Cytoarchitecture of the substantia nigra pars lateralis in the opossum (Didelphis virginiana): A correlated light and electron microscopic study

Background: The substantia nigra has been divided into three subdivisions. However, the cytoarchitecture of one of these subdivisions, the pars lateralis (SNI), has not been previously examined in detail at the light and electron microscopic levels in any species. In the adult opossum, the three nigral subdivisions can be easily distinguished as distinct, rostrocaudally oriented cell groups separated by neuron-free zones. Thus it was possible to determine the boundaries of the SNI unambiguously. This report covers the results of an examination of the morphology and organization of the SNI in the opossum. Methods: Material from 13 opossums was used for this study. Eight of the animals had been previously stained for Nissl substance (n=4) or impregnated by the Golgi technique (n=4). The remaining five animals were prepared for electron microscopic studies using standard procedures. Results: Two cell types were identified on the basis of morphological differences, small and medium-large neurons. Small neurons (10–18 μm long axis) have large nuclei with moderate amounts of heterochromatin and a thin rim of cytoplasm. They have long (up to 500 μm), spine-free dendrites. Medium-large neurons (18–54 μm long axis) have rounded nuclei with electron-lucent nucleoplasm. Few indentations of the nuclear envelope were observed. The surrounding cytoplasm has dense arrays of organelles. Nissl bodies are particularly prominent in the form of pyramids with their bases at juxtanuclear positions and their apices directed toward emerging dendrites. Dendrites of medium-large neurons are long (some>1 mm in length), are primarily oriented in the frontal plane, and extend along the dorsal surface of or into the cerebral peduncle. Some cells have dendrites that are moderately spinous, whereas other neurons possess sparsely spinous dendrites. Relatively few synaptic profiles are observed to contact somata and proximal dendrites. Conclusion: This report provides added morphological support for the idea that the SNI is a distinct subdivision of the substantia nigra, a distinction previously made on the basis of the physiologically characterized relationship between the lateral substantia nigra and orienting behaviors and seizure-related function. © 1995 Wiley-Liss, Inc.     

Efferent connections of the main olfactory bulb in the opossum (Monodelphis domestica): a characterization of the olfactory entorhinal cortex in a marsupial

Olfactory projections have been investigated for decades, but few reports using modern, sensitive neural tracers are available. In marsupials, only lesion-degeneration studies exist and they are restricted to the genera Didelphis and Trichosurus. Some of the territories described as olfactory-recipient such as the upper portion of the rhinal fissure and the vomeronasal amygdala are, however, controversial. Also, the characterization of the olfactory portion of the entorhinal cortex is far from clear in acallosal mammals. The present report investigates, using biotinylated dextran-amine, the olfactory connections in the short-tailed opossum (Monodelphis domestica) and characterizes the olfactory portion of the entorhinal cortex in non-placental mammals. The data indicate that olfactory projections do not reach the upper portion of the rhinal fissure, but partially end in the vomeronasal amygdala, i.e., the medial and posteromedial cortical amygdaloid nuclei; thus, although olfactory and vomeronasal system have largely segregated outputs, areas of overlap should be restudied. The olfactory portion of the entorhinal cortex is much larger than previously described, extending up to the occipital pole of the cerebral hemisphere. Collectively, these data contribute to our understanding of the organization of the hippocampal formation in marsupials.     

A light and electron microscopic study of taurine-like immunoreactivity in the main olfactory bulb of frogs

