bluuebunny/crossref_metadata_2025 huggingface dataset:
Developmental and functional alterations in the fiber composition of the optic nerve in visually deprived mice
Authors: Gyllensten Lars , Malmfors Torbjörn , Norrlin‐Grettve Marie‐Louise
Published: January 2005

During the first four months of postnatal life in mice, an increase occurred in the section area and number of fibers of the optic nerve, as recorded by phase contrast microscopy of epone‐embedded specimens. This was followed by a slight decrease for three months. A skew distribution of nerve fibers according to diameter was recorded, probably due to small groups of larger fibers.

In mice reared in complete darkness for 2–4 months from birth, no significant differences were present in the fiber composition of the optic nerve, compared to corresponding normal controls. Slight retinal hypotrophy (decreased thickness and nuclear diameter) was found in dark‐reared animals.

In adult mice, lack of visual stimulation (complete darkness from 4 to 7 months of age) caused an increase in number and diameter of the optic nerve fibers. No retinal hypotrophy was demonstrated in these animals.

Judging by previous investigations, it is concluded from the present findings that growth of the fibers of the optic nerve is more independent of visual stimulation than is growth of the rest of the cells in the visual system. Point 3, as contrasted to point 2, implies that functional differences exist between apparently normal optic nerve fibers in dark‐reared mice and in controls, the former being unable to react to lack of activity by an increase in fiber size.
The development of hippocampal and dorsolateral pallial regions of the cerebral hemisphere in fetal rabbits. II. Twenty millimeter stage, neuroblast morphology
Authors: Stensaas Larry J.
Published: January 2005

The structure of the pallial region of the cerebral hemisphere of 20 mm rabbit embryos was studied with aniline and Golgi stains. The presence of a cortical plate distinguishes this stage from 15 mm embryos. It is a dense layer consisting of nerve cells which have migrated from the matrix lamina and represents the layer which will form most of the cerebral cortex. Golgi impregnations at this stage show that it consists largely of pyramidal cells whose apical dendrites ascend and branch in the marginal lamina.

Neuroblasts in the matrix and intermediate laminae have distinctive morphology depending on their distance from the ventricular surface: (1) ascending axons arise from the round or elongated somata of cells in the matrix lamina, (2) horizontal axons and multiple short processes arise from neuroblast somata in the lower part of the intermediate lamina, and (3) descending axons originate from the inferior side of bipolar neuroblasts in the upper intermediate lamina. A single radial process, the preapex, arises from the other side. This sequence of changes suggests that neuroblast somata rotate around the axons as they migrate through the lower intermediate lamina and that new lengths of axons are “spun out” as neuroblasts become located at higher levels. It also raises the possibility that the preapex plays an active role in the process of migration.
Ascending projections of the lateral lemniscus in the cat and monkey
Authors: Goldberg Jay M. , Moore Robert Y.
Published: January 2005

The ascending connections of the lateral lemniscus were studied in the cat and squirrel monkey (Saimiri sciureus). In both species, the central nucleus of the inferior colliculus receives a massive projection from the lateral lemniscus. Only a few lemniscal fibers were found to terminate in the external nucleus of the inferior colliculus. The commissure of the lateral lemniscus originates from the dorsal nucleus of the lateral lemniscus and projects to the contralateral dorsal nucleus and the contralateral central nucleus of the inferior colliculus. No lemniscal fibers were seen ascending in the inferior brachium or terminating in the principal division of the medial geniculate body. A bundle of fibers was observed, however, which passed medial to the inferior brachium and terminated in the magnocellular or internal division of the medial geniculate. The bundle degenerated after lesions confined to the lateral lemniscus and is probably identical with the central acoustic tract of earlier workers. Evidence is presented that the fibers of the bundle are of spinal origin. Since the lemniscal fibers which ascend to the thalamus appear to be non‐auditory, it is suggested that the inferior colliculus is an obligatory relay station in the classical auditory system and that the inferior brachium is the only ascending pathway of the system to project upon the thalamus.
The development of the facial nerve in baboon embryos (Papio sp.)
Authors: Gasser Raymond F. , Hendrickx Andrew G.
Published: January 2005

The arrangement of the facial nerve was studied in 21 baboon embroys and fetuses, 2.6–36.0 mm crown‐rump length, (25–54 days fertilization age) and one adult. The head and neck regions of eight specimens were reconstructed graphically or with wax. The extramedullary part of the right nerve was traced microscopically and its configuration mapped.

