bluuebunny/crossref_metadata_2025 huggingface dataset:
Reticulospinal fibers of the opossum, Didelphis virginiana I. Origin
Authors: Beran Robert L. , Martin George F.
Published: December 2004

Complete and partial cervical cord hemisections were placed at different levels according to a modification of the Gudden method (Brodal, '40), as applied to the opossum. Nissl staining techniques were employed and either acute retrograde cellular change of cell loss was studied following 7to 65 day survival periods. The results of a previous cytoarchitectonic study which followed the terminology of Meessen and Olszewski ('49) and Olszewski and Baxter ('54) served as controls.

Chromatolysis or cells loss was found in medium‐sized (20–29 μ), large (30–44 μ) and giant (45–60 μ) cells in the pontine and medial medullary reticular formation. Retrograde changes in the pontine reticular formation were found in the nucleus pontis centralis oralis, the nucleus pontis centralis caudalis and the rostral nucleus gigantocellularis. Within the pons, chromatolysis was particularly evident in the large and giant cells. Following cervical cord lesions, the medullary reticular formation contained chromatolytic neurons within the nucleus gigantocellularis, the nucleus paragigantocellularis dorsalis, the paramedian reticular nucleus and the nucleus interfascicularis hypoglossi.

At pontine levels, chromatolytic cells were present mainly on the side of the lesion. However, cells were found to have undergone retrograde changes in specific areas of the contralateral side. Although the greatest number of reactive cells within the medullary reticular formation were also located on the side of the lesion, there was more contralateral involvement than was the case in the pons.
Rapid phase of axoplasmic flow and synaptic proteins: An electron microscopical autoradiographic study
Authors: Schonbach J. , Schonbach Ch. , Cuénod M.
Published: December 2004

Electro microscopic autoradiography was used to study the distribution of labeled proteins in the pigeon optic tectum, 12 hours after intraocular injection of 3H‐1‐leucine. More than 65% of the grains were detected over synaptic endings, in the fifth layer which is rich in retino‐tectal axon terminals. In the first layer which contains retino‐tectal fibers 70% of the grains were over axons. These data support the proposition that synaptic proteins migrate rapidly in the axon. Detailed examination showed that silver grains were predominatly located over the axolemma and agranular endoplasmic reticulum in axons, and over mitochondria and synaptic vesicles in neuronal endings.
The projection of the visual field to the lateral geniculate and medial interlaminar nuclei in the cat
Authors: Sanderson K. J.
Published: December 2004

Detailed and complete projection maps of the visual field to the whole of the dorsal lateral geniculate (LGNd) and medial interlaminar nucleus (MIN) of the cat have been prepared by plotting the receptive fields of single units in the two nuclei with tungsten‐in‐glass microelectrodes. The standard projection maps show the pattern of isoazimuths (“horizontals”) and isoelevations (“verticals”) in the two nuclei. Particular attention has been given to the projection of the upper visual field to the posterior part of the LGNd/MIN complex where the shape and relationship of the cellular laminae are changing rapidly. A separate projection of the visual field to the nucleus perigeniculatus (NPG) is also described, but the retinotopic organization of this projection is not as precise as for the LGNd and the MIN. Most of the cells in the NPG are binocularly‐activated and the receptive fields have ON/OFF centers. Further observations have been made concerning the distribution of the crossed and uncrossed fibers in the LGNd. In lamina B there is a thick dorsal zone of contralaterally‐activated cells and below this is a zone in which ipsilaterally‐activated cells are occasionally found. A few binocularly‐activated cells were found in the vicinity of the interlaminar regions.
Survival of pattern vision after removal of striate cortex in the adult cat
Authors: Doty Robert W.
Published: December 2004

Behavioral, anatomical and electrophysiological data are presented for three cats. One had complete removal of area 17 as evidenced by gross and histological examination of the remaining cortex and by the degeneration in the lateral geniculate body. Dorsal portions of areas 18 and 19 were essentially intact and much of the central and medial interlaminar nuclei of the lateral geniculate body survived. This cat had excellent pattern vision. So too did a cat in which all of the posterior suprasylvian gyrus, dorsal surface of the middle suprasylvian gyrus and much of anterior marginal gyrus had been extirpated. In contrast, an animal lacking area 18 and most of area 19 in addition to area 17, and thus having near “total” degeneration of the lateral geniculate body, was incapable of pattern discrimination. Photically evoked potentials could nevertheless be demonstrated throughout an extensive suprasylvian field in the latter animal. It is concluded that area 17 is not essential for pattern vision in the cat, but that in its absence, even in the case of ablations performed neonatally, cortex receiving major projection from the central and medial interlaminar nuclei, i.e., areas 18 and 19, is required.
Mutual contact inhibition of extension of chick sensory nerve fibres in vitro
Authors: Dunn Graham A.
Published: December 2004

