[EEG in altricial pied flycatcher nestlings during the functional sates related with natural behavior cycle].

Electrical brain activity accompanying various forms of behavior was studied in 11-day-old pied flycatcher nestlings. Wavelet analysis of EEG, recorded from symmetrical areas of caudomedial nidopallium (higher avian auditory center) during rest, passive and active wakefulness and movements showed that the major rhythmical EEG component was confined to low-frequency range in all four states. The significant difference from other states was observed only during movements: spectral power in the range of 1-3 Hz decreased while that in the range of 5-20 Hz--increased. The range of 3-5 Hz revealed, in all functional states, the interhemispheric asymmetry of spectral power that could be due to asymmetrical embryonic development of avian visual projections. Active wakefulness and movements were characterized by high positive correlations between spectral power in right and left hemispheres. During rest this correlation was negative. The correlation values during passive wakefulness and rest were rather low that could indicate disintegration of neural connections.

[Reduction of the number of neurons in substantia nigra (Pars compacta) positively correlates with a reduction of seizure activity in WAG/Rij rats].

In WAG/Rij rats with a genetic predisposition to absence epilepsy, age-related dynamics of seizure activity in the frontal EEG was studied. In parallel, cellular content in substantia nigra was analyzed at the age of 1 and 10 months. In 10-months animals, the number of neurons in substantia nigra showed a profound decrease, whereas the number of glial calls increased. In parallel to that, the incidence of epileptic discharges and their duration significantly increased between 5 and 9 months of age. Positive correlations were revealed between the incidence of epileptic discharges and the number of neurons in substantia nigra suggesting that animals with lower number of neurons in SN expressed fewer absence seizures, and vice versa. It was suggested that reduction of neurons in substantia nigra is an adaptive process to prevent progressive development of absence seizures.

[Age-related changes in time-frequency structure of sleep spindles in EEG in rats with genetic predisposition to absence epilepsy (Wag/Rij)].

It is known that sleep spindles are produced by thalamo-cortical system spontaneously during the slow-wave sleep; pathological processes in thalamo-cortical network might cause absence epilepsy. The aim of this study was to examine age-dependent changes in time-frequency structure of sleep spindles in parallel to a progressive increase in amount of absence seizures in WAG/Rij rat model. EEG was consistently recorded at the age of 5, 7 and 9 months by means of epidural electrodes implanted in the frontal cortex. Continuous wavelet transform was used for automatic identification and further time-frequency analysis of sleep spindles in EEG. It was found that the mean duration of epileptic discharges and total duration of epileptic activity increased with age, whereas the length of sleep spindles decreased. Mean frequency of oscillations within a spindle was used as a criterion for dividing sleep spindles in three categories: "slow" (9.3 Hz), "tr ansitional" (11.4 Hz) and "fast" (13.5 Hz). "Slow" and "transitional" spindles in 5-months animals displayed an increase in frequency from the beginning towards the end. It was shown that the higher incidence of epilepsy corresponded to the lower duration of sleep spindles (all types). Mean frequency of "transitional" and "fast" spindles was higher in rats with more intensive epileptic discharges. In general, high epileptic activity in WAG/Rij rats corresponded to the most substantial changes within "transitional" spindles, whereas changes within slow and fast spindles were moderate.

[The effect of early sensory experience on development of neuron functional properties in the area of vibrissal projection in the rat neocortex].

The role of specific sensory inflow in the functional maturation of neurons in the area of vibrissal projections in the somatosensory cortex of rats was studied. Animals were subjected to bilateral trimming of whiskers during the first three weeks of postnatal ontogenesis. Quantitative and qualitative characteristics of neuronal responses were analyzed in the "lemniscal" layers IV and Vb and "paralemniscal" layer Va in junior (27-40 PN days) and elder (41-57 PN days) rats. The immediate effect of deafferentation in younger animals consisted in an increase in excitatory responses, which correlated with a deficit of inhibitory reactions. In animals subjected to vibrissectomy, atypical responses were observed in the "lemniscal" and "paralemniscal" layers. This effect may be caused by a derangement of distribution of thalamic afferents in the somatosensory cortex. Elder animals in vibrissectomized group displayed an increase in inhibitory reactions, i.e., the long-term effect of vibrissectomy is the actualization of inhibitory mechanisms.

[Cytomorphological features of the neocortex in rats with genetic predisposition to absence epilepsy].

The aim of the study was to examine putative microstructural changes in the neocortex which accompany absence epilepsy. Rat strains WAG/Rij as a genetic model of absence epilepsy and ACI (control) were examined. Brain slices were stained after Nissl; neuronal and glial cells were identified and counted in the somatosensory, motor, and cingular cortices (in layers II/III, V, and VI, individually). In WAG/Rij rats, the density of neurons in the superficial layers (II/III) of the motor cortex appeared to be lower than in healthy control rats, whereas the density ofglial cells in WAG/Rij rats was higher. In the deep layers of the somatosensory and cingular areas, the density ofglial cells in WAG/Rijrats rats was lower as compared to control rats. The results demonstrate that absence epilepsy is associated with cytomorphological changes in the neocortex.

