Functional topography of afferent projections of the horizontal division of the nucleus of the diagonal band in the dorsolateral neocortex of the cat

EPs recording under Nembutal anaesthesia during stimulation of the medial section of the horizontal part of the diagonal band nucleus (HNDB) shows a wide spreading of HNDB afferentation over the neocortex: from the frontal area to the medial and some posterior parts of the auditory, parietal areas and Ep zone, with the least activation of the latter three regions and activation increasing intensity correspondingly in the somatic zones II, I (SII, SI), motor and frontal cortex. Such reduction of signals flow intensity oriented both in caudal and ventral directions of the cortex goes with foci of maximal activity of these signals in the motor, parietal areas and zones of representation of various body parts in SI and SII. Traits of similarity and differences of signal's projections in the neocortex from HNDB and thalamic relay nuclei have been revealed. A hypothesis is substantiated on different mechanisms underlying peculiarities of influences of these subcortical nuclei on the cortex depending on the type of their afferent-neuronal links in the latter and their functional role in the brain activity.     

Structural organization of mesenteric lymph nodes in postnatal development of the Baikal seal, <Emphasis Type="Italic">Pusa sibirica</Emphasis> Gmel

Structural organization of mesenteric lymph nodes in the Baikal seal has been studied with regard to its age-dependent changes. It has been shown that the relative area of connective tissue structures (the capsule and trabeculae) increases during postnatal development, while the areas of the cortex and medulla decrease. The proportions of secondary lymph nodes and paracortical zone in the cortex become smaller, with the corticomedullary index tending to decrease with age. These phenomena indicate that mesenteric lymph nodes undergo regression during postnatal ontogeny, with their lymphopoietic function being attenuated. Lower values of the corticomedullary index in Baikal seal pups aged 1 month to 4 years are apparently explained by a decrease in the proportion of cortex substance related to the enhancement of the motor function of lymph nodes.     

In vivo imaging of neural circuit formation in the neonatal mouse barrel cortex

Higher brain function in mammals primarily relies on complex yet sophisticated neuronal circuits in the neocortex. In early developmental stages, neocortical circuits are coarse. Mostly postnatally, the circuits are reorganized to establish mature precise connectivity, in an activity-dependent manner. These connections underlie adult brain function. The rodent somatosensory cortex (barrel cortex) contains a barrel map in layer 4 (L4) and has been considered an ideal model for the study of postnatal neuronal circuit formation since the first report of barrels in 1970. Recently, two-photon microscopy has been used for analyses of neuronal circuit formation in the mammalian brain during early postnatal development. These studies have further highlighted the mouse barrel cortex as an ideal model. In particular, the unique dendritic projection pattern of barrel cortex L4 spiny stellate neurons (barrel neurons) is key for the precise one-to-one functional relationship between whiskers and barrels and thus an important target of studies. In this article, I will review the morphological aspects of postnatal development of neocortical circuits revealed by recent two-photon in vivo imaging studies of the mouse barrel cortex and other related works. The focus of this review will be on barrel neuron dendritic refinement during neonatal development.     

The remote consequences of hypoxia influence in perinatal development period on structurally functional characteristics of the rat brain

The study has shown that influence of acute hypoxia in perinatal period leads to structural changes in motor and visual of the neocortex for 20 postnatal days in the form of disturbance of the structural organisation of the neocortex layers. Different fields of hippocampus in perinatal period differently react to hypoxia, and evidence of existence of a long-term perinatal hypoxia was obtained. It is established that after action of acute hypoxia in all the fields there is a cellular destruction, and thinning of pyramidal neurones layers. The most expressed cellular destruction takes place in fields CA4 and CA3. In process of augmentation, the destruction of cells remains appreciable in the field CA4, reduced in the field CA3 and not found in the field CA1; however, in fascia dentate, the destruction of granular neurones with age augmentation increases. Along with in reduction of the dimensions of cellular bodies pyramidal neurones in all fields of hippocampus takes place. Also in all fields of hippocampus, activation of astrocytic reaction occurs, more expressed in the field CA4. The hypoxia influence in the early postnatal period can affect synaptogenes, particularly the formation of giant synapses in a dentate fascia. Study of functional features of the excitatory system of such animals has shown that hypoxia can induce appreciable disturbances of behavioural responses. In rats, disturbances of inhibiting functions of the cerebral cortex, raised anxiety, and spatial learning and working memory disturbances have been noted.     

