bluuebunny/crossref_metadata_2025 huggingface dataset:
Parasol and midget ganglion cells of the human retina
Authors: Rodieck R. W. , Binmoeller K. F. , Dineen J.
Published: January 2005

Golgi‐impregnated ganglion cells were studied in two flat‐mounted human retinas. A number of different morphologic forms were observed, and those showing a thickly branching dendritic field with terminals that stratified within a narrow zone of the inner plexiform layer were selected for further investigation. When the dendritic field diameter of these cells was plotted against distance from the fovea, the scatter diagram showed two distinct clusters. At any given eccentricity, there was no overlap between the cell group with large dendritic fields and the group with small dendritic fields. Those with the larger dendritic fields also tended to have larger somas and thicker axons than the group with the smaller dendritic fields.

The dendritic fields of both groups tended to be elongated, and the orientation and degree of this elongation were quantified by determining the best‐fitting ellipse for each dendritic field. The degree of elongation was independent of eccentricity. The orientation of the dendritic field (major axis of the ellipse) of a cell did not appear to be independent of its position on the retina. To test whether the major axes tended to be directed toward any particular point on the retina, the positions of the cells on the retinal flat mount were transformed to relative positions on the retinal hemisphere, and the orientations of the dendritic fields were expressed in a spherical coordinate system for this hemisphere. A search was made for the position on the hemisphere which minimized the mean square deviation of the orientations from this point. The group with the large dendritic fields showed a significant tendency to be radially oriented toward a specific location on the retinal hemisphere, and that location lay within a few degrees of the fovea. Leventhal and Schall ('83) have reported a similar finding for ganglion cells of the cat retina. For the group with small dendritic fields, the retinal location that minimized the mean square deviation was also near the fovea; however, the set of orientations showed no greater tendency for mutual alignment than did a randomized set.

The cell group with the large dendritic fields appears to correspond to Dogiel's (1891) type II cells, to Polyak's ('41) parasol cells, to the A cells of the monkey retina described by Leventhal et al. ('81), observed following HRP injection to the magnocellular layer of the LGN, and to the Pα cells of the monkey retina, observed by Perry and Cowey ('81), following HRP uptake by cut axons of the optic nerve.

The cell group with the smaller dendritic fields appears to correspond to Dogiel's type III cells, to Polyak's midget ganglion cells, and in the monkey retina to the B cells of Leventhal et al., observed following HRP injection to the parvocellular laminae of the monkey LGN, and to the Pβ cells of Perry and Cowey.
Heterogeneous properties of segmentally homologous interneurons in the ventral nerve cord of locusts
Authors: Pearson K. G. , Boyan G. S. , Bastiani M. , Goodman C. S.
Published: January 2005

The G, B1, and B2 neurons are three prominent interneurons located in adjacent segmental ganglia in the central nervous system of locusts. Previous studies on the adult nervous system have shown that each of these cells has its own distinctive morphology and responsiveness to auditory input. Previous studies on the embryonic nervous system have described the lineage and development of one of these cells, the G neuron, in the mesothoracic (T2) segment. In this paper it is shown that the G, B1, and B2 neurons are segmental homologues in that they arise from equivalent lineages during embryogenesis in the T2, T3, and A1 segments, respectively. Each cell arises (along with its identified sibling neuron) from the division of the second ganglion mother cell of neuroblast 7–4. The segment‐specific morphology of the G homologues was determined in the T3 and A1 segments between 60–70% of embryonic development, and their identity was established as the adult B1 and B2 neurons by comparing the distinctive cell‐specific features of their morphology between embryo and adult. Although all three neurons display striking morphological differences, they all share certain structural features in common, including the location of their primary axons and neurites in specific tracts in the neuropil.

By recording intracellularly from the main neurites of the G, B1, and B2 neurons, clear differences were found in the synaptic inputs each of the neurons receives and the synaptic outputs each makes. For example, G and B2, but not B1, receive direct monosynaptic input from the descending contralateral movement detector (DCMD) interneurons and from auditory afferents; B1, but not B2, connects directly to G; and B2, but not B1 or G, connects directly to flight motoneurons. The main conclusion from these observations is that lineally equivalent neurons in different segments can develop similar primary structures but quite different secondary morphologies and synaptic connections. How these segment‐specific differences arise during embryogenesis remains unknown.
Morphology and laminar distribution of electrophysiologically identified cells in the pigeon's optic tectum: An intracellular study
Authors: Hardy Olivier , Leresche Nathalie , Jassik‐Gerschenfeld Dora
Published: January 2005

