Distribution of afferents from the association nuclei of the thalamus in the projection and association cortex in cats

Patterns of distribution of terminal degeneration in the parietal cortex (field 7) and in the occipital cortex (field 17) were studied after ultrasonic destruction of the pulvinar by the Fink-Heimer and electron microscopy methods. Degenerating fibers and their terminals were observed in the parietal cortex within all the layers; the greatest amount of degeneration was found in the III--V layers. In the occipital cortex the fibers from the pulvinar end predominantly in the IV layer. Degenerating axons end on the dendritic spines and thin dendritic branches both in the parietal and occipital cortex.     

Distribution of neuropeptide Y immunoreactivity in human visual cortex and underlying white matter

Immunocytochemical techniques have been used to study neuropeptide Y (NPY) distribution in the human visual cortex (Brodman's areas 17, 18 and 19) NYP cell bodies belong mostly to inhibitory (multipolar and bitufted) but also to excitatory (bipolar and some pyramidal) neuronal types. Their distribution is similar in the three cortical areas studied: 20 to 40% of the NPY perikarya are located in the cortical gray matter, mostly in the deep layers, while the remaining 60 to 80% are located in the underlying white matter. Immunoreactive NPY processes form a rich network of intersecting fibers throughout the entire visual cortex. A superficial plexus (layers I and II) and a deep plexus (deep layer V and layer VI) of NPY fibers are present in areas 17, 18 and 19. In area 17, an additional well developed plexus is present in layers IVb and IVc. These plexuses receive branches from long parallel fibers arising from deep cortical layers or underlying white matter and terminating in superficial layers. Local or extrinsic NPY terminals wind around vessels in the cortex as well as in the white matter, and either penetrate them or form clusters of club endings on their walls. Our results suggest a role for NPY in human visual circuitry and in cortical blood flow regulation.     

Morphology of the cat auditory cortex

The ultrastructural features of the primary auditory cortex of the cats and the character of the endings of geniculo-cortical afferent fibers in the early stages of experimental degeneration evoked by destruction of the medial geniculate body were studied. In all layers of the cortex asymmetrical synapses with round synaptic vesicles on dendritic spines and on thin dendritic branches of pyramidal and nonpyramidal neurons are predominant. Symmetrical synapses with flattened or polymorphic vesicles are distributed chiefly on the bodies of the neurons and their large dendrites. Because there are few symmetrical synapses which could be regarded as inhibitory it is postulated that inhibitory influences may also be transmitted through asymmetrical synapses with round vesicles. Other types of contacts between the bodies of neurons, dendrites, and glial processes also were found in the auditory cortex. Degenerating terminals of geniculo-cortical fibers were shown to terminate chiefly in layer IV of the cortex on pyramidal and nonpyramidal neurons. Degeneration was of the dark type in asymmetrical synapses with round vesicles. The results are dicussed in connection with electrophysiological investigations of the auditory cortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 519–524, September–October, 1973.     

Quantitative studies on the neuron structure of the rat fascia dentata]

1. In 6 month old male rats the structure of dendrites and the distribution of spines on the apical dendrites of granular cells of the dentate gyrus were investigated by light microscopy and statistical methods. 2. The number of dendrites of the first, second and third order of granular cells increases in this sequence in a ratio of 1:2:3; the total length of the dendrites increases correspondently in a ratio of 1:4:5. 3. The mean number of origin points of dendritic branches is 10, the mean number of free dendritic endings is 12. 4. The number of spines per a 25 mum dendritic segment near to the pericaryon (dendritic segment A), in the middle of the dendrite (dendritic segment B) and in the peripheral dendritic part (dendritic segment C) as well as the distribution of spines in the whole apical dendrite was evaluated. The total mean of spines of granular cell apical dendrites of the dentate gyrus (superior respectively inferior) is 12 respectively 10 for the dendritic segment A, 18 respectively 17 for the dendritic segment B and 17 respectively 15 for the dendritic segment C calculated for a dendritic length of 25 mum. 5. The spine density in each case depends upon the distance pericaryondendritic segment and is in close relation to the adjacent layers with their specific afferents. 6. The averaged total number of spines per 1 mum of dendritic length is 0,62 spines/mum for the dentate gyrus (superior) and 0,57 spines/mum for the dentate gyrus (inferior). 7. The granular cells of the dentate gyrus (superior) have a mean dendritic length of a total of 357 mum with a total of 226 visible spines; the granular cells of the dentate gyrus (inferior) have a mean dendritic length of a total of 450 mum with a total of 258 visible spines.     

