bluuebunny/crossref_metadata_2025 huggingface dataset:
Transplantation of tectal tissue in rats. II. Distribution of host neurons which project to transplants
Authors: Harvey Alan R. , Lund Raymond D.
Published: May 2005

Tectal tissue was dissected from fetal rats and transplanted adjacent to the superior colliculus of newborn rats. The recipient animals were then allowed to survive for 6 or more weeks. Subsequent examination revealed that the transplants generally lay over the host inferior colliculus and rostral part of the cerebellum and had substantial fiber connections with the host superior colliculus. To determine which host areas projected to the transplants, horseradish peroxidase (HRP) was injected into the transplants, and the host brain was examined for the presence of retrogradely filled neurons.

Labeled cells were found in nearly 50 host areas. Most of these areas are known to project to normal superior colliculus. There was a consistency between one animal and another in the frequency and density of cell label in the various areas. The projection from host cortex (particularly from visual cortical areas) was the densest and most consistent projection. Other areas which commonly projected into the transplants included pretectum, parabigeminal nucleus, superior colliculus, and the brachial region of the inferior colliculus. Sparse and infrequent projections were found from ventral lateral geniculate nucleus, substantia nigra, zona incerta, and catecholaminergic nuclei. No unequivocally labeled retinal ganglion cells were found.

The results indicate that the host projection into the transplants is limited to those areas with axons in the vicinity of the host/transplant interconnection. However, the data also suggest that (1) the relative maturity of particular host pathways at the time of transplantation and (2) some form of preferential or absolute affinity expressed between host axons and transplant cells are also factors which influence the pattern of connections formed between host and transplant.
Lectin receptors on cells isolated from the turtle retina
Authors: Sarthy P. Vijay , Bridges C. David , Kretzer Francis L. , Lam Dominic M. K.
Published: May 2005

The presence of specific oligosaccharides on the surface of retinal cells was examined by incubating FITC‐labeled lectins with cells dissociated from papain‐treated turtle retinas. The pattern and intensity of binding was found to vary among the cells examined. With Con A, there was strong surface staining of both rods and cones, with an intense ring of fluorescence above the nucleus. The bipolar and ganglion cells also showed strong surface labeling. In Müller (glial) cells there was intense fluorescence in the apical, microvillous region. In contrast, the horizontal cells and their axons showed weak staining. When RCA‐60, RCA‐120, and WGA were incubated with photoreceptors, bipolar cells, or horizontal cells, little fluorescence was visible. However, all three lectins bound strongly to the Müller cells. In contrast, the Lotus lectin did not bind to any of the cells examined. In all the cases, lectin binding was inhibited by the appropriate haptene sugar. Further, prior treatment of cells with neuraminidase did not alter lectin binding to any cell type. These results suggest differences in the distribution of lectin receptors among specific cell types, and particularly between neurons and glial cells in the vertebrate retina.
Histopathological reactions and axonal regeneration in the transected spinal cord of hibernating squirrels
Authors: Guth Lloyd , Barrett Charles P. , Donati Edward J. , Deshpande Sharad S. , Albuquerque Edson X.
Published: May 2005

The failure of axonal regeneration in the transected spinal cord of mammals has been attributed to many factors, including an intrinsic lack of regenerative capacity of mature CNS neurons, mechanical obstruction of axonal elongation by glial‐connective tissue scars, necrosis of spinal tissue resulting in cavitation, lack of trophic influences sufficient to sustain outgrowth, and contact inhibition resulting from the formation of aberrant synapses. Assessment of the relative importance of each of these factors requires animal models in which one or more of these pathological processes can be eliminated. We therefore examined the effects of spinal transection in the hibernating animal because, during hibernation, collagen formation is depressed while nerve regeneration and slow axonal transport are maintained. Midthoracic spinal transections were performed in hibernating ground squirrels and the spinal cords were examined histologically 1–6 months later. The lesion site was composed primarily of a loose accumulation of macrophages and showed minimal glial and collagenous scarring, or cavitation. There was extensive regeneration of intrinsic spinal cord and dorsal root fibers. These axons grew to the margin of the lesion where they turned abruptly and continued growing along the interface between the lesion and the spinal cord. We conclude (1) that mammalian spinal‐cord neurons have considerable regenerative potential; (2) that such mechanical impediments as collagenous and glial scarring, cyst formation, and cavitation cannot provide the sole explanation of why regeneration in the mammalian CNS is abortive; and (3) that specific physical and chemical properties of the cells in the environment of the growth cone regulate the extent and orientation of regenerative axonal outgrowth.
Identification and localization of the motor nuclei and sensory projections of the glossopharyngeal, vagus, and hypoglossal nerves of the cockatoo (Cacatua roseicapilla), cacatuidae
Authors: Wild J. Martin
Published: May 2005

Horseradish peroxidase (HRP) has been applied to the proximal severed ends of glossopharyngeal (NIX), vagus (NX), and hypoglossal (N XII) cockatoo in order to localize the motoneurons and sensory projections of these nerves which are involved in the control of the bird's feeding and phonatory behaviors.

