Journal of Comparative Neurology

In macaque monkeys, lesions involving the posterior portion of the inferior temporal cortex, cytoarchitectonic area TEO, produce a severe impairment in visual pattern discrimination. Recently, this area has been shown to contain a complete, though coarse, representation of the contralateral visual field (Boussaoud, Desimone, and Ungerleider: J. Comp. Neurol. 306:554–575, '91). Because the inputs and outputs of area TEO have not yet been fully described, we injected a variety of retrograde and anterograde tracers into 11 physiologically identified sites within TEO of seven rhesus monkeys and analyzed the areal and laminar distribution of its cortical connections.

Our results show that TEO receives feedforward, topographically organized inputs from prestriate areas V2, V3, and V4. Additional sparser feedforward inputs arise from areas V3A, V4t, and MT. Each of these inputs is reciprocated by a feedback projection from TEO. TEO was also found to have reciprocal intermediate‐type connections with the fundus of the superior temporal area (area FST), cortex in the most posteromedial portion of the superior temporal sulcus (the posterior parietal sulcal zone [area PP]), cortex in the intraparietal sulcus (including the lateral intraparietal area [area LIP]), the frontal eye field, and area TF on the parahippocampal gyrus. The connections with V3A, V4t, and PP were found only after injections in the peripheral field representations of TEO. Finally, TEO was found to project in a feedforward pattern to area TE and to areas anterior to FST on the lateral bank and floor of the superior temporal sulcus (areas TEm, TEa, and IPa, Seltzer and Pandya: Brain Res. 149:1–24, '78), all of which send feedback projections to TEO. Feedback projections also arise from parahippocampal area TH, and areas TG, 36, and possibly 35. These are complemented by only sparse feedforward projections to TG from central field representations in TEO and to TH from peripheral field representations.

The results thus indicate that TEO forms an important link in the occipitotemporal pathway for object recognition, sending visual information forward from V1 and prestriate relays in V2–V4 to anterior inferior temporal area TE. © 1993 Wiley‐Liss, Inc.

This article is a US Goveriiment work and, as such, is in the public domain in the United States of America.

The nucleus basalis is located at the confluence of the limbic and reticular activating systems. It receives dopaminergic input from the ventral tegmental area/substantia nigra, serotonergic input from the raphe nuclei, and noradrenergic input from the nucleus locus coeruleus. Its cholinergic contingent, known as Ch4, provides the principal source of acetylcholine for the cerebral cortex and amygdala. More than half of presynaptic varicosities along its cholinergic axons make traditional synaptic contacts with cortical neurons. Limbic and paralimbic cortices of the brain receive the heaviest cholinergic input from Ch4 and are also the principal sources of reciprocal cortical projections back to the nucleus basalis. This limbic affiliation explains the role of the nucleus basalis in modulating the impact and memorability of incoming sensory information. The anatomical continuity of the nucleus basalis with other basomedial limbic structures may underlie its early and high vulnerability to the tauopathy and neurofibrillary degeneration of Alzheimer's disease. The tauopathy in Ch4 eventually leads to the degeneration of the cholinergic axons that it sends to the cerebral cortex. The early involvement of Ch4 has a magnifying effect on Alzheimer's pathology, because neurofibrillary degeneration in a small number of neurons can perturb neurotransmission in all cortical areas. Although the exact contribution of the Ch4 lesion to the cognitive changes of Alzheimer's disease remains poorly understood, the cholinergic circuitry of the nucleus basalis is emerging as one of the most strategically positioned and behaviorally consequential modulatory systems of the human cerebral cortex. J. Comp. Neurol. 521:4124–4144, 2013. © 2013 Wiley Periodicals, Inc.