In early embryos (11–36 somites, 2.6–6.0 mm) the facial part of the facioacoustic primordium is either in close proximity or contacts the second arch epibrachial placode. It becomes a separate nerve (6.9–16.5 mm embryos) as the geniculate ganglion forms and the placode disappears. The first branches are the chorda tympani and greater petrosal. The pars intermedia and chorda tympani are large at 9 mm and the parent nerve terminates distally as a loose network of intermingling fibers. In 14.8–16.3 mm embryos connections are established with the deep petrosal and maxillary, and the tympanic, vagus and lingual nerves. Peripheral branches course into the occipital, cervical and mandibular regions. Between 18.3 and 36.0 mm the temporofacial and cervicofacial rami become evident and peripheral branches also extend into temporal, zygomatic and buccal regions. Communications are formed with branches of the auriculotemporal, zygomatic, infraorbital, buccal, mental, transverse cervical and great auricular nerves. Branches to the temporal and zygomatic areas lag in development.
The termination of ipsilaterral and contralateral optic fibers in the lateral geniculate body of Galago crassicaudatus
Authors: Campos‐Ortega J. A. , Gless P.
Published: January 2005

The lateral geniculate body of Galago crassicaudatushas five layers which have nbeen numbered in a ventrodorsal direction. The layers 1, 2, and 5 are composed of large cells and the layer 3 and 4of small ones. The ratio of crssed and uncrossed fiber is 1:1 Following enucleation of one eye, preterminal and terminal (synaptic)degeneration occurs in layers 2 and 4 ipsilaterally, whereas the contralateral fibers terminate in layers 1 and 5. The third layer recieves a small contribution of crossed and uncrossed fibers. As far as can be judged from lightmicroscopy, the type appears to be in the ration 3:1. Synaptic complexes composed of 2‐3 terminals in close approximation are frequently found.
The superior olivary complex and audition: A comparative study
Authors: Irving R. , Harrison J. M.
Published: January 2005

The sizes of the three major nuclei of the mammalian superior olivary complex were examined in a number of different species and variations in size were related to the relative prominence of haring and vision in each species. Size was measured by counting neurons in the several nuclei and by measuring the diameter of the eyes.

The lateral superior olive was large inMicrochiroptera(3850–4340 cells), guinea pig (3780), cat (3360) and chinchilla (3220); of intermediate size in macaque (1830), rat (1430) and squirrel monkey (1300); and small in gerbil (1220), mouse (1190), hedgehog (1090), squirrel (1000) and hamster (980). These data suggest that this nucleus is necessary for complex auditory discriminations (echolocation inMicrochiroptera, for example) and that its size is not primarily determined by the taxonomic order of the animal.

The medial nucleus of the trapezoid body was large in cat (5910), guinea pig (5840), hedgehog (4620) and chinchilla (4590); of intermediate size in rat (3870),Microchiroptera(3700) and macaque (3120); and small in squirrel monkey (2600), squirrel (2700), gerbil (2680), mouse (2270), and hamster (2130). The size of the nucleus was not related to sensory development or the size of the other olivary nuclei.

The size of the medial superior olive was found to be highly correlated with the size of the VIth nucleus and eye diameter.
Architectonic studies of the telencephalon of Iguana iguana
Authors: Northcutt R. Glenn
Published: January 2005

With the atrophy of the aquatic olfactory organ and the increased complexity of locomotion, the amphibian telencephalon was reorganized from a structure dealing primarily with olfaction, to the reptilian structure functioning at four levels of organization. The primary olfactory centers are retained, and the posterolateral and medial basal regions become specialized as secondary olfactory centers.

The anterolateral basal regions are reorganized as primary association centers of somatic information. A dorsal component develops due to the convergence of sensory modalities, and a ventral component develops which influences tectal centers.

Three pallial elements are recognized which function as part of the primary and secondary association systems. The lateral pallial element (pyriform cortex) is functionally related to the secondary olfactory system. Part of the medial pallial element (dorsomedial hippocampal cortex) is functionally related to the secondary olfactory system while the other part (dorsal hippocampus) is related to the secondary association system.

The secondary association system, which integrates all sensory modalites, has evolved along two lines in reptiles. The sauropsid line has lost the motor elements of the dorsolateral component of the dorsal pallium. The dorosomedial component of the dorsal pallium retained its motor elements and functions with the hippocampus as a transitional cortical structure.

In the theropsid line, the motor elements of the dorsolateral component were retained in a system which bypasses the older tectal motor system.
Histogenesis of the dorsal and ventral cochlear nuclei in the mouse. An autoradiographic study
Authors: Pierce Elizabeth Taber
Published: January 2005

The time, site of origin and migration pathways of neuroblasts destined for the dorsal and ventral cochlear nuclei in the mouse have been determined autoradiographically. Neurons of the dorsal cochlear nucleus arise on gestation days 10 through 13, neurons of the ventral cochlear nucleus on days 10 through 14. Neurons of both nuclei arise within the primitive ependyma of the caudal extent of the primary rhombic lip at the level of the lateral recess; neurons of the dorsal cochlear nucleus arise caudal to neurons of the ventral cochlear nucleus. Granular cells arise on days 12 through 18 within the primitive ependyma of the secondary rhombic lip at the same levels.
Laminar structure of the dorsal lateral geniculate nucleus in the tree shrew (Tupaia glis)
Authors: Glickstein Mitchell
Published: January 2005

