bluuebunny/crossref_metadata_2025 huggingface dataset:
Three distinct morphological classes of receptors in fish olfactory organs
Authors: Muller Jay F. , Marc Robert E.
Published: January 2005

Three morphologically distinct classes of receptor‐neurons are proposed: (1) type I ciliar cells, (2) microvillar cells and (3) type II ciliar cells. Retrograde transport of horseradish peroxidase by axons in the olfactory nerve to the olfactory organs of goldfish (Carassius auratus) and channel catfish (Ictalurus punctatus) provided evidence that these axon‐bearing cells are present in the organs of both species. Goldfish olfactory organs were also studied with scanning electron microscopy, dissociated with papain for isolated cell preparations, and processed for ultrastructural localization of acid phosphatase activity. Type I ciliar cells are similar to ciliar olfactory receptors found in all vertebrate classes. Microvillar cells are present in the olfactory organs of most fishes and in the tetrapod vomeronasal organ. In goldfish and catfish, type I ciliar and microvillar cells are concentrated on the inner third of each lamella, nearest to the median raphe. Type II ciliar cells have often been described as respiratory‐type or ciliated nonsensory cells. They are structurally similar to respiratory epithelial cells in the nasal cavities of tetrapods and have motile cilia that beat synchronously, indicative of their role in mediating fluid flow over the olfactory epithelium. In goldfish they occur singly and in aggregates throughout the organ. In catfish they are segregated from type I ciliar and microvillar cells on the outer two‐thirds of each lamella. In goldfish and catfish they have axons that pass through the olfactory nerve to the olfactory bulb; hence, they are receptor‐neurons as well as analogous to respiratory epithelium.

In addition to the three receptor types described above, cells resembling receptors with rodlike distal processes were seen filled with horseradish peroxidase and observed with scanning and transmission electron microscopy. Cells of similar structure have been documented elsewhere, often called “rod cells,” and sometimes considered a separate receptor type in fishes. In this study, a number of rodlike processes were found with their ciliar or microvillar components partially fused. High levels of acid phosphatase activity were localized to these processes, and examples were found that corresponded to each of the three receptor types. Olfactory receptor turnover is believed to persist through life. The evidence presented supports the hypothesis that fusion of their dendritic apical processes marks an early stage of receptor cell senescence.
Central projections of gustatory nerves in the rat
Authors: Hamilton Robert B. , Norgren Ralph
Published: January 2005

The central distributions of gustatory and nongustatory branches of cranial nerves V, VII, IX, and X were examined after application of horseradish peroxidase to the cut nerve. The nerves conveying gustatory information, chorda tympani (CT), greater superficial petrosal (GSP), lingualtonsilar branch of IX (LT‐IX), superior laryngeal branch of X (SL), distributed primarily to the lateral division of the nucleus of the solitary tract (NST) from its rostral pole to the obex. The CT and GSP distributions were coextensive and terminated most densely in the rostral pole of NST. The LT‐IX distribution concentrated between this major CT/GSP distribution and the area postrema with a caudal extension into the interstitial nucleus of NST. This nerve also had a substantial projection, not found in other gustatory nerves, into the dorsolateral aspect of the medial NST. The SL distribution overlapped LT‐IX in the caudal medulla. The lingual and inferior alveolar nerves, two oral trigeminal branches, projected to regions of NST innervated by the gustatory nerves. The cervical vagus nerve distributed primarily to the medial NST in the caudal half of the nucleus and exhibited only minimal overlap with gustatory nerve distributions. The nucleus of the solitary tract appears to have two major functional divisions–an anterior‐lateral oral‐gustatory half, and a posterior‐medial visceral afferent half.
Astrocytic membrane morphology: Differences between mammalian and amphibian astrocytes after axotomy
Authors: Wujek Jerome R. , Reier Paul J.
Published: January 2005

Previous studies have shown that astrocytes in some nonmammalian species provide a favorable environment for axonal elongation, whereas mammalian astrocytes are thought to inhibit fiber outgrowth. The present study was performed to determine whether any plasma membrane differences exist between these glial elements which could account for their contrasting effects upon axonal outgrowth. Astrocytic scars were formed in optic nerves of rats, newts, and frogs by enucleation. Subsequently, the astrocytic membranes were examined with the freeze‐fracture technique. Orthogonal arrays of small intramembranous particles (IMPs) are a prominent component of the plasma membranes of normal mammalian astrocytes; these arrays are most numerous in astrocytic membranes that form an interface between the CNS and nonneural tissue. Astrocytic membranes within the normal CNS parenchyma, however, possess much lower densities of arrays. Following axotomy and Wallerian degeneration, the density of arrays increased threefold within the parenchyma of the optic nerve, while remaining constant at the, glia limitans. In striking contrast, only a few aggregates of IMPs that resembled orthogonal arrays could be found in normal and reactive astrocytes of amphibians, although the cytology of these glial cells and density of the scars are otherwise similar to those of their mammalian counterparts. These findings suggest (1) that a proliferation of orthogonal arrays in astrocytic plasma membranes is a prominent feature of gliosis in the mammalian CNS and (2) that differences in the composition of reactive mammalian and amphibian astrocytic membranes may account for variations in axonal‐glial interactions within the injured CNS.
The dorsal lateral geniculate nucleus of macropodid marsupials: Cytoarchitecture and retinal projections
Authors: Sanderson K. J. , Haight J. R. , Pettigrew J. D.
Published: January 2005

