[THE INFLUENCE OF LOCUS COERULEUS ON DIFFERENT ACTIVITIES OF THE THALAMO-CORTICAL SYSTEMS].

As revealed from our experiments, in facilitation of passage of the thalamo-cortical visual signals a key role is attributed to variability of activity of visual neurons in reticular nucleus of the thalamus. It was demonstrated that a facilitatory action of locus coeruleus gets augmented following functional exclusion of the thalamic reticular nucleus. Nevertheless, stimulation of locus coeruleus stipulated facilitation of neuronal activity in the anterior part of thalamic reticular nucleus. Emerging from this data one may assume that in the inhibition of evoked responses from a sensorimotor area of the neocortex in response to stimulation of locus coeruleus a certain role is played by reticular nucleus of the thalamus. Namely, augmentation of neurons activity in the anterior part of the thalamic reticular nucleus must condition inhibition of neuronal activity in the ventral nuclei. In spite of the stated, it is not excluded locus coeruleus ha-ving an immediate, direct inhibitory action on the neuron activity within the sensorimotor cortex and thalamic ventral nucleus.

INTERACTION BETWEEN THE THALAMIC NUCLEUS AND PREOPTIC AREA NEURONS.

The thalamic reticular nucleus which is known to delineate the dorsal thalamus stipulates development of inhibitory processes in the thalamo-cortical neurons that is necessary for generating slow (8-12 Hz), high-amplitude electric activity in this system. It was demonstrated that majority of preoptic area neurons get activated during slow-wave sleep. Activation of neurons in the anterior hypothalamus and preoptic area during slow-wave sleep and synchronization of the brain electric activity was demonstrated. The study was aimed at clarifying the relationship between the thalamic reticular nucleus and the preoptic area neurons. Under acute conditions experiments were carried out on mature cats. It was shown that blockade of preoptic area neuron activity during mesencephalic reticular formation stimulation and the fact that on the background of mesencephalic reticular formation stimulation thalamic reticular nucleus stimulation elicited preoptic area neurons activation must be in part stipulated by the fact that thalamic reticular nucleus activation leads to suppression of mesencephalic reticular formation neuron activity.

NEOCORTICAL IMPACT ON THE AUDIOGENIC SEIZURE ACTIVITY DEVELOPMENT.

Out of genetically determined epilepsy models a special interest draws the model of audiogenic seizures, which does not require whatever additional intervention (e.g. pharmacological or/and electric stimulation), because epileptic responses are elicited by specific sensory stimulation only. Notwithstanding the fact that different formations of the central nervous system are recruited in audiogenic seizure reactions, critical importance for the manifestation of this type epilepsy is attributed to the inferior colliculus and brainstem reticular nuclei. Significance of the diencephalic structures and the thalamic reticular nucleus, in particular for development and/or modulation of audiogenic seizures is ambiguous. Total of eight Krushinsky- Molodkina (KM) strain rats, weighting 250-300 g, served as the subjects of chronic experiments. The neocortex was bilaterally activated by way of administration of 1 µl strychnine (0.1% solutipon) with a microsyringe through a metal capillary prefixed on the cortical surface. Metal electrodes for recording electrical activity were implanted into the neocortex and brainstem reticular formation. Experiments have shown that against strychnine discharges in the neocortex there occurred an increase in the latency of wild runs and the pause between the first and second wild runs in response to a sound stimulus. Proceeding from the above-said, it can be assumed that activation of the neocortex must stipulate intensification of the thalamic reticular nucleus neuronal activity that, in turn, should have a modulating effect on the audiogenically induced seizure reactions.

Influence of carbamazepine on kindling grades in depressive and non-depressive rats.

It has been clinically established that epilepsy and depression frequently represent a comorbid pair. Most of investigators consider that epilepsy is a cause of emotional disorders such as anxiety and depression. On the other hand, some anti-epileptic drugs were found to aggravate depressive state, even to a suicide outcome. Bearing in mind these findings, we endeavored an experimental study in the laboratory rats, 25% of which display an inborn depressive behavior. An anti-epileptic drug to be tested was carbamazepine, while epileptic state was elicited by means of the kindling method. Selection of animals was made with the Porsolt's forced swimming test. Seven rats possessed clear depression-like traits; similar number of the non-depressive animals served as controls. Along with the inherently depressive rats, the third group of animals was used, in which depression was elicited with the immobilization stress procedure (exogenous depression). Epileptization of the rats was performed with sub-threshold electrical stimulation of the ventral hippocampus. The rapid kindling paradigm has been implemented in these experiments (40 stimulations in one day). Following development of epileptic state up to the grades 4-5 according to the Racine scale, the animals were intraperitoneally administered carbamazepine, once a day, for three consecutive days. On the fourth day the animals were tested again in order to assess their epileptic state; after this procedure, depressiveness of the animals was reevaluated. It was found that: a) the fastest and most vigorous kindling developed in the endogenously depressive rats; b) carbamazepine almost completely abolished the highest grades of convulsions; and c) kindling procedure did not alter initial emotional status of the animals and carbamazepine administration also did not change their behavior. The latter observation allows concluding that in our model depression and epilepsy interact insignificantly.

Double-step procedure screening for modeling reactive (exogenous) depression in rats.

Depressive disorders, which show ever increasing prevalence, urgently require relevant medications. In its turn search for the antidepressant drugs requires valid animal models of depression for a drug screening. The goal of the present study was construction of affordable and simple model of reactive depression in rats, which model could be implemented in the antidepressants screening. To this end the two experimental paradigms have been modified and combined in groups of rats, which had no signs of depressive behavior. In the first experiment animals were subjected to the so-called immobilization stress. In the next step the animals, in which immobilization stress has been elicited, were introduced into the modified Forced Swim Test (FST) apparatus with an exercise wheel. Testing procedure in the FST apparatus lasted 10 min, and it was determined that 120 revs/10 min was minimal activity index for non-depressive animals, while lesser number of revolutions pointed at existence of acquired depressive status. Immobilization-induced depressive behavior was stable enough and remained two weeks following the stress. Therefore, our double-step procedure constitutes versatile, reliable, affordable, and humane screening means for modeling reactive (exogenous) depression in rats.

Effect of multiple generalized seizures on the wakefulness-sleep cycle.

This paper gives the results on the studies of the effect of multiple generalized seizures (MGSs) on the wakefulness-sleep cycle (WSC). The adult Wister rats served as the experimental objects. The animals, under chloral hydrate anesthesia (35-40mg/kg) were stereotaxically implanted with stainless metal electrodes aimed into the neocortex and dorsal hippocampus. Typical EEG and behavioral GSs evoked in response to electrical stimulation of the dorsal hippocampus by the EEG recording of WSC the ration of different phases, latency of sleep and first PS onset were evaluated It have been shown that MGSs produce potent effect on the structure in WSC. In particular MGSs in postconvulsive WSC evoke sharp decrease in the latency of the sleep. Moreover, in ratio of WSC occurs prolongation of sleep and shortening of wakefulness.