The distribution of taurine in the frog olfactory bulb was studied using light and electron microscopic immunohistochemical techniques. At the light microscopic level, taurine-like immunoreactivity (taurine-LI) was found in (i) fibers coursing from the olfactory nerve layer to the glomerular layer, (ii) cell bodies and processes primarily located in the caudal part of the granule cell layer (GCL), and (iii) puncta outlining unstained somata of mitral cells and cells in the GCL. In consecutive sections processed for taurine or GABA, numerous cells of the caudal GCL displayed taurine-LI and GABA-like immunoreactivity (GABA-LI). A bimodal distribution of the cross-sectional cell area for GABA-LI cells implied their morphological diversity, and the peak for larger GABA-LI cells coincided with the maximum for taurine-LI cells. At the electron microscopic level, single immunogold labeling showed that GABA-LI, but not taurine-LI, is present in granule cells, whereas both taurine-LI and GABA-LI were localized in a ‘non-granule’ type of cell. The double labeling procedure demonstrated coexistence of taurine-LI and GABA-LI in neurons of a ‘non-granule’ type. These cells had some ultrastructural features typical of short axon cells in the GCL of the mammalian olfactory bulb and were tentatively considered as short axon-like cells. Results suggest that, in the frog olfactory bulb, taurine is contained in primary olfactory afferents and short axon-like cells of the GCL co-localizing GABA and taurine.     

A degeneration study of efferent connections of the habenular complex in the opossum

Parts of the medial and lateral habenular nuclei were removed unilaterally in each of thirteen opossums and the brains were studied for fiber degeneration by a modified Nauta method. Degeneration was seen in the ipsilateral, but not the contralateral, habenulopeduncular tract, which at the level of the interpeduncular nucleus underwent a partial decussation over it, whereas there were almost no degenerating fibers in the nucleus itself. Caudal to the nucleus extensive degeneration was present bilaterally among nuclei of the raphé and this extended into the predorsal fasciculus. Many terminals were observed in the nuclei of the raphé and within the deep tegmental nucleus. Although degenerating fibers were seen in the region of the dorsal tegmental nucleus, no terminals could be identified with certainty. Degeneration was also present in the superior colliculus. Bilateral degeneration occurred in the stria medullaris and extended to the preoptic area and the olfactory tubercle. In the dorsal preoptic area a small, but quite definite fiber bundle, separated from the posterior surface of the stria medullaris, traversed the lateral hypothalamus and passed dorsal to the mammillary bodies into the midbrain tegmentum, where it became intermingled with fibers of the habenulopeduncular tract just ventral to the red nucleus. Findings appear to indicate that in the opossum relatively few, if any, fibers of habenular origin terminate in the interpeduncular nucleus. In addition, fairly substantial evidence has been obtained to show that there are a number of efferent fibers within the stria medullaris.     

Capillaries in aging rat olfactory bulb: A quantitative light and electron microscopic analysis

Olfactory bulbs from Charles River (Crl) rats from 3 to 36 months have been examined with light and electron microscopy. Total capillary length, surface, and volume, as well as number of endothelial cells, increases during the twofold increase in olfactory bulb volume from 3 to 18 months, but the relative density of these parameters shows no change during this time; from 18 to 36 months when neuronal cell body and dendrites are decreasing markedly in size, the relative density of capillaries shows only a modest decrease. Capillary lumen size and capillary wall thickness remain the same throughout life, but basal lamina thickness doubles from 3 to 24 months and then remains constant from 24 to 36 months. The incidence of several unusual ultrastructural features of the outer capillary basal lamina has been shown to increase with age.     

Postnatal development of blood vessels (capillaries) in the rat olfactory bulb: A light and ultrastructural study

The increase in density and development of blood vessels (capillaries) were studied in the rat olfactory bulb. The density of blood vessels increased significantly over the second ten-day period of postnatal development. Electron microscopy revealed that blood vessels developed from solid cords of cells with thick endothelial cells, slit-like lumina and ill-defined lamina. The majority of these vessels became luminized during the second ten-day period and were characterized by patent lumina, well defined basal lamina and attenuated endothelial cells.     

Central olfactory connections in the microsmatic marmoset monkey (Callithrix jacchus)