[Lemniscal and paralemniscal afferent pathways in rodents' trigeminal system are integrated at the level of the somatosensory cortex].

The present paper demonstrates a functional interaction between lemniscal and paralemniscal sensory pathways in vibrissal projection area in the somatosensory cortex in rats. Single unit activity was recorded in layers IV, Va and Vb. It is found that mechanical stimulation of whiskers elicits characteristic 'lemiscal' (phasic) responses mainly in layers IV and Vb, while neurons in layer Va show typical 'paralemiscal' (tonic). Our data reveal that neurons in layers IV and Vb comprise a population of rapidly adapting neurons and neurons in layer Va are slowly adapting. Our findings suggest that the somatosensory cortex receive lemniscal and paralemniscal projections. A cooperation of lemniscal and paralemniscal projection systems at the somatosensory cortex and strong adaptive capabilities of cortical neurons could increase an accuracy of tactile perception, therefore animals can fine discrimination of sensory stimuli in a given environment.

[Vibrissectomy in rats in early ontogeny leads to disordered functional properties of the cortical projection neurons]. / Vibrisséktomiia u krys v rannem ontogeneze privodit k narusheniiu funktsional'nykh svoistv proektsionnykh neironov kory.

Vibrissae trimming during the first 20 days of postnatal life caused alternations of the properties of the receptive fields of single neurons in the barrel-field cortex in rats. The following changes were found in the deafferented cortex: (i) an extension of the receptive fields of single neurons as judged from an increase in the number of vibrissae with short-latency excitatory responses to stimulation and (ii) a depression of the inhibitory receptive field tuning mechanisms.

[The effect of forelimb deafferentation in early postnatal ontogeny on the development of synaptic transmission in the hippocampus]. / Vliianie deafferentatsii perednei konechnosti v rannem postnatal'nom ontogeneze na formirovanie sinapticheskoi peredachi v gippokampe.

Hippocampal slices from 15-20-day-old Wistar rats were used to study the development of some features of synaptic transmission in hippocampus and the influence of partial limitation of the sensory inflow in the early ontogeny of this transmission. The dynamics of population spike changes was observed in the CA1 hippocampal field in response to stimulation of Schaffer collaterals. The early ontogenetic limitation of the sensory inflow was accomplished by cutting n. medianus on the 13th day. Between the 15th and 20th days, the dynamics of the population spike amplitude increase in the control and experimental animals was similar, however, the response amplitude of the control rats remained higher than in the experimental animals throughout the whole period of observation. It is suggested that the partial limitation of sensory inflow from a forelimb at the early stages of the ontogeny alters the formation of synaptic transmission in hippocampus.

[The effect of the limitation of afferent inflow in early ontogeny on the evoked activity of projective neurons depends on the degree of the maturity of the sensory inputs]. / Vliianie ogranicheniia afferentnogo pritoka v rannem ontogeneze na vyzvannuiu aktivnost' proektsionnykh neironov zavisit ot stepeni zrelosti sensornykh vkhodov.

The study is focused on the influence of a partial limitation of the sensory inflow in rat pups on the development of the sensory systems, which mature earlier and later. In accordance with the ontogenetic rule of proximal-distal maturation, the sensory inflow from the forelimbs matures faster than that from the hindlimbs. Fourteen Wistar rat pups (from 28) were deafferented on the 13th day of postnatal ontogeny (a small portion of the median nerve was unilaterally dissected). The background and evoked activity of single neurons was recorded in 26-47-day-old pups in the somatosensory cortex (in the projection areas of the intact n. medianus, which matures earlier, and n. ischiadicus, which matures later). The changes in firing activity produced by deafferentation were observed. In the projection area of the intact forelimb of the denervated rats, the incidence of inhibitory responses significantly increased, whereas the incidence of completes responses significantly decreased. In the hindlimb projection area of the denervated animals the background firing rate was significantly lower and the incidence of activation responses was increased.

[Sensory information--an important factor in ontogeny]. / Sensornaia informatsiia--vazhnyi faktor ontogeneza.

Ontogenetic process reveals a row of consecutive stages characterized by the gradual increase in complexity and by the changing specificity of sensory mechanisms basic for the adaptive behavior of the young. The study examines the mechanisms of interaction among different sensory systems during the formation of early behavioral patterns and analyzes why, at a certain stage of development, a particular sensory stimulus loses its efficacy in the organization of a given behavior and is substituted by another one, previously ineffective. A special attention is paid to formation of behavior based on sensory information within the limits of ontogenetically fixed developmental critical periods and to the role of the early sensory experience in learning in adult animals.