Three tree shrews (Tupaia glis) were subjected to unilateral enucleation. Two of these were sacrificed seven months after surgery, and their brains were sectioned and stained for study of transneuronal atrophy within the dorsal lateral geniculate nucleus (LGN). The third animal was sacrificed ten days after enucleation; its brain was stained with a modified Nauta method for degenerating axons. Results of the two techniques are in good agreement. Ipsilateral and contralateral fibers were well segregated within the optic tracts. Transneuronal atrophy was found in layers 1 and 5 ipsilateral to the nucleated eye, and layers 2 and 4 contralaterally. Layer 3 did not appear to be differentially degenerated on the two sides, nor did a sixth layer, layer S, situated between layer 5 and the optic tract. Each superior colliculus receives fiber projections from both eyes, although those arising in the contralateral eye are far greater in number.
Organization of the posterior dorsal thalamus of the hedgehog
Authors: Erickson R. P. , Hall W. C. , Jane J. A. , Snyder M. , Diamond I. T.
Published: January 2005

A study of the responsiveness of single neurons in the hedgehog thalamus to sensory stimulation was undertaken with the hypothesis that modality specific relay nuclei characteristic of the mammalian thalamus differentiate out of a pool of multisensory neurons. Support for this hypothesis was obtained in earlier investigations of the opossum thalamus. In some ways the hedgehog may be an even better representative of a primitive stage of thalamic development. For example, there is very little structural difference between the ventroposterior nucleus and the medial geniculate body. The results of the present microelectrode investigation showed that neither the ventroposterior nucleus nor the medial geniculate body was modality specific. Further, many neurons in the ventroposterior nucleus showed wide receptive fields characteristic of the posterior group of nuclei in cats. This finding of convergence of sensory input upon single neurons of the dorsal thalamus in a generalized mammalian type suggests that the specificity characteristic of higher mammals is a product of an evolutionary trend. Thus comparative neurology provides additional evidence that precise receptive fields must play an important role in behavioral adaptation.
The spinal roots in the sloth (Choloepus hoffmanni peters)
Authors: Goffart M. , Gerebtzoff M. A. , Duchesne P. Y.
Published: January 2005

In the lower half of the thoracic region in Choloepus hoffmanni, a didactyl sloth, which possesses 23 dorsal vertebrae, the spinal roots assume a rostralward direction. This situation raises difficult problems in early embryological development as it already prevails — although slightly altered — in the 100 gm foetus. The myelinated nerve fiber diameters in the ventral roots are smaller than in the cat. This conforms to the general rule that “red” and slow muscle fibers are supplied by thinner motor fibers than the “white” fast muscles, because in the sloth the whole of the musculature is of the former type. The γ efferent system is well developed. The sympathetic preganglionic fibers are thought to be mostly unmyelinated. From the fiber spectrum in the dorsal roots it appears that the muscle spindle afferents are also of smaller diameter than in the cat. The cuscle spindles, the sympathetic chain and the aortic origin of the intercostal arteries are described.
Observations on the fine structure and distribution of presumptive baroreceptor nerves at the carotid sinus
Authors: Rees P. M.
Published: January 2005

Comparative nerve fiber counts show that the areas of the carotid bifurcation receiving a rich innervation correspond in extent to areas of the vascular wall with a thinned and elastic tunica media. Presumptive baroreceptor nerves within the carotid sinus wall were examined by electron microscopy in normal rabbits and also after superior cervical ganglionectomy and/or Hering's nerve transection. The glossopharyngeal (baroreceptor) nerve terminals are either denuded of a cellular covering or are thinly clothed in Schwann cell cytoplasm, and are intimately related over wide areas to at least three sinus wall components: to elastin at the medio‐adventitial border, to collagen in the inner one‐half of the adventitia, and to the surfaces of isolated adventitial smooth muscle cells. These muscle cells also receive a terminal innervation from the superior cervical ganglion. There is no nervous penetration of the sinus tunica media. The spatial arrangement of the adventitial muscle cells and their associated sensory and motor nerves simulates a smooth muscle spindle, possibly constituting a morphological basis for an efferent control of baroreceptor output.

The baroreceptor nerve terminals contain large accumulations of mitochondria, and also myelin figures and small dense bodies resembling glycogen granules. Evidence is presented that baroreceptor impulses may be conveyed from the sinus wall in both myelinated and nonmyelinated nerve fibers.
Self‐stimulation in the rabbit: An anatomical map of stimulation effects
Authors: Bruner Alfred
Published: January 2005

An anatomical map of brain stimulation effects in rabbits, based on lever pressing and observational data, revealed close correspondence to the findings from other species, particularly rats. Strongest self‐stimulation was obtained from the posterolateral hypothalamus, fornix, and rostral tegmentum. Rhinencephalic placements occasionally yeilded mild self‐stimulation, but more frequently gave negative or ambiguous effects. Negative effects were obtained in the medial hypothalamus and reticular formation, while caudate nucleus stimulation appeared emotionally neutral. Also in agreement with earlier findings, EEG seizures did not accompany self‐stimulation of the posterolateral hypothalamic area, but did often accompany self‐stimulation of rhinencephalic structures. As in cats, hippocampal θ synchronization was observed to accompany approach behavior, while desynchronization accompanied withdrawal and freezing.
Ascending projections of the substantia nigra in the rat,
Authors: Faull Richard L. M. , Carman John B.
Published: January 2005

