bluuebunny/crossref_metadata_2025 huggingface dataset:
Mixed intra‐ and extrafusal muscle fibers produced by temporary denervation in newborn rats
Authors: Werner Joan K.
Published: May 2005

Temporary denervation of the medial head of gastrocnemius muscle in newborn rats has produced three major changes in muscle spindle development: (1) a modification of the spindles' components, (2) an increase or decrease in the number of spindles that developed in the experimental muscles and (3) an alteration in the location of spindles. The most striking change was observed in a total of 15 spindles from three of the experimental animals and consisted of a modification of the components. The abnormal, modified spindles usually contained only one muscle fiber, which had the morphological characteristics of an intrafusal fiber at one end and in the equatorial zone, and the morphological characteristics of an extrafusal fiber at the opposite end. These peculiar muscle fibers clearly represent a single cell which has differentiated along two distinctly different pathways and they show that the pattern of innervation can influence the course of differentiation of developing muscle cells to a significant extent.
Insular‐diencephalic connections in the Macaque
Authors: Wirth Fremont P.
Published: May 2005

Insular‐diencephalic connections have been studied in five rhesus Macaques with both retrograde and anterograde degeneration techniques. Animals were prepared for study with bilateral symmetrical resections of temporal operculum or fronto‐parietal operculum or both, with or without excision of underlying insular cortex. The resections were staged such that the older was suitable for evaluation of retrograde cell change and myelin tract degeneration (cresyl violet and Loyez stain) and the more recent for anterograde fiber degeneration (Nauta). From the cresyl violet‐Loyez stained hemispheres evidence was obtained for sustaining fiber projections to the insula from n. ventralis caudalis parvocellularis. Nauta stains demonstrated projections from the insular cortex to n. ventralis caudalis, n. ventralis caudalis ventralis and n. ventralis caudalis parvocellularis. Connections were also demonstrated to n. centralis, n. parafascicularis, n. dorsalis oralis and the intralaminar nucleus. These connections closely resemble those of overlying fronto‐parietal operculum and suggest that insular cortex is an extension of sensory‐motor cortex as indicated by physiologic data. Projections from insula to the amygdala were also identified, indicating the association of insular cortex and the limbic system.
Anterograde degeneration study of the cortical projections of the lateral geniculate and pulvinar nuclei in the tree shrew (Tupaia glis)
Authors: Harting J. K. , Diamond I. T. , Hall W. C.
Published: May 2005

Sixty lesions were placed in the pulvinar nucleus or the lateral geniculate nucleus of the tree shrew, and degenerated axons and their terminals were traced to the cortex. In all but two of the animals the electrode approached the thalamic target through the cerebellum and midbrain, thus sparing the cortex and thalamic nuclei other than the target nuclei. The results show that the pulvinar nucleus projects in a topographic fashion to an extensive cortical zone that includes areas 18, 19 and several temporal areas below 19. While there are several architectonic areas in its cortical target, no corresponding subdivisions could be established within the pulvinar nucleus, and its projections are best explained in terms of a single topographic organization. Further, since the pulvinar nucleus receives fibers from the superficial layers of the superior colliculus, its extensive cortical target can be regarded as primary visual cortex. The lateral geniculate nucleus projects in a precisely topographic fashion to area 17. Further, our evidence suggests that each layer of the lateral geniculate nucleus projects to a horizontal strip within the fourth or granular layer of area striata. With respect to the question of the relation between ocular dominance and location in area 17, the pattern of projections from the lateral geniculate nucleus does not reveal ocular dominance columns in layer IV of the tree shrew. In contrast to our results Hubel and Wiesel ('68, '69) have shown that in the monkey there are vertical columns of cells in layer IV driven by either the homolateral or the contralateral eye. The case for the cat (Hubel and Wiesel, '62, '65) may be different from either of the other two species, thus posing the problem of discovering the mammalian plan and departures from the prototypical organization.
Cell proliferation in injured spinal cord. An electron microscopic study
Authors: Adrian Erle K. , Williams M. G.
Published: May 2005

To examine the fine structure of cells synthesizing DNA in the spinal cord in response to injury, mice were given a single injection of 3H‐thymidine two days after stab injury to the spinal cord and were sacrificed at either two hours or one, two, six or 14 days later. The most common type of labeled cell found at a distance from the wound at all the time intervals after 3H‐thymidine injection had an elongated or irregularly oval nucleus with clumps of condensed chromatin at the nuclear envelope and one or more nucleoli. The cytoplasm which was darker than adjacent axoplasm, contained dense bodies, scattered mitochondria, many free ribosomes, only a few rather long cisternae of granular endoplasmic reticulum, a prominent Golgi apparatus, and a few granules. These cells were similar in appearance to the cells that have been identified as microglia or multipotential glia by others. However, they also have many features in common with blood mononuclear cells. In the wound, in addition to the cells already described, the labeled cells at two hours after 3H‐thymidine injection included well developed macrophages, a few endothelial cells, and a large number of cells with large pale nuclei and cytoplasm containing abundant microtubules and granules. At the later time intervals, these cells apparently developed large numbers of cytoplasmic filaments. Although they bore some resemblance to reactive astrocytes, these labeled cells were not typical astrocytes, and their location, their apparent transformation from a cell without filaments, and their pseudopodia and surface vacuoles suggest the possibility that they may be derived from blood mononuclear cells.
Cytoarchitecture of nucleus sphericus in the common boa, Constrictor constrictor
Authors: Ulinski Philip S. , Kanarek David A.
Published: May 2005

