bluuebunny/crossref_metadata_2025 huggingface dataset:
An ultrastructural analysis of afferent terminals to the anterior pretectal nucleus in the cat
Authors: Kitao Yasuko , Nakamura Yasuhisa
Published: January 2005

The synaptic organization of three kinds of afferent projections in the feline anterior pretectal nucleus (PTA) was analyzed by a combination of the degeneration and retrograde transport of horseradish peroxidase (HRP) techniques, along with that of the degeneration and anterograde transport of HRP techniques. Retrograde labeling of PTA neurons was performed by injections of HRP in the dorsal accessory olivary nucleus (DAO). Three kinds of afferent sources of the PTA–the cerebral motor cortex, the anterior interpositus nucleus of the cerebellum, and the gracile nucleus‐were subjected to electrolysis, suction, or injection of kainic acid or HRP for identification of axon terminals of each system. Axon terminals of these different afferent sources identified by degeneration or anterograde HRP transport techniques showed similar morphological features: They were relatively large (1–6.5 μm in diameter), contained round or ovoid synaptic vesicles, and made asymmetrical synaptic contacts. When the degeneration study was combined with the retrograde HRP transport technique, some degenerating terminals from the motor cortex, anterior interpositus, or gracile nuclei were found to synapse directly with HRP‐labeled dendrites or somata of the PTA neurons projecting to the DAO. Each combination of the degeneration and anterograde HRP transport techniques revealed the fact that neither degenerating nor HRP‐labeled terminals were found to synapse with the same neuronal structure.

These observations indicate (1) that the PTA neurons relay afferent inputs from three different sources directly to the DAO, and (2) that there is a possibility of parallel processing rather than convergence of three different afferent systems via the PTA to the DAO.
Evidence for interlaminar inhibitory circuits in the striate cortex of the cat
Authors: Kisvarday Z. F. , Martin K. A. C. , Somogyi P. , Friedlander M. J.
Published: January 2005

An interlaminar, ascending, and GABAergic projection is demonstrated in the striate cortex of the cat. We have examined a basket cell, with soma and smooth dendrites in layers V and VI, that was injected intracellularly with HRP in the kitten. Three‐dimensional reconstruction of its axon revealed (1) a horizontal plexus in layer V and upper VI, extending about 1.8 mm anteroposteriorly and 0.8 mm mediolaterally; (2) a dense termination in the vicinity of the soma in layers V and VI; and (3) an ascending tuft terminating in layers II and III in register above the soma and about 250 μm in diameter. Many boutons of this cell contacted neuronal somata and apical dendrites of pyramidal cells and subsequent electron microscopy snowed that these boutons formed type II synaptic contacts with these structures. A random sample of postsynaptic targets (n=199) in layers III, V, and VI showed that somata (20.1%), dendritic shafts (38.2%), and dendritic spines (41.2%) were contacted. The fine structural characteristics of postsynaptic elements indicated that the majority originated from pyramidal cells. Direct identification of postsynaptic neurons was achieved by Golgi impregnation of four large pyramidal cells in layer V, which were contacted on their somata and apical dendrites by between three and 34 boutons of the HRP‐filled basket cell. Layer IV neurons were not contacted. Golgi‐impregnated neurons similar to the HRP‐filled basket cell were also found in the deep layers. The axonal boutons of one of them were studied; it also formed type II synapses with somata and apical dendrites of pyramidal cells.

Boutons of the HRP‐filled neuron were shown to be GABA‐immunoreactive by the immunogold method. This is direct evidence in favour of the GABAergic nature of deep layer basket cells with ascending projections. The existence of an ascending GABAergic pathway was also demonstrated by injecting [3H]GABA into layers II and III. The labelled amino acid was transported retrogradely by a subpopulation of GABA‐immunoreactive cells in layers V and VI, in addition to cells around the injection site.

The axonal pattern and mode of termination of deep basket cells make them a candidate for producing or enhancing directional selectivity, a characteristic of layer V cells. The results together with our previous data on basket cells terminating mainly either in layer IV or layers II and III demonstrate great specificity in the origin and laminar distribution of axosomatic, GABAergic, and presumably inhibitory synaptic terminals. The laminar specificity suggests that those functional properties that are brought about by basket cells have to be generated and/or reinforced at each level of cortical processing.
Development of substance P‐like immunoreactivity in Xenopus embryos
Authors: Gallagher Betty C. , Moody Sally A.
Published: January 2005

The development of substance P‐like immunoreactivity (SPLI) was studied in the Xenopus embryonic nervous system in order to determine in which neuronal populations and at what developmental times SPLI is expressed. Although Rohon‐Beard neurons initially were thought to be the only substance P‐immunoreactive cells in the embryonic frog spinal cord, we have demonstrated that several neuronal phenotypes are immunoreactive. The earliest evidence of SPLI was seen at stage 28 (Nieuwkoop and Faber, '67), at which time only some trigeminal ganglion cells, their axons in the ophthalmic nerve, and axons in the lateral tracts of the hindbrain showed SPLI. In the embryonic brain at stages 29/30, 37/38, and 42, SPLI was seen in the hypothalamus, trigeminal ganglion cells and their peripheral axons, the sensory roots of cranial nerve IX/X, and axons in the hindbrain lateral tracts. At premetamorphic stages, SPLI was found in several populations that are immunoreactive in adult amphibia.

