Laminar analysis of the origin of the various components of evoked potentials in slices of rat sensorimotor cortex

In slices of rat sensorimotor cortex, extracellular field potentials evoked by electrical stimulation of the white matter were recorded at various cortical depths. In order to determine the nature of the various components, experiments were performed in 3 situations: in a control perfusion medium, in a solution in which calcium ions have been replaced by magnesium ions to block synaptic transmission, and in cortices in which the pyramidal neurons of layer V had been previously induced to degenerate.In the control situation, the response at or near the surface was a positive-negative wave. From a depth of about 150 μm downwards, the evoked response consisted usually of 6 successive components, 3 positive-going, P11, P3 and P6 and 3 negative-going, N2, N4 and N5. P1 and N4 were apparent in superficial layers only. The amplitude of the remaining waves variable in the cortex but all diminished near the white matter.The early part of the surface positive wave arises from a non-synaptic activation of superficial elements, probably apical dendrites. The late part of the surface positive wave and the negative wave are due to the synaptic activation of neurons located probably in layer III.The large negative wave N2 represents principally the antidromic activation of cell bodies and possibly of proximal dendrites of neurons situated in layers III, IV and V, through the compound action potentials of afferent and efferent fibers may contribute to a reduced part to its generation.The late components N4 to P6 are post-synaptic responses. The negative component N5, the amplitude of which is largest in layers III and IV, represents excitatory responses of neurons located at various depths in the cortex. The nature of the positive component P6 is less clear, although the underlying mechanism might be inhibitory synaptic potentials.     

Changes in metabolites of the energy reserves in individual layers of mouse cerebral cortex and subjacent white matter during ischaemia and anaesthesia

The distribution of glucose, glycogen, ATP, P-creatine and inorganic phosphate was measured in layers I, III, IV, V and VI of cerebral cortex and subjacent white matter of mouse brain. ATP, P-creatine and inorganic phosphate were evenly distributed in all regions examined, whereas levels of glucose and glycogen were higher in white matter than the average for the other layers. Anaesthesia increased levels of glucose and P-creatine in layers I and V and subjacent white matter (other layers were not examined). Anaesthesia doubled the level of glycogen in molecular layer I with lesser increases in layers III, IV, V and VI, but with no change in white matter from the unanaesthetized control value. The metabolic rates in the individual layers were estimated from the rates of expenditure of energy reserves during total ischaemia. In non-anaesthetized mice, white matter had a higher metabolic rate than either layer I or V. Anaesthesia reduced the metabolic rates in all layers; however, the largest reduction occurred in subjacent white matter (86 per cent), with reductions of 54 per cent and 76 per cent respectively in layers I and V.     

Connections between the posterolateral nucleus of the thalamus and the parietal and occipital areas of the cerebral hemispheres in the cat

A light optic and electron microscopic investigation on distribution of fibers from the thalamic posterolateral nucleus has been performed in the cat cerebral cortex. The fibers studied are revealed in the fields 7, 19 and 18. In the field 7 they are most numerous, comparatively seldom they are found in the field 19 and still more seldom--in the field 18. In the fields 7 and 19 identical peculiarities on distribution and termination of the fibers are noted: they spread across the whole cortex and end in all the layers with a predominant concentration in the layers III and IV. Most of the fibers make contacts on small dendritic branches and spines. In the field 18 the fibers are mainly limited by the medial layers and terminate predominantly on small, middle-sized dendritic branches, and comparatively rare--on the spines.     

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.     

Medial temporal lobe projections to the retrosplenial cortex of the macaque monkey

The projections to the retrosplenial cortex (areas 29 and 30) from the hippocampal formation, the entorhinal cortex, perirhinal cortex, and amygdala were examined in two species of macaque monkey by tracking the anterograde transport of amino acids. Hippocampal projections arose from the subiculum and presubiculum to terminate principally in area 29. Label was found in layer I and layer III(IV), the former seemingly reflecting both fibers of passage and termination. While the rostral subiculum mainly projects to the ventral retrosplenial cortex, mid and caudal levels of the subiculum have denser projections to both the caudal and dorsal retrosplenial cortex. Appreciable projections to dorsal area 30 [layer III(IV)] were only seen following an extensive injection involving both the caudal subiculum and presubiculum. This same case provided the only example of a light projection from the hippocampal formation to posterior cingulate area 23 (layer III). Anterograde label from the entorhinal cortex injections was typically concentrated in layer I of 29a-c, though the very caudal entorhinal cortex appeared to provide more widespread retrosplenial projections. In this study, neither the amygdala nor the perirhinal cortex were found to have appreciable projections to the retrosplenial cortex, although injections in either medial temporal region revealed efferent fibers that pass very close or even within this cortical area. Finally, light projections to area 30V, which is adjacent to the calcarine sulcus, were seen in those cases with rostral subiculum and entorhinal injections. The results reveal a particular affinity between the hippocampal formation and the retrosplenial cortex, and so distinguish areas 29 and 30 from area 23 within the posterior cingulate region. The findings also suggest further functional differences within retrosplenial subregions as area 29 received the large majority of efferents from the subiculum. ? 2012 Wiley Periodicals, Inc.     