Synapsoarchitechtonics of the parietal and acoustic regions of the cerebral cortex of cats]

The synapse architecture of the simcipital and auditory cortex of the cat (fields 7 and 22 after M. O. Gurevich and oth., 1929) was studied electron microscopically. In the both areas of the cortex there are much more axo-dendritic synapses that axo-somatic ones. In the upper layers the synapses are more often formed on small dendrites and thorns, while in layers IV-VI they often occur on the main trunks of large dendrites. The synapses on small branches and thorns of dendrites contain spherical vesicles, and the synapses on on large dendrites are formed by the terminals of two kinds-with flattened and spherical vesicles. The amount of axo-somatic synapses increases towards the lower layers of the cerebral cortes. The synapses on the soma and apical dendrites of the pyramid neurons always contain flattened vesicles; on the stellate neurons there occur perisynaptic terminals with sperical vesicles as well.     

Interhemispheric connections of the parietal area of the cat cerebral cortex

The interhemispheric connections of the temporal cortical area in the cat cerebrum have been investigated after electrolytic coagulation of separate fields with subsequent study of the degenerated fibers course after Nauta--Gygax method. The fields 5 and 7 give origin mainly to homotopic fibers, terminating in symmetrical fields of the contralateral hemisphere. These fields also give origin to a small number of heterotopic commissural fibers, that provide bilateral connection of the fields 5 and 7 and do not get beyond the limits of the temporal cortex. The commissural fibers of the temporal cortex get into the contralateral hemisphere through the corpus callosum. In the latter, the commissural fibers of the field 5 are situated more rostral of the fibers running from the field. 7. This corresponds to topographic arrangement of the fields on the cortical surface.     

Neuronal organization of field 4 of the motor cortex of the cat brain

By means of the silver nitrate impregnation method after Golgi-Kopsch in kittens and young cats the field 4 in the cerebral motor cortex has been studied. The motor cortex of the field 4 possesses certain heteromorphism. Besides usual stellate and pyramidal neurons, that differ from real ones by some morphological signs: their body is often round, the apical dendrite is much thinner than the corresponding dendrite of a pyramidal neuron, it does not produce oblique branches along the course, never gets into the I layer, the spines arrange less densely. According to the mode of dendrites setting off, the atypical pyramidal neurons can be divided into multipolar and spindle-like with horizontal or vertical branching of the dendrites. According to the spines distribution, the multipolar atypical neurons can be divided into spinous, rare-spinous and aspinous. With respect to various cellular forms and distribution of various types of neurons in layers, every of the areas (gamma, alpha, sfu, fu) possesses specific peculiarities. The greatest variability of the neurons have the field 4 gamma and 4 alpha, where, besides stellate and pyramidal, atypical neurons can be found. The stellate neurons of the field 4 gamma are characterized with a deep arrangement, their number is essentially less, than in other areas of the field 4. In the field 4 alpha they are situated in the layers II-III. Suprafundal and fundal parts of the field do not possess pyramidal atypical neurons and are characterized with presence of large amount of the stellate neurons. In respect to the axonal branching in the suprafundal part of the field 4, 2 types of the stellate cells are distinguished.     