Application of HRP to N IX labeled four rhombencephalic nuclei: (1) a largecelled, retrofacial nucleus supplying M. geniohyoideus, the major tongue extensor; (2) a dorsal nucleus composed of medium‐sized cells, projecting to most branches of N IX; (3) a ventrolateral nucleus supplying, amongst other structures, the floor of the pharynx and larynx; and (4) a ventral portion of the dorsal motor nucleus of the vagus.

Neurons labeled by application of HRP to the cervical vagus comprise the classically defined dorsal motor nucleus and a ventrolateral medullary nucleus which is coextensive with that of the glossopharyngeus: together they probably constitute a nucleus ambiguus.

Application of HRP to hypoglossal branches labeled a large nucleus intermedius (IM) and neurons ventral, ventrolateral, and caudal to it. The rostral third of IM supplies the lingual muscles, the caudal two‐thirds the tracheosyringeal muscles.

Many labeled neurons were found in the “jugular” ganglion following HRP treatment of each of the three nerves, especially N IX and N XII, which innervate the tongue. Central projections of these neurons are to nuclei of the descending trigeminus and to largely nonoverlapping portions of the principal trigeminal nucleus. It is hypothesized that these afferents provide sensory information necessary for the efficient processing and passage of food in the mouth.
Laminar organization of the afferent and efferent systems of the torus semicircularis of Gymnotiform fish: Morphological substrates for parallel processing in the electrosensory system
Authors: Carr C. E. , Maler L. , Heiligenberg W. , Sas E.
Published: May 2005

The torus semicircularis of Gymnotiform fish is an enlarged laminated midbrain structure which receives lemniscal input from electrosensory, mechanoreceptive lateral line, and auditory systems. The electrosensory input is confined to the dorsal torus, while the auditory and mechanoreceptive systems project to the ventral torus. Anterograde and retrograde techniques were used to determine the connections of the dorsal torus in Apteronotus and Eigenmannia. The dorsal torus can be divided into nine major laminae, each of which has distinct afferent and efferent connections. The dorsal torus receives five afferent inputs: (1) A contralateral topographic input from the posterior lateral line lobe (PLLL) projects to laminae III, V, VI, VII, VIIIB, and VIIID. (2) Eurydendroid cells of the caudal lobe of the cerebellum project contralaterally to lamina VIIIB. (3) A portion of the descending nucleus of V projects to laminae VIIIA, VIIIC, and IX. (4) Lamina I is a cap of fine myelinated fibers which may originate in the torus longitudinalis. They project to laminae II and III. (5) The ipsilateral optic tectum projects to the dorsal torus. The dorsal torus projects to six major targets: (1) Laminae VII, VIII, and IX project bilaterally to a lateral region of the diencephalon above n. preglomerulosus, herein named n. electrosensorius. An area below the dorsal thalamus receives a smaller ipsilateral projection. (2) Laminae II, V, VIvn, VII, VIII, and IX project topographically to the deeper laminae of the ipsilateral optic tectum. This projection is in spatial register with the visual map in the superficial layers of the tectum. (3) Lamina VIIID projects ipsilaterally to the lateral reticular formation. (4) All laminae other than I, VI, and VIIIB project topographically to the ipsilateral n. praeeminentialis, which provides a powerful descending projection to the PLLL. (5) Lamina IX projects to a dorsal pretectal area. (6) The ipsilateral inferior olive receives a projection from the dorsal torus.
Branching of sensory axons in the peripheral nerve of the rat
Authors: Langford Lauren A. , Coggeshall Richard E.
Published: May 2005

The currently accepted concept of a primary sensory cell is a cell that gives rise to a central process which passes through the dorsal root to the spinal cord and a peripheral process which passes to the periphery via a peripheral nerve. If this is correct, then there should be equal numbers of sensory axons in the dorsal root, dorsal root ganglion cells, and sensory axons in the proximal peripheral nerve. The present study obtains these counts in animals in which extraneous axons have been removed from the peripheral nerve and root. The counts indicate that there are approximately 2.3 sensory axons in the dorsal root and proximal peripheral nerve for each ganglion cell in the sacral segments of the rat. We interpret these data as indicating that there is significant branching of sensory axons in the dorsal root and proximal peripheral nerve and thus the generally accepted picture of a dorsal root ganglion cell is not correct for some, perhaps all, of these cells. We offer the speculation that this peripheral branching may be an indication of single sensory neurons having receptive fields in two separate locations, and thus this may be an anatomical explanation for certain types of referred pain.
Intercellular junctions in the developing arachnoid membrane in the chick
Authors: Van Rybroek John J. , Low Frank N.
Published: May 2005

The arachnoid membrane of chick embryos was prepared for electron microscopic study by means of thin sections and freeze‐fracture replicas. Particular attention was given to the relationships among junctional complexes during arachnoid maturation. By 14 days of incubation, the arachnoid had differentiated into morphologically distinct inner and outer zones. Both desmosomes and gap junctions were present among the cells of both layers at this time. Desmosomes were most numerous in the inner arachnoid layer and their structure remained constant. Gap junctions showed a great variation in structure. The large gap junctions contained a particle packing pattern in which rows of intramembranous particles were separated by particle‐free zones. Arched gap junctions were also present. Smaller arrays of gap junctions exhibited a variety of configurations on the membrane P‐face. The first tight‐junctional strands clearly identifiable in freeze‐fractured preparations appeared at 15–17 days. These were closely associated with the particles of gap junctions and consisted of single strands on the P‐face. By hatching age (21 days) a “mature” pattern of tight‐junctional strands was interwoven in several layers. In the interim, more complex arrangements of tight‐junctional strands were in intimate relation with gap junctions.
Localization of synaptic and nonsynaptic nicotinic‐acetylcholine receptors in the goldfish retina
Authors: Zucker Charles , Yazulla Stephen
Published: May 2005