Motor responses of the facial muscles to local stimulation of the motor cortex and facial nerve nucleus in the white mouse

The character of motor responses of the facial muscles evoked by stimulation of various regions of the frontal neocortex and of the nucleus of the facial nerve was studied in outbred mice. Motor responses of the vibrissae, of the upper lip and the jaw to monopolar microstimulation in the frontal cortical areas in 55 per cent of the cases had the latencies from 5 to 15 ms. The latencies of the responses to the facial nucleus stimulation ranged from 3 to 12 ms with maximal expressed interval of 4-6 ms. Excitation conduction velocities of the facial nerve estimated on the basis of latencies measurements, were from 1.5 to 12 m/s.     

幼年大鼠视皮层神经元对闪光刺激的反应特性

哺乳动物视觉系统的发育延续到出生后,大鼠出生后 3~5 周是视觉系统发育的关键期 . 在关键期中,视皮层的兴奋性和抑制性突触连接逐渐成熟,形成有效的皮层内回路 . 为了观察发育关键期大鼠视皮层神经元的反应特性与成年大鼠的异同,使用胞外单细胞记录的方法对比研究了幼年和成年大鼠对闪光刺激的视觉反应特性 . 结果显示：与成年大鼠相比较,幼年大鼠视皮层神经元对持续闪光刺激显示出更强的适应性,对光刺激的诱发放电频率更低,而在没有光刺激时的自发放电频率更高,从而导致信噪比更低 . 这一结果表明,幼年大鼠视皮层对连续刺激的反应能力下降,对信号的分辨能力也更弱,其原因可能是兴奋性突触和抑制性突触发育的不同步所致 .     

The effect of electric stimulation of different regions of the cerebral cortex on the alimentary reaction in rabbits]

The influences of different parts of the neocortex on the rabbit alimentary behaviour produced by stimulation of the hypothalamic "alimentary centre" were studied in chronic experiments on rabbits with electrodes implanted in different formations of the limbic system and the midbrain. It has been found that electrical stimulation of the frontal and anterior parietal cortical areas raised the threshold of the evoked alimentary reaction. Inhibitory influences of the frontal areas proved to be stronger and more prolonged than those of the anterior parietal area. Electrical stimulation of the posterior parietal and occipital cortical areas decreased the threshold of the evoked alimentary reaction. Coagulation of the dorsal hippocampus eliminated the inhibitory influences of the neocortex, while coagulation of the mesencephalic reticular formation discontinued the facilitating influences of the neocortex on the alimentary reaction.     

Comparative analysis of the neocortex during the ontogenesis of cetaceae and primates

Comparative ontogenetic investigation of cytoarchitectonics of the cerebral neocortex has been performed in Cetacea and Primates using paraffin frontal and sagittal cerebral sections stained after Nissl. Cerebral hemispheres of dolphins, whales, monkeys and human being have been studied at various periods of prenatal development and in mature individuals. The comparison has been made at similar stages of cytoarchitectonical differentiation of the cortical plate. At two first stages of the prenatal ontogenesis (formation of the cortical plate and its differentiation into layers) there is not any principle differences between the Cetacea and Primates. Peculiarities of the cerebral cortical plate differentiation in the Cetacea (absence of the internal granular layer IV) is determined at the stage of stratification. Similar agranular character of the cerebral cortex differentiation is maintained during the whole subsequent ontogenesis in the Cetacea (heterogenetic type of the neocortex after Brodman). Absence of the layer IV in the cerebral neocortex determines some other principles in the spatial organization of the cortical-subcortical and in the intracortical connections in the Cetacea brain. This is confirmed by modern data of morphological and electrophysiological investigations. Perhaps, a comparatively more simple initial architectonics of the Cetacea brain limited the level of their functional possibilities, the latter is comparable only with anthropoid apes.     

Distinctions between dorsal and ventral premotor areas: anatomical connectivity and functional properties

The dorsal and ventral premotor areas, together with the primary motor cortex, are believed to have major roles in preparing and executing limb movements. Recent studies have expanded our knowledge of the dorsal and ventral premotor areas, which occupy the lateral part of area 6 in the frontal cortex. It is becoming clear that these two premotor areas, through involvement in distinct cortical networks, take part in unique aspects of motor planning and decision making. New lines of evidence also implicate the lateral premotor areas in planning motor behavior and selecting actions.     

Regional aspects of the prevention of learned helplessness by desipramine

Desipramine injected directly into the hippocampus, frontal neocortex, or lateral geniculate body prevented the development of learned helplessness in rats. It did not have this protective effect when injected into the septum, entorhinal cortex, posterior neocortex, nucleus candatus, nucleus accumbens, or amygdala. Neocortical levels of 5-hydroxyindoleacetic acid were significantly higher in rats receiving desipramine in the three behaviorally active ares than in the six other areas or than in saline injected controls.     

