO3 solution (100 mEq/l for the adults, 80 mEq/l for the adolescents). We recorded intra- and inter-dialytic symptoms daily, hematological values and acid-base status monthly. Multimodality evoked potentials were recorded after 3 and 9 months. Biochemical values reached a steady state 9 months from the beginning of the study, metabolic acidosis was corrected more efficiently in both groups at the end of dialysis, but only in the adult patients, were pre-dialysis plasma bicarbonates within normal limits. A clear drop in the number of episodes of intradialytic hypotension was noticed in both groups, but the adolescent patients' tolerance for dialysis did not improve. In conclusion our data show that in adult patients with poor tolerance BF offers a dependable alternative to standard hemodialysis, and the length of treatment can be reduced.

Acid-Base Equilibrium↗
PubMed1985

Electroencephalographic spiking activity, drug levels, and seizure occurrence in epileptic patients.

We investigated the relationships among the electroencephalographic spiking rate, drug levels, and seizure occurrence in 44 patients with focal epilepsy. Seizure occurrence was continuously monitored by personnel or videorecording and spiking rate was quantified by an automatic detection method. Results indicate that drug levels do not influence spiking rate, and spiking rate does not change before seizures but increases markedly after them, particularly secondarily generalized seizures. This increase can last several days and is observed during wakefulness and sleep. High or low spiking rates do not influence the occurrence of seizures. We suggest that interictal spikes may passively reflect damage to the brain, a damage which is worsened by further seizures. Spikes may not be directly related to seizure generation.

Adult↗
PubMed1985

Nervous propagation along 'central' motor pathways in intact man: characteristics of motor responses to 'bifocal' and 'unifocal' spine and scalp non-invasive stimulation.

In 23 healthy adult volunteers motor action potentials (MAPs) were elicited in upper and lower limb muscles during stimulation of appropriate sites at spinal and scalp level, through skin electrodes. 'Bifocal' stimulation of scalp and spine motor tracts was performed with 2 plaques (3.5 cm2 each), delivering single pulses of 440-940 mA, less than 50 microseconds in duration, which elicited high voltage (up to 10 mV) MAPs in arm and leg muscles. 'Unifocal' stimulation of scalp was carried out through a cathode consisting in a belt or in a series of rectangular interconnected plaques secured around the head, 1-2 cm rostral to the nasion-inion plane, and in a circular anode placed on the appropriate scalp site. MAPs with similar amplitude-latency characteristics were recorded with both 'bifocal' and 'unifocal' stimulating methods. However, the 'unifocal' stimulation necessitated 5-10 times less current than the 'bifocal' one. The 'unifocal' device using the interconnected plaques (6-12 in number) provided the most tolerable stimuli with the lowest amount of current (60-106 mA, rectangular pulses of 100-150 microseconds). Conduction times and velocities of motor pathways in various 'central' and 'peripheral' districts were calculated. Voluntary contraction of target muscles remarkably enhanced MAP amplitudes during scalp, but not during spine stimulation. A nerve action potential was recorded from ulnar nerve during scalp stimulation. MAPs in hand muscles to scalp stimulation were obliterated by the simultaneous activation of the peripheral fibres innervating the target muscle, because of collision between ortho- and antidromically propagated motor impulses. Anodal stimuli showed liminal values significantly lower than the cathodal ones. Mapping studies have been carried out with 'unifocal' scalp stimulation by using different types of anode and of stimulus parameters.

Action Potentials↗
PubMed1985

Patterns of seizure activation after withdrawal of antiepileptic medication.

Effects of withdrawal of anticonvulsant drugs on the temporal profile of occurrence and the type of seizures were investigated in 40 intractable epileptic patients who were candidates for surgical treatment. EEG and behavior were monitored while drugs were reduced to allow localization of the epileptogenic region. The rapid withdrawal of drugs caused a rebound effect, triggering either generalized seizures during a brief period or a longer-lasting increase in partial seizures. These increases in seizure frequency appeared related to change in dosage rather than to dosage itself, since they remained largely confined to the early period following reduction of an anticonvulsant.

Adult↗
PubMed1984

Dopaminergic and noradrenergic responses in the hippocampal slice preparation. Evidence for different receptors.

The effects of iontophoretic applications of dopamine (DA) and noradrenaline (NA) on potentials evoked by the stimulation of the hippocampal slice preparations were investigated. Dopamine, ejected at the soma, produced an increase of the amplitude of the population spike of CA1 pyramidal cells; NA had an excitatory action on some responses, inhibitory on others. The field-excitatory postsynaptic potentials (EPSPs) were unaffected by ejection of DA and NA on the dendritic tree. Domperidone, a dopaminergic antagonist, blocked the increase of the population spike induced by DA, but was unable to antagonize noradrenergic responses. Timolol, a beta-adrenergic antagonist, blocked the excitatory action of NA, but did not modify either the effect of DA or the inhibition induced by NA. Phentolamine, an alpha-antagonist, antagonized only the inhibition induced by NA. These results indicate that DA and NA modulate the activity of hippocampal neurones by interacting on different receptors.

