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Biomedical subjects

P Mares

Publications and source records attributed to P Mares.

At least 307 records · Page 17Linked to original sources
PubMed1982

Changes in the excitability of rat cerebral cortex after a self-sustained after-discharge.

Changes in the duration of the cortical self-sustained after-discharge (SSAD) were studied in relation to the preceding SSAD in adult rats. An "excitability cycle" could be constructed by means of different intervals between the end of the first SSAD and the beginning of subsequent electrical stimulation of the sensorimotor cortex. During short intervals (30, 60 and 120 sec) the second SSAD was significantly shorter than the first. No significant differences were found with intervals of 3 and 5 min; all longer intervals, except 120 min, resulted in significant prolongation of the second SSAD. The possibility of elicitation of the second SSAD also increased with increasing intervals, demonstrating thus the presence of a "refractory period." The results with manifold stimulation demonstrated the rather complicated nature of the changes of excitability during post-ictal periods.

Animals↗
PubMed1982

Ontogenetic development of rhythmic thalamo-cortical phenomena in the rat.

Three rhythmic cortical phenomena (rhythmic after-discharges, incremental responses and self-sustained after-discharges formed by spike-and-wave rhythm) were elicited by electrical stimulation of thalamic nuclei during ontogenesis in rats. All three phenomena could be recorded for the first time at the age of 12 days and they matured until the 18th postnatal day. Possible explanation for the delayed development of these rhythmic thalamo-cortical phenomena in comparison with single thalamo-cortical responses are discussed.

Aging↗
PubMed1982

Influence of clonazepam and ethosuximide on ECoG pattern induced by metrazol during ontogenesis in rats.

Metrazol (80 mg/kg s. c.) elicited ECoG episodes of rhythmic activity the shape, frequency and localization of which depended on the age of rats. In 15- and 12-day-old animals there was a progression into sustained ictal activity. Clonazepam (1 mg/kg i. p.) exhibited excellent anti-metrazol action in adult, 25- and 12-day-old rats. The results in 15-day-old animals were inconsistent. Ethosuximide (125 mg/kg i. p.) protected sufficiently only adult and 25-day-old rats. In younger age groups only ictal activity was blocked, while metrazol-induced episodes remained untouched.

Age Factors↗
PubMed1982

Anti-metrazol effects of nitrazepam during ontogenesis in the rat.

Anti-metrazol effect of nitrazepam was studied in male rats aged 7, 12, 18 and 90 days. Nitrazepam protected all age groups against seizures elicited by metrazol (80 mg/kg s.c.); the 50%-protective dose decreased from 165.7 micrograms/kg in adult rats to 70.2 micrograms/kg in 7-day-old animals. The sensitivity of 7-day-old and adult rats to metrazol is nearly the same, so that we may conclude that nitrazepam exhibits higher anti-metrazol potency in 7-day-old rats than in adult ones.

Age Factors↗
PubMed1982

Synchronization of double asymmetrical epileptogenic foci in the cerebral cortex of the rat.

Discharges of two asymmetrical penicillin foci progressively synchronized during 25 min after creation of these foci. Section of the corpus callosum seriously impaired but did not completely block this synchronization. Thalamic spreading depression did not significantly change the synchronization in rats with intact corpus callosum. Noncallosal component of synchronization is probably realized through brain stem structures.

Animals↗
PubMed1981

Electrocorticographic activity induced by gamma hydroxybutyrate in the rat during ontogenesis.

GHB at a dose of 200 mg . kg-1 i.p. elicited groups of slow waves with a frequency of 4--5 Hz in both frontal and occipital ECoG leads in adult rats. In 25- an 18-day-old rats similar slow wave activity became continuous and exhibited a clear-cut maximum in the frontal regions. In 15- and 12-day-old animals slow wave activity was also registered in the frontal region but it was organized into short groups of unstable frequency. No ECoG effects of GHB could be found in 9-day-old rats.

Aging↗
PubMed1981

Effect of phenobarbital on cortical epileptogenic foci in the rat.

The activity of epileptogenic foci was studied in acute experiments on adult male rats without general anaesthesia; the animals first received an intraperitoneal injection of phenobarbital [40 mg/kg] and 30 min later a cortical focus was induced by the local application of penicillin. These foci, which were induced in the sensorimotor area, had a lower discharge frequency than in the controls and the formation of projected discharges was delayed. In two symmetrical and asymmetrical cortical foci, activity was synchronized significantly more slowly after phenobarbital than in the controls. The cortical interhemispheric response was not influenced by the administered dose of phenobarbital. In these experiments, phenobarbital had an anti-epileptic effect both on the primary focus and on the spread of epileptic activity from this focus.

Animals↗
PubMed1981

Effect of antiepileptic drugs on metrazol convulsions during ontogenesis in the rat.

The effect of ethosuximide, dipropylacetate and clonazepam on metrazol convulsions induced by a dose of 80 mg/kg was studied in 314 male albino rats aged from 5 days to adult. In a standard dose of 125 mg/kg, ethosuximide reliably protected only adult and 25-day-old rats, i.e. the age groups in which a mature minimal seizure was the only type of convulsion induced; in younger animals, not even a much higher dose (tested in 12-day-old rats) afforded reliable protection. Dipropylacetate and clonazepam had a manifest protective effect in all age groups, irrespective of the type of seizure. Isolated myoclonic jerks were less sensitive to antiepileptics and only dipropylacetate blocked them in the youngest age groups. In 21-day-old and older animals dipropylacetate induced stereotype head movement reminiscent of the serotonergic stereotypy described in the literature.

Age Factors↗
PubMed1981

Effect of pentobarbital on thalamo- and hippocampocortical processes in rats.

Experiments were carried out on 28 rats immobilized with d-tubocurarine. The effect of three successive doses of pentobarbital (PB--5, 15 and 40 mg.kg-1) on electrocorticographic manifestations (evoked responses, the rhythmic afterdischarge and barbiturate spindles, the self-sustained afterdischarge--SSAD) elicited by electrical stimulation of two thalamic nuclei with a different type of control projection and the hippocampus (CA3) was compared. We found no difference between the effect of PB on cortical electrographic manifestations elicited by stimulation of the dorsomedial part of the ventral nucleus (VDM) and the anterior lateral nucleus (LA) of the thalamus. Cortical responses elicited by stimulation of the hippocampus were heterogeneous and the effect of PB on them was smaller than on thalamocortical responses. Reduction of the hippocampocortical SSAD was likewise not significant until the deepest stage of barbiturate anaesthesia.

Animals↗
PubMed1980

The ontogenesis of cortical self-sustained after-discharges in rats.

An ontogenetic development of cortical self-sustained after-discharges (SSADs) was studied in acute experiments on 98 male albino rats aged from 9 days to adulthood. Rhythmic electrical stimulation of one cortical sensorimotor area regularly elicited SSADs formed by spike-and-wave complexes starting from the postnatal day 15. Frequency of these complexes increased from 2.0 to 2.5 cycles/s in 15- and 18-day-old rats to 3.0 to 4.0 cycles/s in older animals. In younger animals SSADs were better expressed in the stimulated sensorimotor than in the visual area of both hemispheres, whereas in older rats the SSADs were fully generalized. The SSADs became longer with increasing age. A highly significant prolongation of the SSADs was seen in all age groups with repeated stimulations; this finding is discussed as a possible form of kindling.

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