Cytoarchitecture and thalamic connectivity of third somatosensory area of cat cerebral cortex

1. The third somatosensory area (SIII) was identified in the cat cerebral cortex by the recording of surface potentials evoked by deflection of a single contralateral mystacial vibrissa. A small amount of tritiated leucine was then injected at the center of the focus of evoked activity and, after a suitable survival period, the brain was prepared for autoradiography. 2. As defined by the presence of an autoradiographic injection, the SIII focus lay in a cytoarchitectonic field characterized in particular by the presence of very large pyramidal cells in layer V and corresponding to area 5a of Hassler and Muhs-Clement (24). 3. The terminal ramifications of corticothalamic cells, as outlined by axoplasmically transported label, formed clustered aggregations in the medial division of the posterior group of thalamic nuclei (Pom) and not in the ventrobasal complex (VB). This part of Pom is known to receive fibers from the spinal cord. 4. Injections of horseradish peroxidase primarily affecting area 5a retrogradely labeled cells in Pom but not in VB. 5. Injections of isotope in the two other foci of vibrissa-evoked activity usually recorded in each brain were invariably found to label a part of area 3b of the first somatosensory area (SI) in the case of the more anterior focus. The second focus sometimes lay in area 2 of SI and sometimes in the second somatosensory area (SII).

Direction and specificity of the axonal and transcellular transport of nucleosides

The axoplasmic transport of nucleosides or their derivatives has been examined autoradiographically in avian and mammalian brains. Following injections of [3H]-adenosine or [3H]uridine intravitreally in chicks and rats or into the thalamus or neocortex of rats, three findings emerge: (1) axoplasmic transport of these materials occurs both in the anterograde and retrograde direction in birds and mammals; (2) anterograde transport in the axons of injected cells results in considerable cellular labeling in the region in which the axons terminate. This labeling is not exclusively transsynaptic, but probably results from some less specific, trancellular transport, since glial cells at the terminal site and along the path of the axons also become labeled; (3) injection of [3H]uridine in the chick optic and rat thalamocortical systems results in a pattern of labeling which differs considerably from that seen after injection of [3H]adenosine. After [3H]adenosine injections in the chick eye or rat thalamus, retrograde cell labeling is far more obvious than anterograde, transcellular labeling; after injections of [3H]uridine, anterograde, transcellular labeling is more intense than retrograde cell labeling.

A retino-pulvinar projection in the cat

Injections of tritiated amino acids were made in one eye of Siamese and common cats including young kittens. After survival periods of 1--7 days axoplasmically transported label accumulated in a portion of the pulvinar nucleus as well as in the other known sites of termination of the retinofugal pathway. The retino-pulvinar projection is present at birth; it is bilateral and approximately symmetrical in common cats but the ipsilateral component is markedly reduced in Siamese animals. Labeled terminal ramifications of the retinal fibers in the pulvinar take the form of a thin, interrupted sheet oriented dorsoventrally and lying at the extreme lateral edge of the pulvinar nucleus. It appears to be continuous caudally with the medial interlaminar nucleus of the lateral geniculate complex, but the cells about which the grains cluster are clearly different from those of the medial interlaminar nucleus.

Formation of methionine from alpha-amino-n-butyric acid and 5'-methylthioadenosine in the rat

Adult rats may utilize two metabolites of methionine for the biosynthesis of this essential amino acid. In separate experiments methionine, labeled with 14C or with 35S was observed in plasma and urine following the administration of [2-14C]-alpha-amino-n-butyric acid or [35S]-5'-methylthioadenosine by stomach tube. Although alpha-amino-n-butyric acid (ABA) or homoserine, alone or with dietary sodium sulfate, choline, and/or S-methylcysteine, was not utilized for growth, weight loss in weanling rats was decreased by dietary cysteine when fed as an additive to a basal methionine-free, cysteine-free, labile methyl-free, sulfur-free diet. Following the addition of 10 mg ABA and 28 mg 5'-methylthioadenosine/day to the basal diet, growth response was equivalent to that occurring in rats receiving 27 mg of methionine/day with the basal diet. The implications of these findings for adaptation to protein restriction and a discussion of equilibrium and steady state conditions related to the increase in methionine content in the blood are presented.