The localization of nicotinic‐cholinergic receptors in the inner plexiform layer (IPL) of goldfish retina was studied by electron microscopic analysis of the binding pattern of a conjugate of horseradish peroxidase and αbungarotoxin (HRP‐αBTx). Specific HRP reaction product (blockable by 1mm curare) was found at both synaptic and nonsynaptic sites. Synaptic binding sites for HRP‐αBTx, which accounted for only 16% of the total specific reaction product sites, always involved an amacrine process as the presynaptic element, whereas amacrine, ganglion, and bipolar cells could be postsynaptic elements at labeled synapses. Only 17.5% of the total number of amacrine synapses were labeled by HRP‐αBTx. Labeled synapses showed the same distribution in the IPL as unlabeled synapses: bimodal for amacrine‐to‐bipolar synapses with peak concentrations at the 20% and 80% layers and unimodal for amacrine‐to‐nonbipolar synapses with a peak concentration at the 60% layer. Nonsynaptic binding sites for HRP‐αBTx (84% of total) were seen on the dendrites of ganglion, amacrine, and bipolar cells. The distribution of the nonsynaptic sites in the IPL largely accounts for the trilaminar binding pattern of 125I‐αBTx as observed in light microscopic autoradiographs. If, as appears likely, the distribution of synapses is the relevant variable in determining the sites of neuronal interaction for a given transmitter system, then this study further illustrates the importance of distinguishing synaptic from nonsynaptic binding when using receptorligand probes to localize sites of chemical synaptic transmission.
Intrinsic connections and architectonics of posterior parietal cortex in the rhesus monkey
Authors: Pandya Deepak N. , Seltzer Benjamin
Published: May 2005

By means of autoradiographic and ablation‐degeneration techniques, the intrinsic cortical connections of the posterior parietal cortex in the rhesus monkey were traced and correlated with a reappraisal of cerebral architectonics. Two major rostral‐to‐caudal connectional sequences exist. One begins in the dorsal postcentral gyrus (area 2) and proceeds, through architectnic divisions of the superior parietal lobule (areas PE and PEc), to a cortical region on the medial surface of the parietal lobe (area PGm). This area has architectonic features similar to those of the caudal inferior parietal lobule (area PG). The second sequence begins in the ventral post/ central gyrus (area 2) and passes through the rostral inferior parietal lobule (areas PF and PFG) to reach the caudal inferior parietal lobule (area PG). Both the superior parietal lobule and the rostral inferior parietal lobule also send projections to various other zones located in the parietal opercular region, the intraparietal sulcus, and the caudalmost portion of the cingulate sulcus. Areas PGm and PG, on the other hand, project to each other, to the cingulate region, to the caudalmost portion of the superior temporal gyrus, and to the upper bank of the superior temporal sulcus. Finally, a reciprocal sequence of connections, directed from caudal to rostral, links together many of the above‐mentioned parietal zones. With regard to the laminar pattern of termination, the rostral‐to‐caudal connections are primarily distributed in the form of cortical “columns” while the caudal‐to‐rostral connections are found mainly over the first cortical cell layer.
A quantitative analysis of changes in the olfactory epithelium following bulbectomy in hamster
Authors: Costanzo Richard M. , Graziadei Pasquale P. C.
Published: May 2005

Continuous replacement of sensory neurons is a normal process in the olfactory system of adult vertebrates. The capacity for replacement following experimentally induced degeneration of sensory neurons makes this system ideal for the study of the dynamics of neural populations. A quantitative analysis was made to determine the time course and degree of cell replace‐ment in the olfactory epithelium following unilateral bulbectomy in adult hamsters. Histological measurements of number of cells and epithelial thickness were made for up to 194 days postoperatively. Results for each experimental animal were expressed as a percentage of the contralateral control side. There was an immediate degeneration of cells, the number decreasing to 39% by day 4. During days 4–15 new growth resulted in an increase in cell number, which was maintained at a level of 60–70% through day 194. Epithelial thickness decreased to 60–70% during the degeneration period, but there was no recovery during subsequent days 4–194. Analysis of epithelial cells by cell type (supporting, receptor, and basal cells) showed that changes in cell numbers were limited to the neural cell populations (receptor and basal). This study confirms that olfactory sensory neurons are capable of replacement following degeneration in spite of the absence of normal target tissue. However, the observed recovery does not reach control levels and the functional capacity of replacement neurons requires further study.
Comparative study of the glial fibrillary acidic protein in vertebrates by PAP immunohistochemistry
Authors: Onteniente Brigitte , Kimura Hiroshi , Maeda Toshihiro
Published: May 2005

Glial fibrillary acidic protein (GFA) has been visualized by direct peroxi‐dase antiperoxidase (PAP) immunohistochemistry in various vertebrates (cyclostomes, teleosts, amphibians, reptiles, birds, and several placental mammals). In this study GFA‐immunoreactivity (GFA‐I) was observed in all species examined except in cyclostomes and amphibians. Two types of immunoreactive elements were observed: astrocytes and long processes without visible somata.