Connections of various fields of the parietal cortex with the caudate nucleus of the cat brain

By means of the light and electron microscopy methods efferent connections of the fields 5a, 5b and 7 with the caudate nucleus have been studied. These fields are predominantly projected to the dorsolateral corner of the middle and posterior head of the caudate nucleus. The fields 5b and 7, unlike the field 5a, give also origin to the fibers, terminating in the central part of the head and in the caudate nucleus body. The electron microscopic investigation proves the monosynaptic nature of the fields 5a, 5b and 7 with the dorsolateral part of the middle and posterior parts of the caudate nucleus head. The parietal cortex gives origin, mainly, to fine myelin fibers (0.665 +/- 0.029), terminating in the part mentioned of the caudate nucleus. These fibers form small terminals (0.310 +/- 0.014 to 0.430 +/- 0.020 mcm) with asymmetrical membranous thickening; these terminals end on the spines (with a poorly expressed spine apparatus) of the dendrites, evidently, of the middle spine cells. Axonal terminals of the parietal cortex form axodendritic terminals extremely seldom. Axospinous synapses on the dendrites of the middle spine cells, situating in the dorsolateral part of the caudate nucleus head are supposed to be a morphological substrate, ensuring the cortical control of the parietal cortex at the level of the caudate nucleus.     

Morphological characteristics of various segments of local connections in the rat somatosensory cortex

Pyramidal, aspinous, sparsely-spinous bipolar and multipolar neurons of the rat sensomotor cerebral cortex, impregnated after Golgi method, have been studied at an electron microscopical level. The ultrastructural characteristics of the pyramidal neurons differs from that of the nonpyramidal cells. Distribution of various synaptic contacts on the cellular surface and cortical postsynaptic targets of the axonal arborizations of the neurons are revealed. On the body of the pyramidal cells only symmetrical synapses exist, on large dendritic trunks symmetrical synapses prevail, on the spines and the terminal dendritic branches assymetrical synapses mainly predominate. Axonal collateralies of the pyramidal cells form asymmetrical synapses on the spines, small and middle dendrites. There are more axo-somatic synapses on the bodies of the nonpyramidal neurons than on the pyramidal cells, among them both symmetrical and asymmetrical types of the synapses occur. On the trunks and small dendrites of the nonpyramidal cells both types of synaptic contacts are revealed. In the distal direction of the dendrites the number of the asymmetrical synapses becomes predominating. Axons of the bipolar cells form asymmetrical synapses on the spines, small and middle dendrites. Axons of the multipolar cells form symmetrical synapses on the dendrites and the dendritic trunks of the nondifferentiated cells. Differences in the distribution character of the synaptic inlets and various postsynaptic targets of the axonal systems in the cells assume various functional role of the identified neurons.     

Ectopic Purkinje cells in the cerebellar white matter of normal adult rodents: a Golgi study

In Golgi/Río-Hortega preparations of rat and rabbit cerebellar vermis we have occasionally found isolated ectopic Purkinje cells in the white matter. They were located beneath the bases of the folia and their dendritic branches extended within the confines of the white matter without penetrating into the overlying cortical layers. The general morphology of these ectopic cells was variable, particularly in the extension and shape of the dendritic trees, but all of them exhibited a lower density of dendritic branches than normal Purkinje cells. The less-developed ectopic neurons had multipolar dendritic trees with nonplanar branches irregularly studded with spines. The well-developed ones displayed a more extensive arborization of their processes and they usually preserved some morphological features of normal cortical Purkinje cells: distal dendritic branches studded with numerous spines, a pear-shaped soma, clearly defined morphological polarity and a tendency to display planar arrangement of the dendritic arbors. In semithin sections these neurons also showed cytological features of normal Purkinje cells, such as the Nissl substance forming a nuclear cap oriented toward the dendritic pole. We suggest that the abnormal location of the neurons results from a disorder of Purkinje cell migration which occurs naturally during the prenatal development of the cerebellum. The possible morphogenetic mechanisms involved in the migration and differentiation of these ectopic neurons are also discussed.     

