bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of new cerebral ganglion neurons in the snail Melampus: An ultrastructural study
Authors: Moffett Stacia , Austin Daniel R.
Published: January 2005

Reports in the literature have established that reconnection of central neural tracts occurs following commissurotomy and cerebral ganglion excision in the primitive pulmonate snail Melampus bidentatus and have suggested the possibility that long‐term regeneration might result in the appearance of new neurons in the ganglion bud. We have used electron microscopy to examine the ganglion buds that form by reconnection of cerebral nerves, commissure, and connectives following cerebral ganglion excision in adult Melampus. The buds were examined from 2.5 to 12 months postoperatively. By 2.5 months, ganglion buds consist of a mixture of axon tracts that travel through the bud region and some dendritic processes; a few synaptic contacts can be identified at this stage, scattered throughout the bud. By 5–6 months, some of the most advanced ganglia have undifferentiated cells that are distinct from glia. By 7 months, differentiated neurons with clear, small dense‐core or neurosecretory vesicles are present, although these cells are not all concentrated in a rind on the ganglion surface. Another cell type, the pigment‐sheath cell, is present by this stage. By 11–12 months, the most advanced regenerating ganglia have neurons which form a cell rind on the ganglion surface. The gross appearance of a regenerated ganglion at this stage is similar to that of the intact contralateral cerebral ganglion, although the regenerated ganglion is smaller. One 12‐month ganglion was found to possess fairly normal intraganglionic morphology, with lobes and cell types that were recognizable. Hence, nerve cell regeneration can occur in the absence of body part regeneration in adult members of one species of pulmonate snail.
The developmental morphology of Torpedo marmorata: Electric lobe‐electromotoneuron proliferation and cell death
Authors: Fox Geoffrey Q. , Richardson Guy P.
Published: January 2005

Electromotoneuron proliferation and cell death have been quantitativelystudied in the electric lobe of Torpedo marmorata from an embryonic body‐length stage of 26‐mm to adult animals. These neurons project to the electric organ and form synapses with electrocytes which possess a remarkably large postsynaptic target surface. For this reason cell death would not be predicted to occur if synaptic competition were to be hypothesized as thecause. Isolated observations at the ultrastructural level suggested, however, that cell death was indeed taking place and therefore it seemed appropriate to examine this question in detail.

Our findings show first that neuron production appears to be a continuous process throughout the period studied, generating totals of over 70,000 electromotoneurons per lobe by adulthood. Second, two waves of cell death were identified, one occurring early in embryogenesis (stage 30 mm), well before the onset of synaptogenesis, and a second coincident with the onset ofsynaptogenesis (stages 55‐74 mm). It is difficult to reconcile this latter wave with the hypothesis of synaptic competition as the postsynaptic surface at this time of development is largely devoid of synaptic contacts. We conclude that in the electromotor system of Torpedo, synaptic competition is probably not the mechanism of cell death.
Generation of motoneurons in the rabbit brainstem
Authors: Shaw Marjorie D. , Alley Keith E.
Published: January 2005

Autoradiography of 3H‐thymidine incorporation was used to determine the time of origin of motoneurons in the rabbit brainstem. With the exception of the facial nucleus, neurons of the branchial motor column originated earlier (days 9 and 10) than somatic motor column neurons (day 11). Labeling was obtained as early as embryonic day 8 for many motor nuclei and the mesencephalic trigeminal nucleus. The significance of temporal patterns of neurogenesis is discussed.
Afferent connections of the cerebellum in various types of reptiles
Authors: Bangma G. C. , Donkelaar H. J. Ten
Published: January 2005

The origin of cerebellar afferents was studied in various types of reptiles, viz., the turtles Pseudemys scripta elegans and Testudo hermanni, the lizard Varanus exanthematicus, and the snake Python regius, with retrograde tracers (the enzyme horseradish peroxidase and the fluorescent tracer “Fast Blue”). Projections to the cerebellum were demonstrated from the nucleus of the basal optic root, the interstitial nucleus of the fasciculus longitudinalis medialis, the vestibular ganglion, and the vestibular nuclear complex, two somatosensory nuclei, viz., the descending nucleus of the trigeminal nerve and the nucleus of the dorsal funiculus, the nucleus of the solitary tract, the reticular formation, and throughout the spinal cord. A distinct bilateral projection to the cerebellum was found to arise in a nucleus previously called nucleus parvocellularis medialis (Ebbesson, ′67). In the present study this cell mass is termed the perihypoglossal nuclear complex, considering its comparable position and fiber connections to the perihypoglossal nuclei in mammals. In all reptilian species studied a contralateral cerebellar projection of a cell mass located in the caudal brainstem adjacent to the nucleus raphes inferior was observed. It seems likely that this cell mass represents the reptilian homologue of the mammalian inferior olive. Most of the spinocerebellar fibers appeared to arise in neurons located in area VII‐VIII of the gray matter. In this respect the origin of the spinocerebellar projection in reptiles resembles the origin of the rostral and ventral spinocerebellar tracts in mammals. No indications for the existence of a column of Clarke or a central cervical nucleus in the reptilian spinal cord were obtained.