The Nauta method was used to study the fiber degeneration resulting from electrolytic lesions in the midbrain of 34 albino rats. Lesions were placed in the substantia nigra alone (pars compacta, 3; pars reticularis, 8; both parts, 3); in the substantia nigra and surrounding structures (6); immediately caudal (3), dorsocaudal (3), dorsal (4) and ventral (1) to the substantia nigra; and in the hemisphere and lateral midbrain along the track of the electrode (3). All the degeneration resulting from damage by the electrode to the cerebrum and lateral midbrain was accounted for in terms of known fiber pathways. Lesions involving the substantia nigra (pars reticularis and/or pars compacta) with or without damage to surrounding structures produced fine fiber degeneration which passed rostrally in the pars compacta and the dorsal capsule of the subthalamic nucleus, turned dorsomedially and entered the ventrolateral border of nucleus ventralis medialis thalami (VM) where it terminated. This nigrothalamic pathway did not degenerate when the nigra was not involved. Lesions involving the superior cerebellar peduncle, red nucleus or prerubral radiation also produced terminal degeneration in VM. However, the fibers of this cerebellorubrothalamic pathway, which were not interrupted by lesions confined to the substantia nigra, entered the caudal pole of VM. There was no evidence of a direct nigrostriatal pathway. The demonstration of projections from the cerebellum and substantia nigra to VM establishes this nucleus as the homologue in the rat of nuclei ventralis anterior and ventralis lateralis thalami in primates.
Projections of thalamic and cortical gustatory areas in the rat,
Authors: Wolf George
Published: January 2005

The method of Nauta was used to stain axons which degenerated after lesions of the thalamic projection nucleus and cortical zone subserving gustation in the rat. Lesions of the medial subnucleus of the thalamic ventral nuclear complex resulted principally in degeneration which passed rostrolaterally through the thalamus, internal capsule, globus pallidus, and striatum to terminate in insular and inferior parietal cortex around the region of the middle cerebral artery. Lesions of this cortical projection zone resulted in degeneration which passed caudomedially through the same striatal and pallidal areas traversed by the thalamocortical fibers. One component of these fibers continued into the thalamus to terminate just dorsal to the medial subnucleus. A second component turned caudally into the cerebral peduncle to terminate in the substantia nigra. There was evidence of terminal degeneration in the striatum but not in the pallidum after both thalamic and cortical lesions. There was no evidence of degeneration in any structures primarily associated with olfactory or alimentary functions.
The ultrastructure of the conus medullaris and filum terminale
Authors: Miller Carol
Published: January 2005

Electron microscopy of the conus medullaris and intradural filum terminale in the adult cat and monkey show a preponderance of ependymal cells, many of which are oriented around either a central canal or narrow clefts. Some rest directly on connective tissue. Randomly dispersed degenerating neural processes and fibrous astrocytic gliosis are prominent. Some ependymal cytoplasmic abnormalities also are present. The pathogenesis of these changes is unknown.
An electron microscopic study on the innervation of the trout heart
Authors: Yamauchi Akio , Burnstock Geoffrey
Published: January 2005

The neuromuscular inter‐relationship was investigated in three regions of the trout heart: the sinoauricular junction, the auricle and the ventricle. The innervation of the sinoauricular tissue was unusually dense; in one plane of section, the number of axons less than 200Å apart from cardiac muscle cells was approximately equal to the total number of muscle cells. Some muscle cells had up to eight close axon contacts. It is suggested that every muscle cell in this region of the fish heart has at least one and probably many more individual neuromuscular contacts. Many ganglion cells, some with presynaptic terminal were observed in the sinoauricular region. Multivesicular bodies were commonly seen in the cytoplasm. The innervation of the ventricle near the apex was very sparse and that of the auricle appeared to be intermediate between the two extremes.

The ventricular muscle cells were somewhat larger and contained a higher area of myofibrils than those in the auricle and the sinoauricular tissue. M‐lines in the myofibrils were demonstrated in the cardiac muscle of the trout. Intraaxonal vesicles were mostly agranular. However, in about 9.5% of the 1472 axon profiles examined, a number of small (500–700Å) and large (∼800Å) granular vesicles were also present, which suggests that, in contrast to the general view, there are some nerves containing catecholamines supplying the fish heart.