Comparative electron microscopic study of the visual cortex neurons of the cat in postnatal ontogeny

The maturation of layers II-VI of neurons and perineuronal neuropil of the cat visual cortex (field 17) was studied from postnatal day 1 to day 21. The differentiation of large, small (associate) pyramid and stellate neurons was described. During the first postnatal week, the somata of layers II-VI of neurons undergo significant changes, the perikaryal cytoplasm increases in volume. Cell bodies of large pyramidal neurons mature by day 15. During the second postnatal week and almost till day 15, the rough endoplasmic reticulum of small pyramidal and stellate neurons undergoes proliferation; dendritic processes are branching. In stellate neurons the amount of cytoplasmic organelles increases dramatically only after the second postnatal week, and this is presumably induced by the opening of eyes on day 12. The second postnatal week is the period of greatest growth of dendritic, axonal and glial processes in perineural neuropil of layers V-VI. In the perineuronal neuropil of large pyramidal neurons (layers V-VI) there appear symmetric synapses with pyramidal cells, dendritic processes and dendritic spines. This occurs just at the time when kittens first open the eyes. From this time and during postnatal days 15-21, asymmetric synapses appear in the perineuronal neuropil of large pyramidal neurons. In the perineuronal neuropil of small pyramidal and stellate neurons. (layers II-IV), synapses reveal the mature appearance by day 15. After the opening of the eyes and up to postnatal day 21, dendritic growth and spine production occur in the perineuronal neuropil of small pyramidal and stellate neurons.     

Quantitative and qualitative characteristics of synapses in different layers of the auditory cortex

An electron-microscopic study was made of 4520 synapses in different layers of the cat auditory cortex. Of the total number of synapses 53% were located on dendritic spines, 37% on dendrites, and 10% on neuron bodies; 91% of the synapses belonged to Gray's type I, 9% to type II. Most of the type I synapses were located on dendrites and dendritic spines, whereas the type II synapses were distributed on neuron bodies, axon hillocks, and large dendrites. Signs of degeneration were discovered 60 h after complete neuronal isolation of an area of the auditory cortex in 22.8% of synapses. No degenerating type II synapses were found. This indicates that they are formed by axons of intracortical neurons. The quantitative and qualitative composition of the synapses were shown to differ in different layers of the auditory cortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 2, pp. 131–137, March–April, 1980.     

Experience‐dependent plasticity of dendritic spines of layer 2/3 pyramidal neurons in the mouse cortex

Previous studies have shown that sensory and motor experiences play an important role in the remodeling of dendritic spines of layer 5 (L5) pyramidal neurons in the cortex. In this study, we examined the effects of sensory deprivation and motor learning on dendritic spine remodeling of layer 2/3 (L2/3) pyramidal neurons in the barrel and motor cortices. Similar to L5 pyramidal neurons, spines on apical dendrites of L2/3 pyramidal neurons are plastic during development and largely stable in adulthood. Sensory deprivation via whisker trimming reduces the elimination rate of existing spines without significant effect on the rate of spine formation in the developing barrel cortex. Furthermore, we show that motor training increases the formation and elimination of dendritic spines in the primary motor cortex. Unlike L5 pyramidal neurons, however, there is no significant difference in the rate of spine formation between sibling dendritic branches of L2/3 pyramidal neurons. Our studies indicate that sensory and motor learning experiences have important impact on dendritic spine remodeling in L2/3 pyramidal neurons. They also suggest that the rules governing experience‐dependent spine remodeling are largely similar, but not identical, between L2/3 and L5 pyramidal neurons. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 277–286, 2016     

Development of long-term dendritic spine stability in diverse regions of cerebral cortex

Synapse formation and elimination occur throughout life, but the magnitude of such changes at distinct developmental stages remains unclear. Using transgenic mice overexpressing yellow fluorescent protein and transcranial two-photon microscopy, we repeatedly imaged dendritic spines on the apical dendrites of layer 5 pyramidal neurons. In young adolescent mice (1-month-old), 13%-20% of spines were eliminated and 5%-8% formed over 2 weeks in barrel, motor, and frontal cortices, indicating a cortical-wide spine loss during this developmental period. As animals mature, there is also a substantial loss of dendritic filopodia involved in spinogenesis. In adult mice (4-6 months old), 3%-5% of spines were eliminated and formed over 2 weeks in various cortical regions. Over 18 months, only 26% of spines were eliminated and 19% formed in adult barrel cortex. Thus, after a concurrent loss of spines and spine precursors in diverse regions of young adolescent cortex, spines become stable and a majority of them can last throughout life.     