In the embryonic spinal cord, Rohon‐Beard neurons were labeled consistently with reaction product; there was a rostrocaudal time gradient of immunoreactivity with increasing development. The Rohon‐Beard neurons were not immunoreactive at developmental stages in which axonal outgrowth was beginning (stage 21), but were strongly immunoreactive at stages in which target cells had been contacted (stage 29). Several types of interneurons in the spinal cord (as classified by Roberts and Clarke, '82) showed SPLI during embryonic stages. At premetamorphic stages the Rohon‐Beard neurons began to disappear and the immunoreactive interneurons were distributed similarly to those reported in the adult. Dorsal root ganglia differentiated during these stages, and at this time some of the neurons belonging to these ganglia exhibited substance P‐like immunoreactivity.
Subset of neurons characterized by the presence of NADPH‐diaphorase in human substantia innominata
Authors: Ellison David W. , Kowall Neil W. , Martin Joseph B.
Published: January 2005

The substantia innominata encompasses an area of the basal forebrain that is ventral to the lenticular nucleus and anterior commissure, medial to the claustrum and external capsule, and lateral to the hypothalamus. The nucleus basalis of Meynert consists primarily of large acetylcholinesterase (AchE)‐positive neurons embedded within the substantia innominata. Damage to these neurons may be important in the pathogenesis of cortical dysfunction in Alzheimer's disease. In order to characterize other neuronal elements in the substantia innominata and their relationship to the nucleus basalis, we chose to study a biochemically distinct neuronal subset containing the enzyme nicotinamide adenine dinucleotide phosphate diaphorase (NADPH‐d).

The substantia innominata was blocked from six normal brains obtained postmortem and fixed in neutral‐buffered formalin at 4°C for 48 hours. Free‐floating 50‐μm sections from several levels were stained for NADPH‐d or AchE activities. Selected sections were double stained for NADPH‐d and AchE.

NADPH‐d activity was present in a network of pleomorphic neurons that extended through all levels of the substantia innominata and into the striatum and amygdala. NADPH‐d neurons were particularly numerous at the level of the anterior commisure and were closely associated with the cholinergic neurons of the nucleus basalis. They were not seen in the ventral pallidum, or the vertical limb of the diagonal band of Broca or in the islands of Calleja. The cell bodies of NADPH‐d neurons were quite varied in shape, ranging from ovoid to fusiform, and about half the cells were bipolar. Where neuronal density was high, their dendrites formed an interlacing pattern. NADPH‐d‐positive fibres were seen coursing through the external capsule, hypothalamus, and amygdala.

This novel set of neurons in the substantia innominata may be part of a more extensive network that interacts with the magnocellular basal fore‐brain system at the level of the nucleus basalis. Whether other neurotransmitters are present within these neurons and whether NADPH‐d neurons are involved in Alzheimer's disease remain to be elucidated.
Redirected growth of pyramidal tract axons following neonatal pyramidotomy in cats
Authors: Tolbert D. L. , Der T.
Published: January 2005

After the pyramidal tract at the pontomedullary junction in neonatal cats had been cut and the ipsilateral frontoparietal cortex injected with intra‐axonal markers at 40 to 74 days of age, cortical axons were labeled in aberrant pathways that descended into the caudal medulla and spinal cord. Some labeled axons from the damaged pyramidal tract crossed the midline, descended with fibers in the intact pyramidal tract through the pyramidal decussation, and entered the lateral corticospinal tract. Another group of aberrant projections descended bilaterally along the ventrolateral edge of the medulla and either ended in the lateral reticular nuclei or continued into the spinal cord. Finally, some axons descended individually through the central medullary tegmentum and ended bilaterally in the spinal trigeminal, dorsal column, and lateral reticular nuclei. Although these findings suggest that pyramidal tract axons regenerate after injury, the findings from a second series of experiments refute this conclusion. In 2‐to 5‐day‐old cats, the fluorescent dye Fast Blue was injected into the spinal cord, and 7 to 8 days later the contralateral pyramidal tract was cut. In these animals, there were never any cortical neurons retrogradely labeled with Fast Blue in the frontoparietal cortex ipsilateral to the pyramidotomy, although numerous neurons were labeled contralaterally. Control experiments confirmed that the interval between the Fast Blue injections and the pyramidotomies was long enough for retrogradely labeling cortical neurons, that the spinal cord injections did not adversely affect the retrogradely labeled cortical neurons, and following axotomy dying cortical neurons could be demonstrated directly using silver impregnation techniques. We conclude that neonatal pyramidotomy causes the death of all axotomized cortical neurons in kittens, and, therefore, the aberrant cortical projections seen caudal to the lesion must be redirected, late‐developing, and undamaged cortical axons, and not regenerated axons.
Development of myelinated nerve fibers in the sixth cranial nerve of the rat: A quantitative electron microscope study
Authors: Hahn Angelika F. , Chang Yoong , deF. Webster Henry
Published: January 2005