It is likely that the sinoauricular region in the fish heart is homologous to the smus node in avian and mammalian hearts.
Cell origin of the ventral spinocerebellar tract
Authors: Ha Hongchien , Liu Chan‐Nao
Published: January 2005

The cells of origin of the ventral spinocerebellar tract have never been determined conclusively. We attempted to determine the cell origin of this tract by applying anatomical methods. Retrograde changes were observed in the lumbosacral segments following hemicerebellectomy, severance of cerebellar peduncle or hemisection of spinal cord at various levels. The chromatolytic motor‐type neurons were plotted, most occupying the dorso‐lateral portion of the ventral gray, with fewer cells in the medial, lateral and central part of ventral horn. Ablation of these neurons in different animals resulted in axonal degeneration which could be traced to the cerebellum via chiefly contralateral lateral funiculus and from the ventral spinocerebellar tract. The morphology of the ventral spinocerebellar tract neurons was studied by the Golgi method. Incidental findings of axonal degeneration bilaterally in the dorsal spinocerebellar tracts, with ipsilateral domination, following ablation of the ventral spinocerebellar tract neurons were discussed.
The development of the nucleus of origin of centrifugal fibers to the retina in the chick
Authors: Cowan William Maxwell , Wenger Eleanor
Published: January 2005

The development of the isthmo‐optic nucleus – the site of origin of centrifugal fibers to the avian retina – has been studied in normal chick embryos and after early complete or partial removal of the optic vesicle. The nucleus arises from the junctional region between the caudal midbrain tegmentum and roof plate at about the sixth or seventh day of incubation and soon forms a compact, oval cell mass midway between the trochlear nucleus and the medial edge of the tectum. Within three or four days it is invaded by afferent fibers from the optic tectum, through the tecto‐isthmal tract, and becomes transformed into a convoluted, but essentially two‐dimensional sheet, by a large scale degeneration of cells, especially in its central part.

Extirpation of the optic vesicle has no effect upon the initial proliferation, differentiation or migration of the cells, but the ensuing cellular degeneration is considerably exaggerated, so that after complete removal of the vesicle, the nucleus shows a total cell loss by the nineteenth day of incubation. The tecto‐isthmal fibers disappear at, or just before, the period of maximal cell death; the centrifugal fibers from the nucleus (the isthmo‐optic tract) degenerate at a slightly later stage. Large, but incomplete, lesions of the vesicle before Stage 13 result in considerable cell losss throughout the nucleus; smaller lesions at these stages result in only a slight cellular hypoplasia. Incomplete lesions at Stage 13, or later, usually result in a complete cell loss in one or other topographical portion of the nucleus, the remaining parts being unaffected.
Ascending projections of the primary cochlear nuclei and nucleus laminaris in the pigeon
Authors: Boord Robert L.
Published: January 2005

Auditory projections were studied, by the Nauta method, from medullary to mesencephalic levels following lesions in nuclei magnocellularis, angularis and laminaris and transection of the dorsal cochlear decussation and trapezoid body in the midline of the medulla.

Fragmented axons project bilaterally to nucleus laminaris from the medial part of nucleus magnocellularis. Degenerated fibers from the lateral part of nucleus magnocellularis, medial part of nucleus angularis. and nucleus laminaris projects to the homolateral superior olivary nucleus. cross the raphé in the trapezoid body, ascend in the contralateral lateral lemniscus, distribute to the ventral and lateroventral nuclei of the lateral lemniscus and, at least third order axons from nucleus laminaris. terminate in nucleus mesencephali lateralis pars dorsalis. No ascending auditory neurons project, even following midventral section of the trapezoid body, to nucleus isthmi, nucleus semilunaris nor. with certainty, to the dorsal nucleus of the lateral lemniscus.

This study supports the homology of the avian nucleus mesencephali lateralis pars dorsalis and nucleus laminaris with the mammalian central nucleus of the inferior colliculus and medial superior olivary nucleus respectively. Furthermore, on the basis of fiber projections and cellular organization. nucleus magnocellularis of the pigeon appears to correspond to the anterior ventral cochlear of higher mammals and the medial parts of nucleus angularis to the posterior ventral cochlear nucleus.
Morphological characteristics of mouse stellate and basket cells and their neuroglial envelope: An electron microscopic study
Authors: Lemkey‐Johnston N. , Larramendi L. M. H.
Published: January 2005

Sampling of stellate cells from the molecular layer of cerebellar cortex at two distinct levels within yielded two populations of cells referred to as stellate and basket cells respectively. The appearance of the soma, the several kinds of dendrites and their accompanying spines can be characterized on the electron microscopic level for each type of cell and correlate well with Golgi impregnation studies.

Analytical studies were made to determine the proportion of neural and glial elements in direct apposition to stellate and basket soma and their respective dendrites. On the average the glial covering of a basket or stellate cell was 12–14% of the cell profile, reaching 18.6% for the distal portions of dendrites.

A quantitative analysis of the amount of soma and dendritic perimeter in contact with synaptic boutons revealed the percentage of perimeter surface covered by terminal boutons was 15.2% for basket soma, 4.5% for the stellate soma, 21% for basket dendrites and 10.3% for stellate dendrites.

An interesting group of cells located in the Purkinje cell layer had the morphological characteristics of basket cells but an unusual synaptic input and an unusually high proportion of glial envelope due to their unique position.

This report is an introduction to a comparative analysis of the distribution, and densities of different types of synapses upon basket and stellate cells.
Types and distribution of synapses upon basket and stellate cells of the mouse cerebellum: An electron microscopic study
Authors: Lemkey‐Johnston N. , Larramendi L. M. H.
Published: January 2005

The consistent identification of nerve terminals in the molecular layer of the mouse cerebellum has permitted electron microscopic study of the spatial and numerical distribution of synapses upon the soma and dendrites of stellate cells at three depths in the molecular layer.

