bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytochrome oxidase activity in the rat caudate nucleus: Light and electron microscopic observations
Authors: Difiglia Marian , Graveland Gerda A. , Schiff Leora
Published: January 2005

Cytochrome oxidase (CO) activity was examined in the neostriatum of normal adult rats at the tight and electron microscopic level. At the light microscopic level a heterogeneous distribution of CO activity was observed and was characterized by patches of high activity ranging in size from 200 to 800 μm surrounded or adjacent to regions of lower activity. The most dorsomedial and ventromedial regions of the caudate nucleus appeared to be consistently high in activity in all animals. At the ultrastructural level CO reaction product was localized to the membranes and intracristal spaces of mitochondria. The most reactive mitochondria (those containing the densest precipitates of reaction product) were found within the dendrites of spiny neurons in all caudate regions. In areas of high CO activity the mitochondria within bundles of myelinated fibers and in many axon terminals were also highly reactive whereas those in neuronal somata, primary dendrites, and glial cells and processes exhibited relatively little activity.

Quantitative study showed that mitochondria within dendrites accounted for most of the CO activity in caudate neuropil. The mitochondria within dendrites and axon terminals were more reactive in regions of high CO activity than in regions of low CO activity. No differences in the density of synapses or in the proportions of axospinous and axodendritic synapses were observed between CO‐rich and CO‐poor areas.

Heterogeneity in the distribution of CO activity in the caudate nucleus may be related to the “patchy” pattern of localization previously observed for some neostriatal afferents, enzymes, transmitters, peptides, and receptor ligands. Also the present results suggest that differences in metabolic activity between regions of the caudate nucleus may depend more on the relative frequency of neuronal discharge at individual synaptic sites than on the density of synapses present within a given area. The high metabolic demands of spiny dendrites as compared to other neuronal profiles in the neostriatum may reflect their level of synaptic activity, since spines are known to participate in the majority of synapses in the caudate nucleus.
Morphological and physiological survival of goldfish Mauthner axons isolated from their somata by spinal cord crush
Authors: Zottoli Steven J. , Marek Lynn E. , Agostini Mark A. , Strittmatter Sandra L.
Published: January 2005

Axon segments isolated from their somata degenerate within days or months depending on species and neuronal type. To better understand the time course of morphological and physiological changes associated with degeneration of axon segments of vertebrate central neurons, we have studied the goldfish Mauthner axon (M‐axon) when it has been separated from its soma by spinal cord crush.

M‐axon segments survive morphologically for at least 77 days at 14°C. Cross‐sectional areas of isolated M‐axon segments (measured 25–30 mm caudal to the wound site at postoperative days 64 and 77) were greater than those of control axons at the same level. Sheath areas did not change. Electron microscopic observations at the same spinal cord location indicated no clear changes in the configuration or number of neurofilaments or any other organelle. M‐axon segments studied morphologically after 87 postoperative days had all degenerated.

Mauthner axon segments were capable of conducting action potentials and eliciting ipsilateral EMG responses. Repetitive firing of the M‐axon segments elicited EMG responses that fatigued more easily and remained fatigued over a longer interval than did those of control axons.

The long duration of M‐axon segment survival is unusual in a vertebrate and may be due to the low temperature at which the experiments were conducted (14°C) and/or temperature‐independent factors. The increased susceptibility to synaptic depression, which has not reported previously, may represent an early sign of the degenerative process.
Morphological and physiological studies of rod‐driven horizontal cells with special reference to the question of whether they have axons and axon terminals
Authors: Tsukamoto Yoshihiko , Yamada Masahiro , Kaneko Akimichi
Published: January 2005

Rod‐driven (intermediate) horizontal cells were examined in the carp retina to determine whether they bear axons and axon terminals. These cells were injected with HRP after physiological identification of the response type; which consisted of a higher sensitivity to light and a slower response time course than cone‐driven (external) horizontal cells, and spectral sensitivity peaking at 520 nm. The labeled cells were further identified morphologically by tracing their dendrites to rod photoreceptors by light and electron microscopy. About two‐thirds of the labeled cells (18/30) had a slender, axonlike process (<1 μm in diameter, 70–300 μm in length) running horizontally from the soma. No axonlike process was found in the remaining cells. Unlike the axons of external horizontal cells, this axonlike process was short and did not form a long fusiform expansion. No membrane specialization was found along the axonlike process.

Since it has been reported that the syncytium made of axon terminals of external horizontal cells serves as a signal bypass of the syncytium made of the somata, it was asked, in separate experiments, whether the intermediate horizontal cells also had such a double syncytial layer. Response amplitudes to a slit of light were measured by placing the slit at various distances from the recording electrode. The response amplitude decayed with distance with a single exponential function, indicating that the syncytium of intermediate horizontal cells consists of a monolayer. These physiological data are consistent with the morphological observations.
The structural and functional characteristics of tectospinal neurons in the golden hamster
Authors: Rhoades Robert W. , Mooney Richard D. , Klein Bradley G. , Jacquin Mark F. , Szczepanik Ann Marie , Chiaia Nicolas L.
Published: January 2005

