Characterization by Golgi impregnation of neurons that accumulate 3H-GABA in the visual cortex of monkey

Magnetic resonance imaging of the visual system in vivo: Transsynaptic illumination of V1 and V2 visual cortex

Brain nuclei directly receiving retinal projections are readily labeled in magnetic resonance images following intraocular injection of manganese (Mn). To assess whether Mn in retinal ganglion cell axons can be transsynaptically delivered to visual cortex, mice that had previously received intraocular Mn injection were anesthetized with isoflurane, and T1-weighted data sets were acquired of the eyes and brain using a 7-T magnetic resonance imaging machine. Image intensity within contralateral brain structures was evaluated by assessing 1) signal-to-noise ratios, 2) mean image intensity, and 3) mean image intensity normalized to facial muscle intensity. Image intensity was increased throughout the visual pathway including within contralateral visual cortex areas V1 and V2L. Mean normalized image intensity was greater by 53% in the ipsilateral optic nerve and by 31% and 28% in the contralateral lateral geniculate nucleus and superior colliculus, respectively (N=5, P<0.02, paired t test). In contralateral visual cortex areas V1 and V2L, image intensity was increased by 7.5% and 6.8%, respectively (P<0.02 for both, paired t test). Power analysis of the different evaluation methods yielded evidence of superior sensitivity using the normalization method. Reconstruction of the visual system based upon threshold analysis allowed simultaneous visualization of all portions of the major retinal projections to the brain. These results support use of high magnetic field MRI imaging and data normalization for in vivo quantitative analysis of the mouse brain visual system including visual cortex.

Layer V in cat primary auditory cortex (AI): cellular architecture and identification of projection neurons

The cytoarchitectonic organization and the structure of layer V neuronal populations in cat primary auditory cortex (AI) were analyzed in Golgi, Nissl, immunocytochemical, and plastic-embedded preparations from mature specimens. The major cell types were characterized as a prelude to identifying their connections with the thalamus, midbrain, and cerebral cortex using axoplasmic transport methods. The goal was to describe the structure and connections of layer V neurons more fully. Layer V has three sublayers based on the types of neuron and their sublaminar projections. Four types of pyramidal and three kinds of nonpyramidal cells were present. Classic pyramidal cells had a long apical dendrite, robust basal arbors, and an axon with both local and corticofugal projections. Only the largest pyramidal cell apical dendrites reached the supragranular layers, and their somata were found mainly in layer Vb. Three types departed from the classic pattern; these were the star, fusiform, and inverted pyramidal neurons. Nonpyramidal cells ranged from large multipolar neurons with radiating dendrites, to Martinotti cells, with smooth dendrites and a primary trunk oriented toward the white matter. Many nonpyramidal cells were multipolar, of which three subtypes (large, medium, and small) were identified; bipolar and other types also were seen. Their axons formed local projections within layer V, often near pyramidal neurons. Several features distinguish layer V from other layers in AI. The largest pyramidal neurons were in layer V. Layer V neuronal diversity aligns it with layer VI (Prieto and Winer [1999] J. Comp. Neurol. 404:332--358), and it is consistent with the many connectional systems in layer V, each of which has specific sublaminar and neuronal origins. The infragranular layers are the source for several parallel descending systems. There were significant differences in somatic size among these projection neurons. This finding implies that diverse corticofugal roles in sensorimotor processing may require a correspondingly wide range of neuronal architecture.