Astrocytic cells with GFA‐I were first found in the snake, and more cells were in birds where the pattern of distribution was similar to that of mam‐mals. Within mammals, few differences in the manner of localization were observed among different species, except in the corpus callosum and the ependymal and subependymal layers.

Long straight processes were observed in the lower submammalians‐ the lamprey, carp, and turtle. They radiated through the neuropil from the ventricular wall and followed nerve fiber bundles in the white matter. An un‐common feature was observed in the turtle brain, which possessed very in‐tense GFA‐I within the ependymal layer. The presence of GFA‐containing profiles in the ependyma of adult animals is discussed in relation to GFA‐positive structures seen in the human brain during ontogeny or under cer‐tain pathological conditions.
Autoradiographic localization of newly synthesized octopamine to retinal efferents in the Limulus visual system
Authors: Evans Judith A. , Chamberlain Steven C. , Battelle Barbara‐Anne
Published: May 2005

The biogenic amine octopamine is synthesized from both tyrosine and tyramine in the lateral, median, and ventral eyes of Limulus. The auto‐radiographic studies presented here were designed to locate the sites of octopamine synthesis in the ventral and lateral eyes. We found that efferent fibers, which project to ventral and lateral eyes from the central nervous system, became intesely and selectively labeled during in vitro incubationswith 3H‐tyramine. In the ventral eye, more than 95% of the efferent fibers were labeled. Results of biochemical analyses suggested that most of the radioactive substance within these efferent fibers was newly synthesized octopamine.

The selective labeline of efferent fibers during incubation with 3H‐tyramine was used as anatomical tool to study me number ana distribution of efferent fibers within the ventral eye. Light microscopic (LM) reconstructions of the distribution of label in serial longitudinal sections through ventral optic nerves together with electron microscopic (EM) au‐toradiographic analyses revealed between 70 and 200 efferent axons. The results of these studies and of reconstructions of efferent innervation to photoreceptor somata suggest that each ventral photoreceptor cell or each small cluster of cells is innervated by a separate efferent fiber. Both LM reconstructions and EM analyses showed that efferent fibers ramify extensively and specifically in and near the internal rhabdom of ventral photo‐receptor cells.

In EM autoradiographs of lateral eyes incubated with 3H‐tyramine, the silver grains that were located over ommatidia were concentrated exclusively over efferent fibers. All of these efferent fibers, which lay near rhab‐doms and in partitions between retinular cells, were labeled.

The results of our present studies support our hypothesis that octopamine is a neurotransmitter in Limulus retinal efferent fibers. This amine may modulate the biochemistry and physiology of ventral photoreceptor cells and may mediate many of the known effects of circadian efferent innervation to the lateral eye.
The development and postnatal organization of motor nuclei in the rat thoracic spinal cord
Authors: Smithm Carolyn L. , Hollyday Margaret
Published: May 2005

The topographic organization of the motor nuclei supplying individual thoracic muscles in postnatal rats was investigated by horseradish peroxi‐dase (HRP) labelling from the periphery. To determine whether aspects of the same organization are apparent at early developmental stages, we used HRP to label neurons contributing axons to the two primary rami of thoracic nerves in rat fetuses ranging in age from the 13th day of gestation to birth. This developmental period includes stages during which peripheral nerves and muscles are forming. The results show that motoneurons in the appropriate positions in the ventral horn have axons in each primary ramus even at stages prior to the innervation of muscle. However, in fetuses at certain developmental stages, there are also neurons located outside the motor nuclei which send axons into the peripheral nerves.
Spastic Mutant axolotl: Identification of a phenocopy pathway with implications for the control of axolotl swimming by the vestibulocerebellum
Authors: Elbert Oliver E. , Ide Charles F. , Duda Marija , Hunt R. K.
Published: May 2005

The spastic mutant axolotl shows abnormal swimming behavior, which includes a preponderance of “embryonic” swimming elements (coils) versus mature swimming elements (sinusoids) and a failure to entrain sinusoids into a prolonged swimming sequence. The mutant also shows anatomical disorganization in the area acousticolateralis and cerebellar auricle, but it is unclear (1) to what extent the behavioral abnormalities are traceable to the vestibulocerebellar defect or (2) how the vestibulocerebellar pathway modulates swimming behavior in the normal axolotl. We have performed quantitative cine analysis of electric shock‐induced swimming bouts in normal axolotls, spastic mutants, and a variety of neurosurgically altered wild‐type axolotls. We scored the incidence of coil elements (25% in controls, 70‐90% in spastics) versus sinusoid elements, as well as length distributions of coil‐free intervals (short to long trains of sinusoidal swimming) and of sinusoid‐free intervals (of brief to prolonged coiling). We found that bilateral VHIth nerve lesions or surgical undercutting of the cerebellar auricle in wild‐type axolotls almost exactly reproduced the behavioral deficit seen in spastic (75‐81% coils, loss of long sinusoid trains, and appearance of prolonged coiling intervals at least some of which coupled several coils into trains of thrashing behavior). By contrast, neither complete transection of the CNS at low midbrain levels nor section of cranial nerves V, VII, or X (lateral line) resulted in an increased incidence of coil elements beyond 26% nor significantly altered the length distributions of S‐intervals and C‐intervals. Nor did any of the latter lesions disrupt the spasticlike swimming patterns of axolots already subjected to auricle or VIIIth nerve lesions. Our data suggest that spastic behavior is attributable to some defect(s) in the vestibulocerebellar pathway, and that this pathway plays a rather subtle role in the control of swimming that involves, among other features, the selection and entrainment of mature swimming elements over embryonic ones.
Morphology of C‐laminae neurons in the dorsal lateral geniculate nucleus of the cat: A Golgi impregnation study
Authors: Hitchcock Peter F. , Hickey T. L.
Published: May 2005