The number of boutons synapsing per 100 μ of cell perimeter, or general synaptic density (G.S.D.) has been found to vary among stellate cells located at different depths in the molecular layer. It has also been found that the G.S.D. of the dendrites is greater than that of the cell bodies of these cells.

The specific synaptic densities, or number of boutons of specific type (such as parallel fiber, climbing fiber etc.) synapsing upon 100 μ of cell perimeter, have been found to vary significantly for each type of terminal among upper, lower, and very low stellate cells in the molecular layer. Very low stellate cells receive almost exclusively Purkinje collateral synapses upon their cell bodies (the dendrites have not been identified) whereas low stellate cells (basket cells) receive upon both their cell bodies and dendrites mostly parallel fiber synapses and in decreasing order lesser amounts of basket‐stellate, Purkinje collateral and climbing fibers. Uppermost stellate cells, however, receive only parallel fiber and a few stellate terminals.

The distribution of synapses upon stellate cells found in the mouse agrees with physiological data reported in the cat.
Morphology of the regenerated spinal cord in the lizard, Anolis carolinensis
Authors: Simpson Sidney B.
Published: January 2005

The regenerated spinal cord of the lizard, Anolis, was studied with the aid of the light and electron microscopy. The regenerated cord consists of an ependymal epithelium, descending central nerve fibers and the connective tissue of meninges. The ependymal tube is a discrete entity and is separated from the surrounding connective tissue by a basement lamina. The ependymal tube is composed of a morphologically homogeneous epithelial cell population. The ependymal cell itself fits closely the previous descriptions of the ependymal tanycyte.

The majority of the regenerated central nerve fibers are contained within the ependymal tube and are fasciculated in longitudinal rows between the basal processes of adjacent ependyma cells. This association of regenerated central fibers and the ependymal tube and its relation to guidance of intercentral fiber regeneration is discussed.
Lateral‐line organs in some teleosts: Cirrhina mrigala ham. Buch. (Cyprinidae), Ophicephalus (Channa) punctatus Bloch (Channidae) and Gobius striatus Day (Gobiidae)
Authors: Srivastava C. B. L. , Srivastava M. D. L.
Published: January 2005

The structure and location of “ordinary” lateral‐line organs of the fry and the adult specimens of three teleosts, Cirrhina mrigala, Ophicephalus (Channa) punctatus and Gobius striatus, have been studied and the results have been discussed. The stalked condition of surface organs, described for G. striatus, is a new feature reported for the first time in this communication. An attempt has been made to classify “ordinary” lateral‐line organs on morphological grounds, especially the group of “pit organs,” taking into consideration the orientation of the neuromast concerned in relation to the surface of the adjacent skin, the basement membrane, the dermis and the thickness of the surrounding epidermis.
The dermatomes of the sheep
Authors: Kirk Edwin J.
Published: January 2005

The dermatomes of the sheep, first cervical through second coccygeal were isolated by the method of “remaining sensibility” and defined by mapping the areas of residual sensitivity to pinching of the skin with fine‐pointed forceps.

The disposition of these dermatomes was similar to that in other species, but appreciable variations between individual sheep were common. The trunk fields extended between the dorsal and ventral midlines of the body as regular, continuous, serial bands. They showed a cranio‐caudal overlap of approximately one‐half, but only slight overlapping across the dorsal and ventral midlines.

Most of the limb fields reached the dorsal midline of the body, and in both the fore and hind limbs three dermatomes extended to the digits. A close correlation existed between the forelimb dermatomes and those of other species: a less precise correlation was found in the hindlimb. The abrupt flexures in the borders of some limb fields appear to have been produced by the considerable reduction from the primitive pentadactyl condition.

The cutaneous sensory areas supplied by the three main divisions of the trigeminal (fifth cranial) nerve were also charted. Their disposition was again similar to that in other species, and the overlap between them much less than that of the dermatomes.
A single unit analysis of trigeminal projections to bulbar reticular muclei of the rat
Authors: Nord Samuel G. , Kyler Harry J.
Published: January 2005

The lateral bulbar reticular formation of anesthetized rats was explored with microelectrodes in order to compare the response and field characteristics of its somatosensory cells with properties of units located in the adjacent spinal trigeminal complex. Responses were evoked in the cells using natural and electrical stimulation of the skin. Neurons in the reticular nuclei tended to exihibit long latencies, low folowing capacities and large receptive fields. On the other hand, trigeminal complex cells generally revealed opposite characteristics, more typical of primary sensory structures, such as short latencies, high following capacities and punctate‐to‐small fields. The distinction between the regions was emphasized by additional qualities which were peculiar to the reticular neurons: Bilateral peripheral representation, into very coarse mechnical stimulation. In amny respects, the data indicate that the lateral reticular formation is intimately involved in the mediation of facial pain. They also support the view that it participated in this function by regulating the flow of nocioceptive activity from receptive mechanisms of the skin to the lemniscal pathway.
Synaptic analysis of inner plexiform layer in human retina
Authors: Foos Robert Y. , Miyamasu Walter
Published: January 2005