Imaging of radiocarbon-labelled tracer molecules in neural tissue using accelerator mass spectrometry

Autoradiography is widely and successfully used to image the distribution of radiolabelled tracer molecules in biological samples. The method is, however, limited in resolution and sensitivity, especially for 14C. Here we describe a new method for imaging 14C-labelled tracers in sections of biological tissue. A highly focused beam of gallium ions bombards the tissue, which is eroded (sputtered) into constituent atoms, molecules and secondary ions. The 14C ions are detected in the secondary beam by the most sensitive method available, namely accelerator mass spectrometry. The specimen is scanned pixel by pixel (1 x 2 microm), generating an image in a manner analogous to scanning electron microscopy. The method can thus be regarded as a specialized form of scanning secondary ion mass spectrometry (SIMS), referred to here as SIAMS (ref. 2). We have used SIAMS to localize the neurotransmitter gamma-aminobutyric acid (GABA) in thin sections of cerebral cortex, and show that it can generate 14C images that are much improved on 14C autoradiography. A scan takes 10-20 min and reveals individual axons, neurons and glial cells at high sensitivity. In principle, the resolution could be increased by up to tenfold, and the method could be extended to some other nuclides.

Effect of retinal impulse blockage on cytochrome oxidase-poor interpuffs in the macaque striate cortex: quantitative EM analysis of neurons

One of the hallmarks of the primate striate cortex is the presence of cytochrome oxidase-rich puffs in its supragranular layers. Neurons in puffs have been classified as type A, B, and C in ascending order of cytochrome oxidase content, with type C cells being the most vulnerable to retinal impulse blockade. The present study aimed at analysing cytochrome oxidase-poor interpuffs with reference to their metabolic cell types and the effect of intraretinal tetrodotoxin treatment. The same three metabolic types were found in interpuffs, except that type B and C neurons were smaller and less cytochrome oxidase-reactive in interpuffs than in puffs. Type A neurons had small perikarya, low levels of cytochrome oxidase, and received exclusively symmetric axosomatic synapses. The largest neurons were pyramidal, type B cells with moderate cytochrome oxidase activity and were also contacted exclusively by symmetric axosomatic synapses. Type C cells medium-sized with a rich supply of large, darkly reactive mitochondria and possessed all the characteristics of GABAergic neurons. They were the only cell type that received both symmetric and asymmetric axosomatic synapses. Two weeks of monocular tetrodotoxin blockade in adult monkeys caused all three major cell types in deprived interpuffs to suffer a significant downward shift in the size and cytochrome oxidase reactivity of their mitochondria, but the effects were more severe in type B and C neurons. In nondeprived interpuffs, all three cell types gained both in size and absolute number of mitochondria, and type A cells also had an elevated level of cytochrome oxidase, indicating that they might be functioning at a competitive advantage over cells in deprived columns. However, type B and C neurons showed a net loss of darkly reactive mitochondria, indicating that these cells became less active. Thus, mature interpuff neurons remained vulnerable to retinal impulse blockade and the metabolic capacity of these cells remains tightly regulated by neuronal activity.

Organization and plasticity of GABA neurons and receptors in monkey visual cortex

The GABA neurons of monkey area 17 are a morphologically and chemically heterogeneous population of interneurons that are normally distributed most densely within the geniculocortical recipient zones of the visual cortex. In adult monkeys deprived of visual input from one eye, the levels of immunoreactivity for GABA and GAD within neurons of these geniculocortical zones is reduced. Similar changes are seen in the levels of proteins that make up the GABAA receptor sub-type. The effects of monocular deprivation on other substances suggest that specific types of GABA neurons, such as those in which the tachykinin neuropeptide family and parvalbumin coexist with GABA, are greatly influenced by changes in visual input. That some proteins remain normal within deprived-eye neurons and that other proteins are increased indicates the changes in the GABA cells of the cortex are not the result of a general reduction in protein synthesis. Comparisons of what is known about the morphological and synaptic features of GABA cells in area 17 and the characteristics of cells affected by monocular deprivation suggests that certain classes, such as the clutch cell, may be preferential targets of deprivation. Such a selective loss of certain GABA neurons would have broad implications for the possible physiological plasticity of cortical cells, for if ongoing studies determine that specific receptive field properties are affected by monocular deprivation in adults, the correlation of functional properties and classes of GABA cells would be possible.

