Ruggero G. Fariello

Neuroradiological correlates of frontally predominant intermittent rhythmic delta activity (FIRDA)

A correlative, retrospective review of 80 consecutive cases of EEG FIRDA was performed with regard to the neuroradiological findings: 62 of the 80 patients had had CAT scan evaluations. Of the 61 patients with structural pathology, 53 had CAT scans which were abnormal in 40 (76%); of the 19 patients with non-structural (mostly metabolic) brain lesions, 10 had normal CAT scans. In the structural group with normal CAT scans, the presence of pathology was demonstrated by arteriography (5 cases), radionuclide cysternography (1 case), brain scan (1 case), or pathological examination. Patients with non-structural FIRDA had a significantly higher probability of being in an altered state of consciousness and of having abnormal background activity in their EEG. Focal EEG abnormalities are more frequently associated with structural lesions and FIRDA. If FIRDA is present on the EEG, further neuroradiological studies should be considered, especially with other electroclinical information suggests a non-metabolic substrate.

Correlation of abnormalities of interictal n-isopropyl-p-iodoamphetamine single-photon emission tomography with focus of seizure onset in complex partial seizure disorders

Summary: Single‐photon emission tomography (SPECT) scanning with n‐isopropyl‐p‐iodoamphetamine (IMP) was performed on 23 patients with complex partial seizures undergoing long‐term video/electroencephalographic (EEG) seizure monitoring. Twenty‐one of the 23 patients had abnormalities on SPECT scanning consisting of areas of decreased activity reflecting diminished cerebral blood flow. In 15 of these 21 patients, there was good correlation between the site of the abnormality on SPECT scan and the site of origin of seizures monitored by EEG. Of the six remaining patients, four had multifocal SPECT abnormalities, with one of the abnormal areas corresponding with an ictal site. The two remaining patients had SPECT abnormalities and major ictal EEG foci in entirely different areas. In contrast to the high proportion of abnormal SPECT scans, only 10 of 23 focal abnormalities were discovered on magnetic resonance imaging (MRI) scans. Three patients who had seizures within 2 h of an initial scan were rescanned 4–5 h after injection. Focal areas of increased blood flow were noted on all three scans, although not always at the ictal site. The SPECT scan appears to be useful in interictal localization of seizure foci. Postictal scans may also be useful, although our numbers are too small to draw conclusions.

Substantia nigra and pentylenetetrazol threshold in rats: Correlation with striatal dopamine metabolism

Abstract The time course of the metrazol threshold in rats with electrolytic lesions of the substantia nigra presents variations inversely proportional to the changes in dopamine and its metabolites in the neostriatum. Thus initially dopamine is increased and the threshold lowered, then a progressive decrease in dopamine and its metabolite is accompanied by a progressive increase in metrazol threshold. This supports the hypothesis that changes in functional activity of the caudate nucleus are reflected in variations of the brains susceptibility to generalized seizures. When cobalt chloride was injected into the substantia nigra there were biochemical changes in the neostriatum similar to those observed with electrolytic lesions, but the pentylenetetrazol threshold steadily decreased. This is probably due to the fact that cobalt induces a lesion which changes in extent with time to involve adjacent brain stem nuclei sensitive to its epileptogenic action.

Parenteral Penicillin in Rats: An Experimental Model of Multifocal Epilepsy

Parenterally injected penicillin in rats induces a peculiar pattern of multifocal epilepsy. The effective amount is higher than that required in cats. The epileptiform activity initially appears on the cortical mantle of one hemisphere; after a variable delay, contralateral cortical spikes arise in a completely asynchronous way. Spontaneous independent firing is observed, with a further delay in subcortical structures. Although cortical spiking shows a tendency to become bilaterally synchronous, such synchrony has been only occasionally observed between the various subcortical structures. Formation of generalized spike‐and‐wave complexes, as reported in cats, or other features reminiscent of the human petit mal did not occur. This study stresses the differences in pathophysiological responses to the same epileptogenic model according to species variation.

Activating Effects of Homotaurine and Taurine on Corticoreticular Epilepsy

Summary: Homotaurine and taurine are two powerful inhibitory aminoacids with anticonvulsant properties against various experimental models of focal epilepsy. This study reports on their effects in the feline model of corticoreticular epilepsy induced by parenteral administration of large amounts of penicillin. Both aminoacids, but particularly homotaurine, remarkably potentiate epileptiform discharges in cats. Brainstem transection at the precollicular level does not modify the activation, thus ruling out the intervention of mesoromboencephalic structures in the observed effect. The opposing action of these two amino acids on focal epilepsy as compared to corticoreticular epilepsy suggests that the two types of epileptiform activity stem from very different pathophysiological mechanisms. Homotaurine is a powerful GABA agonist that exerts a central action upon parenteral administration. Other GABA analogs such as muscimol, imidazole acetic acid, and γ‐hydroxy‐butyrate have been reported to potentiate experimental models of spike and wave epilepsy. Thus, the activating effects of homotaurine in this epilepsy model are in keeping with the demonstrated GABAmimetic properties of the compound.

Epileptogenic properties of enflurane and their clinical interpretation

Three cases of EEG changes induced by single exposure to enflurane anesthesia are reported. In one patient, enflurane administered during a donor nephrectomy resulted in unexpected partial motor seizures. Until the cause of the seizures was correctly identified, the patient was inappropriately treated with anticonvulsants. Two other patients suffered from partial, complex and generalized seizures uncontrolled by medication. Epileptic foci delineated and activated by enflurane were surgically ablated and the patients are now seizure-free. Previous exposures to enflurane have to be disclosed to avoid mistakes in clinical interpretation of the EEG. On the other hand, enflurane may prove to be a safe fast acting activator of epileptic foci during corticography or depth electrode intraoperative recordings.

Action of inhibitory amino acids on acute epileptic foci: an electrographic study.

Abstract Epileptiform activity was induced in adult cats anesthetized with Ketamine or Na-pentobarbital. Acute models of focal epilepsy were created by application of various epileptogenic agents to neocortical or limbic structures. Inhibitory amino acids were injected intravenously and their effects on epileptiform discharges monitored for 2 h after administration. Amino acid solutions were adjusted to pH between 5.5 and 8. Glycine (to 250 mg/kg) did not induce any change. Short-lasting inhibitory effects (5 s to 9 min) were noted with β-alanine, γ-aminobutyric acid (GABA) (>80 mg/kg), taurine (>50 mg/kg), and 3-aminopropane sulfonic acid (3-APS, >5 mg/kg). The action of 3-APS was particularly powerful in abolishing cortical spiking with only moderate depression of background EEG activity. GABA, taurine, and 3-APS also induced depression of respiration in animals under barbiturate anesthesia. In addition, 3-APS caused a 20% decrease in systolic blood pressure. Similar and even greater pressure decreases were observed after injection of control drugs which did not, however, affect the epileptic firing rate. 3-APS seems to deserve further investigation as a possible antiepileptic and GABA-mimetic agent.

Limbic spindles: Genuine cerebral activity or artifact?

A periodic spindling activity recorded in clinical EEG laboratories from nasopharyngeal (NP) leads has been interpreted as expression of genuine cerebral rhythms originating in the limbic system. Evidence is here presented to suggest that such activity is indeed an artifact. Genuine spindling occasionally occurs in NP leads but this is intimately related to sleep spindles occurring also in other surface electrodes.