On the basis of their dendritic morphology, neurons in the C‐laminae of the cat's dorsal lateral geniculate nucleus (dLGN) have been divided into five groups. These groupings are based on previous descriptions of the neuronal types present in the dLGN of the cat (Guillery, '66; Famiglietti, 70; Updyke, 79). Class 1, 2, 3, and 5 neurons in the C‐laminae are essentially identical to their counterparts in the A‐laminae, with one exception. The dendritic orientation of class 2, 3, and 5 neurons found in the C‐laminae is, for the most part, parallel to the laminar borders. In the A‐laminae, class 2 and 5 neurons show no preference in their dendritic orientation and class 3 neuron dendritic orientation is predominantly perpendicular to the laminar borders.

Class 4 neurons are found in all C‐laminae and make up the bulk of the impregnated neurons. They are morphologically distinct from A‐laminae neurons but exhibit a broad range of structural characteristics.
Afferent connections of the perirhinal cortex in the rat
Authors: Deacon Terrence W. , Eichenbaum Howard , Rosenberg Paul , Eckmann Kenneth W.
Published: May 2005

Connections of the perirhinal cortex in the.rat brain were studied using anterograde (3H‐proline/leucine) and retrograde (horseradish peroxidase) tracers. The perirhinal cortex receives major projections from medial precen‐tral, anterior cingulate, prelimbic, ventral lateral orbital, ventral and posterior agranular insular, temporal, superior and granular parietal, lateral occipital, agranular retrosplenial, and ectorhinal cortices, and from the pre‐subiculum, subiculum, and diagonal band of Broca. Rostral neocortical areas project predominantly to rostral perirhinal regions while more caudal neocortical and subicular areas project predominantly to caudal perirhinal regions.

Terminal fields are further segregated within perirhinal cortex to either the dorsal or ventral banks of the rhinal sulcus. All afferents from frontal areas terminate predominantly in the deep layers of its ventral bank; afferents from temporal, parietal, and lateral occipital areas terminate predominantly in the deep and superficial layers along its dorsal bank; and afferents from ectorhinal cortex terminate in a column within its dorsal bank.

Cortical cells which project to perirhinal areas are found predominantly in layer II and the superficial part of layer III. However, ventrolateral orbital, parietal, and lateral occipital cortex projections originate predominantly from layer V.

Perirhinal areas also receive afferents from the nucleus reuniens of the thalamus, lateral nucleus of the amygdala, claustrum, supramammillary nuclei, and the dorsal raphe nuclei.
Afferent influences on brainstem auditory nuclei of the chicken: N. laminaris dendritic length following monaural conductive hearing loss
Authors: Smith Zaid D.J. , Gray Lincoln , Rubel Edwi W
Published: May 2005

The influence of monaural acoustic deprivation on the size of dendrites in n. laminaris in the chick was examined. Chicks were raised in a controlled acoustic environment with one ear occluded from 2 days prior to hatching until 25 days after hatching by an earplug which provided a conductive hearing loss of approximately 40 dB across the audible frequency range. Each n. laminaris cell receives spatially segregated binaural excitatory innervation; one dendritic field received input from the plugged ear while the other received input from the normal ear. This arrangement allowed comparison of the size (length) of the “deprived” dendrites and the “nondeprived” dendrites for each cell. The tonotopic organization of n. laminaris allowed these comparisons to be made as a function of the frequency organization of the nucleus.

We observed systematic changes in dendritic size which differed as a function of the tonotopic position of the neurons. In high‐frequency regions the dendrites receiving information from the deprived ear were shorter than those receiving input from the normal ear. Unexpectedly, cells responsive to low frequencies showed the opposite result; the dendrites innervated from the deprived ear were longer than those responsive to the nondeprived ear. These results suggests that a relatively flat conductive hearing loss may cause nonuniform changes in activity impinging on high‐ and low‐frequency areas of the auditory system.
Anatomical and physiological studies of the gray matter surrounding the spinal cord central canal
Authors: Nahin Richard L. , Madsen Anne M. , Giesler Glenn J.
Published: May 2005

Recent histochemical evidence suggests that neurons in the gray matter surrounding the central canal may play a role in nociception. We attempted to evaluate this possibility by studying the response properties and ascending projections of these cells in the rat.