Animals↗
PubMed1982

Responses of intracellularly recorded cortical neurons to the iontophoretic application of dopamine.

Considering that a well-defined dopaminergic projection from the mesencephalic structures to the rat frontal cortex has been demonstrated, the purpose of this research was to study the action of iontophoretically applied dopamine (DA) on intracellularly recorded rat frontal neurons. The stimulation of the substantia nigra (SN) and the ventral tegmental area (VTA) evoked EPSP-IPSP sequences in these cells. About 50% of the tested neurons, widely distributed in all the frontal cortex, responded to DA application and no difference in the response to DA was observed between neurons with monosynaptic inputs and neurons with polysynaptic inputs. The catecholamine depolarized the cell membrane and decreased the firing rate, generally without significant changes in membrane resistance, as already observed in rat and cat striatal cells. In some neurons the decrease of the spikes preceded the membrane depolarization. Considering the complex effect of DA on the electrical properties of these neurons, these results seem to be indicative of a mechanism of action dependent on metabolic changes.

Animals↗
PubMed1982

Aspartate-induced changes in extracellular free calcium in 'in vitro' hippocampal slices of rats.

Extracellular free calcium ([Ca2+]0) and neuronal activity were measured with double-barreled Ca2+-selective/reference microelectrodes in the CA1 field of rat hippocampal slices during stimulation of Schaffer collaterals and during iontophoretic application of the excitatory amino acid aspartate (Asp). Baseline [Ca2+]0 was 1.5 mM. Repetitive stimulation and aspartate application caused decreases in [Ca2+]0 (delta Ca), which were largest in the pyramidal cell layer. During iontophoretic application of GABA, aspartate often failed to induce significant alterations in [Ca2+]0. Mg2+ (9 mM) and Ni2+ (3mM) when added to the perfusion medium reduced aspartate-dependent delta Ca by 15 and 70% respectively. In tetrodotoxin (10(-6) M) containing Ringer the aspartate-induced delta Ca were about 10% smaller. These findings suggest that the decreases in [Ca2+]0 are mainly due to a postsynaptic Ca2+ entry through selective Ca2+ conductances.

Animals↗
PubMed1982

Evidence in favor of a neurotransmitter role of glycine in the rat cerebral cortex.

In the present study we analyze whether glycine satisfies some electrophysiological and biochemical criteria to consider it as a putative transmitter in the rat cerebral cortex. Intracellular recordings from rat sensory-motor cortex showed that in 15-20% of the tested neurons glycine hyperpolarized the cell membrane, decreased the firing rate and flattened the evoked EPSP-IPSP sequence by increasing the membrane conductance. The iontophoretic application of strychnine antagonized the block of 'spontaneous' firing and the membrane hyperpolarization induced by glycine. Moreover, in a group of neurons, strychnine decreased the amplitude and duration of the IPSP and brought back the membrane potential to resting values. Previously accumulated [3H]glycine and endogenous glycine were released from cortical synaptosomal preparations by depolarizing stimuli in a Ca2+-dependent way. The release pattern of glycine was qualitatively similar in cortical and in spinal synaptosomes. [14C]Glycine was rapidly synthetized from [14C]serine in cortical synaptosomal preparations, and the newly formed [14C]glycine was released by depolarizing stimuli in a Ca2+-dependent way. It is concluded that glycine, which is generally considered as an inhibitory neurotransmitter in the spinal cord, medulla and pons, may also have a transmitter role in a discrete number of cortical neurons of some mammalian species.U

Animals↗
PubMed1981

The action of glycine on rat epileptic foci.

The action of glycine (Gly) intravenously injected on rat epileptic foci induced by strychnine or penicillin topically applied, was compared with that of GABA. Gly (450 mg/kg i.v.) produced a complete block of the spiking activity. The inhibitory action of GABA (80 mg/kg), in terms of threshold and duration, was stronger than the action of Gly. The same inhibitory effect was also observed if these amino acids were applied topically or intracisternally. These results are consistent with the possibility that Gly has a role in the rat cortical inhibition.

Action Potentials↗
PubMed1980

Action mechanisms of gamma-aminobutyric acid (GABA) and glycine on rat cortical neurons.

The actions of GABA and glycine (Gly), iontophoretically applied to rat cortical neurons, were compared. These amino acids hyperpolarized the membrane cell, decreasing the membrane resistance. The results show that the ionic mechanisms involved in the inhibitory actions of GABA and Gly are probably the same in contrast with the results obtained in cat cortical neurons.

Animals↗
PubMed1979

The inhibitory action of glycine on rat cortical neurons.

The action of glycine (Gly) on rat cortical neurons was studied. Gly, iontophoretically applied, hyperpolarized the membrane potential, blocked the firing rate and decreased the amplitude of EPSP-IPSP sequences. Generally the membrane resistance during the aminoacid ejection decreased. The role of Gly in the rat cortical inhibition is discussed.

Animals↗