The directed growth of axons to their peripheral targets during development may be influenced by a variety of intrinsic and environmental factors, the latter including the pattern of extracellular matrix components in the region through which they grow. We investigated the localization within the chick trigeminal mesenchyme of a variety of extracellular matrix molecules (laminin, heparan sulfate proteoglycan, entactin, collagen type IV) by using indirect immunofluorescence techniques. The trigeminal mesenchyme contained several of these molecules, but only laminin was specifically localized to trigeminal axon pathways. Double immunofluorescence localization of affinity‐purified laminin antibodies and monoclonal antibodies directed against a neuron‐specific β‐tubulin (to visualize growing axons and postmitotic V ganglion neurons) demonstrated that the V motor and sensory peripheral nerves confine their growth to two patches of laminin‐rich mesenchyme—a ganglionic laminin patch colocalized with V ganglion neurons and their axons, and a mandibular laminin patch colocalized with the V motor axons. Thus, laminin pathways in the mesenchyme may help guide V axons along their appropriate routes in the periphery. Double immunofluorescence localization of these laminin antibodies and monoclonal antibodies that recognize neural crest cells (to visualize precursors of V ganglion neurons and glia) demonstrated that the majority of cells within the ganglionic laminin patch were neural crest and differentiating neurons derived from the trigeminal epidermal placode. Since these cells often were laminin‐immunopositive, they might be a source of the ganglionic laminin matrix. The mandibular laminin patch contains nearly no neural crest cells, and probably contains the somitomeric precursors to the mandibular muscle mass. These results suggest that laminin, a matrix molecule implicated in the guidance of trigeminal peripheral axons, might be produced in localized patches by peripheral nervous system components and by muscle targets.

The detailed morphology of the dopaminergic amacrine cell type has been characterized in the macaque monkey retina by intracellular injection of horseradish peroxidase (HRP). This cell type was recognized by its large soma in an in vitro, wholemount preparation of the retina stained with the fluorescent dye, acridine orange. HRP‐fills revealed a large, sparsely branching, spiny dendritic tree and a number of extremely thin, axon‐like processes that arose from the soma and proximal dendrites. The axon‐like processes were studded with distinct varicosities and were traced for up to 3 mm beyond the dendritic tree. The true lengths of the axon‐like processes were greater than 3 mm, however, because the HRP reaction product consistently diminished before an endpoint was reached. Both the dendrites and the axon‐like processes were narrowly stratified close to the outer border of the inner plexiform layer, although in a few cases single axon‐like processes projected into the outer nuclear and outer plexiform layers.

The HRP‐filled amacrines appeared equivalent to a subpopulation of neurons that are intensely immunoreactive for tyrosine hydroxylase (TH). TH‐immunoreactive cells showed a nearly identical soma size and dendritic field size range, the same pattern of dendritic branching and spiny morphology, and also gave rise to distinct axon‐like processes from both the soma and proximal dendrites.

To test this correspondence more directly, the large acridine stained cells were injected with Lucifer Yellow and the retina was subsequently processed for TH immunoreactivity using diaminobenzidine as the chromagen. In all cases Lucifer Yellow injected cells also showed intense TH immunoreactivity.

Spatial densities of the TH amacrine cells were therefore used to calculate coverage factors for the dendritic trees and for the axon‐like components of the HRP‐filled cells. The axon‐like processes showed a coverage factor of at least 300, about 100 times that of the dendritic fields. This great overlap could be directly observed in TH‐immunoreacted retinal wholemounts as a dense plexus of fine, varicose processes. The density of the TH plexus is greater than the density predicted from the lengths (1–3 mm) of the HRP‐filled axon‐like processes however, and suggests that the axon‐like processes have an actual length of about 4–5 mm.

The dual morphology of the dopaminergic amacrine, coupled with the previous studies of identified dopaminergic synapses, suggests the hypothesis that the varicosities on the axon‐like processes are the major source of synaptic output, and that the spiny dendrites are the major recipients of synaptic input from cone bipolar cells and other amacrine cells.

The rare extension of the axon‐like processes into the outer plexiform layer, and current understanding of the morphology of dopaminergic interplexiform cells in teleost fish, supports the hypothesis that the dopaminergic amacrine and interplexiform cells represent a single cell type in which there is quantitative variation across species in the projection pattern of the axon‐like processes.