The responses of 65 cells to electrical stimulation of the contralateral optic nerve were intracellularly recorded in the pigeon optic tectum by using micropipettes filled with a solution of horseradish peroxidase. Nineteen of them were successfully labeled. Microscopic examination of the filled cells shows that our sample includes six pyramidal, ten ganglion, two stellate, and one, bipolar horizontal cells. Thus, pyramidal and ganglion neurons constitute the most numerous types of cells in our sample. Pyramidal cells were located in layer II but mostly in its non‐retinorecipient part, and they had restricted ascending dendritic trees oriented orthogonal to the tectal lamination. Ganglion cells were located in layer in with one exception, which was in sublayer IIi. These cells had non‐oriented dendritic trees which ramify over considerable distances. Terminal dendritic branches from a number of pyramidal and ganglion cells extended superficially well within the region of optic fibers termination. In our study, ganglion cells constituted the efferent tectal elements. Pyramidal cells responded to optic nerve stimulation with a pure EPSP, with an EPSP‐IPSP sequence, or with a pure IPSP. Ganglion cells always exhibited an IPSP either alone or preceded by an EPSP. Stellate and bipolar cells responded with a pure EPSP. The study of the laminar distribution of labeled and non‐labeled cells shows from surface to depth, a gradual increase in the number of cells responding with an EPSP‐IPSP or with a pure IPSP and a gradual decrease in the number of those exhibiting a pure EPSP. The analysis of the sensitivity of EPSPs and IPSPs to high frequency optic nerve stimulation shows that (1) monosynaptic as well as polysynaptic EPSPs can be recorded from cells in the non‐retinorecipient tectal region, (2) a number of ganglion and pyramidal cells receive a direct retinal excitatory input as their dendrites pass through the region of optic endings, (3) most IPSPs are polysynaptic, (4) some cells located in the retinorecipient region may receive direct retinal inhibitory connections.
Postnatal development of axosomatic synapses in the rat visual cortex: Morphogenesis and quantitative evaluation
Authors: Bähr Susan , Wolff Joachim R.
Published: January 2005

Postnatal development of axosomatic synapses was studied in the rat visual cortex in order to obtain experimental data that may explain how the unequal distribution of asymmetric and symmetric synapses evolves on the soma of cortical neurons. Three types of synaptic junctions were identified: (1) asymmetric or type 1 synapses, with postsynaptic densities ≥ 20 nm, (2) symmetric type 2 synapses, and (3) symmetric synapses with an intermediate structure. The third synapse type had a structure similar to that of type 1 synapses, although the postsynaptic densities were thinner than 20 nm.

Type 1 synapses developed in three phases. In phase 1, the first postnatal week, there were many free postsynaptic thickenings and immature synapses whereby a higher degree of postsynaptic differentiation was visible in comparison to the presynaptic elements. During the following 10 days, phase 2, type 1 synapses containing thin postsynaptic densities and intermediate synapses temporarily increased in number. Intermediate synapses are interpreted as precursors of type 1 synapses that have relatively immature postsynaptic elements. Toward the end of synaptogenesis, phase 3, the free postsynaptic thickenings reappeared while type 1 synapses containing well developed postsynaptic elements prevailed. Throughout the whole postnatal period, the numerical density of axosomatic type 1 synapses remained very low and the ratio of asymmetric to symmetric synapses at the neuronal somata was inversely proportional to that at the dendrites. Also, there was a significant decrease in the numerical density of type 1 synapses between postnatal days (P) 17 and 30. Data normalized according to cortical growth suggest that this is probably due to a decrease in the number of axosomatic type 1 synapses. This corresponds to the observation that in layers III and V a few type 1 synapses were found on pyramid‐like cells up to P10 which then disappeared in later stages.

Axosomatic type 2 synapses appear to be formed by two different presynaptic processes. The first presynaptic type contains flocculent material with glycogen granules and resembles axonal growth cones. These junctions contain multiple adhesion patches, intermediate junctions, one or more active zones, narrow synaptic clefts, and small pleomorphic vesicles. All of these are structural features of adult type 2 synapses. The growth‐cone‐like presynaptic elements disappeared after about 3 weeks. The second presynaptic type is smaller in size and also forms contacts with a structure similar to adult type 2 synapses. During the first postnatal week, the numerical density of symmetrical synapses (including intermediate synapses) was very low and increased more or less at a regular pace until P55. These data suggest that during postnatal development fewer type 1 synapses are formed on the somata than in the surrounding neuropil, and there was an additional reduction in the number of axosomatic type 1 synapses during the third and fourth postnatal week.
Somatostatin (SRIF)‐like immunoreactivity in subcortical and cortical visual centers of the rat
Authors: Laemle Lois K. , Feldman Susan C.
Published: January 2005

The distribution of neuronal elements containing immunoreactive somatostatin (I‐SRIF) in the rat central visual pathway was examined by light‐microscopic immunocytochemistry. These studies were concerned with the location and morphology of neurons and innervated cells and the distribution of fiber and terminal plexuses in the primary visual cortex (area 17), visual association areas 18 and 18a, the superior colliculus, the lateral geniculate nucleus, and the pretectum.

