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PubMed1978

The medial geniculate body of the tree shrew, Tupaia glis. II. Connections with the neocortex.

In this study the temporal cortex of the tree shrew was subdivided on the basis of cytoarchitectonic criteria, and the connections of each subdivision with the thalamus and midbrain were analyzed with retrograde and anterograde techniques. The results indicate that, with one exception, each subdivision of the medial geniculate body projects to a separate cortical area. The primary auditory cortex receives projections from the ventral nucleus. Surrounding the primary cortex are at least five additional cytoarchitectonically distinct areas which receive projections from the remaining medial geniculate subdivisions. The evidence suggests that there is very little overlap in the projections from each of these geniculate subdivisions. An exception is the projection of the caudal nucleus of the medial division. This subdivision apparently projects to most, if not all, of the cortical target of the medial geniculate body. Although the cortical projections of the caudal nucleus overlap those of the other medial geniculate subdivisions, the laminar distribution of its terminations in cortex is different. The caudal nucleus projects primarily to layer VI whereas the other subdivisions of the medial geniculate body project primarily to layer IV and the adjacent part of layer III. Anterograde techniques were also used to study the projections from the cortex back to the thalamus and to the midbrain. The projections to the thalamus precisely reciprocate the thalamocortical connections. The projections to the midbrain are to the same areas which the preceding study (Oliver and Hall, '78) showed give rise to ascending projections to the medial geniculate body. An exception is the central nucleus of the inferior colliculus which apparently does not receive a projection from the temporal cortex.

Animals↗
PubMed1979

Somatic neurons in the brainstem and neocortex projecting to the external nucleus of the inferior colliculus: an anatomical study in the opossum.

Some brainstem and neocortical neurons projecting to the external nucleus of the inferior colliculus were identified by retrograde axonal transport of horseradish peroxidase (HRP). Large pressure injections of HRP were used to define the population of cells in the dorsal column and trigeminal nuclei projecting to the entire inferior colliculus. Subsequently, tiny injections of HRP were delivered electrophoretically to various parts of the external nucleus using micropipettes. In each case the electrophoretic placements were made in sites identified as somatic by their response to foot shock or manual stimulation of the body. Receptive fields were found to be large and almost always bilaterally symmetric. Areas excitable by stimulation of the upper body were often found adjacent to areas excitable by stimulation of the lower body, tail, or, rarely, the face and head. In general, sites in the external nucleus which were identified by their responsiveness to stimulation of the body were not responsive to click stimuli. No topographic representation of the body was evident. After small electrophoretic injections of HRP absolutely restricted to the external nucleus, HRP-filled neurons were found bilaterally in the nucleus gracilis, nucleus Bischoff, (the midline and tail representation of the dorsal column nuclei), nucleus cuneatus, and nucleus trigeminalis, subnucleus caudalis. Ipsilateral neocortical cellular filling was found primarily in a continuous strip along the caudal and inferior margin of the parietotemporal cortex, in the area corresponding to SMII (Pubols, '77). Rarely, filled cells were found in the parietal area corresponding to SMI and in the temporal pole. In sum, small somatic-activated loci of the external nucleus receive bilateral, topographically convergent projections from hindbrain somatosensory structures and from the SMII cortex.

Animals↗
PubMed1989

Quantitative autoradiographic mapping of serotonin 5-HT1 and 5-HT2 receptors and uptake sites in the neocortex of the rhesus monkey.