Myelination was studied quantitatively in the sixth cranial nerves of rats by counting and measuring all myelinated fibers during the first three postnatal weeks. In transverse semithin and thin sections cut serially at a well‐defined anatomical site in the midsphenoid region, only a few axons (mean 12) were myelinated at birth. On days 2, 4, and 8, counts of myelinated fibers were respectively 5 times (mean 57), 20 times (mean 230), and 24 times (mean 273) the number seen at birth. During the second postnatal week, the number of myelinated fibers remained constant, whereas growth of axons and their myelin sheaths continued. By 15 days these fibers were large and relatively uniform in size; they had compact, circular myelin sheaths. During the third postnatal week, myelination of previously unmyelinated, smaller axons began. The number of myelinated fibers increased again and the size distribution of myelinated fibers became bimodal. Axon diameters, fiber diameters, and myelin sheath dimensions for all fibers were calculated from measurements made on electron micrographs. The transverse length of the myelin membrane increased exponentially with time. The growth increased rapidly during the formation of the first 20 spiral layers and remained relatively constant during the subsequent enlargement of the compact sheath. The association of axon diameter and myelin sheath thickness was poor at young ages, but it improved progressively with maturation of the sheath. The results show that myelination begins around axons that have a wide range of diameters. Also, the first axons to be myelinated become the large myelinated fibers of the sixth nerve. The small myelinated fibers originate from axons that do not become myelinated until the third postnatal week. Myelination, though differing in onset by 2 weeks, appeared to be similar in both populations as judged by similarity of sheath morphology and growth rates. It is of interest that at the level studied, the sixth nerve also contains a fascicle of unmyelinated cranial sympathetic fibers.
Postnatal development of the feline lateral cervical nucleus: I. A quantitative light and electron microscopic study
Authors: Broman Jonas , Flink Roland , Westman Jan
Published: January 2005

With the aim of obtaining some basic information for future developmental studies, the lateral cervical nucleus (LCN) was investigated in 32 kittens of different ages by electron microscopic and stereologic methods. Corresponding light microscopic measurements of neuronal and nuclear profiles and of the total LCN volume were also performed. The total LCN volume increased sixfold between the ages of 12 hours and 120 days, the most rapid increase occurring during the first month. The neuronal size was fairly constant up to the age of 9 days, whereafter it showed greater variation. The mean profile area increased rapidly during the second week and then more slowly. The relative volume of boutons increased significantly between birth and the age of 34 days and then decreased slightly up to 120 days postnatally. The total bouton volume showed a steady increase, which was most pronounced between the ages of 9 and 34 days. The relative dendritic volume decreased during the 120 days of observation, whereas the total volume of dendrites increased up to the age of 92 days and then decreased. The total volume of glial cells increased during the 120‐day observation period, as did both the relative and total volumes of myelinated axons. The changes in the relative volumes of mitochondria in boutons and dendrites were very similar, with increases that were most marked between the ages of 9 and 34 days and between 92 and 120 days.
Localization of immunoreactive tyrosine hydroxylase in the goldfish brain
Authors: Hornby P. J. , Piekut D. T. , Demski L. S.
Published: January 2005

This report describes the distribution of tyrosine hydroxylase immunoreactive (TH‐ir) structures in the brain of the goldfish (Carassius auratus). The localization of TH‐ir cell groups revealed by immunocytochemical techniques is largely in accordance with catecholamine distribution previously reported in teleosts by using monoamine fluorescence; however, in the telencephalon and diencephalon, several new cell groups are elucidated. In the telencephalon, TH‐ir cell bodies are observed in the olfactory bulb, area ventralis telencephali, and the central zone of the area dorsalis telencephali. TH‐ir fibers and terminals are moderately dense throughout the telencephalon except for a sparse innervation of the area dorsalis, pars medialis. Immunostained cells are present in the suprachiasmatic nucleus and magnocellular and parvicellular components of the preoptic nucleus. Immunoreactive fibers from preoptic cells can be traced caudally in two main tracts to the infundibulum. Dense immunoreactivity around cells in the pituitary provides anatomical support for catecholamine involvement in the neuroendocrine axis probably via preopticohypophysial connections. At middiencephalic levels, immunoreactive cells are present in the ventral thalamus, nucleus pretectalis periventricularis, pars ventralis, and paraventricular organ pars anterioris. In the caudal diencephalon, TH‐ir cells are seen within the posterior tuberal nuclei and dorsal to posterior recess. No immunostained cells are observed in the midbrain. In the hindbrain, tyrosine hydroxylase containing cells comprise three groups similar to that described using Falck‐Hillarp histofluorescence (Parent et al., ′78), i.e., isthmal, central medullary, and medullospinal groups. Tyrosine hydroxylase immunoreactivity is interpreted as evidence for the presence of catecholamines and not only provides an anatomical basis for the functional significance of catechol amines in teleosts, but may be useful in elucidating homologous structures in tetrapod vertebrates, although certain sites of immunoreactivity may prove to be unique to teleosts.
Ultracytochemical distribution of ouabain‐sensitive, K+‐dependent, p‐nitrophenylphosphatase in the synaptic layers of goldfish retina
Authors: Yazulla Stephen , Studholme Keith M.
Published: January 2005