Methods were devised for measuring various aspects of the geometry of nerve fibre outgrowths from chick dorsal root ganglia in short‐term plasma clot cultures. Optical birefringence was used as a measure of the magnitude and direction of stresses which developed within the plasma clots during the incubation period. The data obtained indicated that contact guidance of nerve fibres, along fibrin micelles of the medium, is not of prime importance in determining the courses of nerve fibres in non‐fasciculated outgrowths. A mutual contact reaction, between nerve fibres, was observed using time lapse cine‐photomicrography, and the patterns of nerve fibre outgrowths could be largely attributed to such a reaction. This contact reaction is similar, in many respects, to contact inhibition of locomotion in cultured fibroblasts; and it is proposed that the reaction be termed “contact inhibition of extension.”
Binocular competition in the control of geniculate cell growth
Authors: Guillery R. W.
Published: December 2004

It has been shown previously that, in kittens, geniculate laminae that are visually deprived by a unilateral lid‐suture grow less than normal. However, cell growth is affected only where the deprived laminae lie opposite a normally innervated lamina. The most lateral part of lamina A, which is innervated from the monocular crescent of the visual field and which extends beyond the edge of lamina A1, is not affected by lid‐suture. One interpretation of this result is that a binocular competition controls geniculate cell growth and that the normal competitive balance is upset by the lid‐suture.

In order to test this interpretation further, four kittens had the lids of one eye sutured and in the other eye a patch of temporal retina was destroyed. After 5.5 to 12 weeks′ survival lamina A1 showed a patch of transneuronal degeneration produced by the ipsilateral retinal lesion. Most of lamina A showed a reduced cell growth contralateral to the suture. However, the part of this lamina lying opposite the zone of transneuronal degeneration contained cells that were larger than would be expected if there were no competitive effect. These results show that geniculate cells compete during development, probably for available synaptic surfaces upon cortical cells, perhaps in terms of interlaminar inhibitory mechanisms. Success in this competition depends upon the nature of the visual input. The present results provide no evidence that visual deprivation can change geniculate cell growth by any direct, non‐competitive effect.
Origin and termination of the hippocampal perforant path in the rat studied by silver impregnation
Authors: Hjorth‐Simonsen A. , Jeune B.
Published: December 2004

A detailed study of the origin and termination of the so‐called perforant path of the hippocampal region has been made in the rat. This tract connects the entorhinal area with the hippocampus and the fascia dentata. At all dorso‐basal levels of the hippocampus, the terminal field has been shown to occupy the middle part of the molecular layer of the fascia dentata and that level of the stratum lacunosum‐moleculare of the hippocampal subfield CA3 which is close to the stratum radiatum. The outer and inner parts of the dentate molecular layer, the stratum lacunosum‐moleculare of subfield CA1, and the superficial part of the latter layer in CA3 contained fibers en passage only. The origin of the perforant path has been found to be in the medial part of the entorhinal area, from the most dorsal to the most ventral levels. The fibers arise in part at least from cells in layers I—III. Lesions of the lateral part of the entorhinal area leave the perforant path unaffected. A topical organization has been demonstrated: Lesions dorsal in the entorhinal area evoke terminal degeneration in antero‐rostral (septal) parts of the hippocampus only. More ventral lesions produce degeneration in increasingly caudal (temporal) segments of the hippocampus. Earlier descriptions of the route traversed by the perforant path have been confirmed. In addition, the axons to the most rostral parts of the hippocampus and fascia dentata have been shown to course superficially in the dorsal and rostral parts of the subiculum and CA1 which form an exposed part of the medial aspect of the hemisphere.
A study of the organization of apical dendrites in the somatic sensory cortex of the rat
Authors: Peters Alan , Walsh T. Myrick
Published: December 2004

In the parietal cortex of the rat, sections cut tangentially show that profiles of medium and large apical dendrites are grouped into clusters. The number of apical dendrites in each cluster is variable and the usual separation between individual clusters is about 50 μ. Despite these variations the pattern does not appear to be random. Reconstructions from one micron serial sections show that neurons giving rise to the ascending dendrites forming clusters are located at different levels in layer V. The cell bodies of these neurons are arranged vertically below their dendrites and show a tendency to form groups. All of the neurons have apical dendrites that ascend through the cortex with a few secondary branches occurring close to the base. The principal secondary branching begins in layer III and spreads obliquely up through layer I. Furthermore, beginning in the inferior region of layer III apical dendrites are added to the clusters at their peripheries. These are from layer III pyramids. It is clear that the superior aspects of the cluster arrangements must intermingle with those of the neurons in adjacent clusters. The neuropil surrounding the dendrites forming clusters appears to contain a few smaller dendrites. Small unmyelinated axons are the most frequent component of the surrounding neuropil and these form terminals which synapse on the spines and trunks of the clustered dendrites. There is no obvious function that can be ascribed to the clusters other than they may form a component of the columnar organization in cortex described in part by physiological techniques.
Dorsal root projections to the motor nuclei in the cat spinal cord
Authors: McLaughlin Barbara J.
Published: December 2004