The in vitro autoradiographic technique was used to characterize the distribution of serotonin 5-HT1 and 5-HT2 receptors and uptake sites in 11 cortical areas of frontal, parietal, and occipital lobes in the rhesus monkey; 5-HT1 receptors were labeled with [3H]5-HT; 5-HT2 receptors were labeled with [3H]ketanserin; and 5-HT uptake sites were labeled with [3H]citalopram. Five-HT1 and 5-HT2 receptors and 5-HT uptake sites were found in every cortical area examined with the absolute concentration of 5-HT1 receptors higher than that of 5-HT2 receptors in all areas. In eight regions of prefrontal and parietal as well as in prestriate cortex, 5-HT1 and 5-HT2 receptors had complementary distribution profiles: 5-HT1 receptors were concentrated in layers I and II and the upper strata of layer III, while 5-HT2 receptors had their highest concentration throughout layers III and IV. Only the primary motor and visual cortex had receptor distributions different from that described above. Thus, in the primary visual cortex, both 5-HT1 and 5-HT2 receptors were found in high concentration in sublayer IVc beta, though the density of 5-HT1 receptor was also high in other subdivisions of layer IV and in layers III, V, and VI. In the primary motor cortex, both receptor subtypes were concentrated in layers I and II and the upper strata of layer III. The pattern of distribution of serotonin uptake sites did not match the patterns of distribution of either 5-HT1 or 5-HT2 receptors alone; rather it approximated the combined patterns of distribution of both receptor subtypes. The complementary patterns of distribution of 5-HT1 and 5-HT2 receptors in most areas of the monkey cerebral cortex suggest that these two receptor subtypes may make differential contributions to cortical functions.

Animals↗
PubMed1990

Heterogeneity of chandelier neurons in monkey neocortex: corticotropin-releasing factor- and parvalbumin-immunoreactive populations.

Chandelier neurons are a unique subclass of cortical nonpyramidal neurons. The axons of these neurons terminate in distinctive vertically arrayed cartridges that synapse on the axon initial segment of pyramidal neurons. In this study, the rapid Golgi method and immunohistochemical techniques were used to characterize the morphology, regional distribution, laminar location, and biochemical content of chandelier neurons in the prefrontal and occipital cortices of three monkey species. As in our previous studies of visual areas V1 and V2 (Lund: Journal of Comparative Neurology 257:60-92, 1987; Lund et al.: Journal of Comparative Neurology 202:19-45, 1981, 276:1-29, 1988), Golgi impregnations of areas 46 and 9 of macaque prefrontal cortex show chandelier neurons to be present in layers 2 through superficial 5. The vertical arrays of terminal boutons (axon cartridges) typical of this neuron class are also present in layers 2-6 of the prefrontal cortex, but are not found in layer 1 or the subcortical white matter. In immunohistochemical studies, a calcium-binding protein, parvalbumin, and a neuropeptide, corticotropin-releasing factor (CRF), identify rod-like structures that are morphologically similar to the axon cartridges of chandelier neurons seen in the Golgi material. In addition, both parvalbumin- and CRF-immunoreactive cartridges are located below the somata of unlabeled pyramidal neurons and appear to outline the axon initial segment of these neurons. However, we find that parvalbumin and CRF are present in only subpopulations of chandelier axon cartridges. For example, in adult primary visual cortex, parvalbumin-labeled cartridges are present in very low numbers only in layers 2-3, whereas in prefrontal and occipital association cortices these cartridges are a very prominent component of layers 2-superficial 3 and are present in much lower density in the deeper cortical layers. In contrast to these findings in adult macaque monkeys, prefrontal and occipital association cortices of infant macaque monkeys contain a very high density of parvalbumin-labeled cartridges in layer 4 and relatively few in the superficial cortical layers. Furthermore, in adult squirrel monkey prefrontal cortex, CRF-labeled cartridges are predominately present in layer 4, but these CRF-immunoreactive structures have not been observed in the homologous regions of infant or adult macaque monkeys. These findings indicate that even for neurons of such distinctive morphology and presumably constant functional role as chandelier neurons, factors such as regional and laminar location, age, and primate species are associated with differences in the biochemical content of subpopulations of these neurons.

Animals↗
PubMed1990

Burst generating and regular spiking layer 5 pyramidal neurons of rat neocortex have different morphological features.