The normal anatomy of nucleus sphericus in the common boa (Constrictor constrictor) is described here on the basis of routine light microscopic and Golgi material. Nucleus sphericus is a cup‐shaped aggregation of cells lying in the forebrain posterior to the anterior commissure and consisting of three concentric layers. The marginal layer is subependymal, is continuous rostrally with the anterior commissure, and contains fusiform cells with discoidal dendritic fields tangent to the mural layer, Marginal cell axons entwine mural cell dendrites. The mural layer forms the walls of the cup and appears as a closed ring of cells in transverse sections. Mural cell dendrites extend radially into the marginal and hilar layers and horizontally within the mural layer. All of these dendrites are profusely covered by dendritic spines with conical heads and slender stalks. Mural cell axons ascend to the marginal layer. The hilar layer forms the cup's cavity containing scattered cells whose dendrites extend in all directions and whose axons approach the cup's mouth. Afferent fibers in the nucleus run predominately at right angles to mural cell dendrites bearing varicosities at irregular intervals.
The tract of Lissauer in relation to sensory transmission in the dorsal horn of spinal cord in the macaque monkey
Authors: Denny‐Brown D. , Kirk E. J. , Yanagisawa N.
Published: May 2005

The classical method for study of the area of innervation of skin by one nerve root, isolated by section of three neighboring roots on either side, was used to study the contribution of neighboring segments of spinal cord to transmission at the first sensory synapse. The area from which response to pinscratch could be obtained in the conscious monkey was greatly increased if the spinal cord was sectioned just below the test segment, or hemisected above it, particularly if vascular infarction was avoided. The enlarged area was hypersensitive. The maximal area of skin innervated by any one nerve root was approximately twice as large as had been found by previous investigators. Each sensory point in the ventral parts of dermatomes must be innervated by at least five nerve roots. Work previously reported had shown that the area of test dermatome was reduced by sectioning neighboring roots medial to their ganglia after previous distal section of the same roots, or by section of more than three neighboring roots. These restrictions of area could be reversed by a subconvulsive dose of strychnine. The facilitatory and suppressive effects from neighboring nerve roots and spinal segments respectively were traced to the mechanism of Lissauer's tract, of which the medial division exerts a facilitatory effect and the lateral division a suppressor effect on transmission through the first synapse of the test root.

These excitatory and inhibitory effects, thought to be derived from collaterals of nerve fibers of like and unlike function of all sizes entering the substantia gelatinosa of neighboring segments, must be transmitted by small cells with axons in the tract of Lissauer. The reversal of the inhibition by strychnine indicates a post‐synaptic mechanism at the first synapse. The prolongation of either tonic excitatory or tonic inhibitory influence for as long as five days after section of the corresponding input pathway represents a unique feature of the mass polysynaptic effects of the small interneurones making up the substantia gelatinosa, rather than the presence of a long‐lasting transmitter substance. There was evidence that both dorsal root ganglion cells and substantia gelatinosa continue to contribute to fringe effects after isolation from the periphery. The mechanism of the substantia gelatinosa could provide correlation for the type of sequential directional information such as is necessary for the spinal scratch reflex.
Neuroglial response to sciatic neurectomy. I. Light microscopy and autoradiography,
Authors: Kerns James M. , Hinsman Edward J.
Published: May 2005

The response of oligodendrocytes, astrocytes, microglia, and pericytes to sciatic neurectomy in young adult rats was studied from 1μ Epon sections for quantitative cell counts and autoradiography. Two hours after an IP injection of 3H‐thymidine animals were killed by aldehyde perfusion at survival periods of 2, 4, 7, and 14 days postoperative (dpo).

At 2 dpo there was a marked increase in the number of labeled microglial cell nuclei and mitotic figures on the experimental side. This activation appeared to involve most of the “resting” microglia, which comprise about 6% of the total neuroglia in the normal ventral horn. A significant numerical increase (over fourfold) in perineuronal and total microglia was seen at 4 dpo followed by a gradual decline. Other findings include minimal chromatolysis in ventral horn neurons, contralateral effects, and a slight proliferative response in and around the central canal. A response was not apparent in the other neuroglia, pericytes, or mononuclear leukocytes. The relationship of the microglia to the multipotential glia of neuroectodermal origin is considered.
Distribution of transported proteins in the slow phase of axoplasmic flow. An electron microscopical autoradiographic study
Authors: Schonbach J. , Schonbach Ch. , Cuénod M.
Published: May 2005