In the first series of experiments, the ascending projections of neurons around the central canal were studied by the method of retrograde transport of horseradish peroxidase (HRP). Predominantly contralateral labeling of neurons around the central canal appeared after HRP injections into the paramedian medullary or pontine reticular formation in intact or cerebellec‐tomized animals. Far fewer cells were labeled by injections into the lateral medulla and/or pons. A small number of cells was retrogradely labeled by HRP injections into the vermal and ntermediate regions of the cerebellum or the periaqueductal gray matter. Injections into other brainstem areas outside of the reticular formation also failed to label large numbers of neurons around the central canal.

In a second set of experiments, we recorded extracellular unitary activity from the lumbar enlargement in spinalized, decerebrate, unanesthetized rats. Thirteen units were functionally characterized and histologically localized within 300 μ of the central canal. All of the units identified responded exclusively to noxious stimuli applied within highly circumscrioed receptive fields.

Thus, neurons around the central canal contribute strongly to long ascending spinal cord projections. Physiologically, neurons found within this region are reminiscent of the noxious‐specific cells in the outer most layers of the dorsal horn.
The percentage of interneurons in the dorsal lateral geniculate nucleus of the cat and observations on several variables that affect the sensitivity of horseradish peroxidase as a retrograde marker
Authors: Weber Arthur J. , Kalil Ronald E.
Published: May 2005

Ten cats ranging in age from 4 weeks postnatal to adult received large bilateral injections of horseradish peroxidase (HRP) into cortical areas 17 and 18. In one cat additional unilateral injections of HRP were made into the lateral suprasylvian visual area (PMLS). The purpose of these injections was to label relay cells in lamina A of the dorsal lateral geniculate nucleus (LGN), in order to distinguish them from neurons that could not be labeled retrogradely.

Several factors thought to influence the effectiveness of HRP as a retrograde marker were varied in an effort to label as many relay cells as possible. These factors included the (1) rate and duration of HRP injections; (2) volume and concentration of HRP injected; (3) addition of L‐α‐lysophospha‐tidylcholine or dimethyl sulfoxide to the injected HRP; and (4) aldehydes and buffers used for fixation. In all experiments DAB (3,3′‐diaminobenzidine tetrahydrochloride) was used as the chromogen, either alone or with the addition of cobalt chloride, nickel, and cobalt salts, or cobalt‐glucose oxidase. In l‐μ plastic sections, the influence of each of the above factors and DAB methods was determined by measuring the percentage of unlabeled neurons and the cytoplasmic HRP grain density of cells that were labeled.

Our results show that approximately 22% of the neurons in lamina A of the LGN remain unlabeled following injections of HRP into areas 17 and 18 alone or combined with injections into PMLS. The percentage of unlabeled cells is similar at each of the ages that we studied and is not affected significantly by any of the factors that were varied or DAB methods that were used.

Cross‐sectional area measurements show that unlabeled cells tend to be among the smallest neurons in lamina A. Regardless of age, the mean size of labeled neurons was about twice that of unlabeled cells. However, we found only a weak correlation between the size of a labeled cell and the cytoplasmic density of HRP grains. Thus it is unlikely that small cell body size alone can account for tne unlabeled cells in lamina A, since small neurons can be as effective in transporting HHP retrogradely as large neurons.

We therefore conclude that there is a distinct population of small neurons in lamina A of the LGN that do not project to cortex. Although we cannot rule out the possibility that these cells project subcortically, we believe that it is reasonable to regard them as interneurons.
Axonal patterns and topography of short‐axon neurons in visual areas 17, 18, and 19 of the cat
Authors: Meyer Gundela
Published: May 2005

In a Golgi study of short‐axon cells in areas 17, 18, and 19 of the adult cat, 21 main axonal arborization patterns are distinguished and related to laminar position and dendritic morphology. Multipolar neurons exclusive to layer 2/3 exhibit the greatest diversity of axons: These may be arranged in a local tuft, a single descending stem with recurrent collaterals, a columnar descending plexus, horsetaillike bundles, a dense intralaminar plexus, or a varicose local arbor. Multipolar cells of layers 2–5 may have local basket or chandelier axons or a neurogliform axonal plexus, and axons in layer 4 may branch into a columnar basket plexus. Two types of multipolar cells are described in layers 5 and 6. Also, neurons with a bitufted dendritic tree have different axonal patterns: cone‐shaped axons, arcade axons, profuse ascending plexuses, and columnar or diffuse ascending and descending arbors. The axons of bitufted cells in layer 6 ascend or form a local tuft. Finally, giant bitufted cells with local axons, bitufted or multipolar cells with horizontal axons, and bipolar cells are described. The neuronal types established on the basis of their axonal arbor are compared to previous classifications of cortical neurons.

The location of neurons thus classified has been recorded and evaluated. Most cells show no topographical specificity and occur indistinctly in the three visual areas, while two types are exclusive to area 17. Horsetail neurons accumulate at the 17/18 and 18/19 borders. Multipolar cells of layer 2/3 with a dense intralaminar plexus and chandelier cells are concentrated in the region where the central visual field is represented.
Relationship between preferred orientation and receptive field position of neurons in cat striate cortex
Authors: Leventhal Audie G.
Published: May 2005

It has been known for two decades that neurons in mammalian visual cortex respond selectively to stimuli falling on the retina at a particular angular orientation (Hubel and Wiesel, '62). Recent evidence suggests that most cat retinal ganglion cells (Levick and Thibos, '82) and relay cells (Vidyasagar and Urbas, '82) in the cat's dorsal lateral geniculate nucleus are also orientation selective. In the retina there is a systematic relationship between receptive field position (polar angle) and preferred orientation. Outside of the area centralis, most retinal ganglion cells have oriented dendritic fields (Leventhal and Schall, '83) and respond best to stimuli oriented radially, i.e., oriented parallel to the line connecting their receptive fields to the area centralis (Levick and Thibos, '82). This relationship is strongest close to the horizontal meridian (the visual streak) of the retina (Leventhal and Schall, '83).