On comparison of the cerebellar afferents in reptiles with the known connections of the cerebellum in amphibians, birds, and mammals, a basic pattern of cerebellar afferent projections appears to exist in these vertebrateclasses, including retinal, vestibular, precerebellar, somatosensory, and spinal afferents.
Quantitative analysis of neuronal development in the lateral motor column of mouse spinal cord. I. Genetically associated variations in somal growth patterns
Authors: Holley John A. , Wimer Cynthia C. , Vaughn James E.
Published: January 2005

The relative somal and nuclear sizes of neurons in the lateral motor column (LMC) of adult and embryonic mouse brachial spinal cord were determined by light microscopic morphometry. Three genetically varying mouse strains, previously shown to differ in the development of a forelimb reflex pathway, were studied. In adults, the size distribution of somata, nuclei, and nucleoli were bimodal for each strain, indicating that there are two distinct size classes of LMC neurons. The size division between large and small LMC neurons differed among strains with more large LMC neurons occurring in strain CBA/CaJ than in either LP/J or C57BL/6J. In embryos, the growth of LMC cells was studied by determining the average area of nuclear profiles for specimens ranging in age from embryonic day 11 (E11) to 16. The average nuclear profile area increased significantly during this period in all three strains, and differences were found in the initial size and apparent rate of growth among strains. Early in development (E11‐12), strain differences in apparent cell size were: C57BL/6J>CBA/CaJ>LP/J, and this strain order corresponds to observed strain differences in the onset of reflexogenesis and synaptogenesis (Vaughn et al., ′75). Later in development (E16), strain differences in apparent cell size were: CBA/CaJ>LP/J≥C57BL/6J, and this relationship corresponds to a more rapid increase of presumptive afferent synapses in CBA/CaJ than in the other two strains between E15 and E16. Possible causal relationships among neuronal size, growth, and synaptogenesis are suggested by these strain differences.
Quantitative analyses of neuronal development in the lateral motor column of mouse spinal cord. II. Development of motor neuronal organelles
Authors: Holley John A. , Wimer Cynthia C. , Vaughn James E.
Published: January 2005

The development of organelles within presumptive alpha motor neuronal somata was studied by electron microscopic morphometric analysis. Cells with large nuclei were selected for sampling from the lateral motor column of the brachial spinal cord of mouse embryos ranging in age from embryonic day 11 (E11) through E16. The first objective was to compare the cytodifferentiation of alpha motor neuronal somata among three genetically different strains of mice that differ in the development of forelimb reflex behavior and associated pathway synaptogenesis (Vaughn et al., ′75). On the basis of multiple linear regression analyses, no significant differences were found among strains for either the initial levels or rates of cytodifferentiation. As a result, the data were combined for all three strains to analyze organelle changes during early neuronal development. The average areas of perikaryal cytoplasm and nuclei increased significantly. In addition, the relative areas of nucleoli, mitochondria, Golgi complexes, and rough endoplasmic reticulum increased, while the relative areas of heterochromatin and “free” ribosomes decreased. There were significant increases in the number of mitochondria and Golgi complexes per unit area of perikaryal cytoplasm. The average size of mitochondria appeared to increase during development, but was significantly smaller in adult alpha motor neurons than in embryonic specimens. In contrast, the average size of individual Golgi complexes was relatively constant throughout embryonic development, as well as in the adult. In general, the cytodifferentiation of alpha motor neurons appeared to progress in a relatively constant, linear fashion between E11 and E16.
Sources of olfactory inputs to opossum mediodorsal nucleus identified by horseradish peroxidase and autoradiographic methods
Authors: Benjamin Robert M. , Jackson Jan C. , Golden Gregory T. , West Charles H. K.
Published: January 2005

Some sources of olfactory input to the opossum mediodorsal thalamic nucleus (MD) were identified by retrograde horserdish peroxidase and anterograde autoradiographic methods. One major source originated from the olfactorytubercle and a narrow strip of piriform cortex bordering the tubercle. The tubercle‐MD projection exhibited a definite spatial organization and included all except the most medial part of MD. The fact that the projection reached the most lateral and ventral extent of MD abutting the intralaminar complex suggests that the entire opossum MD may correspond to only the medial, magnocellular division in the primate and that the equivalents of both the parvocellular and paralamellar divisions may be absent.
Basal ganglia pathways to the tectum: The afferent and efferent connections of the lateral spiriform nucleus of pigeon
Authors: Reiner Anton , Brecha Nicholas C. , Karten Harvey J.
Published: January 2005

Previous studies have demonstrated that the lateral spiriform nucleus (SpL) of the avian pretectum receives a major input from the ipsilateral basal ganglia (Karten and Dubbeldam, 1973) and projects to the ipsilateral optic tectum (Brecha et al., 1976). The present study has further detailed the anatomical organization of the afferent and efferent connections of SpL, with particular reference to (1) the sources of afferent inputs to SpL, (2) the projection targets of SpL, and (3) the laminar termination pattern of the SpL projection to the tectum.