The anatomy of the dorsal lateral geniculate nucleus (LGd) is described in five macropodid marsupial species, including two rat kangaroos (bettong and potoroo), two wallabies (pademelon and tammar), and the large grey kangaroo. The distribution of retinal terminals in the LGd was examined following intraocular injections of tritiated amino acids. There are considerable differences in both LGd cytoarchitecture and the patterns of retinal terminations among the five species. Cytoarchitecture in the bettong LGd is relatively simple, displaying a minimal regional differentiation. In contrast, the potoroo LGd is quite complex and displays several well‐defined cell laminae, each of which is associated with input from a single eye. Both rat kangaroos display the same basic pattern of retinal termination with three bands of terminals from the contralateral eye and four from the ipsilateral eye. The bands are less sharply defined in the bettong, in which terminals from each eye overlap to a greater extent than is seen in the potoroo. The wallabies and kangaroos display a more complex LGd architecture and patterning of retinal terminal bands. Bilateral retinal projections within same LGd lamina are unusual in these large macropodids. The number of the terminal bands reaches ten in the grey kangaroo–four from the contralateral eye and six from the ipsilateral eye. The pademelon LGd is unusual in that it shows intraspecies variation with some animals displaying five ipsilateral terminal bands and others only four. The results are discussed in comparison with the patterns of LGd organization observed in other mammalian lines, placental and marsupial. We conlude that LGd lamination and the segregation of retinal inputs to the LGd in marsupials are likely to be the result of evolutionary factors which differ from those which have produced ocular segregation and complex lamination in several lines of placental mammals.
Quantitative light and scanning electron microscopic study of the developing auditory organs in the bullfrog: Implications on their functional characteristics
Authors: Shofner William P. , Feng Albert S.
Published: January 2005

During postmetamorphic development in the bullfrog, there is a downward shift in the distributions of best excitatory frequencies (BEFs) of the three populations of primary auditory fibers. This decrease in BEF distribution suggests that concurrent morphological changes occur in the peripheral auditory system during postmetamorphic growth.

The postmetamorphic development of the auditory organs in the bullfrog was quantitatively investigated with light and scanning electron microscopy. In the basilar papilla, there are dramatic increases in the lumen volume, contact membrane area, and mass of the tectorial membrane (TM). The area of the sensory epithelium and the total number of hair cells also increase slightly. In the amphibian papilla, the mass of the TM is spatially graded in a step‐wise fashion along the length of the organ in both juvenile and adult bullfrogs, but there is an increase in the absolute mass of the TM throughout the papilla with age. The height of the tallest stereocilia of the predominant hair cell type systematically decreases caudally in the juvenile amphibian papilla, but is uniform throughout the adult papilla. The increase in stereociliary height in the caudal end of the organ presumably results in a decrease in stereociliary stiffness with postmetamorphic age. The length of the amphibian papilla sensory epithelium and the number of hair cells also increase during postmetamorphic development. Theoretically, the observed morphological changes alter the micromechanical tuning properties of the auditory organs so that there is a decrease in the BEFs of the auditory fibers that innervate the two papillae.
Retinal synapses of the cat medial interlaminar nucleus and ventral lateral geniculate nucleus differ in size and synaptic organization
Authors: Mize R. Ranney , Horner Linda H.
Published: January 2005

The retinal terminals of the medial interlaminar nucleus (MIN) and ventral lateral geniculate nucleus (VLG) have been examined quantitatively to determine if there are morphological differences in their synaptic ultrastructure which reflect their distinctive physiologies. The cross‐sectional area and density (number per unit area) of synaptic contact zones with conventional and presynaptic dendrites (F2 profiles) were measured for each retinal terminal. The densities of F2 presynaptic dendrites and F1 flattened vesicle axon terminals were also measured.

Retinal terminals in MIN were often large (mean size= 2.7 μm2 area) and had a high density of synaptic contacts (0.14 per μm surface area) with conventional dendrites, presynaptic dendrites, and dendritic spines. A high density of F2 presynaptic dendrites (0.08 per μm2 area) was found in MIN. F1 axon terminals were also found frequently (0.04 per μm2). MIN retinal terminals were often organized in glomeruli like those of the dorsal lateral geniculate nucleus.

The retinal terminals in VLG were almost always small (mean size= 0.94 μm2 area), although they also had a high density of synaptic contacts (0.17 per μm surface area). They frequently synapsed on small dendrites and dendritic spines and less frequently on large dendrites. Unlike MIN, retinal terminals in VLG rarely contacted F2 presynaptic dendrites which were much less frequent in VLG (0.01 per μm2 area). Like MIN, VLG contained numerous F1 axon terminals (0.06 per μm2 area). No typical retinal glomeruli were found in VLG.