Electron microscopic autoradiography has been used to study the distribution of labeled proteins along the axons of the retinal ganglion cells in the pigeon, during the slow phase of axoplasmic flow. After intraocular injection silver grains were found over a small fraction of the axonal population at any given time and at any specific location. Where the slowly advancing wave of radioactivity was detectable, the grains were predominantly located over the axoplasm, microtubules, neurofilaments and mitochondria. When the peak of the radioactivity had passed, the grains were found mostly overlying the axolemma. A large amount of radioactivity was observed over the endings of the retinal ganglion cell axons in the tectum 14 days after the injection of the labeled aminoacid. The grains were for the most part located over the outer membranes of the synaptic processes and over synaptic vesicles. These data support the hypothesis that the slow phase of axoplasmic transport contributes to the continuing growth of the axon and is formed mainly of materials which are distributed to the axonal membrane and to its synaptic endings. In contrast, the fast phase of axoplasmic flow results in a distribution of silver grains over the axolemma and the agranular endoplasmic reticulum in the axons, and over mitochondria and synaptic vesicles in its terminals.
Sequence of developmental abnormalities leading to granule cell deficit in cerebellar cortex of weaver mutant mice
Authors: Rakic Pasko , Sidman Richard L.
Published: May 2005

Golgi, electronmicroscopic and autoradiographic analyses of the developing cerebellar cortex were carried out in homozygous wild‐type (+/+), heterozygous (+/wv), and homozygous weaver (wv/wv) littermates. At 3 to 15 days after birth, when granule cells normally migrate from the external granular layer inward to their adult position, the somas of postmitotic granule cells in +/+ animals move along straight elongated Bergmann glial fibers which span the molecular layer. As early as postnatal day 3 and increasingly for about the next ten days, some Bergmann fibers in the +/wv cerebellum are enlarged, irregular in caliber, electronlucent and may contain dense bodies and vacuoles. Some granule cells contiguous with the altered Bergmann fibers have round rather than elongated somas, while some have lost contact with Bergmann fibers and appear to degenerate several days after their genesis. Most other granule cells migrate slowly but do eventually reach the granular layer, so that the pathology is less striking in adult than in developing heterozygotes. In wv/wv cerebella, radially‐aligned Bergmann fibers appear reduced in number during the developmental period, and few of them display normal cytological features. Few normally migrating granule cells were observed. Most granule cells fail to form axons and die in the external granular layer close to their site of genesis. While the primary genetic defect is unknown, the Bergmann glial disorder appears to precede the migration failure of granule cells and this in turn, along with impaired axon genesis, appears to be a factor leading to granule cell death.
Central projections of the trigeminal nerve in the bull frog (Rana catesbeiana)
Authors: Fuller Peter M. , Ebbesson Sven O. E.
Published: May 2005

The trigeminal nerve was unilaterally transected proximal to its ganglion in ten adult bull frogs. The course and termination of the axons were determined with the aid of Nauta and Fink‐Heimer techniques. The trigeminal primary afferents can be traced to five loci within the central nervous system, namely: the main sensory nucleus of the trigeminus, the descending nucleus of the trigeminus, a hitherto undescribed “ventral trigeminal field”, the rostral part of the nucleus of the solitary tract, and to the commissural nucleus of Cajal.
The neural organization of the lamina ganglionaris in the crayfish: A Golgi and EM study
Authors: Hafner G. S.
Published: May 2005

The lamina ganglionaris in the crayfish is composed of two cell layers and three acellular fibrous zones. The cells composing the layers above the acellular synaptic region (SR) show two distinct nuclear types in light microscopy and two cytoplasmic types with EM. Golgi impregnations of the lamina revealed three groups of elements which contribute processes to the SR; retinula axons from the retina, monopolar elements from the cell layers above the SR and horizontal elements whose perikaryal location is uncertain. Retinula elements terminate at various levels within the SR forming large irregular baglike terminals. Monopolar cells have a single axial fiber with numerous lateral processes which extend across the SR in a veriety of patterns. Horizontal elements have a more extensive lateral spead within the SR than monopolar processes. Electron microscopic data show the retinula terminal bags and monopolar processes to be organized into cartridge units at the superficial levels of the SR. Each cartridge consists of four enlarged terminals, three retinula axons and four to six central moncpolar processes. At deeper levels of the SR, the cartridge arrangement is not evident and the large terminals appear arranged in rows. Specialized synaptic contacts are found along the central borders of the retinula terminals.
The posterior lateral line lobe of a mormyrid fish — a golgi study
Authors: Maler L.
Published: May 2005

The posterior lateral line lobe is a rhombencephalic laminated structure. There is a topographic projection of anterior and posterior lateral line nerves upon the posterior lobe. The six separate lamina of the posterior lobe contain at least six cell types which can be distinguished on the basis of their dendritic trees. One lamina, the plexiform layer, contains the collateral plexus of the lamina of ganglion cells. There is an asymmetry in the dendritic fields and in the collateral plexus of neurons of the posterior lobe, such that their long axis runs in the sagittal plane.