Somatotopic and columnar organization in the corticotectal projection of the rat somatic sensory cortex

Single injections of tritiated amino acids into the first somatic sensory area (SI) of the rat neocortex result in axoplasmically transported labeling of the stratum griseum intermidiale and stratum griseum profundum of the ipsilateral superior colliculus. The terminal labeling in these layers takes the form of multiple, column-like patches. The SI projection is somatotopically organized with the face and head representations projecting to an extensive anterolateral part of the colliculus and the limb representations projecting to a restricted posterolateral part. Injections of horseradish peroxidase into the superior colliculus result in retrograde labelling of corticotectal cells in the superficial part of layer VB of SI and of the second somatic sensory area (SII).

Cells of origin and terminal distribution of descending projections of the rat somatic sensory cortex

The retrograde, horseradish peroxidase technique has been used to demonstrate the cells of origin of corticofugal fiber systems arising in the rat somatic sensory cortex and projecting to the striatum, diencephalon, brainstem, and spinal cord. Correlative experiments conducted with the anterograde, autoradiographic method have been used to confirm the terminal distribution of many of these fiber systems. Corticofugal pathways directed to subcortical structures arise in the first and second somatic sensory areas exclusively from pyramidal cells of the infragranular layers, V and VI. Fibers which descend to the midbrain, pons, medulla and spinal cord arise exclusively from the largest pyramidal cells, the somata of which are found in the deep part of layer V (layer VB). There is some evidence for a sublaminar organization of the different classes of efferent cells within this layer. Fibers projecting to the diencephalon arise from somata situated throughout layer VI and to a lesser extent in layer V. Corticostriatal fibers arise only from cells with somata in layer V, but the somata are more superficially situated than those of the other classes of corticofugal neurons. The laminar distribution of the somata of corticofugal neurons differs considerably from that of commissural and ipsilateral corticocortical neurons.

Cells of origin and terminal distribution of corticostriatal fibers arising in the sensory-motor cortex of monkeys

The cells of origin of the corticostriatal projection have been identified in squirrel monkeys by the use of the retrograde horseradish peroxidase method. In the subfields of the somatic sensory, motor, parietal and frontal areas of the cortex, cells projecting to the ipsilateral striatum are relatively sparsely distributed and form a group of small- to medium-sized pyramidal cells with an average somal diameter from area to area of 14-16 mum. Such cells are found only in layer V of the cortex (mainly in the more superficial parts of the layer). Since they are consistently smaller than the pyramidal cells of layer V that project to the brainstem and spinal cord and since they lie outside layer VI which gives rise to corticothalamic axons, the corticostriatal axons are unlikely to be collaterals of axons projecting to other sites. The cells of origin of the crossed corticostriatal projection are also found in layer V and are pyramidal cells with somal diameters in the same range as above. They are found only in areas 4, 8, and 6. Studies with the anterograde, autoradiographic method in rhesus, cynomologous and squirrel monkeys, indicate that the somatic sensory areas project to most of the antero-posterior extent of the ipsilateral putamen. Subareas 3a, 3b, 1 and 2 of the somatic sensory cortex project to the same region and the projection overlaps similarly extensive projections from the motor and certain other areas of the cortex. However, in each case the pattern of terminal labeling is in the form of interrupted clusters, strips and bands. A single small injection of the cortex is associated with only one or two such clusters of terminal labeling. This seems to imply that individual corticostriatal fibers end in a very restricted manner and that the terminal ramifications of fibers from one cortical area may alternate in the putamen with those arising in other areas.

The organization and postnatal development of the commissural projection of the rat somatic sensory cortex

Anterograde and retrograde tracing experiments have been used to demonstrate the origin and terminal distribution of commissural fibers in the first somatosensory cortex (SI) of the rat. The commissural fibers originate from pyramidal cells of all layers, but predominantly from layers III and V. The fibers terminate in a series of approximately vertical bands. In each of these there are concentrations of terminals extending from the inner portion of the molecular layer to the deep portion of layer III as well as in the superficial part of layer V, and in layer VI. Discrete vertical bands of cortex are reciprocally connected across the midline to give both the origin and terminal regions of the projection a patchy or "columnar" appearance. The commissural fibers arise from and terminate in areas of the cortex that lie between and alongside the aggregations of granule cells that distinguish SI of the rat. No commissural fibers terminate within the aggregations of layer IV cells themselves but the more superficial terminal ramifications may come to overlie these aggregations. A heterotopic projection to the contralateral second somatosensory cortex has been observed and is similar in form to the homotopic projection to SI. Many commissural fibers have crossed the midline in the corpus callosum by the day of birth but lie in the underlying white matter and do not enter the cortical plate until at least the third postnatal day. During the first postnatal week these fibers grow somewhat diffusely into the maturing cortex and their topographic and laminar pattern of distribution attains its adult characteristics by the end of the first week. Commissural axons, thus, arise from immature cells but the maturation of cell form seems to precede the ingrowth of these axons and the acquisition of commissural synapses.