The dorsal root projections to the motor nuclei of the L7 spinal cord segment were examined with light and electron microscopy in cats surviving dorsal rhizotomies of L6–S2 for periods of 2–15 days. Light microscopy demonstrated maximal Nauta‐Gygax and Fink‐Heimer degeneration around large neurons and their dendrites of the motor nuclei within the four to eight day period. Electron microscopy revealed axonal degeneration without any accompanying synaptic knob degeneration. Counts of the synaptic populations in the 12 and 15 day animals revealed that one particular synaptic type, the M knob, occurred less frequently and was smaller in size. In the normal animals the M knob, which was present up to 8 days postoperatively, was a large terminal containing rounded vesicles and making multiple synaptic contacts which had specialized subsynaptic densities. It was found primarily on proximal dendrites of large neurons and was often accompanied by a smaller flattened vesicle knob. All other synaptic knobs described in the normal animal were intact throughout all postoperative periods.

The possibility that dorsal root afferents synapse farther out on the motoneuronal dendritic tree, as well as the possibility that few dorsal root terminals synapse on the motoneuronal surface, is discussed. The lack of any morphological evidence for presynaptic inhibition of dorsal root afferents in lamina IX is also discussed and possible alternative mechanisms are considered.
Propriospinal and supraspinal projections to the motor nuclei in the cat spinal cord
Authors: McLaughlin Barbara J.
Published: December 2004

Propriospinal and supraspinal projections to the motor nuclei of L3–S1 were examined with light and electron microscopy in cats surviving complete transection of L2 for periods of 1–12 days. Light microscopy revealed maximal Nauta‐Gygax and Fink‐Heimer degeneration in the motor nuclei of L3–L5 at three days survival. Maximal degeneration in the motor nuclei of L6–S1 did not appear until six days post‐operatively. In the three and four day animals, electron microscopy revealed degenerating synaptic knobs, making axo‐dendritic and axo‐somatic contacts, and many phagocytosed degenerating synaptic knobs, in the motor nuclei of L3–L5; no synaptic degeneration was observed in the motor nuclei of more caudal segments. In the six to eight day animals, degenerating axo‐dendritic knobs and many phagocytosed degenerating knobs were found in the motor nuclei of S1; no synaptic degeneration and very few phagocytosed degenerating knobs were present in the motor nuclei of L3–L5 at these survival times. Because of the rapid phagocytosis of degenerating knobs in the motor nuclei of the early and late post‐operative animals, it was difficult to attribute the various degenerating knobs to a particular synpatic type.

It is suggested that the synaptic degeneration seen in the motor nuclei near the transection of the earlier post‐operative animals is of mixed propriospinal and supraspinal origin, whereas the degeneration seen in the caudal motor nuclei of the later post‐operative animal represents supraspinal terminations.

The contribution of dorsal root and long and short descending projections to the synaptic population about motoneurons is discussed.
The fine structure of the ependymal tanycytes at the level of the arcuate nucleus
Authors: Brawer James R.
Published: December 2004

The ependymal tanycytes of the third ventricle at the level of the arcuate nucleus were studied with the electron microscope. Criteria were discovered for identifying the tanycyte process as it courses through the arcuate neuropil, making it possible to describe the entire ependymal cell from the apical surface to the end foot. The apical membranes of the tanycytes are characterized by a lack of cilia and by numerous microvilli. The apical lateral membranes may be extensively interdigitated, and the junctional complexes between adjacent apical lateral membranes often lack maculae occludentes. The cells are well endowed with large Golgi apparatus. The endoplasmic reticulum is principally smooth. The tanycyte processes contain small paraxially oriented mitochondria and numerous paraxial microtubules as well as lipid droplets and accumulations of smooth endoplasmic reticulum in the form of concentric rings. Some of the tanycytes end on capillaries in the arcuate nucleus. These pericapillary ependymal sheaths contain irregular inclusions of varying densities. The ependymal tanycytes have been implicated as secretory cells involved in hypothalamic control of the anterior pituitary gland. This concept is discussed in relation to the present fine structural findings.
Ultrastructure of developing Xenopus retina before and after ganglion cell specification
Authors: Grillo M. A. , Rosenbluth J.
Published: December 2004

The neuroretina of Xenopus laevis was examined at embryonic stages 28 and 32 to determine whether the specification of the ganglion cells is accompanied by morphological changes detectable with the light and electron microscopes. Two changes were noted: an apparent increase in the length of polysome helices, and an apparent reduction in the number of pigment granules. The significance of these changes is discussed. In addition to the morphological features common to undifferentiated cells generally, the cells of the neuroretina also exhibit subsurface cisternae, granulo‐filamentous inclusions, and membranous organelles resembling the “spine apparatus.” These structures may be useful in identifying presumptive nerve cells in the proliferative state.
Cytology of the granular layer of the bulbar cochlear nuclei
Authors: Sobrino José A. , Gallego A.
Published: December 2004

The cytology of the granular layer of the cochlear nuclei was studied by aniline and Golgi staining methods. Four types of granule cell are described on the basis of the distribution of their processes and their size. Three types appear to be amacrine cells because they possess no process that has the morphological appearance of an axon. All of these cells are situated in the ventral portion of the granular layer. The granule cells of the fourth type have a distinct axonal process and are situated in the dorsal portion of the granular layer.
A retinohypothalamic projection in the rat
Authors: Moore Robert Y. , Lenn Nicholas J.
Published: December 2004

