The role of pioneer neurons in the development of mouse visual cortex and corpus callosum

The primordial plexiform neuropil is very critical to neocortical development. The pioneer neurons, mainly Cajal-Retzius cells in the marginal zone, and subplate neurons in the subplate, differentiate from the primordial plexiform neuropil. In this study, the development of corpus callosum, visual cortex, and subcortical pathways has been observed in C57BL/6 mice with various methods, such as DiI labeling in vitro and in vivo, DiI and DiA in vitro double labeling, immunocytochemistry, and in vivo BrdU and Fast Blue labeling. As early as E14, the primordial plexiform neuropil can be found in the telencephalic wall, and it contains many pioneer neurons. On E15 the primordial plexiform neuropil differentiates into the marginal zone and the subplate. Cajal-Retzius cells exist in the marginal zone, and subplate neurons are in the subplate. Either Cajal-Retzius cells or subplate neurons have long projections toward the ganglionic eminence, suggesting that they migrate tangentially from the ganglionic eminence. Cajal-Retzius cells are involved in radial migration, and subplate neurons participate to guide pathfinding of subcortical pathways. This study reveals how the pioneer neurons, through radial and tangential migration, play an important role in neocortical formation and in the pathfinding of the corpus callosum and subcortical pathways. Furthermore, DiI labeling in vivo has demonstrated the presence of pioneer neurons all along the corpus callosum pathway, especially in the midline. This suggests that pioneer neurons may also play a role in guiding the pathfinding of the corpus callosum. Accepted: 31 July 2001     

Cognitive impairment in Parkinson's disease: amyloid plaques, neurofibrillary tangles, and neuropil threads in the cerebral cortex

Summary Sensitive silver methods for extracellular amyloid and intraneuronal cytoskeleton abnormalities (neurofibrillary tangles and neuropil threads) were employed to examine the cortical pathology in Parkinson's disease. In cases with cognitive impairment many plaque-like amyloid deposits were found in the cerebral cortex. Neuritic plaques were rare or absent. Neither the Ammon's horn nor the isocortex revealed a sufficiently large number of tangles to permit the diagnosis of a coexisting fully developed Alzheimer's disease. Large numbers of neurofibrillary tangles and neuropil threads were only found in layer Pre- of the entorhinal cortex. This layer gives rise to major portions of the perforant tract, a pathway which serves as a link in the transmission of data from isocortical association areas to the hippocampal formation. During the course of Parkinson's disease the hippocampal formation is thus endangered to become disrupted from isocortical influences. It is concluded that the cognitive impairment shown by many individuals suffering from Parkinson's disease may partly be caused by cortical lesions.     

Average shape standard atlas for the adult Drosophila ventral nerve cord

Neuroanatomy benefits from quantification of neural structures, i.e., neurons, circuits, and brain parts, within a common reference system. Recent improvements in imaging techniques and increased computational power have made the creation of Web‐based databases possible, which serve as common platforms for incorporating anatomical data. This study establishes a standard average shape atlas for the ventral nerve cord (VNC) of Drosophila melanogaster. This atlas allows for the registration of morphological, developmental, and genetic data into one quantitative 3D reference system. The standard is based on an average adult Drosophila VNC neuropil as labeled in 24 whole‐mount preparations with the commercially available antibody (nc82) recognizing the Drosophila Bruchpilot protein (Brp). For the standardization procedure no expert knowledge of brain anatomy is required and global thresholding as well as straightforward affine and elastic registration procedures minimize user interactions. Successful registration is demonstrated for tracts and commissures, gene expression patterns, and geometric reconstructions of individual neurons. Any structure that is counterstained with anti‐Brp can be registered into the standard, allowing for fast comparison of data from different experiments and different laboratories. In addition, standard transformations can be applied to gray scale image data, so that any confocal image stack that is colabeled with anti‐Brp can be analyzed within standardized 3D reference coordinates. This allows for the creation of putative neural connectivity maps and the comparison of expression patterns derived from different preparations. The standard and protocols for histological methods, segmentation, and registration procedures will be made available on the Web. J. Comp. Neurol. 518:2437–2455, 2010. © 2010 Wiley‐Liss, Inc.     

Projection patterns of gustatory neurons in the suboesophageal ganglion and tritocerebrum of mosquitoes

Mosquitoes are heavily dependent on gustatory information when feeding. Following the recent elucidation of the molecular basis of gustation in the malaria mosquito, we present a detailed study of primary central projections of gustatory receptor neurons into the brain in the malaria (Anopheles gambiae) and yellow fever (Aedes aegypti) mosquito. In the brain we provide a detailed map of the areas targeted and describe a number of intrinsic neural elements connecting primary taste areas to higher brain levels. The morphological features described are discussed and compared to earlier reports in other insects as, e.g., the fruitfly, Drosophila.     

Arborization pattern of Engrailed‐positive neural lineages reveal neuromere boundaries in the Drosophila brain neuropil

The Drosophila brain is a highly complex structure composed of thousands of neurons that are interconnected in numerous exquisitely organized neuropil structures such as the mushroom bodies, central complex, antennal lobes, and other specialized neuropils. While the neurons of the insect brain are known to derive in a lineage‐specific fashion from a stereotyped set of segmentally organized neuroblasts, the developmental origin and neuromeric organization of the neuropil formed by these neurons is still unclear. In this study we used genetic labeling techniques to characterize the neuropil innervation pattern of engrailed‐expressing brain lineages of known neuromeric origin. We show that the neurons of these lineages project to and form most arborizations, in particular all of their proximal branches, in the same brain neuropil compartments in embryonic, larval and adult stages. Moreover, we show that engrailed‐positive neurons of differing neuromeric origin respect boundaries between neuromere‐specific compartments in the brain. This is confirmed by an analysis of the arborization pattern of empty spiracles‐expressing lineages. These findings indicate that arborizations of lineages deriving from different brain neuromeres innervate a nonoverlapping set of neuropil compartments. This supports a model for neuromere‐specific brain neuropil, in which a given lineage forms its proximal arborizations predominantly in the compartments that correspond to its neuromere of origin. J. Comp. Neurol. 517:87–104, 2009. © 2009 Wiley‐Liss, Inc.     