The SpL was found to receive clear‐cut major inputs from only three nuclei: (1) the ipsilateral paleostriatum primitivum (PP) of the basal ganglia (the avian homologue of the mammalian globus pallidus), (2) the ipsilateral anterior nucleus of the ansa lenticularis (ALa) of the diencephalon, and (3) the ipsilateral nucleus tegmentipedunculopontinus (TPc) of the mesencephalon. Both TPc and ALa have previously been noted themselves to receive major inputs from the ipsilateral PP (Karten and Dubbeldam, 1973). Two other cell groups may give rise to a slight projection to the ipsilateral SpL: (1) the posterior nucleus of the ansa lenticularis (ALp) of the diencephalon and (2) the nucleus semilunaris (SLu) of the isthmic brainstem. The ALp also receives a major input from PP (Karten and Dubbeldam, 1973), while SLu receives a major tectal projection (Hunt and Kunzle, 1976a).

The ipsilateral tectum was found to be the only projection target of SpL. The present data suggest that the SpL projection to the tectum is restricted to layers 8–13, with layers 11–13 receiving the heaviest projection from SpL. Among layers 8–10, layer 9 receives the lightest projection from SpL.

The present results indicate that SpL receives only a limited number of inputs, which in all likelihood relay largely basal ganglia input to SpL. Since SpL projects only to the tectum, the sole function of SpL apparently is the transmission of ipsilateral basal ganglia influences to the avian optic tectum. Tectal layers 8–15 have been previously found to represent the layers of origin of the descending pathways of the avian tectum to hindbrain motor and “premotor” cell groups (Reiner and Karten, 1982). In view of the purported involvement of the basal ganglia in motor functions, the basal ganglia pathway to the ipsilateral tectum via SpL may represent a major route by which the avian basal ganglia exert influences over motor functions.
Raphespinal projections in the north american opossum: Evidence for connectional heterogeneity
Authors: Martin G. F. , Cabana T. , Ditirro F. J. , Ho R. H. , Humbertson A. O.
Published: January 2005

Retrograde transport studies revealed that the nuclei pallidus, obscurus, and magnus raphae as well as the adjacent reticular formation innervate the spinal cord in the opossum. HRP‐lesion experiments showed that a relatively large number of neurons within the nucleus obscurus raphae and closely adjacent areas of the nucleus reticularis gigantocellularis project through the ventrolateral white matter and that many cells within the nucleus magnus raphae, the nucleus reticularis gigantocellularis pars ventralis, and the nucleus reticularis pontis pars ventralis contribute axons to the dorsal half of the lateral funiculi. Neurons within the rostral pole of the nucleus magnus raphae and the adjacent nucleus reticularis pontis pars ventralis may project exclusively through the latter route.

Each of the above‐mentioned raphe and reticular nuclei contain nonindolaminergic as well as indolaminergic neurons (Crutcher and Humbertson, 1978). When True‐Blue was injected into the spinal cord and the brain processed for monoamine histofluorescence evidence for True‐Blue was found in neurons of both types.

Injections of 3H‐leucine centered within the nuclei pallidus and obscurus raphae and/or the closely adjacent nucleus reticularis gigantocellularis labeled axons within autonomic nuclei and laminae IV‐X. Labeled axons were particularly numerous within the intermediolateral cell column and within laminae IX and X. Injections of the caudoventral part of the nucleus magnus raphae or the adjacent nucleus reticualris gigantocellularis pars ventralis labeled axons in the same areas as well as within laminae I‐III. When the injection was placed within the rostal part of the nucleus magnus raphae or the adjacent nucleus reticularis pontis pars ventralis axons were labeled within laminae I‐III and external zones of laminae IV‐VII, but not within lamina IX. The immunohistofluorescence method revealed evidence for indolaminergic axons in each of the spinal areas labeled by injections of 3H‐leucine into the raphe and adjacent reticular formation. They were particularly abundant within the intermediolateral cell column and within laminae IX and X. These data indicate that raphe spinal systems are chemically and connectionally heterogeneous.
Electron microscopical observations on the indoleamine‐accumulating neurons and their synaptic connections in the retina of the cat
Authors: Holmgren‐Taylor Ingrid
Published: January 2005

The distribution of indoleamine‐accumulating amacrine cells and their synaptic connections in the retina of the cat were analyzed in the fluorescence, phase‐contrast, and electron microscopes. The findings were compared to recently characterized morphological subclasses of amacrine cells.

The indoleamine‐accumulating neurons were visualized after labeling with an exogenous indoleamine, 5, 6‐dihydroxytryptamine. The intravitreal injection of the labeling drug was preceded by treatment with the neurotoxic dopamine‐analogue, 6‐hydroxydopamine, in order to destroy the otherwise interfering dopaminergic processes.

The analysis in the fluorescence and phase‐contrast microscopes confirmed earlier reports that the indoleamine‐accumulating cell bodies and processes have a distribution consistent with that of amacrine cells. A stratified branching pattern of the indoleamine‐accumulating processes in the outer half of the inner plexiform layer was discovered. In the inner half of that layer the branching pattern is diffuse.