Development of dendritic spines in the piriform neurons of the cerebellar cortex in human prenatal ontogeny

The submicroscopic investigation on developmental peculiarities of the dendritic spines in the piriform neurons of the cerebellar cortex has been performed during the human prenatal ontogenesis. The process of morphogenesis of the spines of the tertiary dendrites in the piriform neurons is demonstrated to start rather early--on the 24th week of embryogenesis and goes through three successive stages: 1) formation of a long cytoplasmic processes deprived of any membranous specialization; 2) formation of the terminal spinal head, making synapses with parallel fibers of the cerebellar cortex; 3) definitive stage. A suggestion is made that differentiation processes of the spines depend on inductive influence of the parallel fibers of the cerebellar cortex.     

Ventrolateral nucleus of the cat thalamus and its connection with field 4 of the cerebral cortex

By means of silver nitrate impregnation after Fink-Heimer and Golgi-Kopsch structural peculiarities have been revealed in the neurons of the ventral lateral nucleus (VL) of the cat thalamus and its connections with the motor cortex. The results of the observations demonstrate a complex morphological organization of the VL. It makes reciprocal connections with the field 4 of the motor cortex. Terminal fibers from the VL end in the layers I, III, V and VI of the field 4 gamma and in the whole thickness of the fundal field anatomically having no layers. No degenerating fibers are found after destruction in the fields 4 delta and 4 sfu. Basing on measurements of neuronal nuclei in the VL two cell populations are revealed, that demonstrates presence of two types of the neurons in the VL--large relay and small short axonal, each of them having several varieties. Complex synaptic contacts in the VL in the form of serial synapses and triads are also demonstrated.     

Postnatal development of the corticothalamic projections from the visual association cortex to the lateralis posterior complex in the cat

The postnatal development of the corticothalamic projection from the lateral suprasylvian cortex (LS) to the lateral medialis-suprageniculate nucleus (LM-Sg) of the cat thalamus was assessed by means of the anterograde tracer biocytin. In the adult, two types of corticothalamic fibers were found: type I established a network of fine fibers present throughout the LM-Sg, it was characterized by a linear sequence of small (less than 0.5 microm in diameter), single terminal boutons making contact mainly with thin dendrites and/or dendritic spines. Type II, found less frequently, gave off short, side branches near axon terminals and formed clusters of 5-10 large terminal boutons (0.5-1.5 microm in diameter), making contact predominately with medium-sized dendrites and/or vesicle-containing profiles, forming a synaptic glomerulus. At birth (P0), anterogradely-labeled fibers were found in the LM-Sg as in adults. In the early postnatal period (until P6) as well as around the time of eye-opening (P7-P10) to P21, neonatal fibers were largely unbranched many of them having axons tipped with growth cones. Axon terminals containing synaptic vesicles were rarely observed but when present these exhibited considerable variation in their morphological appearance of synapses. Thus, it was not possible to categorize them into the two types of axons which characterize the adult. After P25, terminal swellings bearing a close resemblance to those of type II fibers begin to appear. In this way, the main two corticothalamic fiber types could be identified. These findings demonstrate that significant postnatal changes occur in the synaptology of corticothalamic fibers in the LM-Sg, particularly with the maturation of type II fibers.     

Basic cerebellar events relating sensorimotor adaptation--structural analysis on extracellular records of Purkinje cells

The heterosynaptic facilitation or suppression of synaptic efficacy between parallel fibers and the dendritic spines of Purkinje cells (PCs) in the cerebellar cortex has been for decades the basic idea of sensorimotor adaptation. Great efforts in order to get direct evidence failed, or were not accepted as direct proofs. A new facility was introduced with the structural analysis of intradendritic records of the PC. These records reveal a generally double (rarely single, triple or quadruple) rhythmic pattern of small spikes, which are proposed to be prespikes of dendritic origin. Moreover, they may take their origin at functionally separated dendritic compartments resulting in a nonlinear, phase-sensitive integrative process, performed by the compound spike generating mechanism of the cerebellar PC.