In the superior colliculus, I‐SRIF‐containing fibers and perikarya were distributed predominantly in the superficial, or visual, layers; these elements were moderately dense and occupied the entire mediolateral extent of these layers. In the intermediate and deep layers, immunoreactive neurons were widely scattered, and fibers were located mainly in the medial third. Immunoreactive cell populations in the superior colliculus included small bipolar neurons with fusiform perikarya and multipolar neurons with round to ovoid perikarya. In the pretectum, the peptide was demonstrable in large and small multipolar neurons of the nucleus of the optic tract and in the posterior and olivary pretectal nuclei. I‐SRIF‐containing neurons were also present in the nucleus of the posterior commissure, the nucleus of Edinger‐Westphal, and the ventral division of the lateral geniculate nucleus. In the visual cortex, the peptide was present in all layers and in a variety of morphologically defined cell populations, including some which are presumed excitatory (pyramidal and bipolar cells) and others which are presumed inhibitory (bitufted and stellate cells).

Our data suggest that somatostatin is involved in visual and visuomotor reflex pathways and in the horizontal optokinetic nystagmus reflex pathway. These results provide a foundation for further studies to evaluate the role of this peptide in visual processes.
Cochlear nerve of the alligator lizard
Authors: Mulroy Michael J. , Oblak Thomas G.
Published: January 2005

The innervation of the auditory organ of the alligator lizard is described. Patterns of distribution of the nerve fibers were studied at the light microscopic level with the horseradish peroxidase technique, and the types of synaptic contacts with hair cells were studied at the transmission electron microscopic level with standard techniques. The innervation of the two regions of the basilar papilla differs in the following ways. In the apical region, some fibers send branches along the length of the basilar papilla, and both afferent (non‐vesiculated) and efferent (vesiculated) nerve endings are present. In the basal region, all fibers terminate in the immediate area where they enter the papilla without sending branches along the length of the papilla; efferent endings are lacking, and nerve fibers are of a smaller average diameter. The punctate nature of the innervation of hair cells in the basal region is consistent with the hypothesis that the systematic organization according to frequency sensitivity observed in electrophysiological recordings from basal nerve fibers may be related to the length of the stereocilia on the hair cells with which the nerve synapses.
Distribution and origin of calcitonin gene‐related peptide (CGRP) immunoreactivity in the sensory innervation of the mammalian eye
Authors: Terenghi G. , Polak J. M. , Ghatei M. A. , Mulderry P. K. , Butler J. M. , Unger W. G. , Bloom S. R.
Published: January 2005

The occurrence, distribution, and origin of immunoreactive calcitonin gene‐related peptide (CGRP) in nerves of rat, guinea pig, cat, and monkey eyes were investigated by immunocytochemistry, radioimmunoassay, and chromatography. A rich network of CGRP‐immunoreactive nerve fibres was noted in the anterior uvea, which was widely distributed in both dilator and constrictor papillae muscles and extended to the ciliary body and uveal blood vessels. Numerous CGRP‐immunoreactive neuronal cells were present in the trigeminal ganglion. The extractable CGRP was 8.6 ± 1.8 pmoles/gm of tissue in the iris and 44.0 ± 8.1 pmoles/gm in the trigeminal ganglion. Following damage to the Gasserian ganglion a marked decrease of CGRP immunoreactivity was observed in the anterior uvea (control 11.3± 1.6 pmoles/gm; operated 1.4 ± 0.1 pmoles/gm) confirming the origin of the immunoreactive fibres from trigeminal primary sensory neurons. The sensory nature of the CGRP‐immunoreactive fibres was substantiated by the depletion of CGRP immunoreactivity observed after treatment with capsaicin, which is known to cause selective degeneration of sensory neurons. Comparative studies on the distribution and colocalisation of CGRP and the putative sensory neurotransmitter substance P revealed a closely parallel distribution of the two peptides in certain regions of the uvea and their coexistence in a subpopulation of trigeminal primary sensory neurons. This study suggests that the sensory nervous system in the eye is more heterogeneous in terms of its putative neurotransmitters than previously indicated.
The distribution of substance P, enkephalin, and serotonin immunoreactivities in the area postrema of the rat and cat
Authors: Newton Bruce W. , Maley Bruce , Traurig Harold
Published: January 2005

With the use of the peroxidase‐antiperoxidase technique the distribution of substance P (SP), enkephalin (ENK), and serotonin (5HT) immunoreactivities were described in the area postrema of the rat and cat. In both species, immunoreactivity in the area postrema was differentially distributed as either fibers only, or cell bodies and fibers. In the rat and cat, ENK had the greatest accumulation of immunoreactive fibers, followed by 5HT and SP. In the area postrema of the rat the majority of SP‐, ENK‐, and 5HT‐immunoreactive fibers were along the ventral and ventrolateral borders, with fewer immunostained fibers at the dorsal surface. The area postrema of the cat had the majority of SP‐, ENK‐, and 5HT‐immunoreactive fibers at the ventral and lateral borders, with fewer immunostained fibers at the dorsal and medial borders. In both species, the area postrema's central region contained the fewest immunostained fibers. In general, for each putative neurotransmitter examined, immunostained fibers in both species progressively decreased in number rostrocaudally. Serotonin‐ and ENK‐immunoreactive cell bodies were found in the rat area postrema; in the cat area postrema only ENK‐immunoreactive cell bodies were present. The area postrema of both species lacked SP‐immunoreactive cell bodies. The heterogeneous distribution of immunoreactive fibers and cell bodies within the area postrema of the rat and cat may reflect the different functions of the area postrema in both species.
Cholinergic projections from the basal forebrain to the basolateral amygdaloid complex: A combined retrograde fluorescent and immunohistochemical study
Authors: Carlsen Jørn , Záborszky László , Heimer Lennart
Published: January 2005