Synaptic connections of neurones identified by Golgi impregnation: characterization by immunocytochemical, enzyme histochemical, and degeneration methods

For more than a century the Golgi method has been providing structural information about the organization of neuronal networks. Recent developments allow the extension of the method to the electron microscopic analysis of the afferent and efferent synaptic connections of identified, Golgi-impregnated neurones. The introduction of degeneration, autoradiographic, enzyme histochemical, and immunocytochemical methods for the characterization of Golgi-impregnated neurones and their pre- and postsynaptic partners makes it possible to establish the origin and also the chemical composition of pre- and postsynaptic elements. Furthermore, for a direct correlation of structure and function the synaptic interconnections between physiologically characterized, intracellularly HRP-filled neurones and Golgi-impregnated cells can be studied. It is thought that most of the neuronal communication takes place at the synaptic junction. In the enterprise of unravelling the circuits underlying the synaptic interactions, the Golgi technique continues to be a powerful tool of analysis.

Effect of retinal impulse blockage on cytochrome oxidase-rich zones in the macaque striate cortex: I. Quantitative electron-microscopic (EM) analysis of neurons

Our previous light-microscopic study indicates that unilateral retinal impulse blockage with tetrodotoxin (TTX) causes a reversible decrease of cytochrome oxidase (CO) in alternating rows of metabolically active zones (puffs) in the adult macaque striate cortex (Wong-Riley & Carroll, 1984b). The goal of the present study was to determine if TTX blockade adversely affects all neurons or only a subpopulation of neurons within the puffs. Three major neuronal types were identified based on mitochondrial CO activities and morphological characteristics. Type A neurons were the most prevalent, consisting of small pyramidal and nonpyramidal neurons that received only symmetrical axosomatic synapses. They had little cytoplasm and relatively low levels of CO activity, and showed the least change with TTX treatment. Type B cells were medium-to-large pyramidal neurons that received exclusively symmetrical axosomatic synapses and were moderately reactive for CO. Impulse blockage caused a decrease in mitochondrial size and packing density, but somal size remained within the control range. Type C cells were medium-sized nonpyramidal neurons contacted by both asymmetrical and symmetrical axosomatic synapses. They contained abundant darkly reactive mitochondria and presumably are metabolically the most active. This cell type suffered the greatest decrease in somal size and packing density of mitochondria, particularly the darkly reactive ones. A rare fourth cell type, type D, was a small, darkly reactive nonpyramidal variety that gave rise to somatodendritic synapses. Their low occurrence prevented statistical analysis under normal and TTX-treated conditions. These data indicate that retinal impulse blockade is most detrimental to the metabolically most active neurons in the adult primate cortical puffs. The alterations are not permanent, because the effects of TTX are fully reversible (Carroll & Wong-Riley, 1987).

Quantitative distribution of GABA-immunoreactive neurons in cetacean visual cortex is similar to that in land mammals

Sections of the anterior portion of the visual cortex in the lateral gyrus of the Black Sea porpoise were studied to determine the neuronal architecture and numerical density, and the distribution of neurons immunoreactive to gamma-aminobutyric acid (GABA). Cytoarchitecture and neuronal density are similar to those described in another cetacean, the bottlenose dolphin. GABA-positive neurons are distributed through all layers of the visual cortex but are especially dense in layers II and III, and comprise some 20% of the total neuronal population in this part of the cortex. The distribution of GABA-positive neurons is similar to that found in land mammals.

Distribution of GABAergic neurons and axon terminals in the macaque striate cortex