Cholinergic structures in the cat auditory cortex (area AI)

Plexuses of cholinergic varicose fibers, differing in density in different layers of the neuropil, were found in area AI of the cat's auditory cortex by the histochemical reaction for acetylcholinesterase: Their density was maximal or average in layer I or deeper layers and minimal in layers II and III. Among cells in area AI those which are cholinergic are a few stellate neurons located in layers II–VI. Axons of some neurons terminate on neighboring cells, those of others (some neurons in layer VI) run into the subcortical layer of arcuate association fibers. Cholinergic terminals are located on the bodies and proximal areas of dendrites of neurons most of which do not contain acetylcholinesterase. Choliniceptive neurons of different sizes and shapes are found in all layers of this region of the auditory cortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 75–81, January–February, 1984.     

Distribution and ultrastructure of thalamic afferents in the cat auditory cortex

Ultrastructural features of thalamic afferent fibers were studied in the cat auditory cortex in the early stages (on the 4th day) of experimental degeneration produced by destruction of the medial geniculate body. A coordinate grid was used in conjunction with an electron micro-scope to study the topography of the degenerating elements over wide areas of sections, so that the density of degeneration could be determined quantitatively in different layers of the cortex. Degenerating axons were found in all layers. Most of the large (5–7 µ) degenerating axons are located in layer VI; their diameters were smaller in the upper layers of the cortex. Degenerative changes affecting synaptic terminals of thalamo-cortical afferents were of the "dark" type. Fibers of the geniculo-cortical tract were shown to terminate mainly in cortical layer IV. A few degenerating synapses were found in the molecular layer. Terminals with sperical synaptic vesicles are found mainly on the spines of dendrites where they form "asymmetrical" contacts. A few degenerating axo-somatic synapses were observed on stellate neurons in layer IV. The results are discussed in connection with electrophysiological investigations of the cat auditory cortex during stimulation of specific afferent fibers.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 612–620, November–December, 1972.     

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.     

Neurons with choline acetyltransferase immunoreactivity and mRNA are present in the human cerebral cortex

 We examined the cerebral cortex of five autopsied individuals without neurological and psychiatric diseases by immunohistochemistry using an anti-human recombinant choline acetyltransferase (ChAT) polyclonal antibody and in situ hybridization with ³⁵S-labeled human ChAT riboprobes. The immunohistochemistry detected positive neurons which were medium-sized or large pyramidal neurons located predominantly in layers III and V. The density of such neurons was higher in the motor and secondary sensory areas than in other cortical areas; the immunoreactive neurons in layer V were more densely distributed in the motor area and those in layer III were distributed in the secondary sensory areas. Positively stained, non-pyramidal neurons were observed in the superficial layer of the cingulate gyrus and parahippocampus. No immunoreactive neurons were found in the primary sensory areas. The in situ hybridization detected some neurons with signals for ChAT mRNA in the cerebral cortex, most of which were distributed in layer V of the motor area and in layer III of the secondary visual area. These results indicate that the human cerebral cortex contains cholinergic neurons and displays regional and laminal variations in their distribution. Accepted: 17 November 1998     

Calcium-binding Proteins Calbindin D28K, Calretinin, and Parvalbumin Immunoreactivity in the Rabbit Visual Cortex

The distribution and morphology of neurons containing three calcium-binding proteins, calbindin D28K, calretinin, and parvalbumin in the adult rabbit visual cortex were studied. The calcium-binding proteins were identified using antibody immunocytochemistry. Calbindin D28K-immunoreactive (IR) neurons were located throughout the cortical layers with the highest density in layer V. However, calbindin D28K-IR neurons were rarely encountered in layer I. Calretinin-IR neurons were mainly located in layers II and III. Considerably lower densities of calretinin-IR neurons were observed in the other layers. Parvalbumin-IR neurons were predominantly located in layers III, IV, V, and VI. In layers I and II, parvalbumin-IR neurons were only rarely seen. The majority of the calbindin D28K-IR neurons were stellate, round or oval cells with multipolar dendrites. The majority of calretinin-IR neurons were vertical fusiform cells with long processes traveling perpendicularly to the pial surface. The morphology of the majority of parvalbumin-IR neurons was similar to that of calbindin D28K: stellate, round or oval with multipolar dendrites. These results indicate that these three different calcium-binding proteins are contained in specific layers and cells in the rabbit visual cortex.     