There is an extensive projection from granule cells of lobus caudalis to the posterior lobe molecular layer. This connection is organized in a fashion similar to that of the parallel fiber system of the cerebellum, i.e., the axons form an inverted T, the arms of which run parallel to the granule cell layer. This projection is confined to the upper part of the molecular layer, while the lower part of the molecular layer contains the axons arising in the posterior lobe granular layer.
Efferent connections of the red nucleus in the brainstem and spinal cord of the rhesus monkey
Authors: Miller Richard A. , Strominger Norman L.
Published: May 2005

Three types of neuron with differences in Nissl pattern were found in the red nucleus of the rhesus monkey. Neurons with coarse Nissl bodies occurred only in the caudal third of the red nucleus except for a small number which extended rostrally a short distance along the dorsolateral margin. Neurons with fine Nissl bodies occupied the rostral two‐thirds of the nucleus. Neurons with slight cytoplasmic basophilia (achromatic) were smaller than the other types and distributed throughout the red nucleus. Perikaryal areas of the coarse and fine neurons, measured with a computer, had widely overlapping distributions.

Electrolytic lesions were made unilaterally in the red nucleus of nine monkeys. Ascending axonal degeneration was studied in sections stained by the Fink‐Heimer method. Two separate descending tracts were followed. The rubrobulbo‐spinal tract took origin from coarse neurons, crossed completely in the ventral tegmental decussation, and terminated as follows: in parts of the superior sensory trigeminal, motor facial and lateral reticular nuclei; in the gracile and cuneate nuclei; in the nucleus medullae oblongata, subnucleus dorsalis; in Rexed's laminae V, VI, VII at all levels of the spinal cord. In contrast, the rubroreticulo‐olivary tract took origin from fine neurons, remained uncrossed, and terminated in some reticular nuclei (pedunculopontine, pontis oralis and caudalis, gigantocellularis) and in parts of the inferior olivary complex. Degeneration was profuse in the dorsal lamina of the main olive, abundant in the ventral lamina, particularly in its lateral side, sparse and inconstant in the medial accessory olive, and invariably absent in the dorsal accessory olive. Thus, nuclei which receive descending projections from the red nucleus may be grouped into those with connections to lower motor neurons, cerebellum, or thalamus.
Anatomy of the cerebral ganglion of the female acanthocephalan, Macracanthorhynchus hirudinaceus
Authors: Miller Donald M. , Dunagan T. T. , Richardson John
Published: May 2005

An atlas of the cerebral ganglion of M. hirudinaceus has been constructed and the cells identified by number. There is a total of eighty‐six cells, three of which are binucleate. These cells (30, 80 and 90) are located in the frontal plane. Most cells give rise to bilateral processes and are organized in such a way that there is an outer coat of somata or cell bodies and a center core or neuropile. Some cell processes are 8 μ in diameter and most exit the ganglion via nerves of the opposite side. The cytoarchitecture of these cells indicates most have perinuclear rings and a well defined nucleolus. However, considerable variation occurs in number and distribution of cytoplasmic granules.
A combined fluorescence histochemical and electron microscopic method for studying special monoamine‐containing cells (SIF cells)
Authors: Grillo Mary A. , Jacobs Louise , Comroe Julius H.
Published: May 2005

This paper describes a method for locating “small intensely fluorescent” (SIF) cells on the basis of their monoamine fluorescence preparatory to study with the electron microscope. After fixation by perfusion with a formal‐dehyde‐glutaraldehyde mixture, the cells develop a bright yellow fluorescence easily seen when thick, unembedded slices of ganglionic tissue are examined with fluorescence optics. Once located, the same cells can then be studied electronmicroscopically following a second fixation with osmium tetroxide and Epon embedding. The resultant images are of good quality and highly reproducible. As an alternative to extensive sampling of plastic‐embedded ganglia, the method has the advantage of being less time‐consuming and more informative. Cells stored in fixative for months or embedded in paraffin retain their specific fluorescence. Since the particular fixative used is compatible with a variety of neurohistological and histochemical techniques, the method provides unprecedented opportunities for correlative studies employing fluorescence, light, and electron microscopy.

The method can also be applied to glomus cells of the carotid and aortic bodies and to adrenal medullary cells.
Synaptic termination of afferents from the ventrolateral nucleus of the thalamus in the cat motor cortex. A light and electron microscope study
Authors: Strick Peter L. , Sterling Peter
Published: May 2005

The synaptic termination in the cat motor cortex of afferents from the ventrolateral nucleus of the thalamus (VL) has been studied with experimental light and electron microscopic methods. The distribution of normal synapses on motor cortex pyramidal, stellate, and Betz cells was also examined.

Synapses in the motor cortex can be classified into two general types. The first and most prominent type contains flat vesicles, lacks a compact postsynaptic density, and corresponds to Colonnier's ('68) symmetrical synapse.

Stellate neurons receive synapses of both types on their cell bodies and proximal dendritic shafts, while pyramidal cells have only symmetrical synapses at these sites. The dendritic spines of both stellate and pyramidal cells are contacted by predominantly asymmetrical synapses. Betz cells, like smaller pyramidal neurons, receive only symmetrical synapses on their cell bodies. The proximal portions of the Betz cells apical dendrites, however, receive both asymmetrical and symmetrical synapses.