These results show that MIN, which contains many Y cells, has a population of large retinal terminals and many F2 presynaptic dendrites. VLG, which apparently has only W cells, contains only small retinal terminals and has fewer F2 presynaptic dendrites. Both have a high density of F1 flat vesicle axon terminals.
Comparative distribution of bombesin/GRP‐ and substance‐P‐like immunoreactivities in rat hypothalamus
Authors: Panula Pertti , Yang Hsiu‐Ying T. , Costa Erminio
Published: January 2005

Immunohistochemical localization of bombesin/gastrin‐releasing peptide (GRP)‐like immunoreactivity (BN/GRP‐LI) and substance P‐like immunoreactivity (SP‐LI) in consecutive sections of rat hypothalamus was studied. Bombesin/GRP‐like immunoreactivity in the hypothalamus was partially characterized by gel filtration chromatography followed by radioimmunoassay.

In the hypothalamus, SP‐LI was more widely distributed than BN/GRP‐LI. Only the anterior and medial parvocellular parts of the nucleus paraventricularis and the nucleus suprachiasmaticus contained numerous cell bodies which exhibited BN/GRP‐LI. Neurons in these areas did not exhibit SP‐LI. In contrast, cell bodies exhibiting SP‐LI were numerous in the nucleus preopticus medialis and lateralis, nucleus anterior, nucleus ventromedialis and dorsomedialis, nucleus lateralis, nucleus arcuatus, and nucleus premamillaris ventralis and dorsalis. Only occasional cell bodies in these areas exhibited BN/GRP‐LI. It is concluded that the neuronal systems in the hypothalamus containing BN/GRP‐LI and SP‐LI are separate, though the terminal fields in many areas overlap.

Two peaks of BN/GRP‐LI were detected after gel filtration chromatography from extracts of the rat nucleus paraventricularis. The high molecular weight form coeluted with synthetic GRP(1‐27), and the small molecular weight form eluted after synthetic bombesin. Thus, the endogenous BN/GRP‐LI is probably not authentic bombesin.
Intracellular marking of physiologically characterized cells in the ventral cochlear nucleus of the cat
Authors: Rouiller E. M. , Ryugo D. K.
Published: January 2005

In the cat ventral cochlear nucleus, separate neuronal classes have been defined based on morphological characteristics; physiologically defined unit types have also been described based on the shape of post‐stimulus‐time‐histograms in response to tone bursts at characteristic frequency. The aim of the present study was to address directly the issue of how morphological cell types relate to physiological unit types. We used intracellular injections of horseradish peroxidase to stain individual neurons after their response characteristics were determined by intracellular recordings. The maintenance of a continuous negative resting potential, the correspondence of the calculated position of the electrode tip at the time of injection to the location of the stained neuron, and the similarity of response properties collected before and after the injection provide evidence that the injected, stained, and recovered neuron corresponds to the functionally defined unit.

In the region around the nerve root in the anteroventral cochlear nucleus, two “primarylike” and one “primarylike with notch” units were “bushy” cells. “Bushy” cells are characterized by primary dendrites arising from one hemisphere of the soma and ramifying repeatedly to produce their bushy dendritic arbor. In this same region, the “chopper” and two “on” units were also “bushy” cells. In the posteroventral cochlear nucleus, the “chopper” unit was a “stellate” cell and the “on” unit was an “octopus” cell.

These results are partially consistent with previous conclusions based on correlations established between the regional distribution of physiological unit types and morphological cell types. More importantly, they confirm and extend recent intracellular marking data (Rhode et al., ′83b). If our classification schemes have functional significance, we are left with the conclusion that the distinction between “bushy” and “stellate” cells in the auditory nerve root region of the ventral cochlear nucleus does not correspond in any simple way to distinctions between physiological unit types. More than one morphological cell type can exhibit the same particular response pattern, and the same morphological cell type can exhibit several different response patterns.
Development of the cochlear innervation of the dorsal cochlear nucleus of the hamster
Authors: Schweitzer Laura , Cant Nell Beatty
Published: January 2005

The development of cochlear fibers and terminals in the dorsal cochlear nucleus of the hamster was studied with light and electron microscopic techniques. Like the dorsal cochlear nucleus of most other mammals, the dorsal cochlear nucleus of the adult hamster is a laminated structure. Three distinct layers can be identified in cresyl‐violet‐stained sections: the molecular layer, the fusiform cell layer, and the deep layer. The deep layer consists of a superficial zone, free of large cell bodies, and a deep zone which contains the somas of giant cells. Horseradish peroxidase and degeneration studies reveal that the cochlear fibers ramify throughout the deep and fusiform cell layers of the adult hamster but do not enter the molecular layer. In the electron microscope, three types of terminals that contact the fusiform and the giant cells can be distinguished. Only one type of terminal (type LR) degenerates after cochlear ablation and is, therefore, thought to be of cochlear origin. Type LR terminals are found throughout the deep and fusiform cell layers and contact the somas of giant and fusiform cells, as well as their intermingled dendrites in the deep layer.

In Golgi‐impregnated material, cochlear fibers are not found in the dorsal cochlear nucleus of the neonatal hamster, although they have entered the ventral cochlear nucleus. Ingrowth of cochlear fibers into the dorsal cochlear nucleus occurs over the first postnatal week and one‐half. A spatial gradient is evident during the ingrowth of the fibers in that they invade the dorsomedial parts of the dorsal cochlear nucleus before they invade the ventrolateral parts. In all parts of the nucleus, the fibers enter the deepest layer and grow progressively more superficially. In the electron microscope, the first appearance of type LR terminals at each depth lags behind the ingrowth of the fibers by about two days.