Laminar distribution of benzodiazepine receptors in visual cortex of adult rat

The characteristics and distribution of benzodiazepine receptors in individual layers of the visual cortex of adult rats were examined with the 3H-flunitrazepam binding technique employed on intact tissue slices. The different visual cortical layers were separated by cutting serial cryocut sections horizontally to the cortical surface and collecting the slices from each individual cortical layer under anatomical control. Highest benzodiazepine receptor densities were found in layers IV and VI. A moderate receptor density was detected in layer V (80% of highest density). The lowest receptor binding was observed in cortical layers I and II/III, still representing 66% of the highest receptor density. Binding affinities varied slightly between layers with dissociation constants somewhat higher for layers IV to VI in comparison to layers I and II/III. The distinct laminar pattern of benzodiazepine receptors in rat visual cortex suggests a differential neuromodulatory significance of these receptors in each individual cortical layer.     

Association connections of the cat's parietal cortex

Intercortical connections of primary sensory (visual, auditory, somatosensory) areas with the parietal association cortex were studied in cats by the retrograde axonal transport of horseradish peroxidase and the Fink-Heimer silver impregnation of degenerated fibers techniques. This combined study revealed the shape, size, and intracortical location of cells connecting the primary sensory areas monosynaptically with the parietal cortex and also the distribution of preterminals and terminals of the fibers of these cells in the parietal association cortex. The greatest number of cells forming connections with area 7 of the parietal association cortex was shown to occur in visual area V1, and with area 5 in somatosensory area S1. Besides pyramidal neurons tagged with horseradish peroxidase, which were located mainly in layers II–IV, a few tagged stellate and fusiform cells also were found. The results supplement and confirm data on afferent connections of the parietal association cortex in cats.M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 3–6, January, 1981.     

Organization of somatic nerve projections in various cortical areas of the cat cerebellum

We conducted a layer analysis of evoked potentials arising in various cortical cerebellar areas (vermis and intermediate zones of the anterior lobe, and the ansiform lobe) of non-anesthetized cats upon stimulation of nerves in fore- and hindlimbs. This analysis yielded the conclusion on the arrival of stimuli at the cerebellar cortex over two types of moss fibers innervating two types of granule cells which we described earlier. Impulses transmitted over type I moss fibers stimulate Purkinje cells. The activation of type II moss fibers has no immediate effect on these cells. Type I moss fibers terminate in the vermis and the intermediate zone of the hemispheres and do not terminate in the lateral hemispheric region. While projections of type I moss fibers are somatotopically organized in the intermediate zone they are diffuse in the vermis. Type II moss fibers terminate in all the regions of the crebellar cortex under study, but their projections show no somatotopic organization. The question of the afferent pathways terminating as type I and II moss fibers is discussed.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 2, pp. 166–174, March–April, 1971.     

Interhemispheric connections through the pallial commissures in the brain of Podarcis hispanica and Gallotia stehlinii (Reptilia,Lacertidae)

The cells-of-origin and the mode and site of termination of the interhemispheric connections passing through the anterior and posterior pallial commissures in the telencephalon of two lizards (Podarcis hispanica and Gallotia stehlinii) were investigated by studying the anterograde and retrograde transport of unilaterally injected horseradish peroxidase. The commissural projections arise mainly from pyramidal cells in the medial, dorsomedial, and dorsal cortices (medial subfield). Additionally some non-pyramidal neurons in the medial and dorsal cortices contribute to the commissural system. Medial cortex neurons project to the contralateral anterior septum through the anterior pallial commissure. The dorsomedial cortex projects contralaterally via the anterior pallial commissure to the dorsolateral septum and to the medial, dorsomedial, and dorsal cortices. The projection to the medial cortex terminates in two bands at the inner and outer border, respectively, of the cell layer; the projection to the dorsomedial and dorsal cortex ends in a zone in layer 1 which previously has been described to be Timm-negative, and in a diffuse band in the inner half of layer 3. The medial subfield of the dorsal cortex projects through the anterior pallial commissure to the dorsomedial and dorsal cortices with a similar pattern of termination to that found for the dorsomedial cortex. The posterior pallial commissure contains only the projections from the ventral cortex to its contralateral counterpart and to the ventral part of the caudal medial cortex. The similarities found between this commissural system and the mammalian hippocampal interhemispheric connections are discussed.     