A direct projection from the retina to the hypothalamus was demonstrated in the rat. Following injection of tritiated leucine or proline into the posterior chamber of the eye, labelled protein was shown autoradiographically in the suprachiasmatic nuclei of the medial hypothalamus, both ipsilateral and contralateral to the injected eye. The labelling of the nucleus was heaviest in its ventral portion but extended throughout the nucleus. No evidence for a projection to the supraoptic nucleus or any other hypothalamic nucleus was observed. All of the known terminal nuclei of the primary and accessory optic tracts were heavily labelled. The projection to the suprachiasmatic nucleus could not be clearly confirmed in material prepared using the Fink‐Heimer method for the demonstration of degenerating axon terminals. Electron microscopic study of the suprachiasmatic nucleus following orbital enucleation showed degenerating endings making synaptic contacts with small dendrites of the suprachiasmatic nucleus cells. These first appeared at three days after operation and were nearly gone by seven days. Thus, the retinohypothalamic tract in the rat appears to arise from the ganglion cells of the retina and to terminate on the smaller dendritic branches of the neurons of the suprachiasmatic nucleus.
The neuronal organization of the inferior colliculus of the adult cat. I. The central nucleus
Authors: Rockel A. J. , Jones E. G.
Published: December 2004

The intrinsic organization of the central nucleus of the inferior colliculus has been studied in the adult cat by means of the Golgi and Nauta techniques. On the basis of cytoarchitecture and fiber connections, the central nucleus can be divided into: (i) a smaller, dorsomedial division consisting mainly of large cells and receiving fibers from the auditory cortex, lateral lemniscus and probably the central nucleus of the other side; (ii) a larger, ventrolateral division consisting mainly of medium and small cells but with some intermingled larger types. This part receives fibers from the lateral lemniscus only.

The ventrolateral division has a pronounced laminar arrangement of cells, dendrites and axons. The laminae, although overlapping extensively, form an onion‐like series of concentric, curved shells, most of which are incomplete except for those closest to the center of curvature in the dorsolateral part of the nucleus. It is probable that these laminae provide a basis for the pronounced tonotopic organization of neurons in the nucleus. The thickness of the laminae is determined by the dendritic ramifications of two principal cell types which are fusiform or bi‐tufted. Other, multipolar and large cells have dendrites which lie across one or several laminae and may form a basis for interaction between laminae.

Four axon types can be distinguished: Type I (lateral lemniscal) and type II (corticofugal) axons run parallel to the laminae but in opposite directions, though type II axons are confined to the parts of the laminae projecting into the large‐celled, dorsomedial division. Type III axons are widely ramifying and may arise within the central nucleus or be another form of afferent fiber. Type I and III axons end in dense clusters of terminals on principal cells but as single en passant terminals on multipolar cells. Type IV axons are the efferents of the inferior colliculus and run a recurrent course through the central nucleus giving off collaterals which sometimes end on the parent cell.
Observations on the fine structure of the central nucleus of the inferior colliculus of the cat
Authors: Rockel A. J. , Jones E. G.
Published: December 2004

The central nucleus of the inferior colliculus has been examined electron microscopically in the adult cat, particular attention being paid to its ventrolateral division in which the majority of lateral lemniscal afferents end.

Two cell types can be recognized: one, which is the equivalent of the spiny principal cell of light microscopy, is distinguished by having its soma and large proximal dendrites covered by axon terminals. More distally situated dendrites have fewer terminals ending mainly on dendritic spines. These spines resemble those of the cerebral cortex and have a modified spine apparatus. The second type of cell is the equivalent of the small multipolar cell of light microscopy. It has spineless dendrites and these and the soma receive relatively fewer axon terminals. It has a very thin axon.

Several types of axon terminal can be recognized. Type I terminals are large, contain spherical synaptic vesicles and end by means of asymmetrical synaptic contacts, on the somata and proximal dendrites of principal cells and on the smaller dendrites of multipolar cells. The extracellular space on one or both sides of the synaptic complex is often characteristically widened. Correlative experimental degeneration studies show that these are the terminals of lateral lemniscal fibers. Various forms of smaller terminal also make asymmetrical contacts and have spherical vesicles. One type has a high concentration of large, densecored vesicles as well.

Two types of axon terminal end in symmetrical synaptic contacts. One contains large, homogeneously flattened synaptic vesicles; the other, which is more common, contains smaller, irregularly flattened or pleomorphic synaptic vesicles.