In hamsters, fibers from the basal turns of the cochlea terminate in the dorsomedial dorsal cochlear nucleus, while fibers from the apical turns terminate in the ventrolateral dorsal cochlear nucleus (DCN). The dorsomedial to ventrolateral gradient in the ingrowth of the cochlear fibers into the DCN indicates that the fibers from the basal turn are the first to arrive. Several components of the mammalian cochlea have been shown to mature at the base of the cochlea before they mature at the apex. The present study suggests that maturation gradients in the cochlear nucleus parallel those observed in the cochlea.
On the fate of sympathetic and sensory neurons projecting into a neuroma of the superficial peroneal nerve in the cat
Authors: Jänig W. , McLachlan Elspeth
Published: January 2005

Cell bodies of sympathetic and sensory axons projecting via the superficial peroneal (SP) nerve supplying hairy skin of the distal hindlimb have been labeled retrogradely with horseradish peroxidase (HRP) on both sides of three cats in which the left SP nerve had been cut and ligated about 5 months previously. Three SP nerves from unoperated cats have also been studied. The location, size, and numbers of labeled somata have been determined from serial sections of lumbosacral dorsal root and sympathetic chain ganglia after standard histochemical processing. The numbers of myelinated fibers in each nerve have also been counted.

The segmental distributions of both sympathetic and sensory cell bodies were identical bilaterally in each operated animal, but the number of labeled neurons was reduced on the lesioned side. There were only about 31% of sympathetic and about 51% of sensory somata relative to the numbers on the contralateral side. The average total number of neurons labeled from SP nerves in unoperated animals was about 8% higher than on the control side of operated animals. The average number of myelinated fibers in the neuromatized nerves was not reduced with respect to that in the contralateral nerve and both of these were not significantly different from the number in unoperated animals.

The dimensions of samples of labeled sympathetic and sensory somata were reduced on the side with the neuroma, both in comparison with the contralateral side and with unlabeled neurons at the same levels. The mean cross‐sectional area of profiles of sympathetic ganglion cells was 76% of the control; of sensory ganglion cells, 65% of the control.

Assuming that HRP labeling was not impaired, we conclude that large numbers of neurons with unmyelinated axons had degenerated in the neuromatized cutaneous nerves.
Immunoreactive leu‐enkephalin in the monkey hypothalamus including observations on its ultrastructural localization in the paraventricular nucleus
Authors: DiFiglia Marian , Aronin Neil
Published: January 2005

The distribution of immunoreactive leu‐enkephalin neurons and fibers in the monkey hypothalamus, including ultrastructural localization in the paraventricular nucleus (PVN), was examined with the peroxidase‐antiperoxidase immunocytochemical method. Immunoreactive leu‐enkephalin cell bodies and fibers were present in the PVN, the region of the dorsal nucleus and nucleus of the anterior commissure, the dorsomedial nucleus, ventro‐medial nucleus, and lateral hypothalamus.

Within the PVN labeled cells were found mostly in the medial parvocellular region, and a smaller proportion including some large cells was present in the lateral, and dorsolateral zones. Immunoreactive neurons contained numerous large granular vesicles (LGV) which ranged from 63 to 235 nm in size, suggesting that at least some enkephalin‐containing neurons belong to the population of neurosecretory cells. Positive neurons were postsynaptic to four types of unlabeled axon terminals. Leu‐enkephalin‐containing fibers (some of which were myelinated) and boutons contained small clear vesicles and numerous LGV. Axon terminals made synaptic contacts with the cell bodies, primary and distal dendrites of unlabeled neurons. The findings show that enkephalin‐containing neurons in the PVN integrate a variety of neuronal inputs and provide morphological evidence for the inhibiting influence of enkephalins on the firing rate of PVN neurons. It may be speculated that the effects of opioids on the release of vasopressin and other substances possibly originating from PVN neurons may be regulated in part within the nucleus by locally synapsing axons belonging to enkephalin‐containing neurons.
Counts of axons in electron microscopic sections of ventral roots in lampreys
Authors: Rovainen Carl M. , Dill Dorothy A.
Published: January 2005

The number of motoneurons in the lamprey spinal cord was estimated by counting axons in electron microscopic sections of ventral roots. Physiologically identified and marked motoneurons had one axon each in an ipsilateral ventral root. The corresponding axons in sections were unmyelinated, individually ensheathed, and 2–20 μm in diameter. Lampreys lack an organized sympathetic nervous system, but a minor and variable population of small axons with dense‐cored vesicles was also present in ventral and dorsal roots. The estimated numbers of motor axons per ventral root in adult Ichthyomyzon unicuspis and I. castaneus were 70.6 ± 9.3 (mean ± S.D), in adult landlocked Petromyzon marinus 100.1 ± 15.0, and in large ammocoetes of anadromous Petromyzon marinus 106.8 ± 14.3. The total estimated numbers of myotomal and fin motoneurons were as many as 13,000 in the spinal cord of adult Ichthyomyzon and 24,000 in adult Petromyzon.
Ipsilateral cortical connections from the second and fourth somatic sensory areas in the cat
Authors: Burton H. , Kopf E. M.
Published: January 2005