In the electron microscope the indoleamine‐accumulating neurons were seen to have synapses of the conventional type. Their main synaptic contacts are reciprocal synapses with rod bipolar terminals in sublamina b of the inner plexiform layer. They also have synapses with flat cone bipolar terminals in sublamina a, and occasionally with amacrine cells and ganglion cells throughout the inner plexiform layer. Synapses with invaginating cone bipolar terminals, in sublamina b, appear to be rare. The synaptic arrangement with reciprocal synapses with rod bipolar terminals is similar to that of the recently reported AI amacrine cells. It is also similar to that of the indoleamine‐accumulating neurons in the retinae of other mammals investigated earlier.
Quantitative studies of retinal ganglion cells in a turtle, Pseudemys scripta elegans: II. Size spectrum of ganglion cells and its regional variation
Authors: Peterson Ellengene H. , Ulinski P. S.
Published: January 2005

Recent evidence suggests that ganglion cell size and its regional variation may be an important feature of vertebrate retinas. Accordingly, we have examined Nissl‐stained, whole‐mounted Pseudemys scripta retinas to determine the soma size spectrum of ganglion cells at different retinal loci. Cell size histograms reveal that at any given point on the retina, a majority of ganglion cells are small (6–10 μm), and in peripheral samples there is some evidence for a second, larger size class (12–15 μm). Comparison of samples along the dorsoventral and nasotemporal axes suggests that there are two major trends in soma size variation. Along the dorsoventral axis, ganglion cell diameter increases sharply from the visual streak (6–7 μm, cf. Peterson and Ulinski, 1979) to the dorsal and ventral periphery (9–10 μm). These changes reflect a tendency towards increased size for the entire distribution as well as a relative decrease in the frequency of small ganglion cells. This soma size variation is significantly correlated with changes in ganglion cell density. Along the nasotemporal axis, temporal ganglion cells are significantly larger than those at more nasal retinal loci. This differences reflects an overall increase in the size of ganglion cells in temporal retina and a small but significant increase in the percentage of neurons larger than 15 μm.
Identified motor neurons in the cockroach exhibit stereotypic peripheral branching and nerve terminal structure
Authors: Denburg Jeffrey L.
Published: January 2005

The peripheral branching of the identified motor neurons Df and Ds which innervate the coxal depressor muscles in the legs of cockroaches was examined using the anterograde transport of a cobaltic ‐lysine complex and the retrograde transport of cobaltous ion or horseradish peroxidase. In all animals the axons of these motor neurons leave the ganglion in the dorsal portion of nerve root 5 and undergo a 180° spiral that brings them directly to the first branch. They leave the nerve root at this branch to innervate the muscles. The pattern of branching of Df within muscles 178 and 179 was highly stereotyped with little variability being observed among identical and homologous muscles within the same and different individuals. The great extent of the neuronal branching within the muscles suggests that a relatively large percentage of the surface area of the muscle fibers is involved in intercellular interactions with the motor neurons. The two motor neurons could also be distinguished by the structure of their axon terminals. Those of Df were beaded and extended either parallel or perpendicular to the muscle fiber. Those of Ds were thinner, wavy, less regular, and appeared with a greater frequency. Identified neurons may therefore be further characterized by their stereotypical peripheral branching and axon terminal structure.
Ultrastructure of the paraphysis cerebri of the water snake Natrix maura L
Authors: Fernández‐Llebrez Pedro , Becerra José , Marín‐Girón Fernando
Published: January 2005

Paraphyseal epithelial cells of Natrix maura have been studied with light and electron microscopy. They showed a clear polarity apically related to the third ventricle and, basally, to a connective tissue layer which surrounded the whole organ. The apical surface of the cells, attached by junctional complexes, showed many microvilli, scarce cilia, and some pinocytotic coated vesicles. In their apical cytoplasm many mitochondria and a well developed Golgi apparatus and endoplasmic reticulum were observed. Whereas lamellar bodies were abundant and closely related with mitochondria, glycogen particles were absent. Basal cell membrane showed infoldings where pinocytotic coated vesicles were detected. In the connective tissue layer, fenestrated sinusoids and fibrocytes, as well as rare unmyelinated nerve fibers engulfed by Schwann cells, were present. The possible active role of paraphyseal cells in exchanging substances between cerebrospinal fluid and blood is discussed.
Afferent and efferent connections of small nuclei in the posterolateral hypothalamus of the cat
Authors: Fujii Masako
Published: January 2005

Four separate neuronal groups, termed the anterior, dorsal, vental, and posterior nuclei of the juxtamamillary complex, were labeled retrogradely form the thalamic lateral posterior nucleus with horseradish peroxidase. The retrograde labeling was predominantly ipsilateral in the anterior, dorsal, and ventral nuclei, while it was predominantly contralateral in the posterior nucleus. The anterior, dorsal, and posterior nuclei could be detected clearly in Nissl sections; the ventral nucleus was only identified by horseradish peroxidase transport. The distribution of afferents to the juxtamamillary nuclei was investigated with the Fink‐Heimer technique. Following lesions of the olfactory tubercle and underlying structures, degenerating fibers in the medial forebrain bundle terminated discretely in the juxtamamillary nuclei. The dense terminal pattern conformed to the borders of the nuclei and was sometimes visible macroscopically. This pattern resembles that of medial forebrain bundle afferents to nuclei gemini in the rabbit and rat. Since the anatomical portions of these nuclei are also similar, it was concluded that the nuclei of the cat are comparable with the nuclei gemini in the rabbit and rat.
Organization of nucleus rotundus, a tectofugal thalamic nucleus in turtles. II. Ultrastructural analyses
Authors: Rainey W. T. , Ulinski P. S.
Published: January 2005

Nucleus rotundus is a large, tectorecipient nucleus in the dorsal thalamus of the pond turtles Pseudemys scripta and Chrysemys picta. Rotundal neurons form a single, morphologically homogeneous population (Rainey, '79) that projects to the dorsal ventricular ridge in the telencephalon. The present paper examines the morphology of and the distribution of synapses upon rotundal neurons.