We have examined the location of cholinergic and non‐cholinergic neurons that project to the rat basolateral amygdaloid nucleus by using choline acetyltransferase (ChAT) immunohistochemistry in combination with retrograde fluorescent tracing on the same tissue section. Since many tracer‐and ChAT‐positive neurons were identified in basal forebrain areas, including the ventral pallidum, we also stained many of the sections for glutamate decarboxylase, a suitable marker for the delineation of pallidal areas.

Cholinergic neurons projecting to the basolateral amygdaloid nucleus were observed in a continuous territory stretching from the dorsal part of ventral pallidum, through sublenticular substantia innominata to ventral parts of globus pallidus and peripallidal areas. Non‐cholinergic neurons projecting to the basolateral amygdaloid nucleus were found intermixed within the same structures and constitute approximately 25% of the amygdalopetal projection neurons in these ventral forebrain structures.

Since amygdalopetal cholinergic neurons were demonstrated in areas generally recognized as giving rise to cholinergic projections to cerebral cortex, several retrograde double‐labeling experiments with two different fluorescent tracers were performed for the purpose of detecting the possible existence of collateral projections. The results obtained showed that the cholinergic basal forebrain neurons in general project to only one forebrain region, and, furthermore, that the cholinergic system consists of partially overlapping subsets of neurons that project to various neocortical and allocortical areas and to the amygdaloid body.
The structure of the fourth abdominal ganglion of the crayfish, Procambarus clarki (girard). I. Tracts in the ganglionic core
Authors: Skinner Kate
Published: January 2005

The organization of the fourth abdominal ganglion of the crayfish, Procambarus clarki, was studied with the light microscope in serial sections stained with osmium ethyl gallate. This ganglion is composed of a ventral rind of somata and a core of alternating layers of through‐tracts and commissures. The longitudinal tracts of the ganglion are named according to the system in use for the orthopteran insects, because the basic plans of the crustacean and insect ventral ganglia exhibit striking anatomical parallels. The dorsal tracts are the largest and the most regular in their path through the ganglion. In the ventral posterior quadrant of the ganglion the tracts diverge from the basic plan to pass around the major synaptic neuropil and the bases of the peripheral nerves.

This paper reports the three‐dimensional anatomy of the major longitudinal through‐tracts, internal tracts and commissures, and bases of peripheral nerves. Landmark features of the ganglion–including the tracts, the major artery of the vascular system, the shape of the ganglionic core in section, and prominent single cells, all of which make it possible to recognize specific regions of the ganglion–are described.
The structure of the fourth abdominal ganglion of the crayfish, Procambarus clarki (girard). II. Synaptic neuropils
Authors: Skinner Kate
Published: January 2005

Four discrete regions of synaptic neuropil in the crayfish fourth abdominal ganglion are described by light and electron microscopy. The largest is the horseshoe neuropil, a horseshoe‐shaped mass of synaptic glomeruli that lies horizontally in the ventral ganglionic core. This neuropil has a substructure of three rings of fused glomeruli associated with the entry of small axons from the first and second nerve roots. The lateral neuropils are large, paired bulges of neuropil that define the sides of the ganglionic core. They contain neuronal profiles of various sizes, filled with clear or dense‐cored vesicles. The neurons are randomly oriented except for occasional dendritic bundles. The tract neuropil is ultrastructurally similar to the lateral neuropils but it is distributed among the largest axons of the through‐tracts and commissures. The midline neuropils are small, U‐shaped clumps of uniformly sized neuronal profiles that contain large numbers of dense‐cored vesicles and distinctive lamellar inclusions.
Neuronal death during development in the isthmo‐optic nucleus of the chick: Sustaining role of afferents from the tectum
Authors: Clarke Peter G. H.
Published: January 2005

Neurons have been counted in the isthmo‐optic nucleus following lesions of the optic tectum, its main source of afferents. Late lesions, made at 10.8–12.2 days of incubation, were employed as they cause the fewest nonspecific side effects. The lesions spared the isthmo‐optic tract, and although they caused many retinal ganglion cells to die, the degeneration did not spread to the inner nuclear layer, which contains the target cells of the isthmo‐optic fibers. Hence the effects on the isthmo‐optic nucleus were due to its being deprived of afferents.