Intracellular recording and horseradish peroxidase (HRP) injection techniques were used to delineate the structural and functional characteristics of the superior collicular cells in the hamster, which could be antidromically activated from the first cervical segment of the spinal cord. Thirty‐one such neurons were characterized, filled with HRP, and recovered. Complete physiological data were obtained from another 21 tectospinal cells for which anatomical data were sufficient only to define the laminar location of the cell body from which recordings were made. Of the total sample of 52 cells, 7.7% had their somata in the stratum griseum intermediale (SGI), 50% were in the stratum album intermedium (SAI), 36.5% were in the stratum griseum profundum (SGP), and 5.8% were in the stratum album profundum (SAP). The tectospinal cells were fairly uniform morphologically. They had large (27.7 ± 5.5 μm diameter) cell bodies, which gave rise to an average of 6.7 ± 1.2 primary dendrites. These were generally smooth and extended up to 500 μm away from the cell body. In many cases, they ascended out of the deep laminae into the stratum opticum (SO) and/or stratum griseum superficiale (SGS). The axons of TS cells averaged 3.4 ± 0.8 μm in diameter, and they generally coursed radially to the SAP where they curved around the periaqueductal gray and entered the predorsal bundle. These axons often gave rise to collaterals that arborized in the deep laminae of the ipsilateral superior colliculus and subjacent reticular formation.

The tectospinal cells were also fairly uniform physiologically. Their average conduction latency was 2.0 ± 2.3 ms, and this variable had a strong negative correlation (−.81) with axon diameter for the recovered cells. Most (63.5%) of the TS cells were exclusively somatosensory and gave rapidly adapting responses to deflection of vibrissae and/or guard hairs; 7.7% were bimodal (visual‐somatosensory); 11.5% had complex (Rhoades et al., '83) somatosensory receptive fields; 1.9% were discharged only by a noxious pinch, and 15.4% were unresponsive. A common feature of all bimodal tectospinal neurons was dendrites that extended at least as far dorsally as the SO. Whereas there were no other clear‐cut correlations between the structural and functional characteristics of these tectal neurons, we did note that all of the cells with complex somatosensory receptive fields received inhibitory input from axons that either originated from, or passed through, the contralateral superior colliculus.
Do early lesions affect cell death in the central nervous system? A study on the effects of early cerebellar hemispherectomy in rats
Authors: Gramsbergen A. , Ijkema‐Paassen J.
Published: January 2005

Cell death patterns in the lateral and interposed nuclei were compared in control rats and rats in whom a unilateral cerebellar hemispherectomy was performed at day 2 of life. Both groups were studied between days 2 and 20 of life. Pyknotic cells and live neuronal and glial cells were counted from Nissl stained sections. After correction of these values, pyknotic to live cell ratios were calculated. In the lateral nucleus of normal rats, around 14–28 pyknotic cells per 1,000 live cells occurred from day 2 to day 12. Thereafter this value decreased, and from day 16 less than 3 pyknotic/1,000 live cells were observed. In the interposed nuclei, 18–28 pyknotic cells/1,000 live cells occurred at day 2, and from this age onward values gradually decreased. At day 20 values ranged around 1.6/1,000. After unilateral cerebellar hemispherectomy, values in both nuclei began to decrease as early as from day 8. Results from the present study strongly suggest that these cells are prevented from dying because they find an aberrant synaptic target in the ipsilateral red nucleus. Our results demonstrate that early lesions interfere with the regulation of fundamental processes of neuro‐ontogeny.
Development of the spinal nerves of the larval lamprey: IV. Spinal nerve roots of 21‐mm larval and adult lampreys, with special reference to the relation of meninges with the root sheath and the perineurium
Authors: Nakao Taisuke , Ishizawa Akimitsu
Published: January 2005

Spinal nerve roots of 21‐mm larval and adult lampreys were electron microscopically studied. In 21‐mm larval lampreys, each ventral and dorsal rootlet contains axons of various diameters enclosed together as groups in individual troughs of a Schwann cell cytoplasm, lying in direct contact with one another, and is further ensheathed entirely by a basal lamina. Dorsal roots possess visceral axons, while ventral roots lack them. In adult lampreys the ventral and dorsal roots possess individual sheaths for larger somatic axons, each being surrounded by a single Schwann cell and the basal lamina and separated from one another by a considerable amount of connective tissue. Visceral fibers are present in both the dorsal and ventral roots of adult lampreys. They aggregate to form fascicles that lie among somatic axons, being separated from them.