Antisera to glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid (GABA) have been used to characterize the morphology and distribution of presumed GABAergic neurons and axon terminals within the macaque striate cortex. Despite some differences in the relative sensitivity of these antisera for detecting cell bodies and terminals, the overall patterns of labeling appear quite similar. GABAergic axon terminals are particularly prominent in zones known to receive the bulk of the projections from the lateral geniculate nucleus; laminae 4C, 4A, and the cytochrome-rich patches of lamina 3. In lamina 4A, GABAergic terminals are distributed in a honeycomb pattern which appears to match closely the spatial pattern of geniculate terminations in this region. Quantitative analysis of axon terminals that contain flat vesicles and form symmetric synaptic contacts (FS terminals) in lamina 4C beta and in lamina 5 suggest that the prominence of GAD and GABA axon terminal labeling in the geniculate recipient zones is due, at least in part, to the presence of larger GABAergic axon terminals in these regions. GABAergic cell bodies and their initial dendritic segments display morphological features characteristic of nonpyramidal neurons and are found in all layers of striate cortex. The density of GAD and GABA immunoreactive neurons is greatest in laminae 2-3A, 4A, and 4C beta. The distribution of GABAergic neurons within lamina 3 does not appear to be correlated with the patchy distribution of cytochrome oxidase in this region; i.e., there is no significant difference in the density of GAD and GABA immunoreactive neurons in cytochrome-rich and cytochrome-poor regions of lamina 3. Counts of labeled and unlabeled neurons indicate that GABA immunoreactive neurons make up at least 15% of the neurons in striate cortex. Layer 1 is distinct from the other cortical layers by virtue of its high percentage (77-81%) of GABAergic neurons. Among the other layers, the proportion of GABAergic neurons varies from roughly 20% in laminae 2-3A to 12% in laminae 5 and 6. Finally, there are conspicuous laminar differences in the size and dendritic arrangement of GAD and GABA immunoreactive neurons. Lamina 4C alpha and lamina 6 are distinguished from the other layers by the presence of populations of large GABAergic neurons, some of which have horizontally spreading dendritic processes. GABAergic neurons within the superficial layers are significantly smaller and the majority appear to have vertically oriented dendritic processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Extensive co-existence of neuropeptides in the rat visual cortex

The peroxidase-antiperoxidase immunohistochemical technique has been used to examine the co-existence of peptides within individual neurons of the rat visual cortex. Pairs of consecutive paraffin sections were stained alternately for 2 of the 4 peptides: somatostatin (SRIF), vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK) and neuropeptide Y (NPY). Analysis revealed the co-existence of SRIF with VIP, CCK and NPY and between VIP and CCK. These results show that the co-localization of neuropeptides in cortical neurons is more widespread than previously demonstrated.

Forms and spatial arrangement of neurons in the primary motor cortex of man

The morphology and the spatial arrangement of neurons in the primary motor cortex (area 4) of the adult human brain have been investigated by the Golgi method. The human motor cortex displays a great variety of pyramidal and nonpyramidal cells, expressed as important differences in soma shape and size, and in the dimensions and the distribution of dendritic trees, which are described in detail. The neuronal composition of each layer and the white matter is analyzed. In sublayers III b and c, the somata and dendritic trees of pyramidal and nonpyramidal cells are grouped into columnar aggregations, 100-300 micron wide and separated by cell-sparse spaces of 50-100 micron width. Within the aggregations, the apical dendrites of pyramidal cells form several bundles. The dendrites of most nonpyramidal cells do not surpass the columnar width. Sections in different planes reveal that the columnar aggregations observed in sections perpendicular to the long axis of the precentral gyrus are actually the cross-sectioned representatives of elongate strips running parallel to the long axis of the gyrus. The dendrites and somata of pyramidal cells in layers III and V show a preferential orientation in the same direction, parallel to the main axis of the gyrus. In layers II, IV, and V, aggregations like those in layer III are not recognizable; however, in layer V, loose assemblages of neurons of all sizes group around the giant Betz cells. Layer VI has a radial appearance due to the radii of myelinated fibers entering and leaving the white matter. The vertical, columnar organization of layer III and the asymmetry of somata and dendritic trees are not observed consistently throughout area 4, but are more pronounced at the boundary of the precentral gyrus and the central sulcus.