Intrinsic organization of the medial cerebral cortex of the lizard Lacerta pityusensis: A golgi study

The morphology of cells and the organization of axons were studied in Golgi-Colonnier and toluidine blue stained preparations from the medial cerebral cortex of the lizard Lacerta pityusensis. In the medial cortex, six strata were distinguished between the superficial glial membrane and the ependyma. Strata I and II formed the outer plexiform layer, stratum III formed the cellular layer, and strata IV go VI the inner plexiform layer. The outer plexiform layer contained smooth bipolar neurons; their dendrites were oriented anteroposteriorly and their axons were directed towards the posterior zone of the brain. Five neuronal types were observed in the cellular layer. The spinous pyramidal neurons had well-developed apical dendrites and poorly developed basal ones. Their axons entered the inner plexiform layer and gave off collaterals oriented anteroposteriorly. The small, sparsely spinous pyramidal neurons had poorly developed dendrites and their axons entered the inner plexiform layer. The spinous bitufted neurons had well-developed apical and basal dendritic tufts. Their axons gave off collaterals that reached the outer and inner plexiform layers of both the dorsomedial and dorsal cortices. The sparsely spinous horizontal neurons had dendrites restricted to the outer plexiform layer. Their axons entered the inner plexiform layer. The sparsely spinous, multipolar neurons had their soma close to stratum IV and their axons entered the outer plexiform layer. In stratum V of the inner plexiform layer were large, spiny polymorphic neurons; they had dendrites with long spines, and their axons reached the cellular layer. On the basis of these results, we have subdivided the medial cortex into two subregions: the superficial region, which contains the neurons of the cellular layer and their dendritic domains, and the deep region, strata V and VI, which contains the large, spiny polymorphic neurons. The neurons in the medial cortex of these lizards resembles those in the area dentata of mammals. On this basis, the superficial region may be compared to the dentate gyrus and the deep region to the hilar region of the hippocampus of mammals.     

Inhibition of axoplasmic transport in the developing visual system of the rat: IV. Quantitative Golgi, electron microscopic, and histochemical analyses of the maturation of the visual cortex

Intraocularly injected colchicine suppresses axonal transport within the developing rat's optic nerve throughout the critical period of visual system development. This results in a stunting of retinofugal terminals and relay neurons in the lateral geniculate nucleus. The present study focuses upon the effects of this unique form of developmental deprivation on the maturation of the visual cortex. Colchicine, in concentrations of from 10(-5) to 10(-2) M, was injected into the eyes of albino rats at birth or at 5, 10, or 15 days of age. Litters were killed at 5 to 50 days after this single injection, and the brains were processed for Nissl, rapid Golgi, histochemical, or electron microscopic analysis. The following results were obtained: Planimetry of coronal sections of the striate cortex revealed a reduction in the thickness of the cortex and in the ratio of neuropil area to neuronal soma area contralateral to the injected eye which was confined principally to layer IV, lower layer III, and upper layer V. This effect was inversely related to postnatal age at injection and directly proportional to colchicine concentration. A rapid Golgi analysis of 51 pairs of layer V pyramidal neurons in control and experimental cortex demonstrated a reduction in the number and size of spines along the portion of the apical dendrite passing through lower layer III and IV following colchicine administration at birth or 5 or 10 days of age but no significant change in the branching pattern of the entire dendritic arbor. Electron microscopy revealed a reduction in the number of small, asymmetric synaptic complexes with the result that the average size of remaining profiles was increased in layers III and IV. Histochemical analysis of cortical succinic dehydrogenase and cytochrome oxidase revealed a distinct band of intense enzyme activity in lower layers III and IV in normal cortex at 20-30 days of age. This band was significantly reduced in intensity after neonatal injection of colchicine as shown by densitometric measurements and comparison of experimental and control cortex. It is concluded that the geniculocortical projection, while not affected directly by colchicine administration, is altered by the secondary effects of axonal transport suppression, leading to an alteration in the establishment of cortical synaptic patterns and arborizations of their postsynaptic neurons whose dendrites are located in those layers recipient to this projection.     