Intracellular recordings were obtained from pyramidal neurons in layer 5 of rat somatosensory and visual cortical slices maintained in vitro. When directly depolarized, one subclass of pyramidal neurons had the capacity to generate intrinsic burst discharges and another generated regular trains of single spikes. Burst responses were triggered in an all-or-none manner from depolarizing afterpotentials in most bursting neurons. Regular spiking cells responded to electrical stimulation of ascending afferents with a typical EPSP-IPSP sequence, whereas IPSPs were hard to detect in bursting cells. Orthodromic activation of the latter evoked a prominent voltage-dependent depolarization that could trigger a burst response. Intracellularly labelled bursting and regular spiking cells were located in layer 5b, but had distinctly different morphologies. Bursting neurons had a large pyramidal soma, a gradually emerging apical dendrite, and an extensive apical and basal dendritic tree. Their axonal collateral arborization was predominantly limited to layers 5/6. In contrast, regular spiking cells had a more rounded soma with abruptly emerging apical dendrite, a smaller dendritic arborization, and 2 to 8 ascending axonal collaterals that arborized widely in the supragranular layers. Both bursting and regular spiking cells had main axons that entered the subcortical white matter. These data show that some subgroups of pyramidal neurons within the deeper parts of layer 5 of rat cortex are morphologically and physiologically distinct and have different intracortical connections. Bursting cells presumably function to amplify and synchronize cortical outputs, whereas regular spiking output neurons provide excitatory feedback to neurons at all cortical levels and receive a more effective orthodromic inhibitory input. These data support the hypothesis that differences in gross neuronal structure, perhaps even the subtle differences that distinguish subclasses of neurons in a given lamina, are predictive of underlying differences in the type and distribution of ion channels in the nerve cell membrane and connections of cells within the cortical circuit.

Animals↗
PubMed1990

Glial process elongation and branching in the developing murine neocortex: a qualitative and quantitative immunohistochemical analysis.

Cells of astroglial lineage in the murine cerebrum undergo a succession of transformations during prenatal and early postnatal development. The bipolar radial cell, the earliest astroglial form to appear, provides a radially aligned, parallel array of fibers that serves as a guide to neuronal migration. The multipolar astrocyte is the representative of this lineage that persists in the adult cerebrum. The processes of the multipolar astrocytes form a complex reticulum, which is considered critical to the development, function, and maintenance of neural circuits. A monopolar radial cell appears to be transitional between the two. The shift from the radial glial fiber system to a diffuse glial network is achieved largely in the E17-P2 interval in the mouse. This phenomenon has been studied qualitatively and quantitatively by staining cerebral tissue with monoclonal antibody RC2, a specific and sensitive ligand for cells of astroglial lineage in the mouse. Elongation and branching of glial processes contribute to the glial transformation. Elongation of radial fibers occurs under the guidance of other radial glial fibers (fasciculated elongation) or independently of other fibers (nonfasciculated elongation). Fasciculated elongation results in an increase in the density of radial glial fibers that span the cortical layers. Nonfasciculated elongation appears to be associated with process branching. This is the initial event in transformation of the bipolar radial cells to monopolar radial or multipolar cells. Only nonfasciculated elongation is characteristic of processes of the monopolar radial cells and multipolar astrocytes. Branching of the processes of all three cell forms appears to occur both by bifurcation at the elongating tip and by sprouting from the fiber shaft. Elongating fibers are tipped by growth cones that are relatively simple in shape as compared to those observed at the tips of elongating axons. Growth cones at the tips of nonfasciculated fibers are more complex in form than those at the tips of radial fibers elongating in contact with other radial fibers.

Animals↗
PubMed1992

Sex differences in the gross size of the rat neocortex.

The pervasiveness of sex differences in the size of the rat cerebral cortex was investigated in ten littermate pairs of socially housed Long-Evans hooded rats at 90 days of age. Overall, the cortex was longer and wider in male than in female rats. Sex differences were detected in most cortical regions with this sample size; the exception was the temporal cortex. While some asymmetries were found, they did not vary with the sex of the animal nor were they consistently in one direction. The contribution of the cortical layers to sex differences in cortical thickness was examined in four locations: the primary motor cortex, the forelimb area of the sensorimotor cortex and the monocular and the binocular areas of the visual cortex. The layers that showed sex differences varied among the areas but were confined to layers II-III, V and VI. Sex differences in cortical size were widespread in the adult rat but showed some regional and laminar specificity.

Animals↗
PubMed1995

Cells of the perireticular nucleus project to the developing neocortex of the rat.