Neuronal uptake and laminar distribution of tritiated aspartate, glutamate, gamma-aminobutyrate and glycine in the prestriate cortex of squirrel monkeys: correlation with levels of cytochrome oxidase activity and their uptake in area 17

The neuronal uptake and laminar distribution of cortically injected tritium-labeled gamma-aminobutyrate (GABA), aspartic acid, glutamate and glycine was examined in the prestriate cortex of squirrel monkeys. The intent of this investigation was not to examine the role of these amino acids as neurotransmitters, but to correlate the distribution of tritium-labeled neurons with their levels of cytochrome oxidase activity. A comparison of the number of these labeled neurons was made between the metabolically active "puff" and the less active "nonpuff" regions. In addition, these results were contrasted with the findings in area 17. With each tritiated amino acid tested, labeled neurons that had either high or low levels of cytochrome oxidase activity were present in all laminae. However, the density of labeled neurons varied between lamina for a given amino acid as well as between different amino acids. While many neurons that were cytochrome oxidase-reactive were also tritium-labeled, cytochrome oxidase activity was not a prerequisite for the sequestering of tritium label. In fact, many of the labeled neurons exhibited relatively low levels of cytochrome oxidase activity. Similar to area 17, few aspartate- or glutamate-labeled neurons were present in laminae II-III. The number of labeled neurons for both amino acids increased in laminae IV-VI, with the greatest increase observed in laminae V-VI. Gamma-aminobutyrate-labeled neurons were more prevalent in laminae I and upper II than in the other laminae, whereas in area 17, a greater proportion of the labeled neurons were found in laminae V-VI. With the exception of the uppermost laminae, where GABA-labeled neurons were more abundant, the number of glycine-labeled neurons was significantly greater throughout most laminae than with the other amino acids examined. The density of glycine-labeled neurons in lamina IV, however, was significantly less than the number observed in lamina III even though lamina III was farther away from the injection site which was at the boundary between laminae V-VI. Glycine-labeled neurons were, on average, larger than those labeled with any other amino acid. Similar to area 17, more GABA- and glycine-labeled neurons were observed within the puff regions than in nonpuff regions. No puff/nonpuff differences were observed in the distribution of leucine-injected controls. Labeled neurons for each amino acid included stellate-, fusiform- and pyramidal-shaped cells, each of varying sizes. However, outside the intensely labeled injection sites, no GABA-labeled pyramidal cells were observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Laminar and cellular localization of cytochrome oxidase in the cat striate cortex

Cytochrome oxidase (C.O.) was histochemically localized in the cat striate cortex at the light and electron microscopic levels. The results indicate that the oxidative metabolic activity within the cat striate cortex may vary between (1) different laminae, (2) neurons and glia, (3) different neuron types, (4) dendrite and soma of the same cell, (5) different types of dendrites, (6) different segments of the same dendrite, and (7) different classes of symmetric and asymmetric axon terminals. Maximal laminar C.O. staining was localized within geniculoreceptive layer IV. Darkly reactive neurons include the large (presumed corticotectal) pyramids of layer V, and various classes of large and medium-sized presumed GABAergic nonpyramidal cells sparsely distributed throughout layers II-VI. The small and medium-sized pyramids of layers II, III, V, and VI, as well as many of the smaller presumed GABAergic neurons, were only lightly or moderately reactive. The darkly reactive neurons tended to be those that received convergent or proximally localized asymmetric axosomatic synapses, implying that they are strongly driven by excitatory synaptic input. The darkly reactive nonpyramids resembled those that form GAD+, symmetric axosomatic synapses with pyramidal cells. The dark reactivity of the symmetric synaptic terminals indicates that they mediate strong inhibition of neuronal discharge. The dark reactivity of a class of large asymmetric terminals in layer IV is likely to represent highly active geniculocortical terminals. The predominant distribution of elevated C.O. reactivity in dendrites is correlated with reported sites of (1) convergent excitatory synaptic input, (2) maximal field potentials, (3) highly active ion transport, and (4) Na+, K+-ATPase.