Even in unoperated embryos, 60% of the isthmo‐optic neurons are known to die between embryonic days 12 and 17. The tectal lesions greatly increased the cell loss ipsilaterally; this was due to cell death, since other explanations such as migration away or differential cellular shrinkage have been ruled out. The fact that additional neuronal death occurred mainly during the latter half of the period of natural cell death implies that the tectal afferents are important for the survival of the isthmo‐optic neurons during this latter half, but not before.
The organization of pudendal motoneurons and primary afferent projections in the spinal cord of the rhesus monkey revealed by horseradish peroxidase
Authors: Roppolo J. R. , Nadelhaft I. , De Groat W. C.
Published: January 2005

The horseradish peroxidase tracing technique was utilized to study the distribution of motoneurons and primary afferent neurons contributing fibers to the pudendal nerve in the monkey. Application of horseradish peroxidase to the central cut end of the pudendal nerve labeled motoneurons in the ipsilateral spinal cord primarily in the S1 and L7 segments. In transverse sections these neurons were distributed within an oval area (Onuf's nucleus) with an average dimension of 360 × 290 μm, located at the base of the ventral horn, medial to the lateral motor nuclei. An average of 418 (range: 170–577) medium‐sized (44 × 26 μm) neurons were labeled per animal. In longitudinal sections the nucleus appeared as a beaded column of cells extending 9.3 mm rostrocaudally with a prominent network of longitudinal dendrites. In the transverse plane, other groups of dendrites were observed: one group extended dorsomedially toward the central canal, while a second group extended dorsolaterally to the intermediolateral gray, with some of the latter dendritic processes following the lateral border of the ventral horn.

An average of 9,200 afferent neurons were labeled in the dorsal root ganglia of each animal. Approximately 85% of these cells were located in a single dorsal root ganglion (S1 or S2). This ganglion was always located one spinal segment caudal to the segment containing the majority of cells in Onuf's nucleus. In the spinal cord, afferent labeling in the dorsal columns and Lissauer's tract extended from S3 to at least L1. The density of afferent labeling in the spinal cord paralleled the number of labeled dorsal root ganglion cells in the corresponding segments. From Lissauer's tract and the dorsal columns a prominent collateral fiber bundle passed medially over the apex of the dorsal horn to the dorsal commissure and to medial laminae I–IV of the dorsal horn. A much less prominent pathway passed ventrally along the lateral edge of the dorsal horn to lamina V, where a few collaterals continued medially to the dorsal commissure. The majority of labeled lateral afferent axons ended slightly dorsal to the sacral parasympathetic nucleus.

A comparison of the present findings with previous descriptions of the sacral visceral pathways shows a considerable overlap in certain areas of the spinal cord of pudendal and pelvic nerve afferent and efferent systems. This close anatomic relationship is consistent with the physiological observation that somatovisceral integration in the lumbosacral spinal cord is essential for the normal regulation of micturition, defecation, and sexual function.
Neurogenesis of the climbing fibers in the human cerebellum: A Golgi study
Authors: Marin‐Padilla Miguel
Published: January 2005

The prenatal and early postnatal neurogenesis of the human climbing fibers of the lateral cerebellar hemispheres have been studied, with the rapid Golgi method, and correlated with the developmental stages of Purkinje cells. A transitional phase has been established in the neurogenesis of the human Purkinje cell between the second and third stages of Cajal. This phase coincides with the arrival of the climbing fibers. It is characterized by the reabsorption and subsequent transformation of Purkinje cell's basal dendrites into somatic spines. Following the arrival of the climbing fibers and the establishment of contacts, the Purkinje cell is progressively transformed from an immature stellate and nonoriented cell into a monopolar and spatially oriented one which acquires all of its mature morphological and functional features.

The human climbing fibers arrive at the Purkinje cell plate by the 28th week of gestation and establish a transient paraganglionic plexus before contacts with these neurons can be recognized. They start to form pericellular nests by the 29th week, and by the 31st week of gestation all Purkinje cells of the lateral hemispheres have pericellular nests around their bodies. These pericellular nests are progressively and rapidly transformed into supracellular “capuchones” which themselves are also short‐lived because the climbing process starts readily in them. Supracellular “capuchones” are recognized by the 34th seek and their fibrils start to climb the dendrites of Purkinje cells (young climbing phase) by the 36th week of gestation. The process of climbing the dendrites of the Purkinje cells will continue through late prenatal and early postnatal life.

The human climbing fibers are distributed, in the internal granular layer, within narrow and long vertical territories which are transverse to the long axis of the follium. A single climbing fiber is (1) able to establish contacts with many Purkinje cells located within its narrow territory of distribution; (2) has a tendency to establish contacts with small groups of Purkinje cells rather than with isolate neurons; (3) able to send collaterals to several contiguous cerebellar folia; and (4) able to send collaterals to the internal granular layer and to form pericellular nests in it. The human cerebellum may be considered to be subdivided into a series of parallel, narrow, and transverse structural/functional planes, each one characterized by the distribution of a climbing fiber. It should be emphasized that the axonic collaterals of the Purkinje neurons are similarly distributed and oriented within the internal granular layer and could represent elements of the same flat functional planes. Observations made in this study suggest that the disappearance of the lamina dissecans may be, in part, related to the reabsorption of the Purkinje cell's basal dendrites and hence to the arrival of the climbing fibers.
Organization and distribution of the rat subdiaphragmatic vagus and associated paraganglia
Authors: Prechtl James C. , Powley Terry L.
Published: January 2005

This experiment analyzed the organization of the rat abdominal vagus. To spare delicate tissues and preserve positional information, untrimmed blocks of the subdiaphragmatic viscera (N = 22) were fixed, impregnated by using a pyridine‐silver protocol, and double embedded. Each block was sectioned transversely at 7 μm, and a section every 70 μm from the diaphragm to the cardia was analyzed. The features of the section were traced and digitized for computer reconstruction. Included in the measurements were sizes and locations of bundles, fascicles, and paraganglia.