Two layers of the meningeal tissue invaginate to form a root sheath around the distal portion of individual dorsal and ventral roots of 21‐mm larval lampreys. In adult lampreys the sheath is similarly formed but extends over most of the dorsal and ventral roots. The perineurium is not developed in 21‐mm larval lampreys, but is present and ensheaths only the proximal portion of spinal nerve trunks outside the meninges in adult lampreys: it is completely absent along most of the length of peripheral nerves. In both larval and adult lampreys, the outer cell layer of the root sheath is open‐ended near the middle of nerve roots with respect to the extramedullary connective tissue space. Similar loosening of the cellular barrier is seen along blood vessels. Thus, the outer meningeal fibrous layer is directly continuous with the extra medullary connective tissue space by way of the inner fibrous layer of the root sheath.
Autoradiographic study of descending pathways from the pontine reticular formation and the mesencephalic trigeminal nucleus in the rat
Authors: Sirkin David W. , Feng Albert S.
Published: January 2005

Descending projections were studied in autoradiographically prepared material after injections of tritiated leucine in the pontine tegmentum of rats. Injections involving the medial pontine reticular formation resulted not only in labeling commissural fibers, the medial reticulospinal tract, and the dorsal cap of the inferior olive, but also, in two cases, in labeling a cerebellar projection that originated from a region near the midline and clearly dorsal to the nucleus reticularis tegmenti pontis. The labeled fibers passed ventrad in the midline to the pontine gray, then laterally through the gray and into the middle cerebellar peduncle to terminate as mossy fibers primarily in the flocculus, lobulus simplex, and Crus I of the ansiform lobule.

Injections involving the mesencephalic nucleus of the trigeminal nerve (Vmes), resulted in labeling of Probst's tract, which descends in the dorsolateral reticular formation. Probst's tract gave off extensive terminal branches to the lateral medullary reticular formation and weaker projections to restricted portions of the descending trigeminal nucleus, the solitary nucleus, and the hypoglossal nucleus. In one case, fibers could be traced into the dorsal horn of the upper cervical cord.
Morphology and distribution of the projection neurons in the cerebellum in a teleost, Sebastiscus marmoratus
Authors: Murakami Takeshi , Morita Yasuhiro
Published: January 2005

Cerebellar efferent neurons in a teleost, Sebastiscus marmoratus, were studied by means of the horseradish peroxidase (HRP) tracing and Golgi impregnation methods. The cerebellar efferents or eurydendroid neurons are classified into two types (A and B) on the basis of the morphology of the dendrites, intracerebellar distribution, and other afferent connections. Type A neurons form a cell cluster in the lobus caudalis and have one thick primary dendrite from which several branches with sparse but long spines extend into the molecular layer of the lobus caudalis. Type B neurons, observed in both the valvula and corpus cerebelli, have two or three primary dendrites running along the ganglion cell layer, and the distal dendritic branches are distributed in molecular layer perpendiculary to the cerebellar surface. Small spines are densely studded on the dendrites of type B neurons. Somata of type A and B neurons are located in and just beneath the ganglion cell layer.

The cerebellum projects to the ipsilateral nucleus lateralis valvulae and torus longitudinalis and bilaterally, but mostly contralaterally to the nucleus ventromedialis thalami of Schnitzlein ('62), nucleus ruber, the vicinity of the oculomotor complex, torus semicircularis, and brainstem reticular formation. Type A neurons send axons primarily to the vicinity of the oculomotor complex and partly to the nucleus ventromedialis thalami and the nucleus ruber, whereas type B cells project to all main cerebellar targets. In addition, type B cells are organized topographically in the cerebellum in relation to the efferent targets in the brainstem.
Relationships between ganglion cell dendritic structure and retinal topography in the cat
Authors: Schall J. D. , Leventhal A. G.
Published: January 2005

The morphology of ganglion cell dendritic trees varies across the cat retina. Evidence is presented that the variation in two attributes of ganglion cell dendritic structure can be accounted for by specific aspects of the topography of the adult and developing retina.

The first attribute considered was the displacement of the center of the dendritic field from the cell body in the plane of the retina. The results of this study provide evidence that most ganglion cell dendritic fields are displaced away from neighboring cells, i.e., down the retinal ganglion cell density gradient. Because of the systematic dendritic displacement locally, the centers of the dendritic fields are arranged in a more precise mosaic than are their cell bodies.

The second attribute considered was the elongation and orientation of the dendritic fields. From approximately embryonic day 50 to postnatal day 10 the cat retina undergoes a process of maturation (reviewed by Rapaport and Stone: Neuroscience 11:289–301, '84) that begins at the area centralis and spreads over the retina in a horizontally elongated wave. We found that the elongation and orientation of retinal ganglion cell dendritic fields is significantly correlated with the shape of the wave of maturation. The orientation of a dendritic field is not predicted by the direction of its displacement nor is it directly related to the distribution of neighboring retinal ganglion cells.

These results indicate that the displacement of a ganglion cell's dendritic field from its cell body results from mechanisms different from those responsible for the orientation of the dendritic field. Factors that may be responsible for these two attributes of ganglion cell dendritic morphology are discussed.
Ganglion cell dendritic structure and retinal topography in the rat
Authors: Schall J. D. , Perry V. H. , Leventhal A. G.
Published: January 2005