The ipsilateral corticocortical connections of the second and fourth somatic sensory areas (SII and SIV) were traced with the aid of anterograde or retrograde axonal transport techniques involving horseradish peroxidase conjugated to wheat germ agglutinin (HRP‐WGA) or tritiated amino acids. The injections were placed into physiological defined components of the body representation in SII or SIV. The results from cases with localized injections into SII showed precise topographically organized, reciprocal connections with SI and motor cortex area 4. The distribution of connections in SI included areas 3a, 3b, and 1–2. A uniform pattern of cell and fiber labeling was seen across area 3b and 1 within the zones that were homotypical to the injection site in SII as though only a single representation of the cutaneous surface of the body existed in SI. Intrinsic connections within SII were also topographically arranged. Additional areas found to be interconnected with SII included, in decreasing order of density: area 5, insula, perirhinal cortex (area 36), and ventrolateral orbital cortex. SII connections with area 6 were seen only in the region of the lateral bank of the presylvian sulcus. There may be interconnections between SII and SIV but these were from possible local intrinsic connections in the AEG. The results from injections involving SIV showed reciprocal connections with area 5, the suprasylvian fringe, insula, dorsolateral orbital area, and area 6. The densest connections for SIV were with area 5. No topography was noted in the connections for SIV.
Distribution of 5‐hydroxytryptamine (serotonin) in the brain of the teleost Gasterosteus aculeatus L.
Authors: Ekström Peter , Van Veen Theo
Published: January 2005

The distribution of serotoninergic neurons in the brain of the three‐spined stickleback was demonstrated with the indirect peroxidase‐antiperoxidase (PAP) immunohistochemical method with antibodies against serotonin. Serotoninergic perikarya were demonstrated in the brainstem reticular formation (nucleus raphe dorsalis, nucleus raphe medialis, and nucleus tegmenti dorsalis lateralis) and in the periventricular ventral thalamus and hypothalamus (nucleus ventromedialis thalami, nucleus posterioris periventricularis, nucleus recessus lateralis, and nucleus recessus posterioris). After pharmacological pretreatment of the animals with a monoamine oxidase inhibitor, serotoninergic perikarya were also visualized in area praetectalis and in the medial brainstem, caudal to nucleus raphe medialis. Whereas the cell groups of the brainstem give rise to both ascending and descending pathways, it was not possible to analyze the distribution of efferent projections from the diencephalic cell groups. Distribution of serotoninergic axons showed marked regional differences. Only scattered varicose fibers were demonstrated in the cerebellum, the facial lobes, and the lateral line lobes. In the mesencephalon, the dorsal periventricular tegmentum and the central gray receive only small numbers of serotoninergic axons, while torus semicircularis and the visual layers of tectum opticum are profusely innervated. In the diencephalon, the hypothalamus and ventral thalamus generally display the highest density of serotoninergic axons. Exceptions are found in nucleus glomerulosus and the ventromedial portion of lobus inferioris, where densities are low. In the telencephalon, the density of serotoninergic axons is very high in area dorsalis pars medialis and pars lateralis dorsalis, but low in area dorsalis pars dorsalis and pars lateralis ventralis, and intermediate in area ventralis.
Callosal and intrahemispheric connectivity of the prefrontal association cortex in rhesus monkey: Relation between intraparietal and principal sulcal cortex
Authors: Schwartz Michael L. , Goldman‐Rakic Patricia S.
Published: January 2005

Horseradish peroxidase (HRP) histochemistry and double labeling with the fluorescent dyes nuclear yellow (NY) and fast blue (FB) were used to examine and compare the laminar and tangential arrangement of ipsilateral (associational) and contralateral (callosal) neurons and their relative density in three regions of prefrontal granular cortex: Walker's area 46 (principal sulcus), area 8A (superior limb of the arcuate sulcus), and area 11 (lateral orbital sulcus). In all three prefrontal regions, neurons with ipsilateral projections were labeled following injections of tracers into the intraparietal sulcus (IPS) and neurons with callosal projections were sequentially or simultaneously labeled with injections into the contralateral principal sulcus (PS). Quantitative analysis indicates that associational and callosal neurons in prefrontal cortex are distinct cell populations with strikingly similar organization including (1) common topography;(2) common laminar positions in layers III, IV, and V; (3) two‐ to three‐fold higher densities in supragranular than infragranular layers; (4) common morphologies including a high proportion of nonpyramidal soma in the deeper cortical layers; (5) common uneven tangential distribution reminiscent of the interdigitation of their terminal fields; and (6) common subpopulations differing on the basis of terminal arbors. These findings indicate that the posterior parietal cortex and the prefrontal cortex form part of an integrated neural system important for spatiotemporal behaviors.
The Timm‐stained hippocampus of the European hedgehog: A basal mammalian form
Authors: West Mark J. , Gaarskjaer Frank B. , Danscher Gorm
Published: January 2005