The anterior and posterior vagi were consistently distinctive in size, distribution, cross‐sectional shape, and paraganglionic content. In the most common pattern (41% of animals), the anterior trunk coursed longitudinally on the ventral surface of the esophagus, giving off at successively more distal levels the hepatic branch, the accessory coeliac branch and then the bundles of the anterior gastric branch. The posterior trunk separated into a coeliac branch and a posterior gastric branch, each consisting of numerous bundles, in the most distal quarter of the esophagus. Fifty‐nine percent of all animals exhibited one or more significant variations in vagal organization (e.g., double primary trunks—41%, supernumerary branches—18%, or atypical branching sequences—9%).

Four to 14 vagal paraganglia (mean = 8 ± 1; equivalent to 32/rat, corrected for sampling) were found in each animal, and no branch was consistently devoid of paraganglia. Ninety‐four percent of the paraganglia were located at nerve branch points. Some of the larger paraganglia contained at their central poles one to six neurons with soma diameters ranging from 14 to 22 μm.
A Golgi study of the cell types of the dorsal torus semicircularis of the electric fish Eigenmannia: Functional and morphological diversity in the midbrain
Authors: Carr Catherine E. , Maler Leonard
Published: January 2005

The dorsal torus semicircularis (torus) of the gymnotiform fish Eigenmannia was examined in Golgi impregnated material. These results were correlated with those of a previous HRP study which used retrograde labelling techniques to identify the efferent cell types of the torus (Carr et al., '81, J. Comp Neurol. 203: 649–670).

The torus is a laminated midbrain nucleus of the electrosensory system. It receives somatotopically ordered electrosensory input from the medulla and caudal lobe of the cerebellum, proprioceptive input from the descending nucleus of the trigeminal nerve, and input from the optic tectum. The torus projects to the nucleus praeeminentialis, the optic tectum, nucleus electrosensorius, parts of the central posterior thalamus, the pretectum, the lateral mesencephalic reticular formation (LMRA), the reticular formation, and the inferior olive.

The torus has 12 laminae and 48 cell types by Golgi criteria. There are three major orientations to the dendritic fields of the toral neurons: (1) purely horizontal neurons with dendrites confined to a single lamina, (2) multipolar neurons whose dendrites often do not respect laminar boundaries, and (3) vertical cells with dendrites that travel in the vertical bundles of dendrites and axons which pierce the torus at regular intervals.

There are four major groups of vertically oriented neurons. The first has a predominantly horizontal dendritic tree with one or two vertical dendrites which connect the cell to a distant lamina. The second consists of “U”‐shaped neurons with a horizontal arbor and two major dendrites which ascend in adjacent vertical bundles. The third group is made up of bilaminar neurons which receive input from two vertically separated dendritic arbors, and the fourth group is purely vertical in orientation. A group of four tegmental cell types in the LMRA also send their dendrites into the efferent tracts of the torus, and into lamina IX.

The torus is similar in complexity and number of cell types to the mammalian inferior colliculus. The large number of cell types in these midbrain sensory nuclei, compared to the number of afferent inputs (seven or more for the torus) is notable and may reflect the parcellation of function associated with the parallel processing of these inputs.
Localization of the synthetic progestin 3H‐ORG 2058 in neurons of the primate brain: Evidence for the site of action of progestins on behavior
Authors: Rees Howard D. , Bonsall Robert W. , Michael Richard P.
Published: January 2005

The location of neurons that concentrate progestin in the brains of female cynomolgus monkeys was mapped by autoradiography using the specific synthetic progestin receptor ligand 3H‐ORG 2058. Three females were ovariectomized and treated with estrogen (20 μg estradiol benzoate daily for 7 days), and one of them was also pretreated with progesterone. Each received an i.v. injection of 1 mCi 3H‐ORG 2058 and was killed 1 hour later. Thaw‐mount autoradiograms revealed intense accumulation of radioactivity in the nuclei of many neurons in the mediobasal hypothalamus, particularly in the ventromedial nucleus (n.), arcuate n., and premammillary n. Neuronal labeling was also observed frequently in the medial preoptic n., and occasionally in the anterior hypothalamic area, paraventricular n., and organum vasculosum of the lamina terminalis. In the pituitary gland, about 5% of cells in the pars distalis were intensely labeled. In the female pretreated with progesterone, however, labeling was almost completely blocked. Analysis of samples by high‐performance liquid chromatography demonstrated that the radioactivity extracted from brain and pituitary gland cell nuclei was almost entirely unmetabolized 3H‐ORG 2058. The nuclear concentration of progestin was much greater in the pituitary gland than in the brain, and was greater in the hypothalamus than in any other brain area. These results revealed well‐localized groups of progestin‐concentrating neurons in the primate brain which presumably mediate the effects of progresterone on both gonadotropin secretion and female sexual behavior.
Topographic organization of tufted cell axonal projections in the hamster main olfactory bulb: An intrabulbar associational system
Authors: Schoenfeld Thomas A. , Marchand James E. , Macrides Foteos
Published: January 2005