The posterior thalamic region and its cortical projection in New World and Old World monkeys

The posterior nuclear complex of the thalamus in rhesus, pigtailed and squirrel monkeys consists of the combined suprageniculate-limitans nucleus and an ill defined region of heterogeneous cell types extending anteriorly from the dorsal lobe of the medial geniculate body towards the posterior pole of the ventral nuclear complex. This region is referred to as the posterior nucleus. It is directly continuous with the ventroposteroinferior nucleus. The cortical projections of each of these nuclei, together with those of the adjacent ventral, pulvinar and medial geniculate complexes, have been studied by means of the autoradiographic tracing technique. The suprageniculate-limitans nucleus, the main input to which is the superior colliculus, projects upon the granular insular area of the cortex. The medial portion of the posterior nucleus projects to the retroinsular field lying posterior to the second somatic sensory area. There is clinical and electrophysiological evidence to suggest that the retroinsular area may form part of a central pain pathway. The lateral portion of the posterior nucleus which is closely related to certain elements of the medial geniculate complex, projects to the postauditory cortical field. The ventroposterioinferior nucleus, which may be involved in vestibular function, projects to the dysgranular insular field. The principal medial geniculate nucleus can be subdivided into a ventral division that projects to field AI of the auditory cortex and a dorsal division that merges with the posterior nucleus; it is further subdivided into an anterodorsal component that projects to two fields on the superior temporal gyrus, together with a posterodorsal component in which separate cell populations project to areas lying anterior and medial to AI. The magnocellular medial geniculate nucleus, sometimes considered a part of the posterior complex, appears to project diffusely to layer I of all the auditory fields. The auditory fields are bounded on three sides by the projection field of the medial nucleus of the pulvinar which also extends into the upper end of the lateral sulcus to bound the fields receiving fibers from the posterior nucleus. The topography of the areas receiving fibers from the posterior, medial geniculate and pulvinar complexes, taken in conjunction with the rotation of the primate temporal lobe, permits all of these fields to be compared with similar, better known areas in the cat brain.

Areal differences in the laminar distribution of thalamic afferents in cortical fields of the insular, parietal and temporal regions of primates

A cytoarchitectonic parcellation has been made of the cortex of the insula and of the adjoining parts of the temporal and parietal lobes in rhesus and squirrel monkeys. In conjunction with this, the intracortical distribution of the thalamo-cortical fibers has been studied by the autoradiographic tracing technique. There is a systematic change in the density, laminar distribution and general character of the intracortical thalamic afferent plexus which seems to follow, in particular, the progressive differentiation of cortical layering that occurs in moving from insular through granular to homotypical cortex. In the dysgranular and granular insular areas in which cortical lamination is indistinct, the thalamic plexus as demonstrated autoradiographically is sparse and extends through much of layers III and IV. In the granular cortex (areas 3b and AI), the thalamic plexus is densest and coarsest; it fills all of layers IV and IIIB and extends into layer IIIA. In the "second" and "third" sensory areas, such as the second somatic sensory and many of the auditory fields, the density of the plexus and its coarseness diminish slightly and the deeper half of layer IV becomes free of terminals. In the homotypical cortex, the plexus becomes sparser, finer and strictly confined to layer IIIB. In many areas there are additional indications of thalamic terminations in deeper layers. Where layers V and VI are not divided into sublaminae (e.g.,in areas 3b and AI) there is labeling of the superficial half of layer VI. Where layers V and VI become subdivided in the homotypical cortex, the auditory and adjacent fields were only observed in cases in which the magnocellular nucleus of the medial geniculate body was involved by the injection of isotope. The boundaries of the cortical projection fields of individual thalamic nuclei, as determined autoradiographically, are remarkably sharp and invariably coincide with a sharp architectonic boundary or with a zone of maximal cytoarchitectonic change. Zones of apparent architectonic transition never showed overlap of thalamic afferents emanating from more than one nucleus. These results raise for discussion the significance of architectonic structure in relation to cortical connectivity and have a bearing upon those studies that have attempted to relate the terminals of thalamic afferents to particular classes of cortical neuron.