NADPH-diaphorase Histochemical Labeling Patterns in the Hippocampal Neuropil and Visual Cortical Neurons in Weaned Rats Reared during Lactation on Different Litter Sizes

Abstract

Tissue distribution of nitric oxide-synthases was investigated in the rat hippocampus and visual cortex under nutritional changes induced by modification of the litter size. Young (30-45-days-old) rats, suckled in litters formed by 3, 6 or 12 pups (called small, medium and large litters, respectively), were studied by using nicotine-adenine-dinucleotide phosphate-diaphorase histochemistry (shortly, diaphorase), a simple and robust procedure to characterize tissue distribution of nitric oxide-synthases. We assessed morphometric features of the diaphorase-positive cells in visual cortex, and the neuropil histochemical activity in hippocampal CA1 and dentate gyrus using densitometry analysis. In the large-litter group, the labeled-cell density in white matter of area 17 was higher, as compared to the small-litter group. There was a clear trend, in the large-litter group, to lower values of soma area, dendritic field and branches per neuron, but the differences were not significant. Densitometry analysis of hippocampus revealed a significant increase in the relative neuropil histochemical activity of the dentate gyrus molecular layer in the larger litters, which may be associated to increased compensatory blood flow in the hippocampus. The pathophysiological mechanisms of the observed changes remain to be investigated.     

Central projections of the brachial nerve in bullfrogs: Muscle and cutaneous afferents project to different regions of the spinal cord

The central projections of muscle and cutaneous sensory neurons in the bullfrog were labeled by filling their peripheral axons in the forelimb with horseradish peroxidase (HRP). Muscle afferent fibers were found to project exclusively to the ventral neuropil of the brachial spinal cord in the intermediate gray zone. Cutaneous afferent axons had their arbors limited to the dorsal neuropil. There is therefore a topography in the central representation of two classes of sensory modalities.     

An Ultrastructural Change in Developing Rat Cerebral Cortex: A Morphometrical Study

Abstract: Five age groups, each composed of four animals from each of the following ages, were used to assess age-related ultrastructural changes with development in the neuropil of the III layer of the frontal cortex (area 6) in rats; 1, 2, 3, 5 and 12 weeks old. Random samplings within the neuropil were taken to produce 25 electron micrographs in each rat (totaling 500). The profiles of axon terminals, dendrites and mitochondria in each element in the neuropil of each micrograph were traced. The percentage of their areas for the area of neuropil (relative volume fraction) was examined using the image analyzer system. The size and number of synaptic terminals were counted. The relative volume fractions of both the axon terminals and mitochondria in the terminals for the neuropil were found to have increased in the mature rats. On the other hand, the relative volume fraction of dendrites for the neuropil had been unchanged and the size of the terminals had gradually decreased. The number of terminals had progressively increased with development.     

The distribution of acetylcholinesterase in the hippocampal formation of the monkey

In order to study the distribution of acetylcholinesterase (AChE) in the primate hippocampal formation, we have stained serial sections through the brains of nine macaque monkeys for AChE by two variants of the Koelle acetylthiocholine method. We have found a distinctive pattern of staining in the hippocampal formation which varies in intensity both from region to region, and along rostrocaudal and radial gradients within each region. In the dentate gyrus, there is intense staining of the inner one-third of the molecular layer with much lighter staining in the rest of the molecular layer except for a moderately stained band at its outer edge. In the caudal half of the dentate gyrus, the inner portion of the molecular layer is less intensely stained though there is a distinctly denser band of staining just above, and partly within, the superficial margin of the granule cell layer. The granule cells are unstained but there are AChE-positive fibers which run through the granule cell layer to the molecular layer. The hilar region of the dentate gyrus has a narrow band of heavy staining (which corresponds to an acellular layer in Nissl-stained sections) just subjacent to the granule cell layer; the remainder of the hilus, where most of the hilar cells reside, is less intensely stained and at caudal levels is almost entirely unstained. In the regio inferior of the hippocampus, there is intense staining of the stratum oriens which extends into the pyramidal cell layer; the stratum radiatum and the stratum lacunosum- moleculare are also stained and here the staining pattern shows some degree of stratification. By contrast, most of the alveus, the pyramidal cell somata, and the layer of mossy fibers (stratum lucidum) are unstained. The border region between regio inferior and regio superior of the hippocampus (field CA2 of Lorente de No, '34) is especially heavily stained. This contrasts markedly with regio superior, which is more lightly stained than regio inferior. Stratum oriens and stratum radiatum of regio superior have a more evenly distributed pattern of staining, though the intensity of staining increases sharply at the border with the subiculum. Stratum lacunosum- moleculare is only lightly stained throughout much of the transverse extent of regio superior but there is also a conspicuous and constant patch of heavier staining at the border with the subiculum.(ABSTRACT TRUNCATED AT 400 WORDS)