In the dorsomedial division of the central nucleus, the terminals of corticofugal fiber have spherical synaptic vesicles and end in asymmetrical synaptic contacts upon large dendritic spines.
Growth of lobster giant axons: Correlation between conduction velocity and axon diameter
Authors: Govind C. K. , Lang Fred
Published: December 2004

The conduction velocity and axon diameter of medial and lateral giant axons in lobsters was followed during growth from early juvenile (13 mm) to adult (250 mm) forms. In both axons, conduction velocity increased more than 4‐fold in the growth period examined. Correlated with the increase in conduction velocity is an increase in axon diameter and the relationship between these two parameters is expressed by the equation CV = krx, where x equals 0.5 for the lateral and 0.7 for the medial giant axons. The sheath surrounding the giant axons also increases in size during growth with that of the medial giant axon being considerably thicker than that of the lateral giant axon. The significance of the increase in axon diameters is to increase conduction velocity and thereby reduce the latency of the escape response mediated by these giant axons.
The efferent connections of the feline nucleus cuneatus
Authors: Hand Peter J. , Van Winkle Thomas
Published: December 2004

Nucleus cuneatus projections to nucleus ventralis posterolateralis pars medialis (VPLm) and other thalamic as well as midbrain and medullary nuclei were studied in cats using the Fink‐Heimer I silver technique. Single electrolytic lesions of very small size were made stereotaxically in different zones of nucleus cuneatus under electrophysiological control. All zones studied projected to contralateral VPLm in a pattern of discrete terminal arborizations or clusters, which were organized in onionskin‐like dorso‐ventral laminae.

The clusters of degeneration varied in size and density according to their dorsoventral location within VPLm. Those in dorsal areas were smaller in diameter (50–125 μ) and contained less dense amounts of degeneration than clusters (150–300 μ) in more ventral regions. The clustered terminal arborizations mirrored the organization of the VPLm neuronal clusters, themselves.

Terminations within VPLm were topographically organized, but were completely inverted, i.e. dorsal nucleus cuneatus projected to ventral VPLm and ventral to dorsal, lateral to medial, and medial to lateral VPLm. A ventral zone of nucleus cuneatus, which contained “deep” units, projected to a separate dorsal zone of VPLm. In addition to its classical connection with VPLm, nucleus cuneatus projected to the following contralateral brainstem or thalamic nuclei: medial and dorsal accessory olives, external nucleus of the inferior colliculus, ventrolateral part of the superior colliculus, nucleus ruber, medial geniculate nucleus pars magnocellularis, suprageniculatus, medial and lateral divisions of the posterior thalamic nuclear group, zona incerta, and Fields of Forel. Very sparse amounts of degeneration were also present within nuclei ventralis posteromedialis (caudal pole) and ventralis posterolateralis pars lateralis. The brainstem and thalamic projections of the dorsocaudal part (cell nest region) of the cuneate nucleus were more restricted than those of its rostral and ventral regions. The clusters of both the VPLm neurons and cuneate terminations within VPLm provides an anatomical basis for the functional characteristics of synaptic security, fine grain somatotopia and modality specificity so prominent in the dorsal column nuclei‐medial lemniscal system.
Structure of the Purkinje cell membrane in staggerer and weaver mutant mice
Authors: Landis Dennis M. D. , Reese T. S.
Published: December 2004

The structure of the plasma membrane of Purkinje cell dendrites was examined in weaver and staggerer mutant mice. Purkinje spines in weaver mice have clusters of intramembrane particles which resemble those at normal synapses with parallel fibers, even though no parallel fibers are formed in this mutant. There are very few spines in the staggerer, and these manifest normal intramembrane structure at contacts with climbing fibers. The spines which would normally be involved in synapses with parallel fibers are never formed in the staggerer, and the intramembrane structures which would have been associated with these spine synapses are also lacking. Thus, during postnatal cerebellar development in the mutants, acquisition of intramembrane specializations requires Purkinje spine formation but can occur independently of the development of parallel fibers.
Efferent projections of the main and the accessory olfactory bulb in the tree shrew (Tupaia glis)
Authors: Skeen L. C. , Hall W. C.
Published: December 2004

The projections of the main and the accessory olfactory bulb in the tree shrew (Tupaia glis) have been analyzed with anterograde degeneration and autoradiographic methods for identifying axonal projections, and with the horseradish peroxidase method for identifying the distributions of neurons from which these projections originate. The cytoarchitectonic features of the paleocortical areas which receive projections from the main and the accessory olfactory bulb have also been described.

The efferent projections of the accessory olfactory bulb are distributed to the bed nucleus of the accessory olfactory tract, the medial amygdaloid area, the posteromedial cortical amygdaloid area, and to the caudal portion of the bed nucleus of the stria terminalis. In contrast, the efferent projections of the main olfactory bulb are distributed to the anterior olfactory nucleus, the tenia tecta, the olfactory tubercle, the pyriform cortex, the anterior cortical amygdaloid area, the posterolateral cortical amygdaloid area, and to the lateral entorhinal cortex. These observations are consistent with the notion that the olfactory system can be divided into at least two major subsystems: one related to the vomeronasal organ and accessory olfactory bulb, and another related to the main olfactory organ and main olfactory bulb.