Following VL lesions, degenerating synapses were mainly found in three cortical layers: the upper third of layer I (18%), layer III (66%), and layer VI (13%). Degenerating synapses were not seen in the lower two‐thirds of layer I or in layer II, and were only rarely seen in layer V (3%).

Ninety‐one percent of the VL synapses were found on spines and 8% on stellate‐type dendritic shafts. Stellate cell bodies rarely received VL synapses (1%) and none occurred on pyramidal or Betz cell bodies and their proximal dendrites. A VL synapse within layer III was found on two dendritic spines of a Betz cell apical dendrite. Thus, part of the VL input to layer III synapses on the processes of both motor cortex output neurons (Betz cells in layer V) and cortical interneurons (stellate cells in layer III).
Lamination of the dorsal lateral geniculate nucleus in carnivores of the weasel (Mustelidae), Raccoon (Procyonidae) and Fox (Canidae) families
Authors: Sanderson K. J.
Published: May 2005

The laminar structure of the dorsal lateral geniculate nucleus was studied in carnivores of the weasel, raccoon and fox families. All have the same basic pattern of laminar organization in their lateral geniculate nuclei. Laminae A and C receive a contralateral projection from the retina and laminae A1 and C1 receive an ipsilateral projection. It is not known whether lamina C2 receives a retinal projection.

There are some variations to the basic pattern of laminar organization. Thus, in the mink and weasel laminae A and A1 are each subdivided into a pair of separate but similar leaflets. In the ferret and coatimundi these laminae are only partly subdivided. In the skunk, raccoon, ringtailed cat and fox there is only one lamina A and one lamina A1 in each lateral geniculate nucleus. There is some variation of the C laminae also. The C laminae are best displayed in the fox, where all three laminae — C, C1 and C2 — can be recognized in Nissl sections. In other carnivores, for example the mink and ferret, the C laminae cannot be distinguished from each other in normal brains and are described on the basis of the degeneration that is seen in Nauta and Fink‐Heimer sections after a unilateral enucleation. In the raccoon lamina C can be identified but lamina C1 may be missing.

The perigeniculate nucleus is variable in structure in carnivores. In the weasel and raccoon family the perigeniculate nucleus is a thick layer containing many large cells while in the cat and fox, it is a thin and rather diffuse group of cells. The perigeniculate nucleus may receive a direct retinal projection but if so, it is only a very sparse one.
Intraretinal differentiation in the synaptic organization of the inner plexiform layer of the pigeon retina
Authors: Yazulla Stephen
Published: May 2005

The inner plexiform layer at ten retinal loci in pigeon was examined by electron microscopy. Photomontages of the entire depth of the inner plexiform layer at each locus were analyzed with respect to the number of amacrine and bipolar synapses, their respective ratios, synaptic densities, percent amacrine synapses in serial configuration, synaptic layering patterns, and the effect of staining procedures on these quantities. The results show that the pigeon retina is not homogeneous regarding the structural complexity of the inner plexiform layer, but may be divided into four general areas in decreasing order of complexity: red field, temporal yellow field, nasal yellow field, and the area centralis. Significant differences in the amacrine synapse to bipolar synapse ration and amacrine synaptic density were observed across the retina, while bi‐polar synaptic density and the percent of serial synapses were rather constant. Amacrine synapses displayed a layering pattern which was consistent throughout the retina; while bipolar synapses showed two patterns. It was further observed that the density of amacrine and bipolar synapses bears little relationship to the density of amacrine and bipolar cells in the immediately overlying inner nuclear layer. This suggests that the various retinal loci may be characterized by different proportions of the morphological types of amacrine and bipolar cells present in the pigeon retina. Based on recent studies which have shown that a relationship exists between the complexity of ganglion cell receptive fields and the synaptic complexity of the inner plexiform layer, it is suggested that the ganglion cells of pigeon would show a physiological differentiation among retinal loci consistent with the observed differences in the anatomical complexity of the inner plexiform layer.
Scanning electron microscopy of the subarachnoid space in the dog. I. Spinal cord levels
Authors: Cloyd Miles W. , Low Frank N.
Published: May 2005

Young dogs six to 14 weeks old were perfused with aldehydes by standard techniques followed by MICROFIL to prevent blood vessel collapse. Tissue pieces possessing natural surfaces of the subarachnoid space at spinal cord levels were removed, post‐osmicated, dehydrated, critical point dried, coated with palladium‐gold and examined in a Cambridge Stereoscan S4 scanning electron microscope.

The surfaces of the spinal pia mater and arachnoid are clearly expressions of connective tissues with fenestrations and underlying connective tissue fibrils. Fenestrations are especially common in the conus medullaris where connective tissue fibrils are more likely exposed to cerebrospinal fluid than covered by pial lining cells. Long and short microvillae and blebs are present in profusion and with distributions comparable to the same structures on other cells. The surfaces of traversing structures; blood vessels, nerve roots, arachnoid trabeculae and denticulate ligaments are covered with tissues comparable to and continuous with pia and arachnoid despite underlying differences in histological makeup. Free cells are present on all spinal leptomeningeal surfaces in surprising profusion. They exhibit extreme pleomorphism of surface contours which is comparable to that observed in the scanning electron microscopy of cells from other sources. It is highly probable that these free cells are macrophages.
The morphology of retinal neurons of the owl monkey aotes
Authors: Ogden Thomas E.
Published: May 2005

The morphology of photoreceptor, horizontal, bipolar and amacrine cells of the owl monkey (Aotes) is described from retinal whole mounts and cross sections stained with the method of Golgi (Colonnier modification).

