Effect of early sensory experience on the exploratory activity in adult animals.

It was previously found that the exploratory activity of adult Wistar rats with their vibrissae cut in the period from 9 to 20 postnatal days was characterized by lower intragroup variability in comparison with control rats [3]. The present study has shown that the earlier limitation of species-specific afferentation (whisker trimming on postnatal days 2-9) does not induce such changes. We conclude that high plasticity of the brain during the early postnatal period provides better adaptation to the deficit of sensory information.

[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.

[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.

[Influence of vibrissectomy in early postnatal ontogeny of rat pups on behavioral development].

The influence of daily all whiskers trimming from the 2nd or 9th to 20th postnatal day on maturation time of walking, rearing, grooming, manipulation activity and eye opening was studied in deprived rat pups and their sibs. In pups trimmed beginning from the day 2 and their sibs, eye opening occurs earlier. Also, grooming and rearing mature earlier, whereas manipulation activity forms later. The structure of correlations between maturation time of behavioral reactions and the day of eye opening changes. In pups trimmed beginning from the day 9, the majority of correlations disappears, dynamics of behavior development do not change. In their sib, maturation of manipulation activity is delayed, but changes in the structure of correlations are manifest less than in deprived pups.

[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.

[Visual deprivation affects the development of auditory sensitivity during the period of maturation of freezing response in pied flycatcher nestlings].

Recording of evoked potentials (EP) from the higher auditory center of birds field L of the nidopallium was used to study the development of the auditory sensitivity in normally developing vs visually deprived pied flycatcher nestlings aged 6-9 days. The visual deprivation was shown to induce a significant decrease in the absolute auditory EP thresholds in the frequency range of species-typical food call (1-3 kHz) during the period corresponding to the time of the vision involvement into the feeding behavior in the normal young (6 days post-hatching). In the frequency range of species-typical alarm call (4-5 kHz), EP thresholds in visually deprived nestlings were significantly lower than in the control birds during the period corresponding to the time of the vision involvement into the defense behavior of the latter (8-9 days post-hatching). With account made for the previous data demonstrating the decrease of efficiency of acoustic signals provoking freezing in visually-deprived nestlings, it is reasonable to suggest that defense behavior develops not just as a response to alarm call or imitating tone pips, but as a whole system, whose norma maturation and functioning requires integration of numerous factors visual afferentation being one of them.

[Prenatal acoustic stimulation and feeding behavior of Japanese quail chicks (Coturnix coturnix japonica)].

Effects of a prenatal rhythmic tone on behavior of Japanese quail chicks were studied on the next days after hatching. The acoustically stimulated chicks demonstrated a significantly more frequent following response, feeding reaction and comfortable behavior when hearing the tone as compared with their controls. Bandwidths stimulating this or another behavior were determined.

[The role of visual afferentation in the development of early defense behavior of pied flycatcher nestlings].

The development of defense behavior in normal and visually deprived pied flycatcher nestlings was studied in the wild. It was demonstrated that the young deprived of the visual afferentation did not develop the freezing posture. In the majority of cases, specific alarm call suppressed begging in visually deprived nestlings less effectively than in the control ones. Visually deprived nestlings could not discriminate between the alarm call and other rhythmically organized acoustic signals even though the latter effectively suppressed begging.

Does the destruction of catecholaminergic neurons in newborn rats influence the modulator function of the cholinergic system?

The influence of the destruction of the catecholaminergic (CA) system on the reactions of neurons of the somatosensory zone of the cortex elicited by stimulation of the sciatic nerve, and on the features of the modulation of these reactions following the stimulation of the region of the basal nuclei (source of cholinergic innervation of the neocortex) and the microiontophoretic application of acetylcholine (ACh), was investigated in mongrel infant rats, 21-31 days of age. It was demonstrated that destruction of the CA system in newborn rats increases the reactivity of neurons somatosensory cortex to sensory stimulation, has no influence on the modulating effect of the cholinergic system, of the forebrain, and leads to intensification of the modulating influence of applied ACh [2].

Ribonuclease improves the state of hippocampal sections in the post-ischemic period.

Living hippocampal slices from Wistar rats were used to study the dynamics of changes in population electrical responses in field CA1 to electrical stimulation of Shaffer collaterals during the development of ischemia (imposed by exclusion of oxygen and glucose from the perfusion solution). These studies showed that during ischemia, addition of ribonuclease (a blocker of protein synthesis) to the perfusion solution resulted in a significantly smaller increase in the latent period of the response and slowed the onset of the reduction in the amplitude of the evoked potential, and promoted faster recovery of the response after the ischemia session ended. It is suggested that the reduction in protein synthesis due to ribonuclease preserved energy reserves in the nerve tissue, which in turn promoted more complete recovery of neuron function in the post-ischemic period.

Endogenous dopamine modulates corticopallidal influences via GABA.

Acute experiments on Sprague-Dawley rats were performed to study the effects of local application of D1 and D2 receptor antagonists (SCH 23390 and raclopride) on the responses of neurons in the globus pallidus induced by stimulation of the somatosensory cortex. SCH 23390 induced short-latency inhibition in response to stimulation of the cortex and blocked long-latency inhibition. Application of raclopride suppressed short-latency inhibition and induced a long-latency inhibitory response to stimulation of the cortex. It is suggested that these changes are based on modulation of GABA release from striopallidal terminals by endogenous dopamine.

