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G Testa

Publications and source records attributed to G Testa.

At least 109 records · Page 6Linked to original sources
PubMed1987

On the intracortical activity during recruiting responses: an analysis of laminar profiles before and after topical application of GABA to the cortex.

Intracortical activity during recruiting responses (RRs) has been studied by recording laminar profiles of intracortical field potentials during repetitive stimulation, at 6 Hz, of nucleus centralis lateralis (CL) and nucleus centralis medialis (NCM) in lightly anesthetized cats, before and after topical application to the cortex of 1% GABA solution. The data obtained underwent current source density analysis (CSD) which disclosed that in the pre-GABA condition, there are two almost simultaneous sinks, one in the most superficial layer and the other in mid-cortical layers. After GABA application, a single large sink was present in mid-cortical layers. Extracellular single cortical unit activity was recorded in different animals, through a microelectrode tangentially inserted into the cortex, during repetitive stimulation of CL or NCM, both before and after GABA application. In 75% of these units there was, after GABA, a mean reduction of about 50% of firing probability while in the remaining 25% there was an increased activity. Topical application of 1% Manganese sulfate to the cortical surface appeared to completely inactivate the whole thickness of the cortex where it was applied, making evident the contribution to RRs of the potentials generated in the cortex buried in the adjacent sulci. Finally, a reciprocal facilitating effect of RRs and augmenting responses (ARs), which was studied by combined stimulation of nucleus ventralis posterolateralis (VPL) and NCM, appeared to be dependent upon an intracortical mechanism. All these data suggest that: RRs are the result of a simultaneous activation of superficial and mid-cortical layers; RRs are contaminated by a volume conducted potential arising from the cortex buried in the sulci; a superficial inhibition following the initial excitation seems to be an usual component of the response; ARs and RRs probably share a similar intracortical mechanism for incrementing the response.

Animals↗
PubMed1986

Laminar field potentials and unit activity in the cortex during visual evoked potentials in feline generalized penicillin epilepsy.

Modifications of the visual evoked potential during generalized epilepsy were investigated in feline generalized penicillin epilepsy. Visual evoked potentials and their intracortical profiles were averaged during intraburst periods and during the wave of the spike and wave complex to a fixed latency from the preceding spike. During interburst periods, the evoked potentials showed an increase in the amplitude of the early positive peak and the appearance after a variable latency period of a second consistent peak during the late phase of the evoked potential. Laminar profiles of visual evoked potentials and their current source density analysis compared with the activity of single cortical units suggested an early excitation of neuronal populations at layers II, III and IV, as seen before penicillin, followed by a variable inhibitory period and by a subsequent rebounded excitation at those same levels. In evoked potentials recorded during the wave of the spike and wave complex, the early phase was unchanged and the late positive peak and the corresponding deep sink were greatly reduced or nonexistent, although the rebounded activation of cortical units was still evident. These data support the conclusion that during feline generalized penicillin epilepsy a larger number of cortical neurons are activated and a sequence of excitation-inhibition-excitation, probably involving also subcortical structures, is brought about. Moreover, the inhibitory phase of the spike and wave complex is soon disrupted whenever a consistent sensory stimulus arrives at the cortex.

Action Potentials↗
PubMed1985

Involvement of cortical, thalamic and midbrain reticular formation neurons in spike and wave discharges: extracellular study in feline generalized penicillin epilepsy.