Rods and cones were often seen and resemble the photoreceptors of other primates. Cone density may be as great as 6400/mm2. Horizontal cells in the area centralis are larger and contact more cones than is the case with rhesus. Peripheral horizontal cells of Aotes are similar to those of rhesus. Midget bipolar cells are common and, even in the area centralis, usually have two basal dendrites. Only midget bipolars with invaginating terminals were clearly identified. Rod and flat bipolars were clearly identified and resembled those of rhesus. A “diffuse” bipolar is described which may represent a variant of either rod or flat bipolar. Some of these cells had dendritic spreads greater than 60 μ. Such bipolar cells have not been described in other primates. Amacrine cells were similar to those of rhesus except that those with coarse processes were all diffuse, i.e., their processes extended vertically through the IPL; those with fine processes were all stratified; their processes were restricted to a narrow lamina of the IPL.
Development of the extrinsic connections of the visual cortex in the cat
Authors: Anker Robyn L. , Cragg Brian G.
Published: May 2005

Lesions were made in the visual system in a series of kittens, and fiber degeneration stained by the Eager or Fink‐Heimer methods. Stereotaxic lesions made in the lateral geniculate nucleus (LGN) in one day old kittens led to the appearance of finely dotted fiber degenerationn in area 17 (concentrated in layer IV) two days later. Thalamic lesions involving the LGN in older kittens caused fiber degeneration in the other visual areas. This was first seen in the lateral suprasylvian gyrus (SSG) at six days, in area 19 at 14 days, and in area 18 at 21 days.

Lesions of visual cortex affecting areas 17 and 18 caused degeneration of descending connections to the LGN, lateralis posterior and superior colliculus when made in kittens one day old. However, ipsilateral cortical connections to area 19 were not seen until the kittens were 19 days old at operation, and connections to the suprasylvian gyrus appeared at 21 days. Contralateral cortical connections carried by the corpus callosum were not seen until the kittens were 26 days old at operation, and a distribution of degeneration comparable with that seen in adults was present at 40 days.

This time sequence of development is discussed in relation to what is known about the time of development of functioning in the cat's visual system.
Efferent fibers of the deep cerebellar nuclei in hedgehogs
Authors: Earle Alvin M. , Matzke Howard A.
Published: May 2005

Three main deep cerbellar nuclei are apparent in hedgehogs belonging to the genera Erinaceus and Hemiechinus; however, at various levels they exhibit a considerable continuity with one another. Electrolytic unilateral lesions were placed in the deep cerebellar nuclei of these hedgehogs, and additional animals were subjected to a midline incision of the cerebellum between the two fastigial nuclei. Degenerating axons were traced from the sites of lesions using the Nauta and Fink‐Heimer techniques.

The typical mammalian pattern is evident in the distribution of the cerebellifugal fibers of the hedgehog. Crossed and uncrossed fastigial efferent fibers are directed primarily toward vestibular nuclei and the bulbar reticular formation except for a relatively small ascending limb of the uncinate fasciculus. The brachium conjunctivum originates from the nucleus interpositus and nucleus lateralis. The efferents of these nuclei are directed rostrally to the contralateral red nucleus. Fibers passing beyond the level of the red nucleus terminate in the thalamic nuclei. Fibers from the brachium conjunctivun also supply the inferior and superior colliculi. Axons forming the descending limb of the brachium conjunctivum are divided into medial and lateral fascicles.
Synaptic interactions of identified nerve cells in the spinal cord of the sea lamprey
Authors: Rovainen Carl M.
Published: May 2005

As part of a continuing study on the organization of the lamprey nervous system, two additional groups of interneurons have been identified by physiological and morphological criteria in the isolated spinal cord of Petromyzon marinus. These and other identified nerve cells were tested for synaptic interactions using separate intracellular microelectrodes for stimulation and recording.

Edge cells were identified by their unusual location in the lateral fiber tracts of the spinal cord. Their axons extended rostrally either on the ipsilateral or contralateral side of the cord.

Some edge cells showed polysynaptic EPSP's and IPSP's after stimulation of sensory dorsal cells, but interactions with other identified neurons were rare. A single cell was excited by a giant interneuron. One edge cell produced IPSP's in a contralateral edge cell, and another produced IPSP's in lateral cells on the opposite side of the spinal cord. Thus, some edge cells have an inhibitory function.

Lateral cells were distinguished from giant interneurons and edge cells by their cell bodies in the lateral grey of the spinal cord in the gill and trunk regions, their ipsilateral dendrites, and their long ipsilateral axons extending as far as the tail.