The dendritic field size, the distribution of the dendrites relative to the cell body, and the overall shape of the dendritic field of type I ganglion cells in the rat retina were analyzed. These features of neuronal structure were related to the topography of the rat retina. As in the cat, the cell bodies of type I ganglion cells are arranged in a nonrandom mosaic. Previous work has demonstrated that the density of type I cells in the rat retina does not covary with the density of all ganglion cells. Type I dendritic field size varies over the retina; the increase in dendritic field size is accounted for better by the decrease in type I density than by the decrease in overall ganglion cell density. The center of the dendritic field of most type I cells is displaced in the plane of the retina from the cell body. Unlike in carnivore retina (Schall and Leventhal: J. Comp. Neurol. 257:149–159, '87), the dendritic fields in the rat are not displaced down the ganglion cell density gradient. Rather, there is a tendency for the dendritic trees, especially in temporal retina, to be displaced toward dorsal retina. Most of the dendritic fields are elongated, but the degree of elongation is less than that observed in carnivore or primate retina. Unlike in carnivore and primate retina (Leventhal and Schall: J. Comp. Neurol. 220:465–475, '83; Schall et al.: Brain Res. 368:18–23, '86), there is no relationship between dendritic tree orientation and position relative to any point on the retina in the rat. The foregoing differences in the morphology of retinal ganglion cell dendritic trees in rat, carnivore, and primate are considered in light of the differences in the development of retinal topography in these species.
A Golgi study of the monkey paraventricular nucleus: Neuronal types, afferent and efferent fibers
Authors: Rafols José A. , Aronin Neil , Difiglia Marian
Published: January 2005

The neuronal organization of the paraventricular nucleus (PVN) was examined in Golgi impregnations of adult monkey. Results showed that at least six types of neurons could be identified in the nucleus on the basis of morphological features of the somata, dendrites, and axons. Four types of neurons with sparse to densely spined cell bodies and dendrites exhibited long axons and included large neurons (types I and II), medium‐sized to large neurons (type III), and small to medium‐sized cells (type IV). Axons of type I, III, and IV neurons had different diameters and were followed out of the PVN. Axon collaterals that arborized within the PVN were seen on the axons of types III and IV cells. Two types of interneurons with small somata were also found. One (type V) exhibited varicose dendrites and a profusely arborizing local axon. The other cell (type VI) had recurved dendrites with long appendages and no impregnated axon. Afferent fibers were also identified. Type 1 was a fine‐caliber axon that coursed long distances in the PVN and exhibited numerous short branches. Additional observations suggested that type 1 afferents originated from the stria terminalis. The other afferent axon (type 2) was thicker and gave rise to terminal arborizations containing clusters of small swellings.

The efferent fibers of the > PVN were also examined in impregnations of the paraventriculosupraopticohypophysial tract. Fibers formed an extensive plexus as they coursed ventrally and passed through the lateral hypothalamus. Axons coursing more laterally in the tract were much larger than those more medially located.

Our findings show a diverse organization of neuronal types within the monkey PVN with evidence for intrinsic connections through axon collaterals of efferent neurons and the locally arborizing axons of interneurons. Correlations are proposed between morphological subtypes of neurons seen in this Golgi study and the known functional output pathways of the PVN.
The serotoninergic fibers in the dorsal lateral geniculate nucleus of the cat: Distribution and synaptic connections demonstrated with immunocytochemistry
Authors: De Lima Ana Dolabela , Singer Wolf
Published: January 2005

The distribution, morphology, and synaptic contacts of serotoninergic fibers were studied with immunocytochemical methods in the lateral geniculate complex of the cat. The serotonin‐immunoreactive fibers are diffusely distributed throughout the main laminae of the dorsal lateral geniculate nucleus (dLGN) and the perigeniculate nucleus (PGN) and reach a particular density in the ventral lateral geniculate nucleus (vLGN). The labeled fibers are in most cases very thin and sometimes varicose. There is no obvious order in their distribution pattern except that they sometimes partially encircle the unlabeled cell bodies of the dLGN.

The synaptic connections of the serotoninergic fibers were investigated mainly in the A laminae of the dLGN. Few synaptic complexes were found, most of them with asymmetric morphology. The postsynaptic elements were small dendritic profiles. Perisomatic serotoninergic fibers were seen, but no convincing synaptic contacts were found between labeled fibers and cell somata. In the dLGN, serotoninergic profiles were almost exclusively confined to the extraglomerular neuropile. In the PGN serotoninergic fibers also contacted dendritic profiles and formed asymmetrical synapses, but as in the geniculate, synaptic specializations were very rare.
Intra‐axonal labeling of saccular afferents in the goldfish, Carassius auratus: Correlations between morphological and physiological characteristics
Authors: Sento Seishiro , Furukawa Taro
Published: January 2005

Lucifer yellow was used to label axons of 32 physiologically defined SI afferent fibers and 23 physiologically defined S2 afferent fibers of the goldfish sacculus. Analysis of these labeled fibers allowed us to study the relationship between electrical activity in these primary neurons and the morphology of their peripheral arborizations in the sensory macula. Morphological characteristics were highly indicative of response type: The peripheral arborizations of individual S1 fibers occupied a relatively small region (approximately 40 μm in diameter) in the rostral one‐fourth of the saccular macula, whereas those of individual S2 fibers covered a larger area (roughly 80 μm across) in the caudal part of the macula. In addition to this rostrocaudal dimension, a ventral projection was related to a rarefaction response, a dorsal projection was related to a compression response, and a two‐sided innervation was related to fibers having both responses. S1 fibers had either large or small terminals; the S2 fibers had only small terminals. On average, S1 fibers gave rise to approximately four terminals (e.g., seven small terminals or one to two large terminals) and S2 fibers approximately ten terminals. Spontaneous discharges were absent in all S1 fibers but present in some S2 fibers. Such S2 fibers showed spontaneous activity of either an irregular type or a burst type. In these, there was a tendency for fibers having more extensive arborizations to exhibit a burst type of spontaneous discharge. We conclude that structure‐function relationships can be determined for these primary neurons.
Patterns of cell death in the ganglion cell layer of the human fetal retina
Authors: Provis Jan M.
Published: January 2005