The mammalian primary olfactory system consists of a set of different telencephalic structures, including paleo-, archi-, periarchi- and mesocortical components. We present the first characterisation of the normal and connectional anatomy of the primary olfactory cortex of the common marmoset, a microsmatic simian species increasingly used in primate research. The centrifugal and centripetal bulbar projections were determined by injections of the anterograde and retrograde tracer wheat germ agglutinin-conjugated horseradish peroxidase and fluorescent dyes into the ipsilateral main olfactory bulb. The efferent projections of the marmoset bulb are organised entirely ipsilaterally and are established via a rudimentary medial olfactory tract and the dominant lateral olfactory tract. Target areas are the anterior olfactory nucleus, the entire prepiriform cortex, ventral tenia tecta, periamygdaloid cortex and the rostral part of the entorhinal cortex. The bulbar axons predominantly terminate in the outer part of layer I. The anterior olfactory nucleus receives a weak additional input within layer II and III, which is not found in macrosmatic rodents. Further anterograde labelling was found in the endopiriform nucleus deep under the prepiriform cortex and within an anterolateral strip of the olfactory tubercle. However, control injections into the olfactory tubercle suggest that the marmoset olfactory tubercle receives a bisynaptic olfactory input only. Retrograde labelling after bulb injections revealed that, except for the olfactory tubercle, all primary olfactory cortices contributed to an ipsilateral bulbopetal feedback projection. Like in rodents, the only bulbopetal projection organised bilaterally in the marmoset is maintained by the anterior olfactory nucleus. With few exceptions, the projections of the marmoset olfactory brain are organised similarly to that of the macaque monkey or those of macrosmatic species.     

Scanning electron microscopic study of degeneration and regeneration in the olfactory epithelium after axotomy

Summary The olfactory epithelium of the adult hamster (Mesocricetus auratus) was examined with the scanning electron microscope following olfactory nerve axotomy. Axotomy results in retrograde degeneration of mature olfactory neurons. Maximum degeneration was observed around day 4. During the degeneration period the epithelium consists primarily of supporting and basal cells. Microvillar columnar supporting cells were observed to have fine cellular processes extending from their lateral border to neighbouring cells. Supporting cells extended to the basal lamina where they terminated in foot-like processes of variable shapes (club, splay and hook). Basal cells which gave rise to new replacement olfactory neurons were observed near the basal lamina. They had a rough cellular surface covered with small granules and fine cellular extensions. Bowman's gland duct cells extended unbranched through the epithelium where they formed funnel duct openings covered with microvilli. During early recovery periods (5–30 days) the number of olfactory neurons in the lower epithelium region increased. We observed olfactory neurons with developing axon and dendritic processes. Specialized growth cone structures were seen at the tips. Olfactory neuron growth cones were elongated or club-shaped and had a ruffled membrane surface. Several thin filopodia extended from the growth cone and made contact with adjacent cells. At late recovery periods (35–120 days) there was a marked increase in the number of olfactory neurons within the middle and lower epithelium regions. Numerous dendritic processes extended to the epithelial surface and terminated in knob-like ciliated structures. Olfactory axons passed basally, forming small intra-epithelial bundles that penetrated the basal lamina then fasciculated into larger bundles within the lamina propria.This study provides detailed three-dimensional observations of the olfactory epithelium following neuron injury, and describes neural degenerative changes, replacement of olfactory neurons, development and maturation. In addition, we describe the structure and basal attachment of supporting cells and their glial-like relation with olfactory neurons.     

The cardiac, oxyntic and pyloric glands in the developing opossum (Didelphis virginiana)

In the opossum the fundic area of the gastric mucosa develops first, and oxyntic glands show early division into gastric pits and glandular components which then grow simultaneously. At 40 d postnatum the oxyntic glands are longer than the gastric pits but in the pyloric glands the pits still are longer than the glands and it is not until the 73rd postnatal day, that pyloric glands are longer than their pits. Development of the cardiac glands is delayed even more and the length of the gland does not surpass that of the pit until about 95 d postnatum. Argyrophil cells are concentrated in the cardia and fundus at birth and during early postnatal life, but the population of these cells shifts to the pylorus in the adult. Argyrophil cells of the cardiac, oxyntic and pyloric glands are concentrated in glandular regions with the highest mitotic activity.     

Ultrastructural observations on the shell membrane of the North American opossum (Didelphis virginiana)

Each developing opossum embryo is surrounded by a shell membrane which completely separates embryonic and maternal tissues. During the eighth and ninth prenatal days, the embryos together with their limiting shell membranes float freely within the uterine lumen, surrounded only by the secretions of the uterus. The shell membrane is transparent, nonelastic, tough, and capable of extreme deformation. It consists of a mat of interwoven fibers which vary in external diameter, are electron dense, and show no apparent substructure. The morphology and arrangement of component fibers are similar throughout the width of the shell membrane.     