Lateral cells were excited and inhibited polysynaptically by sensory dorsal cells and, in turn, produced weak IPSP's in unidentified neurons. Stimulation of lateral cells produced neither visible movements peripherally nor synaptic potentials in other lateral cells, in giant interneurons, or in edge cells.

Giant interneurons were previously identified on the basis of their cell bodies in the caudal half of the spinal cord, their bilateral dendrites, and their long contralateral axons extending towards the brain. Giant interneurons exhibited unitary composite EPSP's when more caudal giant interneurons were stimulated. The two components of the EPSP were due to electrical and chemical transmission. Under the electron microscope a contact between a dendrite of one giant interneuron and the probable axon of another had separate junctions resembling chemical and electrical synapses.

Intracellular stimulation of sensory dorsal cells produced both monosynaptic and polysynaptic EPSP's in giant interneurons. Some dorsal cells produced unitary composite EPSP's Giant interneurons are part of a convergent, multispecific sensory system extending towards the brain.
The relationship between morphogenetic cell death and the development of congenital anophthalmia
Authors: Silver J. , Hughes A. F. W.
Published: May 2005

Glücksmann ('51) observed that during normal mammalin ocular morphogenesis large numbers of cells become necrotic and are resorbed within the eye rudiment prior to and during invagination of the optic cup. Silver and Hughes ('73) observed that these resorptions are largely confined to the ventral aspect of the optic rudiment where the optic fissure subsequently forms. Evidence for the role of cell death during fissure formation and other morphogenetic events during eye development has remained unclear, however, since the quantity of degenerate cells cannot be selectively controlled in developing tissue by experimental means (Saunders, '66).

Chase et al. ('41a) described a congenitally anophthalmic strain of mice in which, he proposed, retarded growth of the eye vesicle and the consequent failure of lens induction result in approximately 90% eyeless and 10% microphthalmic neonates. Upon reexamination of a sequence of embryos of the eyeless strain it was observed that during the earliest stages of ocular morphogenesis the regular sequence of necrotic loci, which Silver and Hughes ('73) have described in rat and other mammalin embryos, is entirely lacking.

Our observations suggest that the first recognizable divergence between the morphology of timed mutant (strain zrdct‐an) and control embryos (strain C57BL/6J) occurs during apposition of the optic vesicle and surface ectoderm but prior to the development of the retinal thickening and lens placode. In control embryos mesenchyme which becomes entrapped between the prospective retina and lens becomes necrotic and is resorbed. Conversely, in eyeless embryos the surfaces of the presumptive retina and lens, while closely apposed, are separated by variable numbers of mesenchymal cells which remain viable and can undergo mitoses throughout development. The failure of mesenchymal cells to degenerate may lead to the reduction in size of both retina and lens primordia. Contrary to Chase's ('41a) observations, in all anophthalmic embryos contact between the optic vesicle and lens epithelium is eventually established and a lens of variable size is induced. In most cases, however, the lens is displaced from the eye chamber by proliferation of the mesenchymal cell mass and the optic rudiment is subsequently resorbed. In the remaining embryos which presumably will become microphthalmic the lens reaches a critical dimension and is retained within the eye cup. In them, although cell death is absent from within the developing eye vesicle and cup, invagination can proceed as far as the retinal fissure stage. However, the optic fissure does not form. These observations suggest that there may be a relationship between morphogenetic cell death, formation of the optic fissure, and the production of severe congenital eye defects.
Developmental changes in neuron size and density in the visual cortex and superior colliculus of the postnatal golden hamster
Authors: Ptacek James M. , Fagan‐Dubin L.
Published: May 2005

Postnatal changes in neuron cell body diameter and neuron density were observed in newborn, two‐week old, and eight‐week old golden hamsters. Quantitative data indicated that in both the visual cortex and superior colliculus, neuron cell body diameter increased nearly twofold during the first two‐week period following birth and reached maximum size by approximately day 14, the stage at which eye opening usually occurs. Neuronal density was highest in the newborn and decreased with age in both visual centers. The decreased neuronal density and, thus, increased neuropil area may reflect a greater number of synaptic connections mediating visual function. Although the development in the visual cortex paralleled that in the superior colliculus, the superior colliculus seemed to mature earlier than the visual cortex, possibly related to its more primitive evolutionary role.
Sequence regularity and geometry of orientation columns in the monkey striate cortex
Authors: Hubel David H. , Wiesel Torsten N.
Published: May 2005