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.     

The structure of the first auditory cortex (A I) in the cat. I.--Light microscopic observations on its organization

The cyto- and mieloarchitecture of the first auditory cortex (A I) was studied in the cat. The cortical layers II, III and IV are very densely populated by relatively uniform, round or stellate cells with 20 to 30 micro perikaryal diameter. The separation between these three layers, which is not possible in Nissl stained sections, becomes visible in 1 to 3 micro thick sections of plastic embedded material. nerve cells in layer II are randomly disposed, whilst they form in laver III loose rounded cellular groups, and in layer IV vertical cylinders which have 50 to 60 micro in outside diameter and a cell poor centre. These cylinders are best visible in 100 micro thick Nissl preparations, cut parallel to the pial surface. The cylinders may extend into layer V, which is comparatively cell poor. The VIth layer contains numerous round, stellate or fusiform cells with 20 to 30 micro in diameter. The IIIrd and Vth layers have few pyramidal perikarya which are small. Large or giant pyramidal cells are not found in A I. The overall thickness of the cortex in the convexity of A I is 2,000 micro, measured in sections of plastic blocks. The thickness of the 6 layers is 200 to 250 micro for layer I; 300 micro for layer II; 300 micro for layer III; 300 to 400, for layer IV; 350 micro for layer V; and 400 micro for layer VI. In preparations stained for myelin sheats A I is characterized by the presence of a very dense plexus of fibres running in all directions in the IVth, Vth anti VIth layers. These plexus obscurs the radiations of Meynert, giving a characteristic appearance to A I, since these radiations are prominent in the neighbouring cortical areas. In preliminary studies of Golgi rapid preparations of A I the cell types commonly present in others cortical areas were found. Pyramidal cells have small perikarya, and very long (600 micro) horizontal basal dendrites. Modified pyramidal cells (star pyramids) are the main cellular element in layer II and constitute one of the main sources of efferent fibres of A I. Several types of stellate cells were found, including a particular cell type, found very often in the IVth layer, with a very long horizontal axon. The specific thalamic afferents were identified as fibres with 5 or 8 micro in diameter, which run obliquely and sinuously through the VIth and Vth layers of A I. These fibres give off many branches with 1 to 2 micro in diameter, which pass to the IVth layer where they give off very thin sinuous branches, ending in small terminal knobs. The ramification of one of these fibres may spread horizontally over 800 micros, at the level of the IVth layer.     

Organization of bilateral spinal projections to the lateral reticular nucleus of the rat

The present study was carried out to analyze the topography of bilateral spinal projections to the lateral reticular nucleus (LRN). We used retrograde transport of fluorescent tracers Fast Blue and Diamidino Yellow to identify spinal neurons projecting to the ipsilateral and/or contralateral LRN, as well as orthograde transport of Phaseolus vulgaris leucoagglutinin to identify the LRN areas where spinoreticular axons terminate. Orthograde labeling confirmed that bilateral spinoreticular projections coming from cervical and upper-thoracic segments terminate in the magnocellular division of LRN, while those coming from the lower-thoracic, lumbar and sacral segments end in the parvocellular division of the nucleus; only a sparse spinal input has been observed in the subtrigeminal division of LRN. Retrograde labeling showed that labeled neurons were present at all spinal levels and in particular large numbers in the cervical and lumbar enlargements. Retrogradely single-labeled cells were located, with contralateral predominance, in all segments of the spinal cord, within laminae IV, V, VI, VIII, and X, whereas in laminae III and VII labeled neurons were mainly observed ipsilaterally. Furthermore, a small fraction of double-labeled cells (7.4%) was observed throughout the spinal cord, mainly in laminae III, IV, VII and VIII.     

Dynamics of protein concentration in the neurons of a chronic "mirror" epileptiform focus

Protein content in the neurons of layers III and V in the rat brain anterior-parietal cortex and the lateral thalamic nucleus was studied 11 and 63 days after cobalt implantation. In the course of the experiment, protein content increased by 44--49% in the neurons of layer III and decreased by 24--32% in the thalamic neurons. In small and large pyramids of layer V, protein content decreased by 21--28%, 11 days after cobalt implantation, and approached normal content by the 63rd day. It was concluded that according to morpho-functional characteristic of certain neuronal types (associative, in layer III, predominantly efferent, in layer V and associative neurons in subcortical formations of the lateral thalamic nucleus) their protein changes in response to convulsive activity were different.