The paleocortical areas receiving olfactory projections have three basic layers: a superficially positioned plexiform layer (layer I), a pyramidal cell layer (layer II), and a polymorphic cell layer (layer III). The projections of both the main and the accessory olfactory bulb terminate in the outer portion of the plexiform layer (sublamina la). Sublamina Ia contains the distal segments of dendrites which originate from a heterogeneous population of neurons located in layer II and, to a lesser extent, layer III.

Although the efferent projections of the main and the accessory olfactory bulb are segregated, evidence for a more refined topographical organization within these projections was not obtained. However, the distribution of retrogradely labeled neurons in the main olfactory bulb, following injections of horseradish peroxidase into its various paleocortical targets, indicates that the olfactory projections to these areas may not all originate from the same population of cells.
Response of the three main types of glial cells of cortex nad corpus callosum in rats handled during suckling or exposed to enriched, control and impoverished environments following weaning
Authors: Szeligo F. , Leblond C. P.
Published: December 2004

The cell populations of the occipital cortex were examined in young rats subjected to different sensory experiences. In one series recently weaned animals were reared in enriched, impoverished or control environments. The enriched environment was obtained by keeping the animals among “toys” and other rats; the impoverished environment, by rearing the animals one pr cage in a darkened, quiet room; and the control environment, by housing the animals three per cage under animal room conditions. Six recently weaned rats were kept ini each environment for 30 days and ten, for 80 days. In a second series suckling rats for 15 minutes per day during the first ten days after birth; twelve rats were studied, six handled and six unhandled controls. In the two series, the animals were sacrificed under anesthesia by perfusion with mixed aldehydes. Semithin epon sections of occipital cortex ere stained with toluidine blue; neurons and the three main types of glia were enumerated. In addition, the thickness of the cortex was measured and the glial cells of corpus callosum counted in the animals exposed to the three environments for 80 days.

Under the influence of the enriched environment, the occipital cortex enlarged, the number of oligodendrocytes increased over the controls by 27‐33% in the 30‐ and 80‐day groups and the number of astrocytes, by 13% in the 80‐day grup. Within the cortex, only certain layers showed the increase in glial numbers. In the corpus callosum, however, the numbers of glial cells did not differ from those in controls. In the animals exposed to the impoverished environment, neither the size of the cortex nor the number of oligodendrocytes and astrocytes differed from controls.

The animals subjected to handling also showed evidence of cortical enlargement, but the only significant change in glial cells was a 12% increase in astrocytes.

It is concluded that handling and enrichment produce changes in anatomical indices of neural function including depth of cortex and numbers of glial cells. The glial response was specific to the type of manipulation since astrocytes were predominantly affected by handling and oligodendrocytes, by enrichment. The effect of handling on astrocytes may be attributed to the stimulation being applied at a time of astrocyte proliferation, whereas the effect of the enriched environment on oligodendrocytes occurred at a time of active production of these cells. The differences in cell numbers were explained by changes in the rate of cell population growth; since the impoverished did not differ from the control animals, the changes probably consisted of growth acceleration in the enriched animals rather than dimiution in the impoverished ones.
Quantitative studies of cell size in the cat's dorsal lateral geniculate nucleus following visual deprivation
Authors: Hickey T. L. , Spear Peter D. , Kratz Kenneth E.
Published: December 2004

The effects of visual deprivation upon dorsal lateral geniculate (DLG) cell size were compared for seven kittens reared with monocular lid‐suture (MD), seven with binocular lid‐suture (BD), and six with one eye lid‐sutured and the other eye enucleated soon after birth (MD‐E). Six additional kittens were reared normally for comparison. For each kitten the cross‐sectional areas of 300 cells were measured in one or both nuclei. Measurements were taken from the binocular segment of laminae A and A1 and th monocular segment of lamina A.

In agreement with previous studies, cells in th binocular segment of the deprived laminae of MD cats were smaller (33‐34%) than those in the non‐deprived laminae. Comparisons with normal animals indicated that this difference was due to an increase (10‐15%) in size of cells in the non‐deprived laminae as well as a decrease (23‐25%) in size of cells in the deprived laminae. Cells in the monocular segment also were affected by deprivation in MD cats, and this effect increased with the age (and duration of the deprivation) of the animal. However, it was always smaller than the decrease in sell size in the binocular portion of the DLG.

In BD kittns, DLG cells were smaller (7‐12%) than normal in all portions of the nucleus, including both the binocular and monocular segments. Direct comparisons between the deprived laminae of MD and BD kittens indicated that the decrease in cell size was greater for MD kittens in the binocular segment, but tended to be greater for BD kittens in the monocular segment. IN MD‐E kittens, DLG cells in the deprived laminae were smaller (11‐17%) than normal in all portions of the nucleus, including both the binocular and monocular segments. Thus, the effects of deprivation were similar to those in BD kittens, even though inputs from the deprived eye had been placed a competitive advantage in MD‐E kittens. These results indicate that two factors may affect cell size in the DLG of visually deprived cats: deprivation per se and abnormal binocular competition.

