The minimal provision principle of functional systems. Neuronal mechanisms.

An important characteristic of the developing nerve cell is its ability to function long before maturity. At this time, the neuron has the basic properties of an excitable membrane, an incompletely developed dendritic tree, and a low level of afferent input. All of these factors hinder the initiation of synaptic and spike potentials. It is proposed that the functional potential of neurons at the early stages of development are provided by an adaptive system, which may include: 1) the excess phenomenon, i.e., increases in the numbers of nerve cells, their processes, spines, and synapses; 2) factors increasing the chances of meeting the expected afferentation, i.e., the orientation and growth of dendrites towards the afferent input and the structure and localization of branch points; 3) factors facilitating the initiation of nerve spikes i.e., juvenile channels for ion current generation, electrical interactions between cells. and additional trigger zones. These groups of properties solve a single common problem: that of facilitating cells to respond to single or weak signals. This is the basic condition supporting the operation of interneuron interactions at the early stages of brain development.

[Visual afferentation deficit during diffuse photosensitivity period in nestlings affects morphogenesis in Wulst neurons]. / Defitsit zritel'noi afferentatsii v period diffuznoi fotochuvstvitel'nosti ptentsov vliiaet na morfogenez neironov Wulst.

Golgi-stained preparations were processed with computerized morphometry to study the effect of the deprivation (eyes covered with nontransparent caps) on the development of neurons in the Wulst (the structure analogous to mammalian visual cortex) of pied flycatcher nestlings. Six-day-old nestlings that have only one form of the visual perception--diffuse photosensitivity--were studied. In the previous paper [Korneeva et al., 1994] in was shown that the Wulst of 6-day-old nestlings consisted of non-differentiated neurons and stellate-like cells at different stages of maturation; the latter group was subdivided into more- and less-mature cells. This work proved that even a 1.5-day-long deprivation (actual duration being counted off from the moment of appearance of the first retinal photoreceptors at the age of 4.5 days) resulted in significant changes in the geometry of stellate-like neurons. The changes in less-mature cells were predominantly destructive (decline of all quantitative indices of a cell, including the significant decrease in the total length of dendrites, maximal radius of the dendritic field and cell branching index), while the changes in more-mature cells were constructive (increase in all quantitative cell indices, including statistically significant increase in the soma section area, total length of dendrites, maximal radius of dendritic field and the number of foci of maximal branching). Different reactions of these cell types to the limitation of visual afferentation may be connected with differences in the afferent inflow to less- and more-mature cells or/and with different maturational stages of these neurons at the onset of deprivation.

[The principle of the minimal support of a functional system. The neuronal mechanisms]. / Printsip minimal'nogo obespecheniia funktsional'noi sistemy. Neironnye mekhanizmy.

Developing nervous cells are characterized by an important trait: a capability for functioning long before the full maturity. During this period, the excitable membrane of a neuron has specific characteristics, the dendritic apparatus is not fully developed, and the level of afferent input is low. All this complicates the initiation of synaptic and impulse potentials. It is suggested that the functioning of neurons at the early developmental stages is underlain by a system of adaptation including: 1) the phenomenon of redundancy (increased number of neurons, spines, and synapses, increased branching); 2) factors increasing the probability to receive the expected afferentation (orientation and growth of dendrites towards the afferent input, structure and localization of branching foci); 3) factors facilitating the initiation of neuronal discharge (juvenile channels generating ion currents, electric interaction between cells, additional triggering zones). The common goal of this whole group of factors is to facilitate the response of a cell to a single or weak signal. This is the principal condition ensuring the realization of neuronal interaction at early stages of brain development. Thus, the essence of the principle of the minimal provision of the early functional systems in Anokhin's theory of systemogenesis that the early functional system involves receptor cells and neurons of hierarchical brain structures that have been the first to mature heterochronously and are at the earliest maturation stage. Achieving the result analogous to that achieved by an adult organism is subserved by additional mechanisms characteristic exclusively for the early maturation stages of neurons and functional systems, which enable the nervous cells to function efficiently even at the early stages of maturity.

[The morphogenesis of Wulst neurons in the pied flycatcher under conditions of limited afferent inflow]. / Morfogenez neironov Wulst mukholovki-pestrushki v usloviiakh ogranicheniia afferentnogo pritoka.

Golgi preparations of the pied flycatcher Wulst region (the structure analogous to the mammalian visual cortex) were analyzed using the method of computerized morphometry, to study the influence of visual deprivation on the development of different types of neurons selected previously. Deprivation was accomplished by covering the young's eye with nontransparent caps. The experiments were carried out in 10-day-old nestlings (the onset of patterned vision) and 13-day-old nestlings (functioning patterned vision). In 10-day-old nestlings, the deprivation produced constructive changes in dendritic apparatus of projective stellate cells (among them, the most pronounced was more than three-fold increase in the number of foci of maximal branching) practically not affecting the small stellate-like cells. In 13-day-old nestlings, cells belonging to all selected cell types underwent destructive changes: their quantitative characteristics were decreased as compared to those in control nestlings. A large number of tree-like neurons were revealed in the Wulst in the deprived 10-day-old nestlings while in the control age-matched nestlings they were virtually never found. This phenomenon may be explained by the increased affinity to impregnation evoked by deprivation-induced biochemical changes in the tree-like neurons or to increase in their number. In the latter case, the phenomenon may be considered as compensatory, directed at the establishing of contacts with nonvisual afferents.