The organization of intrinsic axonal projections of principal neurons in the main olfactory bulb (MOB) was studied in hamsters by using wheat germ agglutinin‐horseradish peroxidase (WGA‐HRP) and fluorescent dyes. Punctate injections of either WGA‐HRP or fast blue (FB) that are restricted to small sectors on one side of the MOB produce comparably restricted fields of retrograde labeling on the opposite side. Label is found predominantly in superficially situated (middle and external) tufted cells that lie near and at the border between the external plexiform and glomerular layers. Few of the deeper middle tufted, internal tufted, or mitral cells and no external tufted cells that lie in the superficial two‐thirds of the glomerular layer are labeled in regions remote to the injection site. Anterograde transport of WGA‐HRP from the injection site labels axons that travel dorsally and ventrally in restricted bands through the internal plexiform layer and then terminate within this layer in the punctate sector on the opposite side that contains retrogradely labeled neurons. Such reciprocal projections between opposing regions of the medial and lateral sides of the MOB are found at all rostrocaudal and dorsoventral levels. When punctate injections of FB into the MOB are paired with restricted injections of a second fluorescent tracer (nuclear yellow or diamidino yellow dihydrochloride) into the appropriate sector of pars externa (pE) of the anterior olfactory nucleus, the punctate region of remote retrogradely labeled principal neurons is embedded within a topographically restricted longitudinal wedge of retrogradely labeled mitral and tufted cells that project extrinsically to or through pE. However, extremely few of these neurons are double‐retrogradely labeled. The results reveal the existence of an intrabulbar associational system in which principal neurons engage in point‐to‐point, reciprocal projections between opposing regions of the medial and lateral MOB. Moreover, the results indicate that this associational system largely arises from superficially situated tufted cells distinct from those that support bulbofugal projections into the topographically organized interbulbar commissural system via pE.
Aging in the rat olfactory system: Relative stability of piriform cortex contrasts with changes in olfactory bulb and olfactory epithelium
Authors: Curcio Christine A. , McNelly Nancy A. , Hinds James W.
Published: January 2005

Previous studies have quantified growth and atrophy of the olfactory bulb and olfactory epithelium of the Sprague‐Dawley rat from maturity to senescence. Major events occurring in these structures include changes in the volume of mitral cells and changes in the number of septal olfactory receptors. These effects are large, consist of a growth phase followed by atrophy, and are temporally related in that events in the olfactory epithelium precede those in the mitral cells. A hypothesis of aging based on transneuronal effects would predict that these changes would be similarly transmitted to the next synaptic station in the olfactory pathway. Therefore, cells and synapses of the piriform cortex were studied in rats 3, 12, 18, 24, 27, 30, and 33 months of age. Alternate Vibratome sections through brains perfused with mixed aldehydes were processed for light and electron microscopy.

No significant age effects were found for the volumes of cortical laminae Ia and Ib. Both numerical and surface density of synaptic apposition zones in layer Ia, formed primarily by mitral cell axons, were stable with age. A modest (18%) but significant decline in the proportion of layer Ia occupied by dendrites and spines was mirrored by an increase in the proportion of glial processes; no change in the proportion of axons and terminals was observed. Neither nuclear volume, nor soma volume, nor numerical density of layer II neurons changed with age.

Thus, contacts made in the piriform cortex by mitral cell axons remain relatively stable in senescence, despite the marked volumetric changes in the mitral cell somata, changes which were confirmed again in this study. Age‐related dendritic regression in layer II neurons may be attributable to functional deafferentation subsequent to reduced receptor input to mitral cells.
Immunocytochemical localization of serotonin in the rat periaqueductal gray: A quantitative light and electron microscopic study
Authors: Clements Jane R. , Beitz Alvin J. , Fletcher Tom F. , Mullett Mary A.
Published: January 2005