Change in the functional significance of structures of the cat brain as a result of reorganization of its activity

A study was carried out on 8 adult cats of functional role of the frontal, parietal and occipital parts of the neocortex, and also of the dorsal hippocampus, mediodorsal thalamic nucleus and caudate nucleus head, in realization of a delayed spatial choice (DSCh) before and after compensatory reorganizations of the brain activity caused by multiple electrical stimulation of the frontal part of the cerebral cortex. Compensatory reorganization led to a change of functional significance of these structures. While before this change the frontal cortex, hippocampus and mediodorsal thalamic nucleus were critically necessary brain areas for the realization of the DSCh, after it parietal and occipital cortical areas acquired such significance. The obtained data are discussed proceeding from the principle of the integrity in the brain activity.     

The early postnatal nonhuman primate neocortex contains self-renewing multipotent neural progenitor cells

The postnatal neocortex has traditionally been considered a non-neurogenic region, under non-pathological conditions. A few studies suggest, however, that a small subpopulation of neural cells born during postnatal life can differentiate into neurons that take up residence within the neocortex, implying that postnatal neurogenesis could occur in this region, albeit at a low level. Evidence to support this hypothesis remains controversial while the source of putative neural progenitors responsible for generating new neurons in the postnatal neocortex is unknown. Here we report the identification of self-renewing multipotent neural progenitor cells (NPCs) derived from the postnatal day 14 (PD14) marmoset monkey primary visual cortex (V1, striate cortex). While neuronal maturation within V1 is well advanced by PD14, we observed cells throughout this region that co-expressed Sox2 and Ki67, defining a population of resident proliferating progenitor cells. When cultured at low density in the presence of epidermal growth factor (EGF) and/or fibroblast growth factor 2 (FGF-2), dissociated V1 tissue gave rise to multipotent neurospheres that exhibited the ability to differentiate into neurons, oligodendrocytes and astrocytes. While the capacity to generate neurones and oligodendrocytes was not observed beyond the third passage, astrocyte-restricted neurospheres could be maintained for up to 6 passages. This study provides the first direct evidence for the existence of multipotent NPCs within the postnatal neocortex of the nonhuman primate. The potential contribution of neocortical NPCs to neural repair following injury raises exciting new possibilities for the field of regenerative medicine.     

Some mechanisms of frontal cortical participation in afferent integration

Experiments on dogs anesthetized with chloralose showed that lowering the level of activity of the frontal cortex (area F₂) by cooling leads to an increase in the negative phase of the primary response of all primary projection areas of exteroceptive stimuli (somatosensory, auditory, visual). Activation of the frontal cortex (by strychninization) increases the amplitude of the positive phase of the primary response. The same treatment applied to the frontal cortex of a cerveau isolé preparation leads to similar changes but only in the positive phase of this response. It can be concluded from the results that the frontal cortex may exert tonic effects of two types on afferent channels. One effect is indirect, through the reticular formation, by inhibition of its activating influence on the afferent channel responsible for the formation of the primary response. The other, activating effect, is aimed at the afferent channel forming the positive phase of the primary response. Under natural conditions the frontal cortex, when activated at the stage of afferent integration, evidently weakens the tone of the brain stem reticular formation and its influences, but facilitates the conduction of afferent volleys through the specific pathways, thus improving the perception of the trigger stimulus.     

Mapping the early development of projections from the entorhinal cortex in the embryonic mouse using prenatal surgery techniques

The purpose of this work was to study the development of specific projections from the postero-lateral cortex during the third trimester of gestation in the mouse. To do this, we labeled undifferentiated lateral cortex with the fluorescent carbocyanine dye, Dil, in the embryonic day (E) 16 mouse embryo using exo utero surgical techniques (Muneoka, Wanek, and Bryant, 1986). Embryos were allowed to develop to term (postnatal day 0, P0) at which time the fiber patterns emanating from the marked regions were studied. Dye placement in the undifferentiated postero-ventral cortex produced labeled fibers in the hippocampal formation. A robust projection of the angular bundle into the CA1 region of the hippocampus was heavily labeled. In addition, in some animals, cortical tracts, such as the anterior commissure, corpus callosum, and a corticotectal tract, were labeled. These tracts have been described previously as scaffolding pathways in the fetal cat (McConnell, Ghosh, and Shatz, 1989), and other vertebrates (Wilson, Ross, Parrett, and Easter, 1990). Dye placement in adjacent, more anterior or dorsal areas showed strong labeling in cortical structures but no labeling in the hippocampal formation. These data indicate that, by birth, the temporal cortex is subdivided along the rostro-caudal axis as entorhinal cortex and perirhinal cortex, and along the dorso-ventral axis, as entorhinal cortex and neocortex. Also, these earliest connections are similar to adult connections in their specificity of target area selection. Therefore, these early, yet specific, connections may play a role in the formation of future connections during postnatal development.     