Astrocytes, oligodendrocytes, and neurons can be identified in both 1‐μm sections stained with toluidine blue and electron micrographs of nucleus rotundus. Rotundal neurons contain euchromatic nuclei and the usual complement of mitochondria, rough endoplasmic reticulum, and free ribosomes in their cytoplasm. They are morphologically homogeneous. Two types of terminal boutons can be defined in rotundus. RA boutons contain round synaptic vesicles and form asymmetric synaptic junctions with rotundal dendrites. FS boutons contain small, flattened or pleomorphic vesicles and form nearly symmetric synaptic junctions with rotundal dendrites and somata. RA boutons occasionally form clusters of contiguous boutons that are presynaptic to one or more thin, central profiles. These profiles are probably the dendritic appendages observed on peripheral dendrites in Golgi material. The distribution of RA and FS boutons along dendrites was investigated by a two‐step procedure. First, rotundal neurons were retrogradely solid‐filled with horseradish peroxidase reaction product. Dendritic diameters were measured at 20‐μm intervals along dendritic shafts to produce a plot of dendritic diameter as a function of distance from the soma. Second, the percentage of membrane on dendritic profiles of different diameters that was contacted by RA and FS terminals was determined from electron micrographs. Comparison of the two plots indicates that both bouton types are distributed along the full extent of the dendritic tree, but RA boutons are much more common on the distal two‐thirds of rotundal dendrites.

This analysis suggests that rotundal neurons form a single population of cells that are morphologically homogeneous and project to the forebrain. There is no indication of interaction between neurons in nucleus rotundus, either via axonal collaterals or presynaptic dendrites. Boutons are distributed on rotundal neurons such that FS boutons are prevalent on the somata and most proximal segments of the dendritic shafts, while RA boutons are most common on the more distal dendritic shafts. RA boutons also contribute to synaptic clusters that may center around complex dendritic appendages.
Influence of neonatal cochlear removal on the development of mouse cochlear nucleus: II. Dendritic morphometry of its neurons
Authors: Trune Dennis R.
Published: January 2005

Right cochleae were aspirated from 6‐day‐old mice to determine the influence of cochlear integrity on the dendritic development of neurons within cochlear nucleus (CN). At 45 days of age, cochlear destruction was confirmed histologically and the brains were stained by the Golgi‐Cox method to permit dendritic morphometry in CN ipsilateral (deafferented) and contralateral (normal) to the neonatally lesioned cochleae. The dendritic field cross‐sectional area of ventral CN bushy cells was reduced on the deafferented side, as was the total dendritic length of stellate cells throughout ventral and dorsal CN. The neonatal deafferentation had no statistically significant effect on the total dendritic length of those dorsal CN fusiform cells that developed. These dendritic changes are interpreted as lack of development due to the loss of auditory nerve afferents during a critical period of development and indicate that any congenital pathology that compromises the cochlear sensorineural structures may lead to central auditory abnormalities as well.
A Comparison of dendritic spine number and type on pyramidal neurons of the visual cortex of old adult rats from social or isolated environments
Authors: Connor James R. , Diamond Marian C.
Published: January 2005

The present study determined the effect of the housing condition experienced by old adult male rats on the appearance and number of dendritic spines. Specifically, 20‐month‐old rats were killed following 6 months of living in either a social environment (three to a cage) or living alone. The total number of dendritic spines per unit length was examined along segments of oblique, basal, and apical dendritic branches of pyramidal cells from layers II, III, Va, and Vb of the visual cortex. In addition to determining the total spine number, the spines were differentiated into two topographical categories: those with a lollipop configuration (type L) and those with a nubbin configuration (type N). Out results show that neither the total spine density nor the type L spine density were generally influenced by the two housing conditions. However, the density of type N spines was almost always greater on neurons from rats which had been living alone irrespective of the cortical layer or the dendritic segment counted.

Some differences in total spine density and type L spine density were noted when neurons from the same environment but different cortical layers were compared, and these findings are discussed. However, the major focus of this paper was to extend our previous report of a selective increase in type N spines with age. We now show that in addition to increasing with age, type N spine density is also selectively increased by the condition of social deprivation.
Ultrastructural observations of the migration and early development of trigeminal motoneurons in chick embryos
Authors: Moody Sally A. , Heaton Marieta B.
Published: January 2005

The migration of immature chick trigeminal (V) motoneurons from a miclline medial column to a lateral nucleus was studied between days 3 and 7 of incubation. The somatic translocation of these cells is preceded by the lateral outgrowth of their axons. At days 3–4 the axons grow within extracellular spaces dorsal to pial end feet at the external limiting membrane. At later ages the axons grow deeper within the intermediate zone. Upon reaching the medial border of the V sensory tract the axons turn ventrally, exit from the neural tube, and grow toward the mandibular arch. The medial column somas rotate from their original radial orientation to lie parallel to the pial surface. They migrate laterally in close association with fiber bundles composed of axonal and trailing processes of medial column and other migrating V motoneurons. Several punctate contacts are made between the migrating cells and the axon bundles; these contacts may stabilize the somas while the growing tips of their axons elongate. During migration the cytoplasm of the V motoneuron matures, acquiring rough endoplasmic retic‐ulum, lysosomes, and multivesicular bodies. Immature synapses contact premigratory, migratory, and postmigratory cells on day 4. Their maturation on day 5 coincides with the onset of active jaw movements.