The distribution of dying cells in the ganglion cell layer (GCL) of retinae from human fetuses has been analysed. Both whole‐mounted and sectioned retinae have been studied. Results suggest that cells are lost from the GCL between weeks 14 and 30 of the gestation period, approximately. This period corresponds to the period during which axons are lost from the developing optic nerve. Cell loss is greatest between weeks 16 and 21 of the gestation period. The pattern of cell loss is nonuniform, and between weeks 16 and 24, the relative frequency of pyknotic cells (pyknotic cells: viable cells) in peripheral retina is considerably higher than in central retina. This pattern of cell loss predominates during the period in which a distinct centroperipheral gradient of cell densities emerges in the GCL of the human fetal retina (between 18 and 23 weeks gestation). It is suggested that the regional loss of ganglion cells may contribute to the formation of the cell density gradient.
GABAergic nonpyramidal neurons in intracerebral transplants of the rat hippocampus and fascia dentata: A combined light and electron microscopic immunocytochemical study
Authors: Frotscher Michael , Zimmer Jens
Published: January 2005

Glutamate decarboxylase (GAD) immunocytochemistry was used to study GABAergic neurons and synapses in intracerebral allografts of the rat hippocampus and fascia dentata. Tissue blocks of regio inferior of Ammon's horn (hippocampal field CA3) or of the fascia dentata were taken from newborn rats and transplanted to the hippocampal region of young adult rats. After 6 1/2 months' survival the recipient brains were fixed by perfusion and serially sectioned on a Vibratome. Sections containing the transplant and/or the host hippocampal region were immunostained for GAD and flat‐embedded in Araldite for a correlated light and electron microscopic analysis. Immunostained neurons and terminals in the transplants were compared to immunoreactive elements in the hippocampus and fascia dentata of the hosts and other, normal rats.

As in the hippocampal formation in situ, GAD‐immunoreactive neurons and terminals in the transplants were observed in all layers. In dentate transplants a preponderance of immunostained cells was found just beneath the granule cell layer. In both hippocampal and dentate transplants, immunoreactive terminals were most abundant in the cell layers where they formed characteristic pericellular baskets around the pyramidal and granule cell bodies.

In the electron microscope, the transplant GAD‐immunoreactive neurons exhibited numerous cytoplasmic organelles, deeply infolded nuclei, and nuclear rods. Immunoreactive terminals formed symmetric synaptic contacts on the cell bodies, dendritic shafts, and spines of transplant pyramidal cells, granule cells, and hilar neurons. These are normal characteristics of GAD‐immunoreactive neurons and terminals as also observed in the hippocampus of the host rats and the normal controls.

Our results demonstrate that GABAergic neurons survive transplantation and develop a cell‐specific morphology that includes the axonal projections.
The peripheral distribution and central projections of the sensory rami of the facial nerve in goldfish, Carassius auratus
Authors: Puzdrowski R. L.
Published: January 2005

Taste buds in goldfish and other cyprinids are found not only within the oropharyngeal cavity but also scattered over the external body surface. The external taste buds are innervated by branches of the facial nerve that terminate centrally in an enlargement of the medulla termed the facial lobe. The peripheral distribution and areas of innervation of the rami of the facial sensory nerve were determined by using a modification of the Sihler technique and by examination of a Bodian‐stained head series. The central projections of individual rami of the facial sensory nerve were traced by means of the horseradish peroxidase (HRP) technique.

Fibers of the facial sensory nerve distribute over the head and trunk via nine rami. The supraorbital ramus distributes fibers to taste buds above the eye. The palatine, maxillary, and mandibular rami innervate taste buds of the rostral palate, upper lip, and lower lip, respectively. The three rami of the hyomandibular trunk innervate taste buds on the operculum, branchiostegal rays, and in the lower cheek region. A facial recurrent ramus was also found that distributes fibers to taste buds on the trunk and pectoral fin via two rami, the lateral recurrent ramus and pectoral recurrent ramus.

The facial sensory rami map somatotopically on the facial lobe. Overall, the projections follow an anteroposterior orientation with the long axis of the body tilted slightly ventrally. The lips and rostral palate make up a disproportionately large portion of the map, taking up nearly the entire ventral extent of the lobe. The trunk and pectoral fin regions map broadly across the dorsal portion of the lobe. Further, projections to the nucleus of the descending trigeminal tract were observed with labeling of the supraorbital, maxillary, and mandibular rami, and the rami of the hyomandibular trunk. Projections to the facial motor nucleus were also observed with labeling of maxillary and mandibular rami, perhaps indicating a monosynaptic reflex arc. These projections have not been reported in previous studies on the teleostean facial taste system.
Accessory optic system of an anthropoid primate, the gibbon (Hylobates concolor): Evidence of a direct retinal input to the medial terminal nucleus
Authors: Cooper H. M. , Magnin M.
Published: January 2005

The accessory optic system (AOS) was studied in an anthropoid primate by using anterograde transport of tritiated amino acids and autoradiographic techniques. The course of the accessory optic tract (AOT) and the retinal projection to the terminal nuclei are described in the gibbon and compared to that of other mammals.