Ouabain‐sensitive, K+‐dependent p‐nitrophenylphosphatase (K+‐pNPPase) activity, which represents the second dephosphorylation step of Na+, K+‐ATPase, was localized histochemically at the light and electron microscopical levels in the goldfish retina. K+‐pNPPase staining was most intense in the outer and inner plexiform layers and less intense over the photoreceptor inner segments. K+‐pNPPase staining was observed on the membranes of horizontal cell dendrites and presynaptic membrane of all cone pedicles but only rarely over rod spherules. Bipolar cell dendrites in the outer plexiform layer were not stained for K+‐pNPPase. In the inner plexiform layer (IPL), K+‐pNPPase staining was observed at 90% of the bipolar cell ribbon synapses but only at 40% of amacrine cell synapses. The proportion of K+‐pNPPase staining at amacrine cell synapses increased from 26 to 49% as one progressed from the outer to inner layers of the IPL, while staining at bipolar cell synapses showed no such trend. Only 16% of the amacrine synapses onto mixed, rod‐cone (mb) bipolar cell synaptic terminals were positive for K+‐pNPPase. We suggest that the differential distribution of K+‐pNPPase staining at retinal synapses can be explained, in part, by the ionic conductances gated at the postsynaptic sites. In addition, the presence of K+‐pNPPase on lateral horizontal cell dendrites in cone pedicles is consistent with the hypothesis that the sodium pump is involved in the release of GABA at feedback synapses from horizontal cells to cone photo‐receptors.
Glycogen phosphorylase activity in the olfactory bulb of the young rat
Authors: Coopersmith Robert , Leon Michael
Published: January 2005

The activity of glycogen phosphorylase, the enzyme that controls glycogen breakdown, was histochemically mapped in the olfactory bulbs of 19‐day‐old rats. The effect of early odor experience on subsequent olfactory bulb phosphorylase activity was also examined. The highest level of phosphorylase staining in the bulb (and seemingly the highest in the brain) was in the glomerular layer, followed by the external plexiform, internal plexiform, granule cell, and olfactory nerve layers. Virtually no activity was visible in the large output neurons of the bulb, mitral, and tufted cells. Early peppermint odor experience, previously shown to increase metabolic activity in specific glomerular foci as measured by 2‐deoxyglucose uptake, had no apparent effect on glomerular‐layer phosphorylase activity. In some odor‐familiar animals, however, patches of activity were seen in the internal plexiform layer in the area of the bulb where foci of high deoxyglucose uptake are seen in response to peppermint. The patches were directly in line with modified glomerular clusters often seen to underlie foci of enhanced deoxyglucose uptake.

The existence of particularly heavy activity in the peripheral third of the glomerular layer, where glycogen‐containing modified Schwann cells have been localized, raises the possibility that the glomerular‐layer activity is at least partially glial in origin. Finally, because of its rich noradrenaline and serotonin innervation and high density of insulin receptors, the olfactory bulb is proposed as a model system to study the interaction of glycogen/glucose metabolism with neural activity in a relatively well‐defined neuronal circuit.
Motoneuron number in the lumbar lateral motor column of larval and adult bullfrogs
Authors: Farel Paul B.
Published: January 2005

Motoneuron number in the lumbar lateral motor column of the bullfrog, Rana catesbeiana, was investigated through the course of premetamorphic development and in postmetamorphic frogs. Motoneurons were distinguished on the basis of histological characteristics into two classes, type L (less differentiated) and type M (more differentiated). The number of type L motoneurons on each side showed a precipitous decline between stages V and VI (6,300 to 2,500) and a slower rate of loss until stage XI (to 550). Type M motoneurons increased in number between stages V and VII (560 to 2,775) and declined precipitously between stages VII and VIII to a value similar to that of juvenile frogs (1,100). These changes in motoneuron number do not correspond to the formation of myotubes or to the appearance of contractile properties in hindlimb muscles. The development of myotubes in the hind‐limb occurs only after total motoneuron number has declined by 35%. Similarly, hindlimb muscle contraction develops after the early decline in type L motoneuron number and is restricted to proximal thigh at the peak of type M motoneuron number.

In postmetamorphic frogs, a weak (r = 0.44) but statistically significant correlation was found between type M motoneuron number and body length. In the largest frogs (greater than 15 cm body length), 1262 ± 157 (mean ± s.d.) motoneurons were present, whereas the smallest frogs (less than 5 cm body length) had 1099 ± 98 motoneurons. These results are not consistent with previous findings that the variance of motoneuron number among small frogs is greater than that among larger frogs. The present results are thus inconsistent with explanations of size‐related differences in motoneuron number that are based on selection of small frogs with greater number of motoneurons for survival. The increase in motoneuron number may be due to a slow addition of newly born motoneurons to the LMC or to the differentiation of existing motoneurons. The latter possibility is supported by the finding that the number of presumptive type L profiles is less in larger frogs.
Stereological analysis of synaptogenesis in the molecular layer of piriform cortex in the prenatal rat
Authors: Newman‐gage Helen , Westrum Lesnick E. , Bertram John F.
Published: January 2005

The development of synapses in the molecular layer of the rat piriform cortex was studied at embryonic days 15, 17, 19, and 21. The present study has sought to extend past studies of synaptogenesis by identifying not only changes in numbers of synapses, but also changes in numbers of potential precursors of synapses. A stereological method (Cruz‐Orive, ′80) was used to make volumetric estimations of the numbers of synapses, axonal puncta, vesicle‐associated puncta, and unapposed postsynaptic specializations. This stereological method was preferred to other morphometric methods because it is not influenced by changes in the size, shape, or orientation of the structures of interest. This was considered important since such changes might be expected during development.