Midbrain, diencephalic and cortical relationships of the basal nucleus of Meynert and associated structures in primates

The structure and connectivity of the basal nucleus of Meynert, the substantia innominata in which it lies, and certain related areas have been examined in New World and Old World Monkeys, using retrograde and anterograde axonal transport methods. Experiments using the retrograde, horseradish peroxidase method confirm the observations of Kievet and Kuypers ('75) that the basal nucleus and substantia innominata project directly, heavily and with a somewhat crude topography upon the neocortex. Experiments involving the anterograde, autoradiographic method show that the basal nucleus and substantia innominata form part of a complex pathway that links them together with the lateral hypothalamus, certain parts of the amygdala and the peripeduncular nucleus of the midbrain. The peripeduncular nucleus is often regarded as a part of the central auditory pathway; it gives rise to a fiber bundle of considerable size that ascends on the dorsal surface of the ipsilateral optic tract and terminates ultimately in the lateral hypothalamic area of both sides. As well as distributing fibers to the basal nucleus, substantia innominata and lateral hypothalamus, this pathway provides a heavy projection to a cytoarchitectonically distinct posterior part of the lateral nucleus of the amygdala, the medial and intercalated nuclei of the amygdala and a less dense projection to the bed nucleus of the stria terminalis. Certain parts of the hypothalamus and possibly the preoptic areas give rise to a complementary descending pathway that distributes fibers to the ipsilateral basal nucleus, substantia innominata and amygdala, and ends in the peripeduncular nuclei of both sides. Decussating fibers in both the ascending and descending pathways cross in the ventral supraoptic commissure. It is concluded that the basal nucleus should include most of the aggregated and unaggregated large cells that lie in the substantia innominata and which in places intrude upon the preoptic regions and the nucleus of the diagnonal band of Broca. Together, these may form a complex that receives inputs from a variety of brainstem sources, and projects widely and diffusely upon all cortical structures of the telencephalon.

Serum and intestinal fluid immunoglobulins and jejunal IgA secretion in Crohn's disease

Immunoglobulins in serum and proximal intestinal fluids and secretion of IgA by cultured jejunal mucosa were measured in 12 healthy subjects and 36 patients with Crohn's disease. Concentrations of IgA, IgG, IgM, and IgE in serum and intestinal fluids were similar in the two groups, except for increased serum IgA concentrations in the patients. Elevation of IgA and chronicity of disease were correlated, which suggests that the IgA alteration was a response to duration of disease rather than a primary pathogenetic factor. IgA secretion by cultured jejunum was similar in control and patient groups. Thus, no evidence was found that abnormalities of secretory immunoglobulins are pathogenetically involved in Crohn's disease.

Commissural and cortico-cortical "columns" in the somatic sensory cortex of primates

Anatomical experiments demonstrate that commissural and cortico-cortical fibers arising and terminating in the somatic sensor- cortex of monkeys terminate in layers I through IV in a mosaic of precisely ordered vertical bands. The cells of origin of these fibers, found predominantly in layer III, are also arranged in vertical aggregations.

Some aspects of the organization of the thalamic reticular complex

Anatomical methods which depend upon the anterograde axonal transport of isotopically labeled neuronal proteins or the retrograde axonal transport of the enzyme, horseradish peroxidase, have been used to elucidate the relationships between the reticular complex and the dorsal thalamus and cerebral cortex. Injections of tritiated amino acids in the dorsal thalamus or cerebral cortex in rats, cats and monkeys, show that as the bundles of thalamo-cortical and cortico-thalamic fibers joining a particular dorsal thalamic nucleus to its associated area of the cerebral cortex traverse the reticular complex, they each give rise to a dense zone of terminals occupying a sector of the reticular complex which is relatively constant for that dorsal thalamic nucleus and cortical area. However, because of the wide extent of the dendritic fields of the reticular cells and the degree of overlap between the sectors of the complex subtended by adjacent dorsal thalamic nuclei and adjacent cortical areas, it is likely that the reticular complex samples thalamo-cortical and cortico-thalamic activity in a somewhat unspecific manner. Fibers passing to the reticular complex from the intralaminar nuclei of the thalamus appear to be associated with the projection from the intralaminar nuclei to the striatum. Injections of tritiated amino acids in the reticular complex itself and injections of horseradish peroxidase in various other parts of the brain show that the only efferent pathway from the reticular complex terminates in the nuclei of the dorsal thalamus. The reticular complex does not appear to send fibers to other components of the ventral thalamus nor to the cerebral cortex.