Age‐related changes in cell proliferation, neuronal differentiation, and cell death in mouse olfactory neuroepithelium were investigated. Mice at the age of 10 days through 16 months were given a single injection of bromodeoxyuridine (BrdU). The olfactory mucosae were fixed at 9 timepoints ranging from 2 hours to 3 months after the injection and examined using double immunostaining for BrdU and olfactory marker protein (OMP), and double staining with terminal deoxynucleotidyl transferase‐mediated biotinylated dUTP nick end labeling (TUNEL) and immunostaining for OMP. The number of BrdU‐labeled cells/mm epithelial length initially increased, peaked at 2–3 days after the BrdU injection, then declined at each age. The number of BrdU‐ and TUNEL‐labeled neuronal cells both decreased with increasing age, suggesting that the rates of both cell proliferation and cell death in the olfactory neuroepithelium decrease with increasing age. Double‐labeled cells for BrdU and OMP appeared at 7 days after injection in all age groups, suggesting that the time required for neuronal differentiation is broadly similar irrespective of age. In older age groups, smaller amounts of the newly produced cohort are integrated into the OMP‐positive ORN population, and even once it is integrated it is eliminated from the population more rapidly compared to the younger age groups. Furthermore, TUNEL assay showed that the fraction of apoptotic cells distributed in the OMP‐positive layer/total apoptotic cells decreased with age. This observation suggests that the turnover of mature ORNs is slower in the older neuroepithelium compared to the younger neuroepithelium. J. Comp. Neurol. 518:1962–1975, 2010. © 2010 Wiley‐Liss, Inc.

The basal forebrain (BF) is known to play important roles in cortical activation and sleep, which are likely mediated by chemically differentiated cell groups including cholinergic, γ‐aminobutyric acid (GABA)ergic and other unidentified neurons. One important target of these cells is the lateral hypothalamus (LH), which is critical for arousal and the maintenance of wakefulness. To determine whether chemically specific BF neurons provide an innervation to the LH, we employed anterograde transport of 10,000 MW biotinylated dextran amine (BDA) together with immunohistochemical staining of the vesicular transporter proteins (VTPs) for glutamate (VGluT1, ‐2, and ‐3), GABA (VGAT), or acetylcholine (ACh, VAChT). In addition, we applied triple staining for the postsynaptic proteins (PSPs), PSD‐95 with VGluT or Gephyrin (Geph) with VGAT, to examine whether the BDA‐labeled varicosities may form excitatory or inhibitory synapses in the LH. Axons originating from BDA‐labeled neurons in the magnocellular preoptic nucleus (MCPO) and substantia innominata (SI) descended within the medial forebrain bundle and extended collateral varicose fibers to contact LH neurons. In the LH, the BDA‐labeled varicosities were immunopositive (+) for VAChT (∼10%), VGluT2 (∼25%), or VGAT (∼50%), revealing an important influence of newly identified glutamatergic together with GABAergic BF inputs. Moreover, in confocal microscopy, VGluT2+ and VGAT+ terminals were apposed to PSD‐95+ and Geph+ profiles respectively, indicating that they formed synaptic contacts with LH neurons. The important inputs from glutamatergic and GABAergic BF cells could thus regulate LH neurons in an opposing manner to stimulate vs. suppress cortical activation and behavioral arousal reciprocally. J. Comp. Neurol. 496:453–467, 2006. © 2006 Wiley‐Liss, Inc.

Structural features of astrocytes in the rat dentate gyrus were studied by means of light and high‐voltage electron microscopy of Golgi‐impregnated materials, conventional electron microscopy, combined Golgi‐electron microscopy, and immunohistochemistry for glial fibrillar acidic protein.

Astrocytes in the dentate gyrus were of the protoplasmic type and were classified into six subtypes based on the location of their somata: i.e., astrocytes 1) in the polymorph layer, (2) in the subgranular zone, (3) in the granular cell layer, (4) at the border of the granular cell layer and the molecular layer, (5) in the molecular layer, and (6) subjacent to the pia surface.

Stereoscopic observations of 5‐μm‐thick sections of Golgi‐impregnated materials revealed three‐dimensional structural details of astroglial processes not apparent in either the light microscope or in conventional thinsection electron microscopy. Most of them were basically thin sheets, varying in shape and size in accordance with their sites. In the granule cell layer, thin veillike sheets or lamellae, originating from three kinds of astrocytes (subtypes 2, 3, and 4), intervened between granule cell somata, whereas in the plexiform and molecular layers small leafletlike appendages originating from astrocytes (subtypes 1, 2, 4, and 5) intermingled with one another, making spongelike conglomerates. Thus astrocytes in the subgranular zone and those at the border of the granule cell layer and the molecular layer showed prominent regional differentiation of their processes among layers. In addition to these sheetlike processes, thin threadlike processes were also common.