Large numbers of unapposed axonal specializations (axonal puncta and vesicle‐associated puncta) were found in all three sublaminae (lateral olfactory tract, Ia, and Ib) at all ages. The numerical density (number per unit volume of neuropil) and relative frequency of these structures changed significantly with time. In all three sublaminae, these changes were associated with changes in the number of synapses, although the numerical density and relative proportions varied between the sublaminae. These results suggested that axonal puncta could accumulate vesicles, thus becoming vesicle‐associated puncta, and that vesicle‐associated puncta could contact dendrites, thus forming synapses. In contrast, the numerical density of lone postsynaptic specializations remained low and no significant changes in their relative proportion in the population were found. This suggested that although lone postsynaptic sites were observed, they did not appear to play a major role in synaptogenesis in this region of the cortex. In addition to documenting developmental differences between the three sublaminae in the molecular layer, the results support a synaptogenic hypothesis in which the axon can form surface specializations that appear to be involved in synaptogenesis, independent of direct dendritic contact.
Distribution of external cuneate nucleus afferents to the cerebellum: II. Topographical distribution and zonal pattern‐an experimental study with radioactive tracers in the cat
Authors: Jasmin L. , Courville J.
Published: January 2005

Small injections of tritiated leucine and the autoradiographic method were used to demonstrate efferents from restricted portions of the external cuneate nucleus (NCE) to the cerebellum. Sites of injection were analyzed by reference to the distribution of primary muscle afferents in NCE. On transverse sections, the silver deposits form longitudinal bands that, in certain regions, are packed together and label the entire surface of the granular layer; in other parts, they are separated by empty longitudinal bands. The longitudinal deposits are not continuous in the rostrocaudal direction. On the basis of the distribution of the longitudinal bands, 14 zones have been described for lobules II‐VI, and 6 zones were recognized in lobules I, VIII, and the paramedian lobule. Afferents from NCE are distributed topographically. Regions of the nucleus receiving axial and neck muscles project mainly to vermal regions of lobules I‐III, and to parts of lobules VIII and IX. Regions receiving afferents from forelimb muscles send their fibers preferentially to the vermian region of lobule V, to paravermian regions of lobules IV‐VI, to parts of lobules VIII and IX, and to the paramedian lobule. These distributions in several respects are in agreement with the somatotopical maps of the cerebellum. However, other features support a “mosaic” arrangement: efferents from a region of NCE are distributed over several distinct sites of the cortex and efferents from different parts of the nucleus also converge to neighboring cortical regions.
Retinal ganglion cells projecting to the accessory optic system in the rat
Authors: Dann Joan F. , Buhl Eberhard H.
Published: January 2005

The present data identify the distribution and morphological features of a homogeneous group of rat retinal ganglion cells. These cells were labelled after injection of either horseradish peroxidase or a fluorescent tracer, Fast Blue, into the medial terminal nucleus (MTN) of the accessory optic system. After retrograde fluorescent labelling, MTN‐projecting retinal ganglion cells were intracellularly injected with Lucifer Yellow to reveal their complete dendritic morphology.

There were on average 1,750 MTN‐projecting cells fairly evenly distributed over the entire retinal ganglion cell layer. Their density ranged from 40–49 cells/mm2 in superior retina to 10–19 cells/mm2 towards the peripheral regions of both inferior and superior retina. The area of highest density formed a nasal‐temporal band suggestive of a visual streak.

Soma diameters ranged from 8.7 to 14.5 μm centrally and from 9.9 to 17.1 μm peripherally. Maximal dendritic field diameter ranged from 431 to 644 μm and averaged 516 μm with no obvious eccentricity dependence.

The majority of MTN‐projecting cells were bistratified. Dendrites stratified predominantly in the inner sublamina of the inner plexiform layer (IPL) with a varying number of branches from the remaining dendrites contained within the outer IPL, both strata presumably corresponding to the electrophysiologically determined on‐off dichotomy.

Cells projecting to the MTN were characterised by higher‐order dendritic branching patterns that resulted in a dense dendritic tree with minor dendritic overlap. The slender dendrites had a beaded appearance and displayed spiny protrusions. The dendritic coverage of 5–6, stratification pattern, and overall morphological appearance of rat MTN‐projecting cells renders them suitable candidates for on‐direction‐selective cells shown electrophysiologically to be linked with the MTN of the accessory optic system.
Variation in the mode of receptor cell addition in the electrosensory system of gymnotiform fish
Authors: Zakon Harold H.
Published: January 2005

