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Biomedical subjects

J Mares

Publications and source records attributed to J Mares.

At least 91 records · Page 5Linked 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

Ultrastructural changes in cortical synapses shortly after termination of a seizure during kindling.

Repeated electrical stimulation of the sensorimotor region of the rat cerebral cortex at 10-min intervals led to progressive lengthening of the self-sustained after-discharges (SSAD). 50-60 s after termination of the third SSAD we examined, in the electron microscope, type I synapses (after Gray) in the second cortical layer of the sensorimotor region of the contralateral hemisphere. In the experimental animals we demonstrated swelling of both the pre- and post-synaptic elements, a decrease in the number of agranular synaptic vesicles and variability of their shape and size. Frequent manifestations of exo- and endocytic activity and a frequent incidence of complex vesicles have been described. Saccular dilatation of the space between the outer and inner mitochondrial membrane in the presynaptic terminal and dilatation of the terminal cisternae and extracellular space occurred. Alteration of the spine apparatus was observed in the postsynaptic elements. At the margin of the active zone we described simultaneous invagination of the pre- and postsynaptic membrane up to the formation of rounded structures with two concentric membranes. The changes in the synapses are conceived as signs of exhaustion due to the previous epileptic seizure, which on the other hand, activated the restitution mechanisms of the structure of the synaptic apparatus.

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.

Age Factors↗
PubMed1980

Number of synaptic vesicles in the rat somatosensory cortex after repetitive electrical stimulation prolonging self-sustained after-discharges.

The sensorimotor area of the cerebral cortex of rats was repetitively electrically stimulated (8 Hz for sec) at 10-min intervals, inducing a gradual prolongation of self-sustained after-discharges (SSADs). At 10 min after termination of the third SSAD, the animals were perfused with a fixation solution. The homotopic area of the contralateral hemisphere was examined in the electron microscope. In the II cortical layer, the agranular synaptic vesicles in type I synapses (after Gray) were counted close to the synaptic cleft. The number of synaptic vesicles was significantly increased in the experimental animals.

Animals↗
PubMed1980

Changes in some parameters of the presynaptic bag in synapses of the somatosensory cortex of the rat brain after repetitive electrical stimulation prolonging self-sustained after-discharges. An electron microscopic morphometric study.

The sensorimotor area of the rat cerebral cortex was subjected to repeated electrical stimulation at 10 min intervals; this progressively prolonged the duration of self-sustained after-discharges (SSAD). Ten minutes after the third SSAD ended, the animals' brains were perfused with fixing fluid. The homotopic area of the contralateral hemisphere was examined electron microscopically. In type I synapses in the second cortical layer we determined A) the mean areas of sections of the presynaptic bag, B) the length of the active zone of the presynaptic bag, C) the mean total number of agranular synaptic vesicles per 0.01 micron2 area of the presynaptic bag in the experimental and control rats. In the experimental animals value A) rose by 34%, value B) by 14%, value C) by 95% and value D) by 52%. The differences are all statistically significant. Findings A) and B) are most likely evidence of ionic shifts, while findings C) and D) testify to the increase in the number of synaptic vesicles in the whole presynaptic bag and also to their redistribution towards the synaptic cleft. The possibility that findings C) and D) are the morphological correlate of increased synaptic transmission during experimental treatment leading to the kindling phenomenon cannot be ruled out.

Animals↗
PubMed1978

The influence of GABA on discharges of cortical epileptogenic focus.

GABA, when applied locally, acted similarly on both primary and mirror cortical focus: the negative component of the spike discharge was suppressed or inverted in polarity, whereas the late slow negative wave was strongly potentiated. Recordings from deep cortical layers suggested a different origin of these 2 surface-negative components of focal discharges.

Action Potentials↗
PubMed1978

Triggering of discharges from an epileptogenic focus in the rat by stimulation of the contralateral hemisphere. an ontogenetic study.

Fifty-two male albino rats aged 7, 9, 12 and 18 days and adult, immobilized with d-turbocurarine, were studied. Discharges were triggered from a penicillin focus with electrical pulses of double the threshold intensity needed to evoke an interhemispheric response (IHR). Developmental changes in the IHR and in spontaneous interictal discharges did not differ from the results described in earlier studies. Practically no discharges could be triggered in 7-day old animals (only a few at a very low stimulation frequency). In the other age groups, discharges were triggered at two optimal frequencies, of which the lower one rose from 0.1 to 0.6 c/s during development, while the higher one was relatively stable (about 1 c/s). With higher frequency triggering, marked signs of fatigue of the focus (intermittent triggering, loss of the main negative wave) appeared, especially in young animals. The averaged shape of triggered discharges was similar in 9- and 12-day-old rats. It consisted of a first IHR positivity which triggered the first positive wave of the focal discharge, followed by a high negative wave. In the 18-day-old and adult group, both initial positive waves merged to form a single wave. The duration of the individual waves of the triggered discharge was not significantly shorter than the duration of the corresponding waves of spontaneous discharge.

Animals↗
PubMed1978

The role of the corpus callosum in the interhemispheric transmission of epileptic electrical activity.

In acute experiments on 49 curarized adult rats without general anaesthesia, we studied the transmission of discharges of cortical penicillin foci between the two hemispheres after transecting the corpus callosum. Projected discharges of the cortical penicillin focus appeared in the contralateral hemisphere later than in the controls and had a very different shape. The interhemispheric response of the experimental rats consisted of a small positive and a small negative deflection with long latent periods. Focal discharges could be triggered by electrical stimulat;on of the contralateral hemisphere only irregularly and for short periods of time. In rats with a transected corpus callosum, two symmetrical cortical foci at first behaved independently of each other; their synchronization then slowly improved, but never attained 100 per cent. The corpus callosum is the preferential pathway for interhemispheric transmission of focal activity. Transection of this pathway makes the transmission conditions much worse, but further connections, with a longer conduction time and lower efficacy, gradually come into action.

Animals↗