The perireticular nucleus is a recently described thin sheet of small cells among the fibres of the internal capsule, lying lateral to the thalamic reticular nucleus and medial to the globus pallidus (Clemence and Mitrofanis [1992]. J. Comp. Neurol. 322:167-180). During development, the perireticular nucleus is relatively large, lying in the path of the growing corticofugal and thalamocortical axons and filling the area of the internal capsule lateral to the thalamic reticular nucleus. After these axons have formed their connections, the perireticular nucleus rapidly decreases in size, leaving only a few cells in the adult (Mitrofanis [1992] J. Comp. Neurol. 320:161-181). In this study, we aimed to investigate the connections between the developing cortex and thalamus by making injections of tracer into the cortical plate. Injections of Horse Radish Peroxidase (HRP), Wheat Germ Agglutinin bound to HRP (WGA-HRP) and 1'dioctadecyl-3,3,3',3 tetramethycarbocyanine perchlorate (DiI) were made in vivo between embryonic day (E) 18 and adult and DiI was placed in the fixed brains of rats aged between E16 and postnatal day (P)1. Between E17 and P10, the retrograde perikaryal labelling resulting from these injections revealed a transient projection from the perireticular nucleus to the ipsilateral cortical plate. No cells were labelled in the thalamic reticular nucleus. This suggests that the perireticular nucleus must be regarded as a group of cells distinct from the thalamic reticular nucleus and having a separate role in development. Comparisons between the perireticular cells and the cells of the cortical subplate suggest that both may be playing comparable roles in early development, possibly guiding fibres towards their end stations or serving to rearrange the complex mapped projections linking the thalamus and cortex.

Animals↗
PubMed1983

Interactions between amino acid neurotransmitters and flurazepam in the neocortex of unanesthetized rats.

The effects induced by the benzodiazepine flurazepam (FLU) upon neuronal responses to glutamic acid (GLUT), gamma-aminobutyric acid (GABA), and glycine (GLY) were studied in the cortex of unanesthetized rats using single-unit extracellular recordings in conjunction with iontophoretic techniques. The application of FLU (5-20 nA) did not affect excitatory responses to GLUT, but the spontaneous firing rate was depressed by equivalent doses of this benzodiazepine. A selective increase of GABA, but not of GLY-induced responses was seen when either low currents (5-10 nA) of FLU or GLUT driving currents were used to study the neuronal responses of the inhibitory amino acids upon steady neuronal firing. Our data demonstrate that in unanesthetized animals FLU does not affect GLUT-induced effects while it selectively increases GABA-mediated inhibition.

Amino Acids↗
PubMed1992

Perforated synapses are present during synaptogenesis in rat neocortex.

It has been known for some time that perforated synapses increase in number and size with increasing age. Initially, these trends were used to support the concept that nonperforated synapses enlarge until an optimal size is reached, at which point they perforate and may subsequently split. More recent stereological and three-dimensional reconstruction investigations, however, suggest that this may not be the case and that perforated and nonperforated synapses constitute separate synaptic populations. In order to test the separate population hypothesis, synapses have been studied ultrastructurally in the parietal cortex of rats aged 19 and 20 days gestation, and 1 and 4 days postnatal. By examining synapses serially, and also by studying three-dimensional reconstructions, it has been demonstrated that perforated synapses are present at each of these ages. Some are relatively simple in organization, resembling previously described perforated synapses at 14 days of age, although others appear to consist of two or more separate PSD components. These findings demonstrate that perforated synapses are present from early on in synaptogenesis and that developing perforated synapses may have distinct characteristics that cast light on their developmental course.

Animals↗
PubMed1996

Dystrophic neurite formation associated with age-related beta amyloid deposition in the neocortex: clues to the genesis of neurofibrillary pathology.