Age‐related changes in ampullary and tuberous receptor organ morphology were studied in six species of gymnotiform weakly electric fish. Cheek skin was silver‐stained, whole‐mounted, and viewed under Nomarski differential interference contrast optics. The ampullary receptor units of all species show an increasing number of receptor organs per afferent fiber with fish size, presumably the result of addition of newly formed receptor organs. Ampullary units composing over a dozen organs were observed in large specimens of a few species. Receptor cells were also added in the tuberous receptor system of all species, but in different ways. As previously reported for Sternopygus, small specimens of Eigenmannia had only a single tuberous receptor organ per afferent. Fish of increasing size retained a population of afferents that innervated only a single receptor organ and, in addition, had a population of afferents that innervated a cluster of receptor organs. The mean number of receptor organs per cluster increased in fish of increasing size. In addition, the mean number of sensory receptor cells per organ increased. New organs presumably derive from older ones, which divide under the stimulus of continued addition of new receptor cells. Apteronotus, Adontosternarchus, and Hypopomus all added more receptor cells to their tuberous organs. In these species, every afferent innervated only a single tuberous organ and there was no indication of division of receptor organs. Gymnorhamphichthys and Gymnotus were intermediate in that they added new receptor cells to each receptor organ, and, in larger fish, these were segregated into discrete patches within a single receptor organ. It is likely that the additon of new receptor cells aids in increasing sensitivity of both ampullary and tuberous receptors as fish grow.
Synaptic structure of the monoamine and peptide nerve terminals in the intermediolateral nucleus of the guinea pig thoracic spinal cord
Authors: Chiba Tanemichi , Masuko Sadahiko
Published: January 2005

Synaptic organization of the intermediolateral nucleus of the guinea pig thoracic spinal cord was examined with particular focus on monoamine‐ and peptide‐containing nerve terminals. Axon varicosities having flat synaptic vesicles constituted 17% of all axons in the nucleus and formed exclusively symmetric synapses. Enkephalin‐, substance P‐, somatostatin‐, 5‐hydroxytryptamine‐, and catecholamine‐immunoreactive nerve terminals were densely distributed, while neurotensin‐, vasoactive intestinal polypeptide‐, oxytocin‐, and cholecystokinin‐8‐immunoreactive nerves were sparse in the nucleus. Coexistence of 5‐hydroxytryptamine and enkephalin was demonstrated, and coexistence of somatostatin and enkephalin as well as somatostatin and 5‐hydroxytryptamine in the same axons was also shown by serial semithin sections. Catecholamine axons labelled by 5‐hydroxydopamine formed axodendritic and axosomatic synapses and made direct synaptic contacts on the preganglionic sympathetic neurons identified by retrograde transport of horseradish peroxidase. Direct synaptic contacts from enkephalin‐ and substance P‐immunoreactive axons to preganglionic sympathetic neurons were also revealed. Enkephalin‐, substance P‐, and 5‐hydroxytryptamine‐imunoreactive axons formed axodendritic and axosomatic synapses. Catecholamine axon varicosities constituted 19% of all axon varicosities in the nucleus and 30% of them showed synaptic specializations in a sectional plane. Axon varicosities immunoreactive to enkephalin, 5‐hydroxytryptamine, and substance P constituted approximately 35, 19, and 13% of all axon varicosities, respectively, while those with synaptic contacts made up 27, 30, and 26%, respectively, in a sectional plane. Enkephalin‐, 5‐hydroxytryptamine‐, and noradrenaline‐immunoreactive axons showed mainly symmetric synaptic contacts.
Retinotopic organization in the dorsal lateral geniculate nucleus of the tammar wallaby (Macropus eugenii)
Authors: Wye‐Dvorak J. , Levick W. R. , Mark R. F.
Published: January 2005

Electrophysiological recordings were made from 187 single cells in the tammar wallaby (Macropus eugenii) dorsal lateral geniculate nucleus (LGNd). The results show that it is topographically organized such that the superior visual field is represented dorsally, the inferior field is represented ventrally, the nasal visual field is represented ventrally, and the temporal visual field is represented rostrally.

The visual field of one eye ranges from −30° nasal to +179° temporal in azimuth and +73° superior to −49° inferior in elevation. Ganglion cells that had receptive field positions between −9° and +179° projected to the contralateral LGNd while the ganglion cells that projected to the ipsilateral LGNd had visual fields from 0 to +30°.

The binocular visual field extends 60° in azimuth. This representation in the LGNd is expanded relative to the monocular representation. There is also an increased representation of the horizon in the temporal field corresponding to the visual streak of retinal ganglion cells. The binocular visual field is located where contralateral and ipsilateral laminae are shown to interdigitate by proline autoradiography.

There are nine eye‐specific laminae in the LGNd. Four receive afferents from the contralateral eye and five receive afferents from the ipsilateral eye. The lines of isoelevation are perpendicular to the coronal plane of section while the lines of isoazimuth are nearly parallel to the coronal plane. The lines of projection representing one visual direction are inferred to be perpendicular to the tangent of curvature of the laminae as in the LGNd of other mammals.

The majority of cells (85%) recorded had on‐ or off‐centre responses. On‐and off‐centre responses were not apparently segregated in the LGNd but segregation may not have been revealed by the single‐unit recording technique.
Organization of anterogradely labeled spinocervical tract terminations in the lateral cervical nucleus of the cat
Authors: Craig A. D. , Sailer S. , Kniffki K.‐D.
Published: January 2005

The anterograde transport of horseradish peroxidase following injections into the cervical, thoracic, or lumbosacral spinal cord was used to examine the organization of spinocervical tract terminations in the lateral cervical nucleus (LCN) of the cat. A somatotopic organization of the labeling originating from different spinal levels was observed in the mediolateral dimension. Cervical labeling generally occurred in the ventromedial portion and lumbosacral labeling in the dorsolateral portion of the LCN. Thoracic labeling occurred both in the middle and the most lateral edge of the nucleus. In all cases, labeling was distributed over most of the rostrocaudal extent of the LCN. In addition, distinct patches of labeling were present in the medialmost portion of the nucleus, regardless of the spinal level injected. These observations corroborate the topographical organization of the LCN described previously on the basis of physiological and retrograde labeling data, and support the identification of the medialmost part of the LCN as a distinct portion of the nucleus.