To determine if a relationship between preferred orientation and polar angle exists in visual cortex, the preferred orientations and receptive field positions of 768 striate cortical neurons were studied. As in the retina, a systematic relationship exists between preferred orientation and visual field position in area 17. In parts of striate cortex 15–80° from the area centralis projection there is a strong tendency for cells to respond best to lines oriented radially. In regions 4–15° from the area centralis projection this relationship appears weaker. In regions subserving the central 4° of visual angle no such relationship exists. Throughout area 17 the relationship between preferred orientation and polar angle is strongest in regions subserving the horizontal meridian.

It is suggested that the systematic relationship between preferred orientation and polar angle which begins in the retina provides an intrinsic framework for the organized arrangement of orientation “columns” in visual cortex (Hubel and Wiesel, '63). This relationship may also be responsible for the “oblique effect” as well as the visual system's preferential response to radially oriented gratings (Rovamo et al.,'82).
Time course of morphological differentiation of cat retinal ganglion cells: Influences on soma size
Authors: Rapaport David H. , Stone Jonathan
Published: May 2005

We have examined the growth of ganglion cell somas during development of the cat's retina. Until approximately E (embryonic day) 50, ganglion cell somas show no sign of the several variations in their size apparent in the adult. At about E50, the somas begin to accumulate granular cytoplasm. The accumulation proceeds first among area centralis cells which, for a few days, are the largest ganglion cells in the retina (whereas in the adult they are the smallest). By E57 three of the adult soma size trends have become apparent: the differentiation of soma size related to functional class, the nasal‐temporal difference in soma size, and the small mean size of somas in the visual streak. The early appearance of these trends in soma size suggests that individual cells may be intrinsically programmed to develop as cells of a particular class, such as alpha‐, beta‐, or gamma‐cells, even before their morphological differentiation begins. A fourth trend in soma size, the centro‐peripheral difference, appears only after an initial period of ganglion cell growth; the small size of ganglion cells at the area centralis seems to be determined, at least partly, by a local “environmental” factor, the crowding of ganglion cells.
The olivocerebellar projection to the uvula in the mouse
Authors: Eisenman Leonard M. , Sieger David D. , Blatt Gene J.
Published: May 2005

The organization of the olivocerebellar projection in the mouse was studied with the use of microinjections of horseradish peroxidase (HRP) or HRP conjugated to wheat germ agglutinin (WGA‐HRP). Injections were made in medial, intermediate, and lateral sites along the width of the uvula. The purpose of this investigation was to determine the subnuclear origin of olivary afferents to different mediolateral regions of the uvula. Injections made in or adjacent to the midline of the uvula resulted in the retrograde labeling of cells, bilaterally in the caudal portion of the medial accessory olive (MAO). These labeled cells were located primarily in subnucleus C and nucleus β of the MAO. Injections into the intermediate part of the uvula resulted in the labeling of cells in the caudal MAO (primarily nucleus β), the dorsomedial cell column (dmcc), and a few cells in the ventral lamella of the principal olive (vPO). Laterally placed injections produced labeling of cells in dmcc and the vPO. These results are discussed in reference to the parasagittal organization of olivary afferents to the cerebellar cortex in the mouse (Beyerl et al., '82) and the organization of afferents to the involved regions of the inferior olivary (IO) complex. It is suggested that these parasagittal zones in the uvula may play different roles in the control of eye movements.
Developmental changes in the relationship between type 2 synapses and spiny neurons in the monkey visual cortex
Authors: Mates Sharon L. , Lund Jennifer S.
Published: May 2005

This study continues an exploration of synaptic development in the primary visual cortex of the monkey (Macaca nemestrina). In a prior study (Mates and Lund, '83a), we observed that type 2 synapses on the cell bodies of spiny stellate neurons of lamina 4C appeared not only to increase in number during early postnatal development but also subsequently decreased during maturation. Using quantitative, stereological electron microscopic methods, we examined the maturation of this synapse population from embryonic day 159 to adult, on spiny stellate neurons of 4Cα and β and, for comparison, on pyramidal neurons in upper and lower lamina 6. Tissue was also taken for comparison from two animals reared to 8 weeks of age with binocular eyelid closure from birth. We confirmed that a marked increase and subsequent decrease occurred in this somal type 2 synapse population on both neuron populations. However, due to the infrequency of the smooth dendritic neurons (approximately 5% of the neuron population) giving rise to the type 2 contacts, and due to expansion of the neuropil during maturation increasing intercell distances against constant volume of the type 2 axon arbors, it is concluded that the decrease in, type 2 somal synapses may represent a redistribution to dendrites rather than loss from the neuropil. Cells of lamina 4Cβ (receiving input from the parvocellular lateral geniculate nucleus‐LGN) show a slower initial accumulation of type 2 contacts compared to neurons of lamina 4Cα (receiving input from magnocellular LGN), or to pyramidal neurons of lamina 6. The type 2 synapse population of the 4Cβ neurons also showed no reduction in the animals visually deprived to 8 weeks of age, unlike the populations of type 2 synapses in 4Cα and 6, which were fewer than normal.
The abducens nucleus in the carpet shark Cephaloscyllium isabella
Authors: Montgomery John C. , Housley Gary D.
Published: May 2005