Sampling of stellate cells from the molecular layer of cerebellar cortex at two distinct levels within yielded two populations of cells referred to as stellate and basket cells respectively. The appearance of the soma, the several kinds of dendrites and their accompanying spines can be characterized on the electron microscopic level for each type of cell and correlate well with Golgi impregnation studies.

Analytical studies were made to determine the proportion of neural and glial elements in direct apposition to stellate and basket soma and their respective dendrites. On the average the glial covering of a basket or stellate cell was 12–14% of the cell profile, reaching 18.6% for the distal portions of dendrites.

A quantitative analysis of the amount of soma and dendritic perimeter in contact with synaptic boutons revealed the percentage of perimeter surface covered by terminal boutons was 15.2% for basket soma, 4.5% for the stellate soma, 21% for basket dendrites and 10.3% for stellate dendrites.

An interesting group of cells located in the Purkinje cell layer had the morphological characteristics of basket cells but an unusual synaptic input and an unusually high proportion of glial envelope due to their unique position.

This report is an introduction to a comparative analysis of the distribution, and densities of different types of synapses upon basket and stellate cells.

A method is presented for individually mounting serial sections on one‐hole specimen holders. Also a technique for constructing stereograms based upon serial sections is described including a method for obtaining perspective foreshortening. Ultrastructural findings revealed the surface of the motoneuron to be covered with synaptic boutons which frequently pressed against each other. Surface area not contacted by boutons was covered with astroglial processes. The latter processes wedged around and sometimes between the boutons. On occasion finger‐like astrocytic processes (spines) were found to invaginate the terminal boutons. No synaptic thickenings were found between adjacent boutons (axo‐axonal contacts) on the perikaryal surface. However, in view of the enormous size of the motoneuron contrasted to the small volume of tissue thus far investigated, this observation is regarded as inconclusive. Three‐dimensional studies revealed an astrocytic process with disproportionately large amounts of surface membrane in the form of many interconnected pockets. The initial unmyelinated segment of a large anterior horn cell was encountered and found to have synaptic boutons on its proximal half. Its distal half was surrounded by an extracellular space containing electron dense material similar to that found in the goldfish by Robertson, Bodenheimer, and Stage ('63).

Factors that regulate the formation, spatial patterning, and maturation of CNS synapses are poorly understood. We used organotypic hippocampal slice cultures derived from developing (P5–P7) rat to test whether synaptic activity regulates the development and organization of postsynaptic structures at mossy fiber (MF) giant synapses. Antibodies to a prominent postsynaptic density (PSD) scaffold protein, PSD95, identified large (>1 μm) and irregularly shaped PSD assemblies that codistributed with synapsin‐I or metabotropic glutamate receptor 7b (mGluR7b) ‐immunolabeled MF terminals in area CA3. To investigate the spatial organization of synaptic PSDs on individual pyramidal cells, neurons in slice cultures were transfected with a vector encoding a GFP‐PSD95 fusion protein. Confocal three‐dimensional reconstructions revealed clusters of PSDs along proximal dendrites of transfected pyramidal neurons in area CA3, but not in CA1. Clusters averaged 7.6 μm in length (range, 2.2–29 μm) and contained up to 35 individual PSDs (mean, 8.3). PSD clusters failed to form when slices were cultured without MFs, indicating that MFs induce cluster assembly. Chronic blockade of N‐methyl‐D‐apartate– and AMPA/kainate‐type glutamate receptors did not disrupt MF targeting or de novo formation of PSD clusters with a normal distribution on target cells. Additionally, glutamate receptor blockers did not alter the ultrastructural development of MF giant synapses containing multiple puncta adherens‐like junctions and asymmetric synaptic junctions at dendritic shaft and spine domains, respectively. The results indicate that MF axons can induce the assembly and clustering of PSD95‐containing postsynaptic complexes, displaying a normal subcellular and tissue distribution, by mechanisms that are independent of ionotropic glutamate receptor activation. J. Comp. Neurol. 440:284–298, 2001. © 2001 Wiley‐Liss, Inc.