Terminal labeling in the LCN always occurred in multiple, longitudinally distributed fields. The afferent input to each terminal field coursed in separate, loose bundles of fibers that descended from the superficial dorsolateral funiculus. Large injections resulted in more extensive, overlapping terminal fields. These observations indicate that collateral projections result in several discrete representations of a given portion of the skin over the longitudinal extent of the LCN, but that topographical relationships are longitudinally maintained. It is suggested that these multiple terminal fields are the anatomical correlate of the functionally selective convergence of spinocervical tract terminations, that has previously been postulated on physiological grounds to explain the generation of LCN receptive fields with homogenous receptor input within a somatotopic framework.
Counting sectioned cells via mathematical reconstruction
Authors: Rose Robert D. , Rohrlich Daniel
Published: January 2005

A new method for determining the number of neurons in sectioned tissue is presented. The method does not involve identification of subcellular structures; rather, it uses estimates of the mean diameters of sections of the neuronal somata (with or without nuclei). All such sections are termed profiles. A mathematical model is developed to reconstruct the cell population from a size histogram of the profiles. Although the model is simple, the calculations are numerous and best done on a computer. A program that performs these calculations is provided. We discuss the idealizations on which the model is based and test the method in various ways: on hand‐ and computer‐generated data in which imaginary spheres of known size were sectioned; on two small samples of real cells for which both cell and profile size histograms were available; and on a sample of potatoes, sliced by hand. In every case the estimate was within 10% of the actual number of cells (or potatoes). The method is robust in that it is relatively insensitive to section thickness, sample size, somal morphology, and observer error with respect to missing the small or thin profiles from any given cell. Results from the present model are compared to those obtained by using other cell count correction schemes that are currently employed. We call our method recursive translation.
A horseradish peroxidase study of the olfactory system of the frog, Rana esculenta
Authors: Kemali M. , Guglielmotti V.
Published: January 2005

The olfactory system of the frog Rana esculenta was studied by using horseradish peroxidase (HRP) tracing of axonal pathways. Injections of HRP were made in the main olfactory bulb (MOB), accessory olfactory bulb (AOB), anterior olfactory nucleus (AON), the amygdala (AMY), and in a zone of the leteral wall of the telencephalic hemisphere immediately posterior to the AOB. Projections from these sites are described and are generally similar to those obtained by degeneration methods. However, HRP reveals more extensive olfactory connections than previously reported. Ipsilateral, contralateral, and bilateral projections arc described. The MOB, AOB, and AON have ipsilateral connections to each other. The MOB and AOB have very different projections. The MOB and AON project via the habenular commissure (HC) to the contralateral medial wall of the telencephalon. Ipsilateral MOB fibers also terminate in this cell‐free zone where the medial forebrain bundle (MFB) originates. The AOB projects to the lateral cortex of the contralateral telencephalic hemisphere via the HC and also to the ipsilateral AMY and lateral forebrain bundle (LFB) from where some fibers project contralaterally. HRP injections in the AMY retrogradely fill cells in the ipsilateral AOB, two nuclei of the ipsilateral hypothalamus and a nucleus of cells caudal to the ipsilateral nucleus isthmi. Fibers are also labeled that project to the contralateral AMY. Few fibers were observed to decussate in the interpeduncular nucleus or optic chiasma. No olfactory fibers were found to project to the habenular nuclei, and no labeled neurons were found to project to the olfactory bulbs. No morphological asymmetry was observed qualitatively in the distribution of olfactory fibers in the two halves of the brain.
Development and distribution of substance P in the spinal cord and ganglia of embryonic and newly hatched chick: An immunofluorescence study
Authors: Du Fu , Charnay Yves , Dubois Paul
Published: January 2005

The development and distribution of substance P(SP) immunoreactivity were studied in the spinal cord and ganglia of embryonic and newly hatched chick by using the indirect immunofluorescence method. Substance P immunoreactivity was first detected in the spinal cord at embryonic stages 18–20 (incubation day 3). Before stage 32 (day 7), it was mainly found in regions corresponding to the dorsolateral funiculus and Lissauer's tract. Subsequently, SP fibers appeared in the dorsal horn. By stage 38 (day 11), they were demonstrated almost throughout the gray matter, but mostly in laminae I and II. During this period, however, many SP‐positive cells were found just ventral to the central canal at the thoracic level, although a few were also detected in other areas throughout the cord. In the white matter, very dense longitudinal SP fibers were observed in Lissauer's tract and the dorsolateral funiculus, where extremely dense plexuses of SP immunoreactivity were also detected around a group of nonimmunoreactive cell bodies. At later stages, no remarkable differences were noticed in the distribution of SP fibers, but the SP‐positive cells decreased gradually in number and disappeared after hatching. However, they reappeared following colchicine treatment. In the spinal ganglia, SP immunoreactivity appeared initially at stage 25 (day 4). It was mostly located in small neurons of the mediodorsal region. These cells also decreased in number from later stages but increased by colchicine treatment after hatching. The development and distribution of SP immunoreactivity in the spinal cord and ganglia were generally comparable at all levels examined, except where indicated.
Distribution of GABAergic neurons and axon terminals in the macaque striate cortex
Authors: Fitzpatrick D. , Lund J. S. , Schmechel D. E. , Towles A. C.
Published: January 2005