The distribution of serotonin‐like immunoreactivity in five regions of the rodent midbrain periaqueductal gray (PAG) was studied by using light and electron microscopic immunohistochemistry in combination with quantitative analysis. Light microscopic analysis revealed the presence of serotonin‐like immunoreactive cell bodies located in the ventrolateral and ventromedial regions of the caudal PAG and serotonin‐like immunoreactive processes throughout the PAG. Ultrastructural analysis showed dendritic profiles that stained positively for serotonin primarily in ventral regions, although an occasional profile was seen dorsally. Numerous synaptic contacts between unstained axon terminals and ventral dendritic profiles were seen. Axonal profiles that contained reaction product were identified throughout the PAG, but were rarely observed to make any type of specialized contact. Ultrastructural quantification of serotonin‐like immunoreactive processes indicated that the highest volume fraction of serotonin immunoreactivity occurred caudoventrally where stained processes constituted 2.6% of the neuropil volume. Rostroventrally stained processes constituted only 0.14% of the neuropil volume at the level of the posterior commissure. By contrast the amount of serotonin‐like immunoreactivity found dorsally remained relatively constant at all rostrocaudal levels. Analysis of serotonin staining among PAG regions demonstrated the lowest overall volume friction in the dorsal region and the highest overall volume fraction in the ventromedial region. No significant differences were observed between medial and lateral regions. A comparison of the results of light microscopic quantitative analysis of serotoninergic processes with electron microscopic quantitative analysis indicated that both techniques produce comparable results.
Compensatory climbing fiber innervation after unilateral pedunculotomy in the newborn rat: Origin and topographic organization
Authors: Angaut P. , Alvarado‐Mallart R. M. , Sotelo C.
Published: January 2005

In neonatal rats the unilateral transaction of the cerebellar peduncles causes a fast and complete degeneration of the contralateral inferior olive. Axons from the remaining olive recross the cerebellar midline and partially innervate the deprived hemicortex. Analysis of the topographic organization of this compensatory projection studied with the axonal tracing method provided the following results.

Retrograde tracing experiments revealed that the bulk of compensatory afferents originates from neurons in the ipsilateral medial accessory olive, especially from its medial region, whereas afferents from the principal olive and the dorsal accessory olive contribute to a much lesser degree. In case of incomplete neonatal pedunculotomy, neurons with a similar location in the ipsilateral intact olive still contribute to the innervation of the partially deprived hemicortex, along with the atrophic contralateral olive. Moreover, these experiments revealed important information about the organization of the compensation. Although its specificity was not totally maintained, the mediolateral distribution of sprouted afferents in the cerebellum matched the caudorostral disposition of parent neurons in the olive, as in the case in normal olivocerebellar projection.

Anterograde studies showed that compensatory fibers recrossing the cerebellar midline spread throughout the whole extent of the deprived cortex and terminate solely in the molecular layer as typical climbing fibers. The latter were not homogeneously distributed, their density being markedly reduced according to a mediolateral gradient. Compensatory projection followed a sagittal striped pattern, as does the normal climbing fiber projection. Moreover, if the cortex is divided broadly into vermal, intermediate, and hemispheral regions, an apparent reciprocity seems to exist concerning the relative involvement of the various cortical subdivision in both hemicerebella.

Our present results indicate that the immature olivocerebellar system is capable of anatomical plasticity, although to a limited extent. More important, they suggest that a certain degree of specificity is maintained during the process of sprouting, resulting in a topographical arrangement of the transcommissural climbing fiber projection. This indicates, in turn, that cues which guide the growth of olivocerebellar fibers during normal development could also direct the compensatory innervation.
Retinofugal and retinopetal projections in the cichlid fish astronotus ocellatus
Authors: Springer Alan D. , Mednick Adam S.
Published: January 2005

The retinofugal and retinopetal projections of the cichlid fish Astronotus ocellatus were studied by applying cobaltous‐lysine to the optic nerve. Retinal axons terminate bilaterally in a preoptic‐suprachiasmatic region between the base of the third ventricle and the anterior genu of the horizontal commissure and among periventricular cells along the sides of the ventricle. Other retinal axons innervate the tuberal region of the hypothalamus anterior to the infundibulum. Targets innervated in the pretectum include nucleus lateralis geniculatus and dorsal, medial, and ventral pretectal nuclei. Three other targets (nucleus opticus dorsolateralis, nucleus opticus commissurae posterior, nucleus opticus ventrolateralis) are innervated by fibers that leave the medial edge of the dorsal optic tract. Two other targets (basal optic nucleus and accessory optic nucleus) are innervated by fibers from the ventral optic tract. These retinal projections are similar to those previously reported for goldfish in an experiment that used the cobaltous‐lysine method (Springer and Gaffney, J. Comp. Neurol. 203:401–424, 1981). Retinotectal optic axons were found in a superficial lamina just above the stratum opticum, in the stratum opticum, in three layers of the stratum fibrosum et griseum superficiale, in a lamina just beneath the stratum fibrosum et griseum superficiale, and in the stratum album centrale just above the stratum periventriculare. This result is similar to that previously reported for goldfish; however, the spatial relationships between the various retinorecipient laminae differ for goldfish and Astronotus ocellatus.

Efferents to the retina originate in two nuclei and both project contralaterally. The first is the nucleus olfactoretinalis, which is located ventrally between the olfactory lobe and telencephalon. It consists of about 400 cells, of which, approximately 200 cells project to the retina. The second retinopetal nucleus, nucleus thalamoretinalis, is a diffuse group of about 200 cells that project to the retina.