A quantitative and qualitative description has been made of the components of the Timm‐stained hippocampus of the European hedgehog. While the laminar organization and the relative size of the major subdivisions of the hippocampus (i.e., area dentata, Ammon's horn, and subiculum) are similar to those of the albino laboratory rat, the relative proportions and the staining characteristics of some of the components of the subdivisions are different. The differences are particularly evident in Ammon's horn where regions are poorly differentiated along the dentatosubicular axis and the mossy fiber zone is relatively extensive. The description characterizes a hippocampal form that can be used as a basal reference in comparative studies of the mammalian hippocampus.
Relationship of the vestibular hair cells to magnetic particles in the otolith of the guitarfish sacculus
Authors: Vilches‐Troya J. , Dunn R. F. , O'Leary D. P.
Published: January 2005

Magnetite particles were systematically localized within the otolithic mass as a conspicuous curved band in the most ventral region of the guitar‐fish sacculus. The magnetite band overlaid two separated segments of neuroepithelium in the macula, a long segment oriented parallel to the longitudinal body axis, and a short segment oriented in a transverse plane. The exogenous magnetite particles differed from the endogenous otoconia both in their capacity of orienting to magnetic fields, and their difference in mass due to the higher atomic weight of iron. In addition to the normal gravistatic function of the sacculus, two additional receptor functions are hypothesized based upon the differences between the endogenous and exogenous otoconia. A geomagnetic field could induce magnetite displacements detectable by the hair cells for purposes of geomagnetic orientation. Alternatively, the greater atomic weights of magnetite, relative to that of otoconia, could result in gravitational and linear acceleration, which differed in different regions of the macula.
A quantitative assessment of the development of synapses and neurons in the visual cortex of control and undernourished rats
Authors: Warren M. A. , Bedi K. S.
Published: January 2005

Male rats undernourished from the 18th day of gestation until 100 days of age were nutritionally rehabilitated until 200 days of age. Six control and six experimental rats at each of 12, 25, 50, 100, and 200 days of age were killed by perfusion with buffered 2.5% glutaraldehyde. Pieces of visual cortex from each rat were postfixed in osmium tetroxide and embedded in resin. Stereological procedures at the light and electron microscope levels were used to estimate the synapse‐to‐neuron ratios in cortical layers II to IV.

There were no statistically significant differences in the synapse‐to‐neuron ratio between control and undernourished rats at 12, 25, and 50 days of age. However 100‐day‐old undernourished rats had a significant deficit in this ratio compared to age‐matched controls. Despite this, 200‐day‐old nutritionally rehabilitated rats were found to have, on average, 23% more synapses per neuron than controls.

In both the control and the undernourished groups the synapse‐to‐neuron ratio increased to a peak by 50 days of age. This was followed by a significant fall in the ratio by 100 days of age. Although there was no further change in the control rats, the experimental group showed a substantial increase in the ratio by 200 days of age. This latter increase appeared to be related to the period of nutritional rehabilitation.
Cartwheel neurons of the dorsal cochlear nucleus: A Golgi‐electron microscopic study in rat
Authors: Wouterlood Floris G. , Mugnaini Enrico
Published: January 2005

Cartwheel neurons in rat dorsal cochlear nucleus (DCN) were studied by Golgi impregnation‐electron microscopy. Usually situated in layers 1–2, cartwheel neurons (10–14 μm in mean cell body diameter) have dendritic trees predominantly in layer 1. The dendrites branch at wide angles. Most primary dendrites are short, nontapering, and bear only a few sessile spines. Secondary and tertiary dendrites are short, curved, and spine‐laden. The perikaryon forms symmetric synapses with at least two kinds of boutons containing pleomorphic vesicles. The euchromatic nucleus is indented and has an eccentric nucleolus. The cytoplasm shows several small Nissl bodies, a conspicuous Golgi apparatus, and numerous subsurface and cytoplasmic cisterns of endoplasmic reticulum with a narrow lumen, joined by mitochondria in single or multiple assemblies. In primary dendrites mitochondria are situated peripherally, while in distal branches they become ubiquitous and relatively more numerous. Dendritic shafts usually form symmetric synapses with boutons that contain pleomorphic vesicles. The majority of the dendritic spines are provided with a vesiculo‐saccular spine apparatus. All dendritic spines have asymmetric synapses. Most of these are formed with varicosities of thin, unmyelinated fibers (presumably axons of granule cells) running parallel to the long axis of the DCN or radially. These varicosities contain round, clear synaptic vesicles. On the initial axon segment few symmetric synapses are present. The axon acquires a thin myelin sheath after a short trajectory. Cartwheel neurons outnumber all other neurons in layers 1–2 (with the exception of granule cells), and presumably correspond to type C cells with thinly myelinated axons described by Lorente de Nó. The axons of these neurons provide a dense plexus in the superficial layers without leaving the DCN. The possible functional role of cartwheel neurons is discussed.
Identifiable neurons in the locust central nervous system that react with antibodies to serotonin
Authors: Tyrer N. Mark , Turner Jon D. , Altman Jennifer S.
Published: January 2005

A detailed account is given of a number of neurons in the locust central nervous system that react with antibody raised to serotonin‐albumin complex. The antibody was applied to a series of frozen sections of locust ganglia and visualized by using the peroxidase immunohistochemical procedure. The neurons described include certain afferents and their related neuropiles, a small number of efferents and several systems of interneurons, some of which are segmentally repeated, some run from the brain through the whole nerve cord, while others are confined to the brain. It has been possible to identify many of the neurons from previous descriptions obtained from cobalt, Golgi, and osmium ethyl gallate methods.
Long‐term effect of mossy fiber degeneration in the rat
Authors: Anderson W. A. , Flumerfelt B. A.
Published: January 2005