The AOT consists of a superior fasciculus, which includes both an anterior and a posterior fiber branch. An inferior fasciculus of the AOT is absent. In contrast to previous reports in haplorhine primates, which describe the AOS as consisting of only the dorsal (DTN) and the lateral (LTN) terminal nuclei, we find that in the gibbon, three cellular groups receive a bilateral projection, predominantly from the contralateral retina. According to cytoarchitecture and topographic location, two of these nuclei correspond to the DTN and the LTN. The third cellular group, situated dorsomedial to the substantia nigra, receives a distinct retinal projection and extends rostrocaudally for 2.0 mm in the mesencephalon. This nucleus is homologous to the dorsal division of the medial terminal nucleus (MTN) in other mammals. There was no evidence for a ventral division of the MTN, which in nonprimates is typically situated at the ventromedial base of the cerebral peduncle.

Examination of brain morphology in primates suggests that the ventral division of the MTN has been displaced from its phylogenetically stable location in the medial part of the ventral midbrain to a more dorsal position. This shift appears to be a consequence of the overall morphological influences resulting from the relative enlargement of the pons in this region. The demonstration of a direct retinal projection to the MTN in the gibbon, as well as recent reports in other primates, indicates that a complete AOS consisting of three terminal nuclei is a feature common to all mammals.
Neurosecretory neurons and their projections to the serotonin neurohemal system of the cockroach Periplaneta americana (L.), and identification of mandibular and maxillary motor neurons associated with this system
Authors: Davis Norman T.
Published: January 2005

The neuroanatomy of a serotonin neurohemal system in the head of Periplaneta americana was studied by means of immunohistochemistry, cobalt backfilling, transmission electron microscopy, and nerve transection.

This neurohemal system is supplied by bilateral groups of two or three neurons whose somata are located ventrally in the subesophageal ganglion, near the root of each mandibular nerve. Axons of these serotoninergic neurons extend into all of the nerves of the mouth parts but reach most of these nerves by a very circuitous route. Initially the axons extend from the subesophageal ganglion, through the ipsilateral mandibular nerve trunk, and into the third branch of the mandibular nerve. From here the axons extend into the second branch of the maxillary nerve by way of a link nerve, and then they project retrogradely to reenter the subesophageal ganglion. In the ganglion, branches of these axons extend into the labial nerves, and the axons run dorsally through the subesophageal ganglion, circumesophageal connectives, and tritocerebrum to reach the labral nerves. In the nerves of the mouth parts the serotoninergic axons give rise to numerous secondary branches that form an extensive neurohemal system at the surface of these nerves. The relatively large surface and cephalic location of this system probably indicate that the timely release of relatively large amounts of serotonin plays an important role in the physiology of feeding in this insect.

The somata, neurites, and dendritic fields of the serotonin neurohemal neurons and those of the motor neurons of the mandibular abductor muscle occur together, and some of the mandibular abductor motor neurons also stain for serotonin. In order to distinguish clearly between these neurohemal and motor neurons, the anatomy of the mandibular abductor motor neurons has also been determined. Similarly, in the course of this study it has been necessary to work out the anatomy of the motor neurons of the maxillary retractor and cardo rotator muscles in order to distinguish them from the serotoninergic neurons.

A nonserotoninergic peripheral neuron is associated with the serotonin neurohemal system, and its soma is located on the mandibular‐maxillary link nerve. This link nerve neuron appears to be neurosecretory.
Morphology of labeled afferent fibers in the guinea pig cochlea
Authors: Brown M. Christian
Published: January 2005

Cochlear afferent and efferent fibers in the guinea pig were labeled by focal extracellular injections of horseradish peroxidase into the spiral ganglion of the basal turn. The morphology and pattern of termination of these fibers were studied by light microscopy. Fibers labeled by injections into the peripheral side of the ganglion could be grouped on the basis of their courses and terminations in the cochlea into two classes of afferent fibers, two classes of efferent (olivocochlear) fibers, and other presumably autonomic fibers. This paper describes the characteristics of labeled afferent fibers and their parent ganglion cells.

Peripheral afferent fibers were grouped into two major classes: (1) thick (mean diameter 1.7 μm)radial fibersprojecting in a primarily radial fashion from the spiral ganglion and terminating on single inner hair cells and (2) thin (mean diameter 0.5 μm)outer spiral fibersthat spiral basalward in the organ of Corti to terminate on outer hair cells, usually in one row. For outer spiral fibers, the number of outer hair cells contacted and the length of the terminal region depend on the row of outer hair cells contacted, with third‐row fibers forming, on the average, the most extensive region of termination. Within the spiral ganglion, two types of ganglion cells could be distinguished:(1)type‐Iganglion cells of large size (mean soma area = 216 μm2) with a ratio of central process diameter to peripheral process diameter greater than one and (2)type‐IIganglion cells of smaller size (mean soma area = 100 μm2) and a central to peripheral process ratio near one. In three cochleae in which injections were made central to the ganglion, 11 type‐I ganglion cells have been traced to radial fibers contacting inner hair cells and eight type‐II ganglion cells have been traced to outer spiral fibers contacting outer hair cells. Thus the afferent innervation of the guinea pig cochlea is similar to the pattern described in other mammals, in which there is separate innervation of the inner and outer hair cells by the two types of ganglion cells.