[The quantitative morphological characteristics of the spinal neurons in the kitten developing under conditions of limited afferent input]. / Kolichestvennaia morfologicheskaia kharakteristika spinal'nykh neironov kotennka, razvivaiushchikhsia v usloviiakh ogranicheniia afferentnogo pritoka.

Golgi preparations of cervical part of the spinal cord were used to study sparely and densely branching neurons of lamina VII, sparely and densely branching neurons of lamina VIII and large densely branching motor neurons of lamina IX in 30-day kittens developing under the conditions of limited reticulospinal input. Limitation was induced by electrocoagulation of bulbar magnocellular nucleus and caudal reticular pontine nucleus performed at the 7th day. Computerized morphometry revealed that partial deafferentation affects the geometry in all studied cell types except densely branching neurons of lamina VIII. Adaptive nature of structural reorganization of spinal neurons and possible relationship between morphological properties and functional profile of cells are discussed.

[The quantitative morphological characteristics of the neurons of the anterior horns of the spinal cord in the kitten]. / Kolichestvennaia morfologicheskaia kharakteristika neironov perednikh rogov spinnogo mozga kotenka.

Golgi preparations of cervical part of the spinal cord of 30-day kittens were used to study sparely and densely branching neurons of lamina VII, sparely and densely branching neurons of lamina VIII and big densely branching motor neurons (as classified by Leontovich) of medial and lateral regions of lamina IX. Qualitative morphological characteristics of geometry of each cell type were obtained by the method of computerized morphometry. The details of the structure of neurons belonging to different laminae of grey matter are discussed.

Features of the establishment of the spontaneous activity of neurons of the trigeminal sensory nuclei of viable sections of the rat brainstem in postnatal ontogenesis.

An attempt was made to characterize the features of the development of the neurons of the sensory trigeminal nuclei, a basic structure of the sensory support of alimentary behavior, in the late stages of postnatal ontogenesis. A technique involving viable sections of the brainstem of infant rats at the ages of two, four, and eight weeks was utilized. An increase with age in the number of neurons possessing spontaneous activity (44% at two weeks; 69% at eight weeks), an increase in the frequency of discharges, the appearance by the fourth week of a population of cells with high-frequency spontaneous activity, and an increase in the number of such neurons by the eighth week. Three types of background-active neurons were distinguished: episodic, continuous, and group; and the dynamics of the change in the ratios of these types with age was demonstrated. Significant changes with age were not found in resting potentials, although a tendency to its increase takes place between the second and eighth weeks of postnatal development.

[Dendrite orientation in neurons of the reticular brain stem nuclei of a kitten after oral deafferentation]. / Orientatsiia dendritov neironov stvolovykhiader retikuliarnykh kotenka posle oral'noi deafferentatsii.

Deviations in orientation of dendrites in neurons of the reticular brainstem nuclei are demonstrated in the Golgi preparations of the brain of 30-day old kittens by means of the computerized morphometry. Changes in the density of dendrite orientation occurring after bilateral and unilateral lingual nerve section are considered with respect to the following afferent inputs: midline structures and trigeminal and vestibular nuclei.

[The morphometric characteristics of the neurons of the reticular nuclei in the brain stem in the kitten]. / Morfometricheskie kharakteristiki neironov retikuliarnykh iader stvola mozga kotenka.

In the brain stem of 30-day-old kittens three types of Golgi-stained neurons are distinguished: sparsely branched reticular neurons, densely branched arborescent neurons and multipolar giant neurons (according to the classification by Leontovich). Implication of the new method of computer morphometry permits obtaining formalized characteristics of 23 parameters of the above types of neurons. An analysis of the quantitative characteristics of the studied neurons has revealed statistically significant differences in most parameters. This fact permits advancing a conclusion about morphological identity (stability) of each type of the neurons. Structural differences and similarities in reticular nuclei are discussed with respect to their functional features.

[The effect of sectioning the lingual nerve on the morphometric characteristics of the reticular nuclei in the brain stem in the kitten]. / Vliianie pererezki iazychnogo nerva na morfometricheskie kharakteristiki neironov retikuliarnykh iader stvola mozga kotenka.