Some V motoneurons secondarily migrate dorsally from the lateral nucleus while their trailing axons are in the head mesenchyme. Few punctate contacts are observed between these cells and their substrate, the longitudinal fibers of the lateral longitudinal fasciculus. Postmigratory dorsal V motoneurons are organelle poor and have few synaptic contacts by day 7. This undifferentiated state may reflect a later onset of the spontaneous movement of their target, the levator palpebrae muscle.
Structure of the piriform cortex of the opossum. II. Fine structure of cell bodies and neuropil
Authors: Haberly Lewis B. , Feig Sherry L.
Published: January 2005

The fine structure of cell bodies and neuropil in the piriform cortex of the opossum has been examined. A close similarity in ultrastructure of many features has been demonstrated between this pylogenetically old cortex in a primitive mammal and the neocortex of higher mammals.

Cell bodies of pyramidal cells are very similar to those in the neocortex: The nucleus is pale with a smooth surface, the cytoplasm has a modest number of organelles, and the soma receives a small number of exclusively symmetrical synapses. Semilunar cells, which have apical but no basal den‐drites, are very similar to pyramidal cells in ultrastructure of their cell bodies.

Two populations of neurons with nonpyramidal ultrastructural features have been distinguished: (1) cells in layer III that closely resemble the well‐known large multipolar cells in neocortex by virtue of a large number of symmetrical and asymmetrical somatic synapses and long cisterns of rough endoplasmic reticulum (ER); and (2) large cells in layer I with very few somatic synapses, a large number of mitochondria, and short cisterns of rough ER that may correspond to cells with somatic appendages described with the Golgi method.

Large numbers of profiles are found in all layers that contain round vesicles and make asymmetrical synapses onto dendritic spines, and occasionally, dendritic shafts. Theseprofileshavedistinctly different morphological features in layer Ia, in which olfactory bulb afferents are concentrated, and in layers Ib, II, and III, which contain terminals of association and commis‐sural fibers. A smaller number of profiles containing pleomorphic vesicles make symmetrical contacts onto initial segments, dendritic shafts, cell bodies, and occasionally, dendritic spines.

Most dendritic spines in all layers are small to medium in size (0.3–1.2 μm) and presumably originate from pyramidal cells. In layer Ia, however, large, flattened spines are also present which appear to originate from semi‐lunar cells. In layer III, and to a lesser extent other layers, large irregular spines are present that may be branched appendages on dendrites of complex appendage cells (Haberly, 1983).
Postmetamorphic changes in the lumbar lateral motor column in relation to muscle growth in the toad, Bufo americanus
Authors: Sperry David G. , Grobstein Paul
Published: January 2005

Motoneuron number and size (nuclear cross‐sectional area) were measured from serially sectioned spinal cords of Bufo americanus to investigate the relation between changes in the lumbar lateral motor column (L‐LMC) and postmetamorphic increases in hindlimb muscle fiber number. Previous studies of neuron number in a variety of anuran species reported a correlation between number and body size, suggesting the possible addition of neurons during growth. Our results show a poor correlation between motoneu‐ron number and body size with at most a 25% increase in neuron number occurring over the body size range where previous work had shown a hind‐limb muscle fiber increase often to 20‐fold. Thus, most new muscle fibers must be incorporated into motor units that exist at metamorphosis. Moto‐neurons, but not ependymal cells, showed a significant size increase with increasing body size; this is perhaps related to an increased motor unit size that results from axonal sprouting. The range of variation of L‐LMC cell numbers in newly metamorphosed toads was nearly equal to that of all other toads examined. This suggests that the weak correlations between motoneu‐ron number and size observed in this and previous studies may be due to differential survival of individuals with larger neuron populations rather than to postmetamorphic addition of motoneurons. Our findings also show a strong bilateral correlation of motoneuron numbers, a finding suggesting that factors other than peripheral size may be important in regulating motoneuron number.
Cortical connections between rat cingulate cortex and visual, motor, and postsubicular cortices
Authors: Vogt Brent A. , Miller Michael W.
Published: January 2005

The connections of rat cingulate cortex with visual, motor, and postsubicular cortices were investigated with retrograde and anterograde tracing techniques. In addition, connections between visual and the postsubicular (area 48) and parasubicular (area 49) cortices were evaluated with the same techniques. The following conclusions were drawn

Area 29 connections: Afferents to area 29 originate mainly from cingulate areas 24 and 25, visual cortex (primarily area 18b), motor cortex area 8, area 11 of frontal cortex, areas 48 and 49, and the subiculum. Efferent connections of area 29 within cingulate cortex and to visual areas differ for each cytoarchitectural subdivision of area 29. Thus, area 29c has limited projections both within cingulate cortex and to areas 48 and 49, while area 29d projects to these areas as well as to area 8, area 18b, and medial area 17. These visual cortex afferents originate mainly from layer V neurons of areas 29b and 29d, while areas 29a and 29c have virtually no projections to visual cortex