The central axons of both types of ganglion cells were traced individually through serial sections of a block of tissue containing the cochlea, the auditory nerve, and the cochlear nucleus. They followed similar courses in the auditory nerve, and the axons followed into the cochlear nucleus bifurcated in similar regions of the interstitial portion. Type‐I central axons were thick (mean diameter = 2.1 μm) whereas the central axons of type‐II neurons were thin (mean diameter = 0.5 μm). Type‐I axons had periodic constrictions interpreted as nodes of Ranvier; these were lacking on the thin axons of the type‐II ganglion cells. The morphological differences between the two types of afferent fibers suggest that they may play very different functional roles.
Mammalian motoneuron cell death: Development of the lateral motor column of a wallaby (Macropus eugenii )
Authors: Comans P. E. , McLennan I. S. , Mark R. F.
Published: January 2005

We have investigated the development of the lumbar lateral motor column of the tammar as a model of mammalian motoneuron cell death that is accessible to experimental manipulation. The tammar is an Australian marsupial, belonging to the subfamily of wallabies and kangaroos. After a gestational period of 26–28 days, the pup crawls to its mother's pouch using its forelimbs. The major morphometric events that shape the formation of the hindlimb occurred between 21 days gestation and birth. At birth the premuscle masses had divided and motor nerves had begun to penetrate the muscles of the thigh and shank. The period of motoneuron cell death was biphasic and occurred entirely postnatally. During phase I, between birth and 40 days, 59% of motoneurons were lost. Cell numbers then stabilised before falling a further 24%, to give an overall loss of 70%. Most of phase II cell loss occurred between 90 and 150 days. The possibility that a second period of motoneuron cell death maybe a common feature of mammals is discussed.
Cholinergic innervation of hippocampal GAD‐ and somatostatin‐immunoreactive commissural neurons
Authors: Léránth Csaba , Frotscher Michael
Published: January 2005

This study describes the cholinergic innervation of chemically defined nonpyramidal neurons in the hilar region of the rat hippocampus. Cholinergic terminals were identified by immunocytochemistry employing a monoclonal antibody against choline acetyltransferase (ChAT), the acetylcholine‐synthesizing enzyme, and the avidin‐biotin‐peroxidase (ABC) technique. Nonpyramidal neurons in the hilar region were characterized by immunostaining with antibodies against glutamate decarboxylase (GAD), the gamma aminobutyric acid (GABA)‐synthesizing enzyme, and somatostatin (SS). The immunoreactivity to these antibodies was detected by using biotinylated secondary antibodies and avidinated ferritin as an electron‐dense marker. This electron microscopic double immunostaining procedure enabled us to demonstrate that immunoperoxidase‐labeled ChAT‐immunoreactive terminals established symmetric synaptic contacts on the ferritin‐labeled GAD‐and SS‐immunoreactive hilar cells.

In additional experiments at least some of the GAD‐ and SS‐immunoreactive hilar neurons were further characterized as commissural neurons by retrograde filling with horseradish peroxidase (HRP) following an injection of the tracer into the contralateral hilus. From these triple labeling experiments, we concluded that at least some GABAergic and somatostatin‐containing neurons in the hilar region, which are postsynaptic to cholinergic terminals, project to the contralateral hippocampus. Together with previous studies on the cholinergic innervation of the hippocampus and fascia dentata, our present results thus demonstrate that different types of hippocampal cells, including GABAergic and peptidergic commissural neurons in the hilar region, receive a cholinergic input.
Alteration of mouse cerebellar circuits following methylazoxymethanol treatment during development: Immunohistochemistry of GABAergic elements and electron microscopic study
Authors: de Barry J. , Gombos G. , Klupp T. , Hamori J.
Published: January 2005

Methylazoxymethanol (MAM) injected postnatally affects cerebellar development in mice. A single injection at the fifth postnatal day produces hypogranular cerebella whereas a single injection at birth produces, in addition, a disorderly cytoarchitecture of the folium and alteration of Purkinje cell positioning (Bejar et al.: Exp. Brain Res. 57:279–285, ′85). In the present study we have used immunohistochemistry with anti‐GABA immune serum and electron microscopy to further characterize these alterations. In addition to the already‐described nonoccupied dendritic spines of Purkinje cells both in mice injected the day of birth and or at the fifth postnatal day, we have observed, in animals injected at birth, the absence of pericellular baskets around Purkinje cells and the presence of heterologous synapses between mossy fibres and Purkinje cell dendrites. These heterologous synapses apparently disappear after postnatal day 20.