Three subpopulations of Golgi-stained neurons of the brainstem reticular nuclei have been studied by the method of computer morphometry in 30-day old kittens. 23 parameter of the neuronal geometry were analyzed after uni-and bilateral lingual nerve section 5-7 days after birth. All of cells display statistically valid changes in some parameters, typically differing in every group: for reticular neurons--free distribution of dendrite endings in the dendritic field; for arborescent ones--the length of dendritic segments; for giant multipolar neurons--distribution of foci of maximal dendrite branching in the dendritic field. Unilateral lingual nerve section gives more pronounced quantitative deviations from the normal state, than bilateral one.

[The characteristics of the formation of spontaneous neuronal activity in the trigeminal sensory nuclei of surviving slices of rat brain stem in postnatal ontogeny]. / Osobennosti stanovleniia spontannoi aktivnosti neironov trigeminal'nykh sensornykh iader perezhivaiushchikh srezov stvola mozga krysy v postnatal'nom ontogeneze.

An attempt was made to characterize the development of neurones of sensory trigeminal nuclei--basic structure of sensory provision of alimentary behaviour at late stages of postnatal ontogenesis. The method of the brain-stem slices of rat pups [correction of ratlings] aged 2.4 and 8 weeks was applied. An increase with the age was shown of the number of neurones with spontaneous activity (44%-2 weeks; 69%-8 weeks), growth of discharges frequency, appearance of cells population with high-frequency spontaneous activity by the fourth week and an increase of such neurones number by the eighth week. Three types of background-active neurones were singled out: episodic, continuous and group; the dynamics of correlations change of these types with the age was shown. No significant changes of rest potential with the age were found, though there was a tendency to its increase between the 2-nd and 8-th weeks of postnatal development.

[Organization of early forms of kitten behavior after partial oral deprivation]. / Organizatsiia rannikh form povedeniia kotiat pri chastichnoi oral'noi deprivatsii.

Study of development of early forms of behaviour was carried out on intact kittens of the first month of life, who endured in 5 days age uni- and bilateral sections of the lingual nerve, and on shame-operated and undernourished animals. It was shown that bilateral deafferentation caused significant disturbance of alimentary behaviour at the stage of sucking, manifested in disturbance of natural sucking and appearance of shame sucking, i.e. rhythmic sucking movement without nipple grasping. At the one-month age, in conditions of artificial feeding, natural sucking in operated animals was restored and the shame one disappeared. Bilateral section of the lingual nerve led to acceleration of ripening of sensory and motor systems and accelerated development of homing, exploratory and playing behaviour. Possible role is discussed of sensory trigeminal nuclei neurones in organization of normal patterned sucking and at limited sensory inflow. It is suggested that elimination of sensory input developing in the norm earlier than others, changes natural terms of other channels development, what accelerates the change of early behaviour forms.

[Quantitative morphologic characteristics of neurons of the sensory nuclei of the trigeminal nerve developing after partial deafferentation]. / Kolichestvennaia morfologicheskaia kharakteristika neironov sensornykh iader troinichnogo nerva, razvivaiushchikhsia v usloviiakh organicheniia afferentnogo pritoka.

Five types of neurons were studied in the sensory nuclei of the trigeminal nerve stained by the Golgi method in kittens aged 30 days with bilateral transection of the lingual branches of trigeminal nerve made on the fifth postnatal day. Partial deafferentation resulted in changes of dendrite apparatus of reticular, arborescent and bushy neurons (68.61 and 48% of neurons changed). Short-dendritic cells changed slightly. The multipolar giant neurons underwent practically no changes. All the changes could be divided into two groups: destructive changes and constructive changes. The destructive changes consisted in the decrease of cell body sizes, number, length and ramification of dendrites and constructive changes--in the increase of these parameters. Various types of trigeminal neurons responded to deafferentiation in different ways. Bushy neurons displayed mainly destructive changes and reticular and arborescent neurons--both destructive and constructive ones.

[Quantitative morphologic characteristics of developing neurons of the sensory nuclei of the trigeminal nerve in the kitten]. / Kolichestvennaia morfologicheskaia kharakteristika razvivaiushchikhsia sensornykh iader troinichnogo nerva kotiat.

The paper presents a quantitative Golgi study of the kitten sensory trigeminal complex. Kittens of 1-5 and 30 days were used. Trigeminal neurons were divided into five groups. Neurons of two groups ramified sparsely and were defined as "reticular" and "short dendritic" neurons. Neurons of three other groups ramified densely and were defined as "bushy" neurons, "arbory dendritic" and "multipolar giant" neurons. The quantitative morphological data were obtained by measuring cell sizes, number, length, relative length, degree of branching of dendrites and total cell branching. The neurons of different groups had different parameters and a special mode of their maturation. "Bushy" neurons showed regressive changes during ontogenesis. All their parameters were reduced during the first month. Foci of maximal dendritic branching were displaced towards the distal portions of dendrites during the processes of cell maturation. All trigeminal neurons reached the high degree of maturity at birth.