Antisera to glutamic acid decarboxylase (GAD) and γ‐aminobutyric acid (GABA) have been used to characterize the morphology and distribution of presumed GABAergic neurons and axon terminals within the macaque striate cortex. Despite some differences in the relative sensitivity of these antisera for detecting cell bodies and terminals, the overall patterns of labeling appear quite similar. GABAergic axon terminals are particularly prominent in zones known to receive the bulk of the projections from the lateral geniculate nucleus; laminae 4C, 4A, and the cytochrome‐rich patches of lamina 3. In lamina 4A, GABAergic terminals are distributed in a honeycomb pattern which appears to match closely the spatial pattern of geniculate terminations in this region. Quantitative analysis of axon terminals that contain flat vesicles and form symmetric synaptic contacts (FS terminals) in lamina 4Cβ and in lamina 5 suggest that the prominence of GAD and GABA axon terminal labeling in the geniculate recipient zones is due, at least in part, to the presence of larger GABAergic axon terminals in these regions.

GABAergic cell bodies and their initial dendritic segments display morphological features characteristic of nonpyramidal neurons and are found in all layers of striate cortex. The density of GAD and GABA immunoreactive neurons is greatest in laminae 2–3A, 4A, and 4Cβ. The distribution of GABAergic neurons within lamina 3 does not appear to be correlated with the patchy distribution of cytochrome oxidase in this region; i.e., there is no significant difference in the density of GAD and GABA immunoreactive neurons in cytochrome‐rich and cytochrome‐poor regions of lamina 3.

Counts of labeled and unlabeled neurons indicate that GABA immunoreactive neurons make up at least 15% of the neurons in striate cortex. Layer 1 is distinct from the other cortical layers by virtue of its high percentage (77–81%) of GABAergic neurons. Among the other layers, the proportion of GABAergic neurons varies from roughly 20% in laminae 2–3A to 12% in laminae 5 and 6.

Finally, there are conspicuous laminar differences in the size and dendritic arrangement of GAD and GABA immunoreactive neurons. Lamina 4Cα and lamina 6 are distinguished from the other layers by the presence of populations of large GABAergic neurons, some of which have horizontally spreading dendritic processes. GABAergic neurons within the superficial layers are significantly smaller and the majority appear to have vertically oriented dendritic processes. These results provide support for the idea that GABAergic neurons make up a significant proportion of the neurons within the macaque striate cortex and that there are laminar differences in the number and the types of GABAergic neurons—differences that may be relevant for understanding the contributions of GABA‐mediated inhibition to striate cortex function.
Oculomotor system of the weakly electric fish Gnathonemus petersii
Authors: Szabo T. , Lazar G. , Libouban S. , Toth P. , Ravaille M.
Published: January 2005

The peripheral and central aspects of the extraocular system were studied in the weakly electric fish Gnathonemus petersii.

All six extraocular muscles show a similar composition of large and small fibers grouped characteristically in the proximal and distal regions respectively.

The exit of the three extraocular nerves from the brain is similar to that in other vertebrates. However, the intracephalic and intracranial course of the trochlear nerve is unusual, partly because of the extraordinary hypertrophy of the cerebellum. The three nerves course rostrally on the ventral brain surface; the trochlear nerve penetrates the orbital cavity separately from the two other nerves. The fiber‐diameter spectrum of each extraocular nerve is bimodal; unmyelinated fibers were not observed in any of the nerves.

The location of the extraocular motor nuclei was established by retrograde axonal transport of HRP or cobaltic‐lysine complex. The oculomotor nucleus is situated ventral to the posterior pole of the magnocellular mesencephalic nucleus and the trochlear nucleus is found caudal and dorsal to this. The abducens nucleus is situated at the level of the octavolateral efferent nucleus and consists of a single group of cells on each side of the ventral tegmentum.

The oculomotor nucleus of G. petersii shows a somatotopic organization. The superior rectus muscle receives a contralateral innervation whereas the inferior rectus and oblique muscles and the internal rectus muscles receive an ipsilateral innervation. The superior oblique muscle is innervated by contralateral trochlear motoneurons and the external rectus by ipsilateral abducens motoneurons.

The majority of extraocular motoneurons have piriform perikarya and long beaded dendrites that extend laterally in the oculomotor and abducens nuclei and rostrally in the trochlear nucleus. The terminal dendritic portions of trochlear motoneurons widely overlap with oculomotor dendrites and perikarya. In all three nuclei the axon originates opposite to the main dendrite. Collaterals of the hairpin‐bend abducens axons could be identified in a few cases.

The oculomotor system of G. petersii appears basically similar to that of other teleosts; the differences observed concern mainly the structure of the abducens nucleus, the intracranial and intracephalic course of the trochlear nerve, and the relatively small number of axons in each nerve.