By using an appropriate timing of MAM injection, different types of hypogranular cerebella, phenocopies of different mutants, can be obtained in large enough number to carry out extensive biochemical studies at each developmental age.
Caudal topographic nucleus isthmi and the rostral nontopographic nucleus isthmi in the turtle, pseudemys scripta
Authors: Sereno Martin I. , Ulinski Philip S.
Published: January 2005

Isthmotectal projections in turtles were examined by making serial section reconstructions of axonal and dendritic arborizations that were anterogradely or retrogradely filled with HRP. Two prominent tectal‐recipient isthmic nuclei–the caudal magnocellular nucleus isthmi (Imc) and the rostral magnocellular nucleus isthmi (Imr)–exhibited strikingly different patterns of organization. Imc cells have flattened, bipolar dendritic fields that cover a few percent of the area of the cell plate constituting the nucleus and they project topographically to the ipsilateral tectum without local axon branches. The topography was examined explicitly at the single‐cell level by using cases with two injections at widely separated tectal loci. Each Imc axon terminates as a compact swarm of several thousand boutons placed mainly in the upper central gray and superficial gray layers. One Imc terminal spans less that 1% of the tectal surface. Imr cells, by contrast, have large, sparsely branched dendritic fields overlapped by local axon collaterals while distally, their axons nontopographically innervate not only the deeper layers of the ipsilateral tectum but also ipsilateral Imc. Imr receives a nontopographic tectal input that contrasts with the topographic tectal input to Imc.

Previous work on nucleus isthmi emphasized the role of the contralateral isthmotectal projection (which originates from a third isthmic nucleus in turtles) in mediating binocular interactions in the tectum. The present results on the two different but overlapping ipsilateral tecto‐isthmo‐tectal circuits set up by Imc and Imr are discussed in the light of physiological evidence for selective attention effects and local‐global interactions in the tectum.
Histological characterization of neurones innervating functionally different muscles of Locusta
Authors: Kutsch Wolfram , Schneider Henning
Published: January 2005

The innervation of four functionally different muscles (subalar, remoter 1, remoter 2, pleuroalar), all served by the same nerve branch, was studied in both winged segments of the locust, Locusta migratoria. Several anatomical techniques were applied: With the cobalt backfill and silver intensification technique four cell types (motoneurone, dorsal unpaired median neurone, common inhibitory neurone, and small median neurone) were demonstrated. Serial sections enabled the morphology of the motoneurones to be described in more detail and in respect to a possible functional organization of the arborizations. A differential staining technique allowed us to stain various neurones in different colours in the same preparation. With this technique the anatomy of both the “rostral” and the “caudal” subalar motoneurones could be described in parallel, thus avoiding errors in comparison due to possible individual variations from preparation to preparation. Axon counts in the peripheral nerve branch enabled us to compile a list of the total innervation for each muscle. Results from other orthopterans are integrated and whether differences in the dendritic fields might be of functional significance is discussed.
Trajectory of group Ia and Ib fibers from the hind‐limb muscles at the L3 and L4 segments of the spinal cord of the cat
Authors: Hongo Toshinori , Kudo Norio , Sasaki Shigeto , Yamashita Masayuki , Yoshida Kaoru , Ishizuka Norio , Mannen Hajime
Published: January 2005

Nineteen physiologically identified group Ia and five group Ib fibers at the L3 and L4 levels of the spinal cord originating from various hind‐limb muscles were intraaxonally injected with horseradish peroxidase (HRP). The trajectories of the stained axons were reconstructed. They extended for distances of 8.6 mm–18.0 mm rostrocaudally.

Ascending axons ran in various regions of the dorsal funiculus: The ascending axon from a toe muscle (3 μm in diameter) ran in the ventralmost part of the paramedian region; those from shank muscles (3.0–5.0 μm) in both dorsal and ventral paramedian regions; those from thigh muscles (5.0–7.0 μm) in both the paramedian and the more lateral regions; and those from hip muscles (6.0–7.0 μm) in the lateral region. Main collaterals arising from the parent fiber were given off at intervals of 0.5–6.2 mm (mean 2.4 mm). Collaterals of a fiber from a toe muscle (1.0 μm in diameter) entered Clarke's column from the dorsomedial side and ramified mostly in the dorsomedial one‐third of the column. Collaterals of fibers from shank muscles (1.0–2.0 μm) entered Clarke's column from the dorsal side and terminated in its middle parts as well as in laminae V–VII. Collaterals of fibers from thigh muscles (1.0–2.5 μm) passed lateral to or through the lateral part of Clarke's column and terminated in its ventrolateral part and in laminae V–VIII. Collaterals of fibers from hip muscles (1.5–2.5 μm) passed lateral to Clarke's column and ramified mostly in laminae VII–IX. As the muscle of origin became more proximal, the proportion of termination outside of Clarke's column progressively increased. Thus, the trajectory of group I fibers was somatotopically organized both in the dorsal funiculus and in the gray matter.

The long axis of boutons ranged from 0.5 to 17 μm in Ia fibers and from 0.5 to 8 μm in Ib fibers. “Giant” Ia boutons (above 7 μm) were found both in and outside Clarke's column.