The striate cortex of the macaque monkey is subdivided into two independent and overlapping systems of columns termed “orientation columns” and “ocular dominance columns.” The present paper is concerned with the orientation columns, particularly their geometry and the relationship between successive columns. The arrangement of the columns is highly ordered; in the great majority of oblique or tangential microelectrode penetrations the preferred orientations of cells changed systematically with electrode position, in a clockwise or counterclockwise direction. Graphs of orientation vs. electrode track distance were virtually straight lines over distances of up to several millimeters; such orderly sequences were often terminated by sudden changes in the direction of orientation shifts, from clockwise to counterclockwise or back. The orientations at which these reversals occurred were quite unpredictable. Total rotations of 180–360° were frequently seen between reversals. In tangential or almost tangential penetrations orientation shifts occurred almost every time the electrode was moved forward, indicating that the columns were either not discrete or had a thickness of less than 25–50 μ, the smallest order of distance that our methods could resolve. In penetrations that were almost perpendicular to the surface, the graphs of orientation vs. track distance were relatively flatter, as expected if the surfaces of constant orientation are perpendicular to the cortical surface. Stepwise changes in orientation of about 10° could sometimes be seen in perpendicular penetrations, each orientation persisting through several clear advances of the electrode, suggesting a set of discrete columnar subdivisions. The possibility of some kind of continuous variation in orientation with horizontal distance along the cortex was not, however, completely ruled out. Occasionally a highly ordered sequence was broken by an abrupt large shift in orientation of up to 90°. Shifts in ocular dominance occurred roughly every 0.25–0.5 mm and were independent of orientation shifts. In multiple parallel penetrations spaced closer than about 250 μ the slopes of the orientation vs. track distance curves were almost the same; reconstruction of these penetrations indicated that the regions of constant orientation are parallel sheets. On crossing perpendicular to these sheets, a total orientation shift of 180° took place over a distance of 0.5–1.0 mm. Column thickness, size of shifts in orientation, and the rate of change of orientation with distance along the cortex seemed to be independent of eccentricity, at least between 2° and 15° from the fovea. A few penetrations made in area 17 of the cat and in area 18 of the monkey showed similar orderly sequences of receptive‐field orientation shifts.
Genetically‐associated variations in the development of reflex movements and synaptic junctions within an early reflex pathway of mouse spinal cord
Authors: Vaughn James E. , Henrikson Charles K. , Chernow Charlene R. , Grieshaber Judith A. , Wimer Cynthia C.
Published: May 2005

The embryonic development of reflex forelimb movements produced by cutaneous stimulation of the forepaw was examined in five inbred strains of the house mouse, Mus musculus. A quantitative electron microscopic study of synapse formation between the neurons that comprise the spinal cutaneous reflex arc was also carried out on specimens from three of the strains subjected to reflex testing. This investigation provides evidence that there is significant genetically‐associated variability in the developmental timing of synapse formation within this disynaptic pathway and in the reflex behavior which it mediates. Specifically, it was found that C57BL/6J embryos had greater numbers of synaptic junctions in the reflex pathway at embryonic days 14–16, and they also showed reflex movements earlier than LP/J embryos. C57BL/6J embryos also showed a more rapid increase in the number of boutons during this embryonic period. CBA/CaJ embryos displayed a temporal pattern of development that differed from both C57BL/6J and LP/J. At E15, CBA/CaJ embryos were more similar to LP/J with regard to both reflex activity and synapse number, but by E16, CBA/CaJ values for both of these measures were more similar to C57BL/6J. On the basis of the data detailed in the text, we suggest that the strains differ in the following manner: C57BL/6J embryos develop boutons rapidly but appear to be relatively inefficient in the actual formation of synaptic junctions; CBA/CaJ embryos develop boutons at a slower rate than C57BL/6J but form synaptic junctions more efficiently; LP/J embryos develop boutons slowly and are also relatively inefficient in forming synaptic junctions. The genetic implications of — and some developmental processes which might be responsible for — the observed strain differences in the timing of synaptic development are discussed in the text.

There was no detectable genetic variability of the basic sequence in which the neurons of the cutaneous reflex arc develop their synaptic connections. For all three strains examined, the data indicated that synaptic closure occurred in a retrograde sequence with respect to the direction that neurotransmission normally flows between the neurons of this pathway. This finding agrees with results obtained by other investigators from a number of diverse vertebrate species, and such a widespread lack of variability implies that a retrograde sequencing of synapse formation is involved in the development of specific neuronal connectivities.
The fine structure of pulse labeled (3H‐thymidine cells) in degenerating rat optic nerve
Authors: Skoff Robert P.
Published: May 2005

The ultrastructure of pulse labeled (3H‐thymidine) cells in rat optic nerve undergoing Wallerian degeneration is described. The study was limited to the first ten days after enucleation since cell proliferation during this interval is greater than in normal optic nerve (Skoff and Vaughn, '71). Approximately one‐third of the pulse labeled cells are astrocytes. The majority of the proliferating astrocytes are in a reactive state, having changed their normal fibrous appearance to one showing a paucity of filaments. Thirty percent of the pulsed cells can be classified as microglia. Only immature oligodendrocytes proliferate, and they account for less than 10% of the pulse labeled cells. About 30% of the labeled population are undifferentiated glial precursor cells. Electron microscopic autoradiographic data obtained from normal optic nerve and presented in this paper indicates that glial precursor cells which have divided shortly before enucleation continue to proliferate after it. The evidence suggests that recently formed glial precursor cells transform into phagocytes following enucleation. Less than 3% of the pulse labeled cells examined in this study are ultrastructurally similar to mononuclear leukocytes. The results of the present study together with previous studies of degenerating optic nerve indicate that most phagocytes in Wallerian degeneration are derived from proliferation of intrinsic glia rather than from an invasion of exogenous cells.