Mossy fiber‐deafferentated rats (20) were permitted to survive from 34 to to 120 days and subsequently examined following Golgi‐Cox preparation or after processing for electron microscopy. The primary response to mossy fiber deafferentation was transneuronal degeneration of the granule cell system. Morphological evidence is provided that suggests that the mossy fiber varicosity plays an important role in the fragmentation and removal of the granule cell digitiform dendrite. Computer‐assisted image analysis of Golgi‐impregnated Purkinje cells indicated significant losses in both smooth branch and spiny branchlet numbers following loss of the mossy fiber input. Ultrastructural examination revealed that a secondary transneuronal degeneration occurred within the dendritic arborization of both Purkinje cells and molecular layer interneurons. Although an overall reduction in the number of dendritic spines occurred along the terminal branchlets following mossy fiber deafferentation, several of the existing spines underwent marked changes in length, with some elongating to more than twice their size. By increasing the length of their spines, denervated Purkinje cells may acquire new synaptic contacts.
Cerebellar cortical efferent fibers in the North American opossum, Didelphis virginiana. I. The anterior lobe
Authors: Klinkhachorn P. S. , Haines D. E. , Culberson J. L.
Published: January 2005

The distribution of cerebellar corticonuclear and corticovestibular fibers from the anterior lobe of the North American opossum, Didelphis virginiana, was studied using the Fink and Heimer (1967) technique.

Corticonuclear fibers from medial areas of anterior lobe project into the medial cerebellar nucleus (NM) in a topographically organized manner. Fibers from lobules II and III enter rostral and rostrodorsal NM, while those from lobules IV and V terminate in progressively more caudal parts of the nucleus. Collectively the terminal fields in NM for axons from lobules II–V occupy about the rostral two–thirds of the nucleus.

Those areas of lobules II‐V of opossum that project into NM presumably correspond to zone A of cat and primate. Cerebellar corticovestibular fibers originate from cortex located immediately lateral to areas projecting to NM. The predominance of corticovestibular projections into the lateral vestibular nucleus suggests the presence of a B zone and identifies its points of interface with the A zone. The results further suggest that zones A and B overlap at their respective margins. In contrast to other mammals studied to date, zones A and B of opossum anterior lobe are comparatively wide. Corticonuclear fibers to anterior and posterior interposed nuclei and to the lateral cerebellar nucleus (NL) originate from relatively narrow lateral portions of anterior lobe. These results also suggest that the intermediate cortex of opossum anterior lobe is not clearly divisible into individual zones C1, C2 or C3. The cortical area that innervates NL is very narrow and presumably corresponds to zone D of other forms.
A developmental gradient of dendritic loss in the avian cochlear nucleus occurring independently of primary afferents
Authors: Parks Thomas N. , Jackson Hunter
Published: January 2005

Cochlear nerve axons and their target neurons in nucleus magnocellularis (NM) of the chicken undergo extensive parallel structural transformations during development. Between embryonic days 12 and 17 (E12–E17), each immature highly branched axon condenses into a mature calyxlike ending applied to a single NM neuron. Simultaneously, NM neurons are transformed from multipolar cells with many long dendrites into spherical unipolar neurons with only an axon. We tested the hypothesis that cochlear nerve input is necessary for the transformation of NM cells by surgically destroying one otocyst on E3, thereby preventing formation of the nerve. Nucleus magnocellularis neurons from embryos at E11–E12, E13–14, and E17–18 were stained by horseradish peroxidase injected into their axons or by a Golgi‐Hortega method. In camera lucida drawings, the number of dendrites on each cell was counted and the cell's position along the posteriorto‐anterior and lateral‐to‐medial axes of the nucleus quantified. At E11–12, neurons throughout NM on both the deafferented and normally innervated sides of the brain have about ten dendrites. At E13–14, there is a steep spatial gradient in dendritic number bilaterally; cells at anteromedial positions have about two dendrites, while cells in posterolateral positions have an average of nine dendrites. By E17–18, only 14% of the neurons on either side have a dendrite, and these cells are evenly distributed throughout the nucleus. We conclude that cochlear nerve axons are not required for normal spatio‐temporal gradients of dendritic loss, even though the absence of these axons causes severe atrophic changes in NM. Thus, it appears that the characteristic forms of the afferent axon and target neuron in this system must develop in one of two ways. Either NM cells control the structural differentiation of their cochlear nerve afferents, or the forms of axon terminals and their target cells develop independently. These alternative, hypotheses can be evaluated experimentally.
The visual field representation of the rat ventral lateral geniculate nucleus
Authors: Nagata Tetsu , Hayashi Yasumasa
Published: January 2005

The representation of the visual field in the ventral lateral geniculate nucleus (LGNv) was studied in rats anesthetized with urethane by recording the response of single units to visual stimulation. Receptive fields of LGNv units were plotted on a campimeter, 60 cm in diameter, which was placed 30 cm from the contralateral eye. LGNv neurons responded mainly to stimulation of the contralateral eye with on‐tonic characteristics. Few neurons responded only to stimulation of the ipsilateral eye and no binocular interaction was observed.

