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Different types of epilepsy may be found in nearly 1 % of population. Many epileptic syndromes
originate during infancy and childhood and there are some age-specific
syndromes demonstrating the influence of the level of brain maturation on
generation, spread, arrest and consequences of epileptic seizures. Therefore,
the main topics of the laboratory are epileptic seizures and epilepsies
induced at different levels of postnatal development. Methods used in the
laboratory include electrophysiology (acute and long term EEG recording,
video-EEG monitoring, evoked potentials, electrical stimulation of different
brain structures, activity of individual neurons), behavior (spontaneous
behavior in open field, learning and memory tests), tests of motor
performance, biochemistry, classical histology, histochemistry and
immunohistochemistry. In collaboration with other laboratories molecular
biology techniques are used. In addition, there is research in the field of
computational neuroscience
Resarch is focused on the following topics
Status epilepticus
as a life-threatening situation is modeled in adult as well as in developing
rats. Status is induced by pilocarpine in lithiumpretreated animals at the age
of 12, 25 or 90 days. video-EEG monitoring demonstrated that treatment with
benzodiazepines and/or paraldehyde did not block but only interrupted seizures
in all age groups. Epileptic EEG activity (mostly without motor correlates)
reappears after a few tens of minutes and continues for at least 24 h. In
contrast to older rats the youngest group exhibit frequently nongeneralized
EEG seizures. Status epilepticus in immature brain is manifested in a little
different way than in mature brain but the amount of epileptic activity is
large enough to lead to permanent changes of the nervous system. Low doses of
pilocarpine induce nonconvulsive seizures lasting approximately 90 minutes.
Behavioral and EEG symptomatology of these seizures correspond with human
complex partial seizures, i.e. our model is related to human nonconvulsive
status epilepticus. These seizures can be elicited in all three age groups
tested.
Spontaneous recurrent seizures which appear as a consequence of motor
status epilepticus after a latent (silent) period represent a model of
epilepsy because seizures appear repeatedly for the rest of life of the
animals. Using the pilocarpine model of convulsive status epilepticus
pathologic EEG activity (isolated spikes) can be recorded in all rats without
any relationship to the age when status epilepticus was elicited. In contrast,
ictal activity and especially convulsive, i.e. motor seizures are age-dependent;
they regularly appeared when the animals have been seized during adulthood or,
less regularly, at the age of 25 days.
Consequences of epileptic seizures during development are studied also behaviorally and morphologically.
Convulsive status epilepticus during early development resulted in compromised
motor development of rats (tested by a battery of tests on motor performance)
and the changes are age-dependent, they have different time course in animals
seized at the age of 12 or 25 days. Spatial memory task (Morris water maze)
examined two months after status cannot be mastered by rats seized during
adulthood, animals undergoing convulsive status at the age of 25 days learn
more slowly than their control littermates but the youngest group do not
exhibit any changes in comparison to controls. Spontaneous behavior in open
field is characterized by a marked hyperactivity of all groups of animals
after status. Both older age groups exhibit serious widespread brain damage
seen in Nissl-stained brain sections – not only in the limbic system but
also in neocortex, some thalamic nuclei and other structures. No obvious
neuronal necrosis is present in rats seized at the age of 12 days but if
immunohistochemical techniques are used, marked changes can be demonstrated
even in this age group (e.g.loss of parvalbumin and calbindin positivity in
piriform cortex). The findings lead us to a conclusion that motor status
epilepticus is deleterious also for immature brain but its consequences differ
from those in older animals. Nonconvulsive status epilepticus induced in adult
rats resulted in morphological changes in motor neocortical area, i.e. even
these innocent-looking seizures lead to longlasting changes in the brain.
The role of endogenous excitatory amino acids in the pathogenesis of
epileptic seizures is investigated in immature rats, using systemic and
intracerebroventricular administration of homocysteic acid. In addition to
behavioral and EEG description of seizures, energy metabolite changes are
studied. The findings suggest that the immature rat brain has a high ability to compensate for the increased energy demands
associated with seizure activity, most likely due to increased glycolysis.
Seizures could be attenuated or prevented by antagonists of both NMDA and
nonNMDA receptors and by metabotropic glutamate receptor subtypes of selective
agists and antagonists, as evaluated by suppression of behavioral
manifestations of seizures and also from the protection of metabolite changes
which normally accompany these seizures. A pronounced anticonvulsant effect
could be achieved by combined treatment with subthreshold doses of NMDA and
nonNMDA receptor antagonists. This finding may be of potential significance
for treatment of epilepsies.
The role of GABAergic inhibition in epileptogenesis in developing brain
is mainly focused on the GABA-B system. An antagonist of GABA-B receptors CGP
35348 is able to suppress rhythmic spike-and-wave activity at all
developmental stages where this activity could be evoked. In contrast,
baclofen increased the incidence of spike-and-wave episodes in an age-dependent
manner (from the fourth postnatal week). The GABA-B receptors participate in
postictal depression after cortical epileptic afterdischarges. Development of
Gproteins and adenylyl cyclase activity is studied in collaboration with the
Department of Membrane Receptor Biochemistry. Glutamate decarboxylase activity
is studied biochemically (in collaboration with the Faculty of Pharmacy,
Charles University) and immunohistochemically. These studies are directed to
possible changes induced by severe seizure activity. Molecular biology of GABA-B
receptors is studied in the Laboratory of Molecular Physiology, a joint
laboratory with the 3rd Medical School. The
main topic is represented by the structure-function relationship of the
metabotropic glutamate receptors and the GABA-B receptors. These G-protein-
coupled receptors have certain similarities with other heptahelical receptors,
but also many differences. Mutagenesis studies together with functional tests
of heterologously expressed mutated proteins allow us to map contact sites of
G-proteins with the receptors. Heterodimerization of BR1 and BR2 subunits of
the GABA-B receptor is studied using protein chemistry and immunochemitry with
the aim to disclose possible interaction sites that take parts in the receptor
formation.
Action of antiepileptic drugs against different seizure models is studied during development. Two common
models are motor seizures elicited by pentamethylenetetrazol administration
and epileptic afterdischarges induced by rhythmic electrical stimulation of
the sensorimotor area of cerebral cortex. These models make it possible to
evaluate three or four different phenomena with known mechanisms of generation.
There are not only quantitative but also qualitative changes of antiepileptic
drug action with maturation of the brain - e.g.mixed GABA-A and GABA-B agonist
progabide and GABA uptake blockers (NNC 711 and tiagabine) exhibit different
action against generalized motor seizures in rats during the first three
postnatal weeks and in adult animals. Ontogenetic changes in the action of
phenytoin were demonstrated also electrophysiologically by means of evoked
potentials. These results have not only theoretical but also direct practical
significance.
In addition, mathematical analysis and modeling is focused on the information transfer from the input to a neuron
to its output. This concerns either the first-order sensory neurons which are
in direct contact with an external environment or neurons of higher orders
receiving their input as integrated activity in a neuronal network. The main
attention is oriented towards the sensory systems, mainly the olfactory one,
however, due to the application of theoretical approaches closely related to
experimental data, the results are of general validity. Methodologically, this
is the type of computational neuroscience research using biophysical,
mathematical and numerical tools.
Publications
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