Area 24 connections: Afferents to area 24 originate primarily from cingulate areas 25 and 29 and visual area 18b and medial area 17. Efferent projections of area 24a are distributed within cingulate cortex, while area 24b has more extensive projections to posterior cingulate and visual cortices. Area 24b is the cingulate subdivision which is both the primary recipient of visual cortex afferents as well as the source of most of the projections of anterior cingulate cortex to visual areas

Visual cortex has reciprocal connections with parts of the postsubicular and parasubicular cortices. Neurons of the internal pyramidal cell layer of both areas 48 and 49 project to areas 17 and 18b, while layers I and III of these parahippocampal areas receive projections from areas 17 and 18b

In conclusion, areas 29d and 24b have particularly extensive interconnections with visual cortex, while area 29d also maintains projections to area 8 of motor cortex. This connection scheme supports the view that cingulate cortex may have a role in feature extraction from the sensory environment, as well as in sensorimotor integration. Finally, the postsubiculum may be classified as alimbic association cortex in which extensive visual and cingulate efferents converge.
Intrinsic laminar lattice connections in primate visual cortex
Authors: Rockland Kathleen S. , Lund Jennifer S.
Published: January 2005

Intracortical injections of horseradish peroxidase (HRP) reveal a system of periodically organized intrinsic connections in primate striate cortex. In layers 2 and 3 these connections form a reticular or latticelike pattern, extending for about 1.5–2.0 mm around an injection. This connectional lattice is composed of HRP‐labeled walls (350–450 μm apart in Saimiri and about 500–600 μm in macaque) surrounding unlabeled central lacunae. Within the lattice walls there are regularly arranged punctate loci of particularly dense HRP label, appearing as isolated patches as the lattice wall labeling thins further from the injection site. A periodic organization has also been demonstrated for the intrinsic connections in layer 4B, which are apparently in register with the supragranular periodicities, although separated from these by a thin unlabeled region. The 4B lattice is particularly prominent in squirrel monkey, extending for 2–3 mm from an injection. In both layers, these intrinsic connections are demonstrated by orthogradely and retrogradely transported HRP and seem to reflect a system of neurons with long horizontal axon collaterals, presumably with arborizations at regularly spaced intervals. The intrinsic connectional lattice in layers 2 and 3 resembles the repetitive array of cytochrome oxidase activity in these layers; but despite similarities of dimension and pattern, the two systems do not appear identical. In primate, as previously described in tree shrews (Rockland et al., 1982), the HRP‐labeled anatomical connections resemble the pattern of 2‐deoxy‐glucose accumulation resulting from stimulation with oriented lines, although the functional importance of these connections remains obscure.
The nucleus isthmi as an intertectal relay for the ipsilateral oculotectal projection in the frog, Rana pipiens
Authors: Grobstein Paul , Comer Christopher
Published: January 2005

Reconstruction of serial sections through the nucleus isthmi in the frog Rana pipiens shows that the cortex of the nucleus consists of a sheet of cells which is folded back on itself to form two more or less parallel faces. Cyto‐architectural features allow three regions to be distinguished: a 7“rim region,” which previous work had suggested may be involved in the physiological pathway from one eye to the ipsilateral tectal lobe, and two additional regions which are here termed the anterior and posterior “nonrim cortex,” re‐spectively. The cytoarchitectural features which distinguish the rim region from the other two regions are largely absent in the tadpole.

Analysis of retrograde transport of horseradish peroxidase (HRP) following widespread injections into one tectal lobe indicates that the anterior nonrim cortex projects ipsilaterally while the rim cortex and posterior nonrim cortex both project contralaterally. The differing projections of the three regions are paralleled by the pattern of retrograde degeneration observed after unilateral tectal lesions.

We have studied the topographic organization of the connections between the nucleus isthmi and the two tectal lobes by making small injections of HRP at tectal loci with known visual field input. Patterns of retrograde cellular labelling show that the anterior nonrim cortex projects topographically to the entirety of the tectal lobe on the same side of the brain. The rim region projects topographically to the binocularly activated part of the opposite tectal lobe; the posterior nonrim cortex projects to the monocularly activated part. There is a discontinuity in the mapping from the nucleus to the opposite tectal lobe which corresponds to the border between binocular and monocular tectum. Patterns of anterograde labelling indicate that the afferent projection from the ipsilateral tectal lobe is topographic and organized so that afferents from a given tectal locus contact cells in the rostral part of the nucleus which project back to that locus. Afferents from tectal re‐gions representing binocular visual field in addition continue across the nucleus to terminate within the rim region. The organization of the afferent and efferent projections of this region is such as to link tectal loci which relate to the same direction in visual space.

Our findings provide new evidence that the nucleus isthmi is involved in the pathway from one eye to the ipsilateral tectal lobe. They also show how the nucleus is organized to distribute information from a given locus in one tectal lobe to cells which project to the visually corresponding but in general anatomically different pairs of loci in the two tectal lobes. Finally, our findings confirm the existence of a projection from the nucleus isthmi to the opposite monocular tectum and suggest that this may be part of an intertectal circuit linking anatomically corresponding rather than visually corresponding pairs of tectal loci.
Neuronal organization in fly optic lobes altered by laser ablations early in development or by mutations of the eye
Authors: Nässel Dick R. , Geiger Gad
Published: January 2005

The role of afferent and efferent connections in the differentiation of optic lobe interneurons was investigated by using laser ablations of neuronal precursors in the brain of Musca domestica and analysis of two eye mutants of the same species.