Finally, separate analyses for the ten largest and the ten smallest cells in each lamina of each cat were carried out in an attempt to determine if the changes in cell size were limited to the largest cells. In every case, differences observed for the total sample of cells were paralleled by differences from normal of both the largest cells present and the smallest cells present in the deprived laminae. Since at least two alternative interpretations can account for this finding, the question of whether the large cells are selectively affected by visual deprivation remains unanswered in the cat.
Regeneration of fungiform taste buds: Temporal and spatial characteristics
Authors: Cheal Marylou , Oakley Bruce
Published: December 2004

The gross morphology of the tongue of the Mongolian gerbil (Meriones unguicultatus), the location of papillae and taste buds, and the normal innervation pattern of the tongue asnd taste buds were determined. The chorda tympani nerve was interrupted to produce degeneration of fungiform taste buds. Regenerating chorda tympani axons followed the original nerve pathways in the tongue en route to the furniform papillae in the epithelium where they initiated the regeneration of taste buds. The spastial distribution of reinnervated fungiform papillae and reformed taste buds was examined 7 to 19 days following surgery. Beginning at eight days following chorda tympani interruption there was a progressive increase, first, in the proportion of fungiform papillae that were reinnervated, and later in the number of reformed taste buds. On the basis of these measures it was concluded that a taste bud is reformed one to two days after reinnervation of its papilla. From the time course of reinnervation of the fungiform papillae it was calculated thast some fibers regenerated at rates in excess of 2mm/day. Regeneration was precise and systematic. The regenerating chorda tympani fibers accurately returned to the fungiform papillae; they did not follow the pasthways of lingual nerve axons. In the initial stages of recovery both reinnervated papillae and reformed taste buds weere preferentially located toward the front of the tongue; the reinnervation of posterior fungiform papillae was delayed.
Taste fiber responses during reinnervation of fungiform papillae
Authors: Cheal Marylou , Dickey William P. , Jones Lef B. , Oakley Bruce
Published: December 2004

Crushing or transecting the chorda tympani nerve of the gerbil (Meriones unguiculatus) caused ipsilateral degeneration of taste buds in the fungiform papillae. In less than two weeks some taste fibers regenerated into the tongue and formed new taste buds and receptor cells. The recovery process was evaluated electrophysiologically in 53 gerbils by acute recording proximal to the nerve injury site. Initially the chorda tympani was electrically silent. In gerbils tested at later times spontaneous activity appeared. This was followed by responses to pressure on the tongue. Taste responses returned as early as dasy 11. The receptive field of regenerated taste fibers was limited to a small number of fungiform papillae. Taste responses were always associasted with the presence of one or more taste buds in the receptive field. Taste buds identified as responsive to chemicals contained some fusiform cells.

We found thast the taste responses of single fiber, few‐fiber and multi‐unit preparations reflected the diversity of responses found in normal taste axons as determined by recording from 26 normal single fibers and 27 normal whole nerves. The early emergence of a variety of fiber types and responses to many chemicals in regeneration is inconsistent with the proposition that the relative chemical responsiveness of a receptor cell is strictly a function of its age; the response of a given young taste receptor is not necessarily limited to a few of the standard taste stimulants.
Topographic organization of the projections from cortical areas 17, 18, and 19 onto the thalamus, pretectum and superior colliculus in the cat
Authors: Updyke B. V.
Published: December 2004

The distribution of cortical projections from areas 17, 18, and 19 to the lateral thalamus, pretectum, and superior colliculus was investigated with the autoradiographic tracing method. Cortical areas 17, 18 and 19 were demonstrated to project retinotopically and in register upon the dorsal lateral geniculate nucleus, medial interlaminar nucleus, lateral zone of the lateral posterior complex, nucleus of the optic tract and superior colliculus. Area 19 was shown to project retinotopically upon the pulvinar nucleus. Clear retinotopic organization was not demonstrable in the projections of areas 17, 18 and 19 to the reticular complex of the thalamus and ventral lateral geniculate nucleus, or in the projection of area 19 to the anterior pretectal nucleus.

The cortical projections were employed to define the retinotopic organization of the nucleus of the optic tract, pulvinar nucleus, and lateral zone of the lateral posterior complex. The cortical projections show the vertical meridian to be represented caudally, with the lower visual field represented laterally, and the upper visual field medially, within the nucleus of the optic tract. The projections of area 19 to the pulvinar nucleus demonstrate the lower visual field to be represented rostrally and the upper visual field caudally in this nucleus; the vertical meridian to be represented at the lateral border and the visual field periphery to be represented at the medial border of the pulvinar nucleus. Cortical projections to the lateral zone of the lateral posterior complex demonstrate the lower visual field to be represented rostrally and the upper visual field caudally; the vertical meridian to be represented at the medial limit and the visual field periphery at the lateral border of the termination zones.