Mapping the early development of projections from the entorhinal cortex in the embryonic mouse using prenatal surgery techniques.

The purpose of this work was to study the development of specific projections from the postero-lateral cortex during the third trimester of gestation in the mouse. To do this, we labeled undifferentiated lateral cortex with the fluorescent carbocyanine dye, Dil, in the embryonic day (E) 16 mouse embryo using exo utero surgical techniques (Muneoka, Wanek, and Bryant, 1986). Embryos were allowed to develop to term (postnatal day 0, P0) at which time the fiber patterns emanating from the marked regions were studied. Dye placement in the undifferentiated postero-ventral cortex produced labeled fibers in the hippocampal formation. A robust projection of the angular bundle into the CA1 region of the hippocampus was heavily labeled. In addition, in some animals, cortical tracts, such as the anterior commissure, corpus callosum, and a corticotectal tract, were labeled. These tracts have been described previously as scaffolding pathways in the fetal cat (McConnell, Ghosh, and Shatz, 1989), and other vertebrates (Wilson, Ross, Parrett, and Easter, 1990). Dye placement in adjacent, more anterior or dorsal areas showed strong labeling in cortical structures but no labeling in the hippocampal formation. These data indicate that, by birth, the temporal cortex is subdivided along the rostro-caudal axis as entorhinal cortex and perirhinal cortex, and along the dorso-ventral axis, as entorhinal cortex and neocortex. Also, these earliest connections are similar to adult connections in their specificity of target area selection. Therefore, these early, yet specific, connections may play a role int he formation of future connections during postnatal development.     

Interaction of brain macrostructures during organization of behavior

The data on anatomical connections, injury consequences, summate and unit activity records may be represented as a chain of events running in sequence and in parallel in the brain of higher mammals. Internal (metabolism) and external (odour, pain, etc.) incentive unconditioned stimuli activate motivational structures of the hypothalamus, which in turn activates the frontal areas of the neocortex and the hippocampus. In case of coincidence of earlier neutral external stimuli with the action of reinforcing unconditioned ones, the hippocampus becomes the first place of convergence of combined afferentiations. After formation of the act, those external stimuli or their engrams which have been accompanied earlier by satisfaction of a certain need, are selected as a result of joint action of the hippocampus and the frontal cortex. By comparison of motivational excitation with available stimuli or their engrams retrieved from memory with the participation of the temporal cortex, an emotional colouring of the stimuli and engrams is formed in the amygdala leading to isolation of a dominant motivation, destined to be satisfied in the first instance. The program formed in the frontal cortex, comes to the basal ganglia where, by means of interaction with the parietal cortex, it confirms to the spatial coordinates of the forthcoming action. From the fronto-striate system, the excitation comes through the motor cortex to the effector organs accomplishing the behavioural act.     

Correlative formation of functions as one of mechanisms of functional evolution (by example of development in child’s ontogenesis of central maintenance of stereognosis and speech function)

The paper considers a possibility of correlative formation in ontogenesis of central mechanisms of stereognosis and speech function by example of comparison of changes in spatial organization of interregional interaction of various cortex areas in children of three age groups (5–6, 7–8, and 9–10 years) and in adults subjects during their performances of stereognostical, verbalmnestic, and motor manual activity (the tapping test). With age dynamics of children there was observed a significant increase in the degree of similarity of the spatial structure of interregional relations during periods of performance of stereognostical test with patterns of changes in the EEG distant relationships revealed at performance of verbal tasks. In turn, similarity of patterns of interregional EEG relationships characteristic of stereognostical tasks with the patterns revealed at periods of performance of the tapping test was not increased with age. On the whole, the obtained data allow believing that with increase of children’s age there rose the degree of topological similarity of the spatial structure of systemic interactions of the cortex zones, on which there were “supported” processes of realization of stereognostical and verbal functions. The progressing increase with children’s age of the degree of similarity of the distributive organization of neurophysiological mechanisms of central provision of the verbal and stereognostic functions can argue in favor of the concept of correlative formation of these higher psychical functions in postnatal ontogenesis. The obtained data show that the correlative interfunctional interactions promoting progressive development of cognitive functions in the child ontogenesis can be realized through the long association fibers and commissural pathways composing the morphofunctional longitudinal-transversal “skeleton” of neocortex in the close interaction with thalamo-cortical integrative systems.