Retinotopic organization was clearly seen in the LGNv; the nasal visual fields were represented dorsally, the temporal fields ventrally, and the upper to lower visual fields were in the rostrolateral to caudomedial parts of the LGNv. A given point in the visual field is represented along a line running through the LGNv in a rostrocaudal direction.

Almost the entire horizontal extent of the contralateral visual field was represented in the LGNv, whereas vertically the visual field between 40° above and 20° below the distribution axis was represented. The major axis of the strip of the visual field containing all the RF centers, which is referred to as the distribution axis, inclined nasally up and temporally down at an angle of 10.4° to the 0° horizontal meridian line. The representation of the distribution axis in the retina was in accordance with the major axis of retinal ganglion cell distribution (Fukuda, 1977; Schober and Gruschka, 1977).
Somatosensory thalamocortical connections in the racoon: An HRP study
Authors: Warren Susan , Pubols Benjamin H.
Published: January 2005

In the North American raccoon (Procyon lotor), representations of the glabrous surfaces of the hand digits are found within separate subnuclei of the thalamic ventrobasal complex (VB) and on separate subgyri of the somatosensory cortex (SmI). In the present study, the retrograde transport of horseradish peroxidase from SmI to VB was utilized to study relationships between physiologically identified cortical subgyri and somatotopically corresponding thalamic subnuclei.

Single large or multiple small injections confined to a single gyral crown led to retrograde labeling of large groupings of cells filling the entire VB subnucleus for the appropriate digit. In the aggregate, the regions of label appeared as thin, wedge‐shaped sheets extended in the dorsoventral and anteroposterior dimensions, but flattened mediolaterally, and curving to form a laterally directed convexity; these appear to correspond to the lamellae of monkey VB described by others. These large injections led to labeling of approximately 80% of all large (18–30‐μm diameter) cells within the lamella. Single, small, focal injections of a gyral crown led to variable amounts of labeling, ranging from an entire digital lamella to only a small focal cluster of cells. No evidence was obtained for the existence of anteroposteriorly extending “rods” of cells, as reported in primates. Finally, there was a sparse, but consistent labeling of cells of the posterior nuclear group (Po) following gyral crown injections.

These results are in agreement with expectations based on prior electrophysiological studies of raccoon VB and SmI, as well as prior anatomical studies of thalamocortical relationships.
Anterograde degeneration in the superior colliculus following kainic acid and radiofrequency lesions of the macaque pulvinar
Authors: Bender D. B. , Baizer J. S.
Published: January 2005

Several studies have reported behavioral deficits following thermocoagulation of the primate pulvinar. However, these deficits may have resulted from damage to corticotectal fibers as they pass through the pulvinar. To evaluate this possibility and to determine whether kainic acid can be used to destroy pulvinar cells without damaging corticotectal fibers, we compared anterograde degeneration in the superior colliculus following kainic acid and radiofrequency lesions of the pulvinar. Kainic acid injections into the pulvinar produced total loss of neuronal perikarya within the inferior and lateral pulvinar. Four to 7 days following the kainic acid lesions, terminal and fiber degeneration within the superior colliculus was no greater than that produced by control injections of saline. By contrast, thermocoagulation lesions of the inferior and lateral pulvinar produced dense fiber and terminal degeneration throughout the superficial and intermediate layers of the superior colliculus. We conclude that whereas thermocoagulation of the pulvinar severely damages the corticotectal tract, kainic acid lesions spare these fibers of passage. Thus kainic acid lesions should provide an effective tool for studying the functional significance of the pulvinar.
Somatic and visceral primary afferents in the lower thoracic dorsal root ganglia of the cat
Authors: Cervero F. , Connell Lynne A. , Lawson Sally N.
Published: January 2005

Anterograde transport of horseradish peroxidase (HRP) through somatic and visceral nerves was used to estimate the proportions of somatic and visceral dorsal root ganglion (DRG) cells of the lower thoracic ganglia of the cat. A concentrated solution of HRP was applied for at least 5 hours to the central end of the right greater splanchnic nerve and of the left T9‐intercostal nerve of adult cats. Some animals remained under chloralose anaesthesia for the duration of the HRP transport time (up to 53 hours) whereas longer HRP application and transport times (4–5 days) were allowed in animals that recovered from barbiturate anaesthesia. Visceral DRG cells were found in approximately equal numbers in all ganglia examined (T7–T11). Population estimates were obtained for the T8 and T9 ganglia where visceral DRG cells were found to be 6.2% (T8) and 5.2% (T9) of the total cell population. In contrast, somatic DRG cells were found in large numbers in the ganglia examined (T8 and T9) where they amounted to over 90% of the cell population. Measurement of cross‐sectional areas and estimates of cell diameters of the DRG cells showed greater proportions of large somatic cells (diameter > 40 μm) than of large visceral cells. Similar distributions of cell size were found for both somatic and visceral DRG cells with diameters less than 40 μm.

These results show that the proportion of visceral afferent fibres in the dorsal roots that mediate the spinal cord projection of the splanchnic nerve is very small. Since viscerosomatic convergence in the thoracic spinal cord is very extensive, the present results suggest considerable divergence of the visceral afferent input to the central nervous system.