[Formation of serotonin- and GABA-ergic mechanisms of synaptic transmission in the cat neocortex during early ontogenesis]. / Formirovanie serotonin- i GAMKergicheskikh mekhanizmov sinapticheskoi peredachi v neokortekse koshki v rannem ontogeneze.

In acute experiment on 5-20 days kittens, the reactions were studied of neurones in the cortical somatosensory zone to stimulation of the dorsal raphe nucleus (DRN) and application of serotonin, ethanolamine-O-sulphate and bicucullin. The identity is established of the effect of DRN stimulation and serotonin application eliciting inhibition of the background activity and appearance of inhibitory phases in response to sensory stimulation, beginning from the 10-12th day after birth. A suggestion is made about serotoninergic regulation of GABA-ergic interneurones' in young animals. The dynamics of GABA-ergic brain system formation has been studied. Specific sensitivity of neocortical neurones to GABA increased to the end of the second week of life--the period when modulating serotoninergic influences appear.

[Role of raphe nuceli in the development of somatosensory cortex neuronal activity in the kitten]. / O roli iader shva v formirovanii aktivnosti neironov somatosensornoi kory kotenka.

The formation of background and evoked unit activity in the I somatosensory cortical zone was traced in acute experiments on 5 to 20 days old kittens. Stimulation of anterior (median, dorsal) raphe nuclei inhibits the spike activity of cortical units in kittens beginning with the age of 11 to 12 days and modulates evoked responses. This is manifested in the transformation of immature tonic reactions into phasic, which are inherent in a more definitive type of reaction. The role of the serotoninergic mechanisms in the formation of recurrent inhibition in the cortex is discussed, as well as heterochroneous formation of monoaminergic brain systems in the process of postnatal development.

[Cholinergic regulation of the activity of somatosensory cortex neurons during early postnatal ontogeny of the cat]. / Kholinergicheskaia reguliatsiia aktivnosti neironov somatosensornoi kory v rannem postnatal'nom ontogeneze koshki.

In 11-14 days kittens, about 20% of neurones in the somatosensory cortical zone react to stimulation of subpallidal region which is a source of cholinergic projections to the cerebral cortex. The effect of subpallidal region stimulation is reproduced in case of microiontophoretic acetylcholine application and blocked by atropine what points to its cholinergic nature. Cholinergic stimulation causes inhibition of the background and evoked activities of the cortical neurones while, as it is known, in adult cats, acetylcholine mainly stimulates a reaction of activation. It is postulated that in kittens at the end of the second week of postnatal development, cholinergic innervation of the cortex significantly differs from the definitive one by its quantitative and functional parameters.

[Does the destruction of the catecholaminergic neurons in newborn rat pups influence the modulatory function of the cholinergic system?]. / Vliiaet li razrushenie katekholaminergicheskikh neironov u novorozhdennykh krysiat na moduliatornuiu funktsiiu kholinergicheskoi sistemy?

On outbred ratlings aged 21-31 days the influence was studied of the destruction of catecholaminergic (CA) system on the reactions of the neurones of the cortical somatosensory zone, elicited by the stimulation of the ischiatic nerve and modulation of these reactions after stimulation of the basal nuclei area (the source of the neocortex cholinergic innervation) and acetylcholine (ACh) microiontophoretic application. It is shown that destruction of CA system in newborn ratlings increases the reactivity of the somatosensory cortical neurones in 21-31 days old animals to sensory stimulation; it does not influence the efficiency of modulating action of the cholinergic system of the forebrain and leads to the increase of modulating influence of the applicated ACh. It is postulated that as the result of perinatal destruction of CA brain system, in the neocortex a specific morpho-functional organization is formed of structures and processes at which the modulating function of the forebrain cholinergic system turns out, by quantitative criterion, at least, to be compensated.

[The cholinergic system of the forebrain modulates the activity of the GABA-ergic interneurons which realize presynaptic regulation in the neocortex of kittens]. / Kholinergicheskaia sistema perednego mozga moduliruet aktivnost' GAMKergicheskikh interneironov, osushchestvliaiushchikh presinapticheskuiu reguliatsiiu v neokortekse u kotiat.

It has been found that at the end of the second week of postnatal life, stimulation of cholinergic ascending paths causes a selective inhibition of cortical neurones reaction to sensory stimulation, without influencing the background activity. The observed inhibition is blocked both by atropine and picrotoxin, but not by bicuculline. It is suggested that the observed phenomenon characterizes, presynaptic control of cortical neurones activity in the early ontogenesis. This inhibition is formed on the basis of cooperative choline- and GABA-ergic brain systems participation and is performed not through GABA-receptors.

[Ribonuclease improves the function of hippocampal slices in the postischemic period]. / Ribonukleaza uluchshaet sostoianie srezov gippokampa v postishemicheskii period.

Population spike amplitude was measured in hippocampal slices under conditions of 20-min glucose and oxygen deficit ("in vitro ischemia") with or without ribonuclease A. In control slices the response was gradually decreased within 3 +/- 2 min after the onset of hypoxia/hypoglycemia. This process continued during 13 +/- 6 min of reperfusion. The reperfusion restored the amplitude up to 70 +/- 17% of its initial level within 1.5 h after the onset of this procedure. Addition of ribonuclease delayed the beginning of the response decrease (by 8 +/- 2 min) and increased the level of its restoration (up to 113 +/- 23%) after the reperfusion. It is suggested that ribonuclease prevents from the energy exhaustion by preserving the cellular energy stores.

[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.

[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.