Varieties and distribution of non-pyramidal cells in the somatic sensory cortex of the squirrel monkey

The morphology and distribution of cells which do not conform to the conventional pyramidal pattern have been investigated in rapid Golgi, Golgi-Kopsch and Golgi-Cox preparations from cortical areas 3, 1 and 2 of juvenile and mature squirrel monkeys. The material has been analyzed qualitatively and quantitatively by means of a computer program which permits cells to be rotated so as to display their three-dimensional architecture. Nine non-pyramidal types are identified of which one is a rare giant cell and another, forming a major proportion of the cells in layer VI, is considered to be a modified form of pyramidal cell. Of the other seven types, two have horizontally distributed axons, one essentially confined to layer II, the other sending long (up to 1 mm) branches anter-posteriorly through all layers. Two types have vertical axons. One, corresponding to the "double bouquet dendritique" cell of Cajal, is mainly situated in layer II or the upper part of layer III and has a cluster of large axon branches which descend to layers IV and V and which enclose and terminate on the apical dendrites of pyramidal cells. The other type is the only non-pyramidal cell which has a relatively high concentration of dendritic spines in the adult animal. Its soma lies in layer IV and it has several strongly recurrent, thick axonal branches ascending to layer II, also enclosing the apical dendrites of pyramidal cells. The dendritic field is not truly stellate but is drawn out into a pronounced ascending tuft which ascends into layer IIIb. The cell thus resembles a "star-pyramid" of Lorente de Nó. Nevertheless such cells have many features, notably the distribution of their axons and the distribution of dendritic spines which are identical to those of the well-known "spiny stellate" cell of the visual cortex. Conversely the same features both in these cells and in the spiny stellate cells of the visual cortex (which were also eamined) differ markedly from those of small pyramidal cells with somata of similar dimensions. The three remaining non-pyramida cell types have locally ramifying axons which appear to terminate predominantly on pyramidal cells. In one, the axon forms smoothly curving arcades in layer III, in another it is intensely tangled in layer IV and in the third it is bush-like in layers II-IV. continued.

Lamination and differential distribution of thalamic afferents within the sensory-motor cortex of the squirrel monkey

The structure of the first somatic sensory area (areas 3, 1 and 2), of the motor area (area 4) and the intervening transitional field (area 3a) is described in the squirrel monkey (Saimiri sciureus) using Nissl, Bodian, Weil and Golgi preparations. The laminar arrangement of both cells and axons is briefly described and this correlated with the distribution of thalamic afferents as identified in experiments conducted with the Nauta and autoradiographic techniques. The latter method was used particularly in order to assess quantitative differences in the density of thalamic projections to the five cytoarchitectonic fields. In the somatic sensory areas thalamic afferents terminate not only in layer IV but a large extent also in a recognizable part of layer III (layer IIIb). In area 4 thalamic terminals fill much of layer III, reaching almost to layer II. In area 3a the extent is intermediate between that seen in areas 3 and 4. It is thought that the extensive spread of thalamic terminals is related to the elongated form of a particular class of spine-bearing cell whose somata are situated in layer IV (Jones, '75). In all areas a small proportion of thalamic afferents end also in layer I. Evidence is presented to indicate that specific afferent fibers emanating from the ventrobasal and ventrolateral complexes of the thalamus terminate in both the deep and superficial parts of layer I while "non-specific" afferents from other thalamic sources end in the superficial part. The autoradiographic studies indicate that there are considerable differences between the number of thalamic afferents ending in area 3 on the one hand and in areas 1 and 2 on the other. Given this and the nature of the degenerating thalamic afferents observed in Nauta preparations, it is possible to identify thalamic afferents in normal Golgi preparations and significant differences are detectable in areas 4, 3 and 1 and 2. It it is as yet uncertain whether the slightly thinner, more sparsely distributed thalamic afferents ending in areas 1 and 2 are branches of those directed primarily to area 3.

Interhemispheric pathways in the absence of a corpus callosum. An experimental study of commissural connexions in the marsupial phalanger

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On the mode of entry of blood vessels into the cerebral cortex

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