An ultrastructural synaptic analysis based on observations from 33 serial thin‐sections of the inner plexiform layer in a volume sample of midperipheral human retina is presented. Of the 152 identifiable neuronal processes 7lpar;total 187) 14 were bipolar, 112 amacrine, and 26 ganglion. One hundred and forty‐seven synapses were present — 31 bipolar (ribbon) and 116 amacrine (conventional). The ribbon synapses were divided on the basis of their postsynaptic processes into: amacrine, ganglion (16); amacrine, amacrine, ganglion (9) amacrine, amacrine (3) amacrine, amacrine, amacrine (1) ganglion (2), both incomplete in sections(. Of the 116 conventional synapses, 28% were amacrine‐bipolar, 34% amacrine‐amacrine and 38% were amacrine‐ganglion. The occurrence of extra amacrine process(es) and the occasional absence of a ganglion cell dendrite at bipolar (ribbon) synapses, as well as the relative abundance of amacrine‐amacrine (conventional) synapses, suggests a relatively greater role of amacrine cells in mediating visual transformations in the midperipheral human retina than has been described previously.
Kinetics of proliferation and latency between final cell division and onset of differentiation of cerebellar stellate and basket neurons
Authors: Rakic Pasko
Published: January 2005

Thymidine‐3 autoradiographic, Golgi, and electonmicroscopic methods were combined to analyze proliferation kinetics and to determine the interval between final cell division and initial differentiation of interneurons of the cerebellar molecular layer (stellate and basket cells). The protracted span of development makes rhesus monkeys particularly suitable for unravelling temporal sequences in neurogenesis. Labeling index measurements in autoradiograms of adult animals injected at different developmental ages indicate that interneurons are generated at a steady rate of about 1% per day from the eightieth embryonic day to just after birth. The precursor pool is about 300,000 cells, each yielding on the average one differentiating and one proliferating daughter cell. The rate of interneuron proliferation parallels neither the exponential production of granule cells nor the 40‐fold expansion of cerebellar surface.

Adult position of interneurons correlates with time of cell origin; the deep cells are generated first, the more superficial ones progressively later. By comparison of autoradiographic maps with Golgi impregnations and electronmicrographs at developmental stages, the interval from final mitosis to dendritic outgrowth and onset of synaptogenesis was found to increase systematically, reaching a maximum of two months for the last‐forming interneurons. Postmitotic interneurons, as yet without dendrites, accumulate at the interface between the external granular layer and the thickening molecular layer, and only later become enveloped by newly‐forming processes of other cells. Identified among these were mainly parallel fibers, some climbing fibers, axons of previously generated interneurons, and Purkinje dendrites. It is speculated that any or all of these may induce interneuron differentiation, since proliferation of any given interneuron is completed relatively early while it differentiates only later when its local milieu has developed.
Fluorescence histochemistry of monoamine‐containing cell bodies in the brain stem of the squirrel monkey (Saimiri sciureus). The locus caeruleus
Authors: Hubbard Jack E. , di Carlo Vincenzo
Published: January 2005

A study of the locus caeruleus is presented as the first in a series of papers describing the monoamine‐containing cell bodies in the brain stem of the squirrel monkey (Saimiri sciureus) using the fluorescent histochemical technique. Found most caudally in the roof of the ventriculus quartus, the locus caeruleus attains its greatest density of cell bodies medial to the tractus mesencephalicus n. trigemini at the level where the tract lies medial and ventral to the brachium conjunctivum. More rostrally, the cells are found dorsal, medial, and ventral to the brachium conjunctivum. Finally, in a location to a few cells closely associated with the fibers of the nervus trochlearis. Careful examination of closely packed cells medial to the tractus mesencephalicus n. trigemini reveals that almost all of the cell bodies of this region fluoresce, thus displaying a positive reaction for monoamines. On the basis of the fluorescent histochemical technique, therefore, the authors conclude that this region which often is indicated in the literature as the nucleus tr. mesenceph. n. trigemini is actually composed of the catecholamine‐containing cells of the locus caeruleus.
Time of origin of corresponding cell classes in the cerebral cortex of normal and reeler mutant mice: An autoradiographic analysis
Authors: Caviness V. S. , Sidman R. L.
Published: January 2005

Reeler, a recessive mutation in mice, causes cytoarchitectonic abnormalities of the cerebral and cerebellar cortices. Although the relative positions of classes of cells in the cerebral cortex are markedly abnormal, the time of origin of cells in each class appears to be normal by autoradiographic criteria. In the retrohippocampal cortical structures and in the adjacent neocortex, the earliest generated cell class, the polymorphic, arises at the same embryonic time in normal and reeler littermates. Whereas these cells come to form the deepest stratum of the normal cortex, they lie in an immediately subpial position in the mutant, there being no cell‐sparse external plexiform (molecular) layer. A population of larger cells is generated next; these normally come to lie in more superficial layers but instead lie deep to the polymorphic cells in the mutant. Granule cells of the neocortex arise last, simultaneously in normal and reeler; they form the most superficial neocortical cell stratum in the normal, but lie at a more restricted level within the large cell zone in the mutant. These data indicate that the cytoarchitectonic anomaly in reeler is independent of the spatiotemporal program of cell generation. It appears likely that the reeler genetic locus governs embryonic events, as yet undefined, that direct the postmitotic migrating young neuron to class‐specific levels within the cortex.
A morphological investigation of an early reflex pathway in developing rat spinal cord
Authors: Vaughn James E. , Grieshaber Judith A.
Published: January 2005