Extracellular activity of single units, simultaneously recorded in cortex, thalamus, and midbrain reticular formation was investigated during feline generalized penicillin epilepsy. The firing activity of neurons recorded in the cortex was invariably and consistently enhanced in coincidence with the positive peak and the positive-negative transient of the "spike" of the spike and wave complex, and it was greatly decreased during the wave. In the nonspecific thalamic nuclei three classes of neurons were identified according to their patterns of activity during the spike and wave complex: (i) neurons behaving like cortical units, (ii) neurons with enhanced firing activity during the wave and a decreased activity during the "spike," and (iii) unmodified neurons. In the nucleus lateralis posterior neurons of the third class were not found. Most midbrain reticular neurons could be classified in the same three classes of the nonspecific thalamic nuclei; however, 11% of those units increased their activity 20 to 30 ms earlier than did the cortical units (class IV). Investigation of the activities of all these neuronal populations immediately prior to a spike and wave discharge showed that the rhythmic cycle of excitation-inhibition commenced earlier in the cortical neurons than in any other subcortical neuron. Moreover, there were some nonspecific thalamic neurons of class II with an inhibitory phase exactly coincident with the activation of class IV midbrain reticular neurons. These data suggest (i) a leading role of cortical neurons in initiating and maintaining a spike and wave burst; (ii) the involvement of a corticothalamocortical circuit in timing the bursts, and (iii) an accessory reticulothalamic loop also involved in regulating the intraburst frequency of the spike and wave complex.

Action Potentials↗
PubMed1985

Effects of GM1 ganglioside in cerebrovascular diseases: a double-blind trial in 40 cases.

A randomized, double-blind trial on the effects of GM1 ganglioside in cerebrovascular diseases was done on 40 patients; the treatment (40 mg/day i.m. injection) began after the acute phase and lasted 6 weeks. 18 cases took the drug and 16 the placebo. The evaluation of the cases was made by graduating the severity of the clinical signs, and some neurophysiological and morphological parameters, i.e., EEGs, flash-evoked potentials and computer tomography scans. We found that the drug, in comparison with the placebo treatment, improved the clinical signs and also the neurophysiological parameters, whereas it was ineffective for the morphological damage. These data seem of some interest in relation to the action of GM1 ganglioside in the processes of neurotransmission and neuronal plasticity as described in the experimental animal.

Adult↗
PubMed1982

Feline generalized epilepsy induced by tranexamic acid (AMCA).

Epileptic activities induced by topical application of tranexamic acid (AMCA) and penicillin to the cortex of 12 cats in acute experiments were compared. Both substances when diffusely applied on a wide cortical area of both hemispheres at very low concentration produced an EEG pattern consisting of spike-wave bursts similar to the electrographic manifestations seen in feline generalized epilepsy induced by large parenteral doses of sodium penicillin. These epileptic bursts could be triggered by repetitive stimulation of nucleus centralis medialis. Increased concentrations of both AMCA and penicillin led to the appearance of bilaterally synchronous spikes and poly-spikes which were not further excited by NCM stimulation. Two factors seem to play an important role in eliciting spike-wave bursts in both models: (1) the area of the cortex exposed to the epileptogenic agent and (2) the concentration of the epileptogenic agent used. The similar effects observed in 5 chronic animals either by intravenous injection of high doses of AMCA or by intramuscular injection of sodium penicillin confirm the results obtained in acute experiments and suggest a new way of inducing feline generalized epilepsy.

Administration, Topical↗
PubMed1980

[Althesin-induced EEG changes in patients with central nervous system lesions].

The EEG changes produced by Althesin (75 microliter/kg intravenously administered over 60 sec) were evaluated in 18 unpremedicated patients wih CNS diseases who were scheduled for cerebral angiography. Three parameters were analyzed: the EEG patterns of anaesthesia, the appearance of a fast activity during stabilized burst suppression (Level V), and enhancement of the registered epileptiform abnormalities. The EEG depth of anaesthesia was correlated with the EEG pattern at rest and the preexisting neurological signs. The 15 Hz fast activity which occurred during the suppression phase of Level V was recorded unilaterally over the healthy hemisphere, while it was observed bilaterally in a case involving lesion of the midline structures. The exaltation of the epileptiform EEG discharges following Althesin administration suggests that this agent might be utilized as a convenient provocative test in the diagnosis of epilepsy.

Alfaxalone Alfadolone Mixture↗