The first mutant, split eye, had no connections between the retina and the optic lobes. In this case the optic lobes were drastically reduced in volume and the neural organization within the neuropil regions was altered. The other mutant, spindle, had reduced retinae that innervated reduced optic lobes with a normal‐appearing orderly arrangement of neurons. In addition disordered neuropil, composed of identified visual interneurons, was found that had no afferent innervation.

Three main types of alterations resulting from laser ablations were analyzed. These ablations removed entire neuropil regions or parts of these: (1) removal of the first optic neuropil region (the lamina) resulting in receptor axons projecting directly to the second neuropil (the medulla) and sprouting of medulla neurons toward the receptor layer; (2) removal of one part of the third optic neuropil (the lobula plate) and severe alteration of the other part (the lobula) resulting in sprouting of lobula neurons into the medulla neuro‐pil; and (3) removal of the entire optic lobe resulting in reduction of the volume of the lateral midbrain and photoreceptor axons forming a tangle beneath the retina.

Our findings confirm that afferent retinal input is essential for normal differentiation and maintenance of many optic lobe interneurons. Furthermore, it was seen that a normal columnar organization of the neuropils and the dendritic patterns of visual interneurons are dependent on afferent inputs. A common response to removal of inputs was a reorganization of axo‐nal and dendritic projections.
Ultrastructure of neurons in the nucleus basalis of meynert in squirrel monkey
Authors: Walker Lary C. , Tigges Margarete , Tigges Johannes
Published: January 2005

The nucleus basalis of Meynert in the squirrel monkey exhibits numerous labeled neurons following the retrograde transport of horseradish perox‐idase from occipital cortical injection sites. The typically large, often clustered, labeled cells are seen most frequently in association with the fibrous bordering structures of the substantia innominata and in the internal and external laminae of the globus pallidus. Ultrastructurally the copious cytoplasm of nucleus basalis neurons abounds with organelles. Large, vacuo‐lated lipofuscin granules proliferate as a function of age and are not evident in younger monkeys. Approximately 4% of the somal surface is occupied by symmetrical synapses with either flat or pleomorphic vesicles. The remainder is covered mostly by neuroglial processes. Somatic spines bearing synapses are occasionally observed. In the neuropil surrounding nucleus ba‐salis somata, the synapses onto dendrites and spines are mostly asymmetrical with large, round vesicles. Labeled nucleus basalis cells in the substantia innominata immediately lateral to the optic tract are larger and rounder than cells in the internal and external pallidal laminae. However, no remarkable ultrastructural differences were observed between nucleus basalis so‐mata in the substantia innominata and external pallidal lamina, or between horseradish peroxidase‐labeled and unlabeled large cells.
Late appearance and deprivation‐sensitive growth of permanent dendrites in the avian cochlear nucleus (Nuc. magnocellularis)
Authors: Conlee John W. , Parks Thomas N.
Published: January 2005

The second‐order auditory neurons in the avian nucleus magnocellularis (NM) do not begin to grow permanent dendrites until about embryonic day 17 (E17), a few days before hatching. Since the auditory periphery and brain‐stem auditory nuclei are functional by E14 at the latest, the late appearance and growth of permanent dendrites in NM provides an unusual opportunity to examine the role of sensory experience in the very early stages of dendritic growth. We studied the development of NM dendrites in normal chickens and in animals with sustained monaural acoustic deprivation. In Golgi‐Hortega preparations at E17 and posthatching days 4 (P4), 10 (P10), and 60 (P60), the proportion of stained NM neurons with a dendritic process (“dendritic neurons”) and the length of these dendrites were measured. In normal animals the mean proportion of dendritic neurons rose from about 14% at E17 to 40% at P4 and thereafter. The mean length of NM dendrites in normal animals, however, grew significantly until P10, rising from about 14 μm at E17 to 48 μm by P4, and about 100 μm at P10 and P60. A 40‐dB monaural conductive hearing loss maintained with plastic earplugs from E18 on produced substantial retardation of dendritic growth after P4; at P10 the difference in length between deprived and nondeprived dendrites was 32% and at P60 was 38%. The proportion of dendritic neurons in the deprived NM and the mean diameter of the deprived dendrites were not affected by deprivation. Deprived dendrites in experimental animals were also significantly shorter than those in normal control animals. The length of nondeprived dendrites in experimental animals did not differ from that of controls, arguing against any compensatory hypertrophy. The functions of NM dendrites in the central processing of auditory information are as yet unknown. The facts that these dendrites (1) undergo their most rapid growth during the period of the animal's first exposure to airborne sound and (2) are markedly stunted by a nondeafferenting moderately severe acoustic deprivation suggest that acoustic experience has a strong facilitative function in the posthatching development of the cochlear nucleus. These results also suggest that afferent synaptic stimulation can affect the subsequent elongation, but not the initial outgrowth, of dendrites.