The relationship between GABA immunoreactivity and labelling by local uptake of [3H]GABA in the striate cortex of monkey

An antiserum to GABA was used in the macaque monkey to determine whether neurons that accumulate exogenously applied [3H]GABA in vivo are also immunoreactive for GABA. Following the injection of [3H]GABA into different laminae of striate cortex in two untreated animals and in one animal treated with amino-oxyacetic acid, selective accumulation of the labelled amino acid was demonstrated in perikarya by autoradiography. Radiographically labelled neurons (n, 519) and their unlabelled neighbours were tested in consecutive 0.5 micron thick sections by immunocytochemistry for GABA immunoreactivity. Injection of [3H]GABA did not increase the number of neurons showing GABA immunoreactivity. On the contrary many of the cells that accumulated [3H]GABA were immunonegative. These neurons were mostly located in layers IVC and VA following [3H]GABA injection into layers II-III, and in layers upper III and II following injection into layers V and VI. A comparison of the position of these neurons with known local projection patterns in the striate cortex of monkey suggests that GABA-immunonegative neurons may nevertheless become labelled by [3H]GABA if most of their local axon terminals fall within the injection site. The interlaminar projection of GABA-immunopositive neurons, which probably contain endogenous GABA, could be deduced from the position of the [3H]GABA injection site that leads to their autoradiographic labelling. Although the present study confirmed our previous results on the interlaminar connections of neurons that accumulate [3H]GABA, it demonstrated that [3H]GABA labelling alone may not be a sufficient criterion to assess the GABAergic nature of neurons in the striate cortex of monkey.

Correlation between cytochrome oxidase staining and the uptake and laminar distribution of tritiated aspartate, glutamate, gamma-aminobutyrate and glycine in the striate cortex of the squirrel monkey

The cellular uptake and laminar distribution of tritium-labeled gamma-aminobutyrate, aspartate, glutamate and glycine were examined in the primary visual cortex of squirrel monkeys. The purpose was to correlate the distribution of these labeled neurons with their level of cytochrome oxidase activity, particularly in laminae II-III (puffs) and adjacent non-puff regions. In general, tritium-labeled neurons that had either high or low levels of cytochrome oxidase activity were present in all laminae with each amino acid tested; however, their density varied between laminae and with the amino acid injected. Specifically, in laminae II-III, very few neurons were labelled with either of the putative excitatory amino acids (aspartate and glutamate). An increased uptake for both was observed in lamina IVC, with the greatest increase for each occurring in laminae V and VI. Significantly more neurons in each lamina were labeled with the putative inhibitory transmitters (gamma-aminobutyrate and glycine) than with either aspartate or glutamate. gamma-Aminobutyrate-labeled neurons were more prevalent in lamina II than III, and an increase in labeling was observed in laminae IV-VI, with the most prominent increase found in laminae V and VI. Glycine-labeled neurons were larger, more uniformly distributed and more abundant throughout all cortical laminae than those labeled with the other amino acids. Significantly more gamma-aminobutyrate- and glycine-labeled neurons were found in the puff regions than in the non-puff areas. No difference was found between puff and non-puff regions for the tritium-labeled leucine controls. Labeled neurons included stellate, fusiform and pyramidal-shaped cells of varying sizes; however, gamma-aminobutyrate-labeled pyramidal cells were not observed outside of the intense injection site. Large glycine-labeled cytochrome-oxidase-reactive pyramidal cells (24-32 micron in diameter) were present at the boundary between laminae V and VI. In addition, a row of large glycine-labeled, fusiform neurons were present in lamina IVB. With each amino acid injected, the tritium-labeled neurons that were darkly reactive for cytochrome oxidase were, on average, larger than the tritium-labeled neurons that were only lightly reactive for cytochrome oxidase. Thus, each of the four amino acids tested had its unique pattern of distribution in the primate striate cortex. Whether one or all of them served as neurotransmitter(s) for distinct neuronal groups is beyond the scope of this study. Glycine, in particular, might be used in part or in whole for metabolic purposes.(ABSTRACT TRUNCATED AT 400 WORDS)