This study utilizes retrograde axonal transport of cobaltous‐lysine, and conventional silver and Golgi staining techniques to study the abducens motor nucleus innervating the external rectus muscle of the carpet shark. The nucleus consists of 300–400 motoneurons located immediately ventrolateral to the medial longitudinal fasciculus (MLF), distributed over about 1.25 mm in a rostrocaudal direction at the level of exit of the VI nerve. The axons of the motoneurons form seven or eight discrete ventrally directed fascicles which, having exited from the brainstem, group together to form the abducens (VI) nerve. The motoneurons are on average about 16 μm in diameter, are bipolar, and their dendrites have a transverse orientation. Typically one set of dendrites penetrates the MLF and the other set extends ventrally into the reticular formation.
The intrinsic architectonic and connectional organization of the superior temporal region of the rhesus monkey
Authors: Galaburda Albert M. , Pandya Deepak N.
Published: May 2005

The superior temporal region (STR) in the rhesus monkey includes the circular sulcus (Cis), the supratemporal plane (STP), and the superior temporal gyrus (STG). Rostrally the STR is continuous with the periallocortices of the prepyriform and anterior insular regions; caudally it borders the isocortices of the inferior parietal lobule and the superior temporal sulcus. The STR contains 12 cytoarchitectonic areas: four fields on the Cis, four on the STP, and four on the STG. The sulcal fields (root fields) are adjacent to the insula and resemble it in the possession of a relatively strong layer V; the STP fields (core fields) are characterized by well‐developed layer IV; and the STG fields (belt fields) exhibit strong differentiation of layer III. In each line of fields the more rostral ones show relative prominence of the deeper layers, with increasing prominence of the superficial layers occurring caudad in a stepwise fashion.

Analysis of the connectional organization of the fields within the STR suggests an assembly of four rostrocaudal stages, each composed of one field from each line–a root, a core, and a belt field. There is a specific arrangement of connections among the fields of a given stage and between fields in adjacent stages. Projections directed caudally from one field to another field in the adjacent stage arise in layers V and VI and terminate in the superficial layers (mainly layer I). Projections directed to a field in a rostrally adjacent stage arise from layer III neurons and terminate in layers III and IV, usually in columns. There is also a laminar specificity between fields lying within a given stage.
Transient cerebrocerebellar projections in kittens: Postnatal development and topography
Authors: Tolbert Daniel L. , Panneton W. Michael
Published: May 2005

Orthograde and retrograde labeling techniques were used to study the ontogenesis of transient cerebrocerebellar projections in kittens. Tritiated amino‐acid or horseradish peroxidase injections were made into the coronal gyms of the primary somatosensory cortex of kittens 1–70 postnatal days old. Orthogradely labeled axons were observed bilaterally in the superior and inferior cerebellar peduncles in kittens between 6 and 49 postnatal days of age. Most cerebrocerebellar axons labeled on the ipsilateral side arise from the pyramidal tract as it courses through the pontine nuclei. These axons descend through the pontine tegmentum as a diffusely organized corticotegmental tract and enter the ipsilateral superior cerebellar peduncle. Fewer cerebrocerebellar axons leave the pyramidal tract caudal to the pontine nuclei and project into the contralateral superior cerebellar peduncle. Cerebrocerebellar projections through the superior cerebellar peduncles terminate pri‐marily in the cerebellar nuclei, where they are localized in the interpositus nuclei and in immediately adjacent areas of the dentate and fastigial nuclei.

More caudally, labeled axons exit from the pyramidal tract and take a superficial route around the ventrolateral brainstem into the inferior cerebellar peduncles bilaterally. These projections are more numerous contralaterally and are directed primarily to the internal granule cell layer of the posterolateral folia of the anterior lobe, the posteromedial simplex lobule, and the dorsal paramedian lobule.

Horseradish peroxidase injections were made into the cerebellar posterior lobe and deep nuclei and the results from these cases showed that the cerebrocerebellar pathway originates from pyramidal neurons in layer V primarily in the coronal, the precoronal, and the anterior and posterior sigmoid gyri on both sides. In these gyri, many of the HRP‐positive neurons were found in clusters of two to five neurons, aligned in anterior‐posterior strips.

The results from all experiments provide evidence about the ontogeny of cerebrocerebellar projections. Projections through the superior cerebellar peduncles generally develop at 6–8 postnatal days of age, whereas projections through the inferior cerebellar peduncles first are seen at 8–10 days postnatally. Cerebrocerebellar projections reach their maximum development in the second postnatal week but sharply decrease in density during the third postnatal week. No cerebrocerebellar projections were observed after the seventh postnatal week of development. Possible functional implications for this transient projection are discussed.