Postnatal development of mitral cell perikaryon in the olfactory bulb of the rat. A light and ultrastructural study

The differentiation of the mitral cell perikaryon in postnatal rat olfactory bulb was studied with the light and electron microscope. At birth the mitral cell was distinguishable and occupied a definitive position in the mitral cell layer. The cell contained a large oval nucleus surrounded by a thin rim of cytoplasm. Ribosomes, free and clustered, were scattered in the cell cytoplasm. Rough endoplasmic reticulum was relatively scarce. The Golgi complexes were made up of stacks of smooth-surfaced cisternae and associated vesicles. In certain cases the Golgi complexes projected into cellular processes. Mitochondria were present in all regions of the cytoplasm and contained well developed cristae. At the end of the first week, the mitral cell had developed significantly in size, and the cytoplasm contained well-developed rough endoplasmic reticulum. The Golgi complexes were made up of several stacks of smooth-surfaced cisternae with the association of vesicles and electron dense bodies. The apical dendrites o mitral cells at this periiod had increased significantly in length. Subsequently, during the second and third week, the rough endoplasmic reticulum and Golgi complexes became well developed. Associated with the Golgi complexes were electron dense lysosomal bodies. At three weeks and in older cells it was observed that dense lysosomal bodies. At three weeks and in older cells it was observed that dense lipofuschin granules increased significantly. It is suggested that the mitral cell matures and differentiates earlier than cells in the cerebral cortex.     

A histopathological study on senile changes in the human olfactory bulb

Senile changes in the human olfactory bulb were studied histopathologically in 133 individuals ranging in age from 40 to 91 years with a mean age of 64.3 years. Neurofibrillary tangles (NFTs) in the olfactory bulb were observed in 47 subjects aged over 50 years. The frequency of NFTs was 35.3% (47/133) in total and 40.5% (47/116) among subjects 50 years of age or older. The frequency of individuals with NFTs increased linearly with age. Senile plaques (SPs) were observed in 5 individuals over 60 years old at a frequency of 3.8% (5/133) in total and 5.7% (5/88) among individuals 60 years old or more. Granulovacuolar degeneration was rarely seen, and amyloid angiopathy was not recognized. Senile changes in the hippocampus and parahippocampal gyrus were also examined. In some cases, the frequencies of NFTs and SPs in the hippocampal region were not identical to those in the olfactory bulb. However, it was not apparent whether senile changes first appear in the olfactory bulb or in the hippocampal region.     

Number of mitral cells and the bulb volume in the aging human olfactory bulb: A quantitative morphological study

The present study documents the morphological changes in the aging human olfactory bulb. Eight bulb pairs from white females between the ages of 25 and 102 years were used. The number of mitral cells in layers IV and III was determined for each bulb and corrected for spilt cell error. Counts were made on 10-μm thick Nissl-stained sections at 250-μm intervals. The mean number of mitral cells per olfactory bulb at age 25 was estimated from linear regression to be 50,935; at age 60, 32,718; and at age 95, 14,501. The average loss over the time interval studied was 520 mitral cells per year. The volume of each bulb layer, except layer IV, was determined. The difference in the volume of each layer within individuals with age and the total volume with age was not significant (P < 0.11). The estimated mean bulb volume was found to be 50.02, 43.35, and 36.68 mm³ at ages 25, 60, and 95 years, respectively. The estimated reduction in bulb volume per year increase of age was 0.19 mm³. The ratio of mitral cells to bulb volume for layer III decreased by 19.4 units for every year increase in age. No significant difference was found between the left and the right bulbs in regard to the number of mitral cells and the bulb volume. Histologically, the glomerular layer thickness as well as the mitral cell size and concentration per unit area decreased with age. The intrabulbar anterior olfactory nucleus was discontinuous, highly variable in size, and presumably variable even in neuronal numbers.