The formation of dystrophic neurites associated with beta amyloid plaques in Alzheimer's disease (AD) appears to involve a transformation of normal neuronal cytoskeletal proteins. In order to investigate what may be the earliest neuronal changes associated with the development of dystrophic neurites, we have examined the neurochemical profile of abnormal neuritic processes associated with the beta amyloid deposition in non-AD, aged cases. In all non-AD individuals demonstrating some degree of beta amyloid deposition in the superior frontal gyrus, clustered swollen and ring-like structures, located principally in layers II and III, were labeled with antibodies to phosphorylated and nonphosphorylated domains of the middle and high molecular weight neurofilament subunits. These abnormal neurites were not immunolabeled for tau or ubiquitin or stained with thioflavine S. Double labeling for neurofilaments and thioflavine S confirmed that these clusters of dystrophic neurites were associated with plaque-like deposits. These results show that anatomically and neurochemically specific forms of dystrophic neurites can occur in non-AD cases that contain beta amyloid deposition. If these abnormal neurites correspond to an immature form of the dystrophic neurites found in the neuritic plaques of Alzheimer's disease, then neurofibrillary pathology associated with this disease may begin with an initial misprocessing and accumulation of neurofilament proteins. Furthermore, these data are consistent with the proposal that the development of neurofibrillary pathology may begin with neurofilamentous hypertrophy in damaged distal processes followed by reactive changes in the cell bodies of origin of these fibers involving cytoskeletal alterations that ultimately lead to neurofibrillary tangle formation.

Aged↗
PubMed1997

The expression of creatine kinase isoenzymes in neocortex of patients with neurodegenerative disorders: Alzheimer's and Pick's disease.

Creatine kinase (CK) activity was found decreased in the brains of patients with Alzheimer's disease (AD) and Pick's disease (PD). However, the decrease of total CK activity in AD was more pronounced than in PD. Analysis of the activity of two CK isoforms, BCK and ubiquitous mitochondrial CK, demonstrated that the decrease of total CK activity in AD and PD was related to the decrease of BCK activity. The decline of CK activity both in AD and PD correlated well with the decline of the content of immunoreactive BCK in brain extracts. The BCK mRNA level in AD and PD was not significantly different from control patients and could not be the primary reason for decreases in CK content and activity. The decreased level of BCK in AD and PD brains might be caused by posttranscriptional events, which could affect the translation of BCK mRNA and/or lead to the inactivation and degradation of the enzyme. Because CK is sensitive to oxidative modification, it is possible that the changes observed in this study result from free radical damage.

Aged↗
PubMed1991

Developmental profile of a fetuin-like glycoprotein in neocortex, cerebrospinal fluid and plasma of post-natal tammar wallaby (Macropus eugenii).

A fetuin-like glycoprotein (FLG) has been shown to be present in early cortical plate cells in the developing brain of the tammar wallaby (Macropus eugenii). The developmental sequence of the occurrence of glycoprotein-positive fibres and cells in the dorsolateral telencephalic wall from newborn to day 40 is described. The level of FLG in CSF (cerebrospinal fluid) and plasma of the tammar wallaby has also been measured during pouch life. The presence of FLG in early postnatal fibre systems and in some cells in the primordial plexiform layer, as well as in early cortical plate cells of the tammar is similar to that of fetuin in fetal brain in sheep, pig and cow, and alpha 2HS glycoprotein in human fetal brain. The sequence of appearance of FLG-positive cells during neocortical development in the tammar is strikingly similar to that of a transient population of early cortical plate cells previously described in fetal cat and sheep cortex. During postnatal development, levels of FLG in tammar plasma and CSF follow a pattern different from that of other species. The developmental expression of all three related glycoproteins in their respective species is discussed.

Animals↗
PubMed1992

On the computational architecture of the neocortex. II. The role of cortico-cortical loops.

This paper is a sequel to an earlier paper which proposed an active role for the thalamus, integrating multiple hypotheses formed in the cortex via the thalamo-cortical loop. In this paper, I put forward a hypothesis on the role of the reciprocal, topographic pathways between two cortical areas, one often a 'higher' area dealing with more abstract information about the world, the other 'lower', dealing with more concrete data. The higher area attempts to fit its abstractions to the data it receives from lower areas by sending back to them from its deep pyramidal cells a template reconstruction best fitting the lower level view. The lower area attempts to reconcile the reconstruction of its view that it receives from higher areas with what it knows, sending back from its superficial pyramidal cells the features in its data which are not predicted by the higher area. The whole calculation is done with all areas working simultaneously, but with order imposed by synchronous activity in the various top-down, bottom-up loops. Evidence for this theory is reviewed and experimental tests are proposed. A third part of this paper will deal with extensions of these ideas to the frontal lobe.

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