The early development of the disynaptic cutaneous reflex pathway in the brachial spinal cord of rat fetuses was investigated both light and electron microscopically. The spinal cord areas which contain the neurons (association interneurons and lateral motor nucleus neurons) involved in this reflex pathway were identified in both neurofibrillar (silver‐stained) and semithin plastic embedded specimens. Equivalent areas were identified in adjacent ultrathin preparations for electron microscopy and micrographs of these sample areas were taken of specimens at embryonic days 13.5–19.5 as well as for postnatal day 4 and adult specimens. The relative volume of association and dorsolateral motor neuropils occupied by synaptic boutons in these micrographs was determined using stereological methods. The mean number of synaptic junctions and boutons per 100 μ2 was also determined for the two neuropil areas at each developmental stage. These analyses show that synaptic junctions and boutons occur in the dorsolateral motor neuropil before they can be found in association neuropil. Synapses within motor neuropil are first seen at embryonic day 13.5. Synaptogenesis in the dorsolateral motor neuropil is temporally correlated with the presence of numerous fibers which, in silver‐stained specimens, can be seen to arise from the association interneurons and to course into the dorsolateral aspects of the motor nucleus. Synaptic junctions and boutons are not observed in the association neuropil until embryonic day 14.5 and this correlates well with the time when collaterals of the primary afferent fibers can first be observed penetrating into the dorsal half of the intermediate zone from the anlage of the dorsal funiculus. The precocious development of synaptic junctions in dorsolateral motor neuropil in comparison to the association neuropil continues throughout the developmental period examined. These data support a retrograde pattern of synaptogenesis in the early development of the spinal cutaneous reflex pathway. Association interneurons make synaptic contacts with motor neurons before synapses are formed between primary sensory neurons and association cells. This sequence is the reverse of the normal flow of nerve impulses through spinal reflex pathways.
The distribution of rods and cones in the retina of the cat (Felis domesticus)
Authors: Steinberg Roy H. , Reid Miriam , Lacy Paula L.
Published: January 2005

The distribution of rods and cones in the cat retina was studied by light microscopy. The rods and cones were counted from the area centralis to the temporal periphery in photomicrographs of transverse sections through the inner segments. A 16% correction for the effect of tissue shrinkage was applied to the densities obtained in fixed‐dehydrated tissue, by comparing these counts with those obtained from similar retinal areas in fresh tissue.

The cone distribution was characterized by a steep increase in cone density centrally, which was elongated in the nasotemporal axis, and coincided approximately with the central increase in ganglion cell density (Stone, '65). Cone density in the area centralis peaked at 26,000–27,000/mm2, and fell to a plateau of 4000/mm2 in the periphery and to less than 3000/mm2 near the ora serrata. The density of rods was greater than the density of cones in all regions. The rods reached a maximum density of 460,000/mm2 at an eccentricity of 10–15°, in a region which completely surrounded the central cone elevation. Centrally, the rod distribution was characterized by a sharp fall in density, reaching a low of 275,000/mm2 at the point of peak cone density. Peripherally, there was a plateau of high rod density at above 400,000/mm2, out to about 30° temporal eccentricity. Beyond this plateau, rod density steadily fell, and reached a low of 250,000/mm2 near the ora serrata. The rod/cone ratio reached a low value of 10.5–11.0 in the central region of maximum cone density. It then rose steeply to reach a plateau of about 65 in the periphery, while near the ora serrata there were 100 rods for each cone.

The rods were arranged in well defined rows, and each rod was surrounded by six other rods. The cones were interspersed throughout the rod mosaic and were less regularly arranged than the rods. In fresh tissue, rod outer segment diameters ranged from 1.0 μ to 1.6 μ. rod diameters were smallest in the region of maximum rod density and increased, along with the decrease in rod density, both in the periphery and in the area centralis. Two thirds of the central decrease in rod density from the pericentral peak could not be accounted for by the increase in the percentage of space occupied by cones, and was consistent with a central increase in rod diameter.

Receptor‐ganglion cell convergence was estimated by comparing receptor densities with the ganglion cell densities of Stone ('65). Cone‐ganglion cell convergence reached a minimum in the area centralis at the cone density peak, probably indicating the retinal region in which photopic acuity is at an optimum. Minimum rod‐ganglion cell convergence, as estimated from the rod/large ganglion cell ratio, reached a minimum at about 7.5° central to the peak of rod density, and at about the same eccentricity as the human scotopic acuity optimum.