On the basis of the experimental findings, a new terminology is introduced for the feline lateral posterior complex. Divisions are proposed which correspond to zones with demonstrably distinct afferent input. The pulvinar nucleus is defined by the distribution of projections from area 19. Three flanking divisions are defined within the lateral posterior complex; a lateral division recipient of projections from area 17, 18 and 19, an interjacent division recipient of projections of the superficial layers of the superior colliculus, and a medial division flanking the tectorecipient zone medially.
Tectal efferents in the banded water snake, Natrix sipedon
Authors: Ulinski Philip S.
Published: December 2004

Visual information reaches the dorsal thalamus by two distinct routes in most reptiles. Retinal efferents terminate directly in the dorsal lateral geniculate nucleus (DLGN). Retinal information is also channeled indirectly through the tectum to nucleus rotundus. Retinal projections to DLGN and tectum are also well esablished in snakes, but the status of the tecto‐rotundal link of the indirect visual pathway is uncertain.

Thus, tectal efferents were studied with Fink‐Heimer methods in banded water snakes (Natrix sipedon). The tectum gives rise to crossed and uncrossed projections to the brainstem reticular formation. Commissural connections are effected with the contralateral tectum via the tectal and osterior commissures. tectum projects densely to the ipsilateral basal optic nucleus. Bilateral ascending projections reach the pretectal area, nucleus lentiformis mesencephali, lateral habenular nuclei, and posterodorsal nuclei. Ascending projections reach the ventral lateral geniculate and suprapeduncular nuclei. there is a diffuse projection to the central part of the caudal thalamus and a dense, bilaternal projection to the DLGN.

These results indicate that the relation of the tectum to the dorsal thalamus is different in snakes than in other reptiles. Nucleus rotundus is either absent or poorly differentiated and there is a strong convergence of the direct and indirect visual pathways at DLGN.
Development of the geniculocortical pathway in rat
Authors: Lund R. D. , Mustari M. J.
Published: December 2004

Most cells of the dorsal lateral geniculate nucleus of rats are generated of fetal days 12 to 14. Their axons invade the telencephalon on fetal day 16 and run in the intermediate zone just below the cortical plate, reaching the visual area on fetal day 18. The axons do not invade the cortical plate significantly until close to birth (day 22 of gestation) and reach their zone of terminal distribution between postnatal days 1 and 4. In subsequent days the projection becomes progressively more heavily distributed in layers IV and I, and synapses of thalamic origin can be identified in these layers. While cells destined for layers IV cross the intermediaste zone at the time that thalamic axons first arrive, this coincidence of growth does not seem to be a factor which determines the specificity of patterns of thalamocortical connections since the cells reach layer IV several days before the axons. It is unclear why the axons should wait several days in the region immediately below the cortical plate before invading, although there is a parallel in previous studies on the development of the chick retinotectal pathway (Crossland et al., '75).
Telencephalic efferents of the tiger salamander Ambystoma tigrinurn tigrinum (Green)
Authors: Kokoros James J. , Northcutt R. Glenn
Published: December 2004

The efferent projections of the telencephalon in the tiger salamander were examined by the Nauta and Fink‐Heimer methods following unilateral hemispherectomies, rostral hemispheric ablations and pallial lesions. The cerebral hemisphere connects with most areas of the contralateral hemisphere via the pallial, anterior and habenular commissures. The descending fibers travel in the medial and lateral forebrain bundles and in the tracts comprising the stria medullaris. Degenerating fibers and terminals were present throughout the diencephalon but were more abundant ipsilaterally. Fibers reach the pretectum and optic tectum via dorsal and ventral pathways. There is a heavy projection to the midbrain tegmentum and a sparse projection to the tectum via the ipsilateral lateral forebrain bundle. This tract continues into the medulla oblongata and the cervical spinal cord. Rostral and dorsal hemispheric ablations revealed that the majority of fibers forming the olfacto‐peduncular tract originate in the ventral, rostral one‐third of the hemisphere. It was also determined that the majority of the descending efferent fibers located in the lateral forebrain bundle originate from the caudal lateral hemispheric wall, and that these fibers form connections characteristic of mammalian corticofugal and striatofugal systems. The cytoarchitecture and connections of the caudal lateral hemispheric wall suggest that it is homologous to parts of motor isocortex and amygdala of amniotes.
An autoradiographic study of the efferent connections of the superior colliculus in the cat
Authors: Graham Jean
Published: December 2004

The differential projections of the three main cellular strata of the superior colliculus have been examined in the cat by the autoradiographic method. The stratum griseum superficiale projects caudally to the parabigeminal nucleus and rostrally to several known visual centers: the nucleus of the optic tract and the olivary pretectal nucleus in the pretectum; the deepest C laminae of the dorsal lateral geniculate nucleus; the large‐celled part of the ventral lateral geniculate nucleus; the posteromedial, large‐celled part of the lateral posterior nucleus of the thalamus. Several of these projections are topographically organized.

The stratum griseum profundum gives rise to most of the descending projections of the superior colliculus. Ipsilateral projections pass to both the dorsolateral and lateral divisions of the pontine nuclei, the cuneiform nucleus, and the raphe nuclei, and to extensive parts of the brainstem reticular formation: the tegmental reticular nucleus, and the paralemniscal, lateral, magnocellular, and gigantocellular tegmental fields. Contralateral projections descending in the predorsal bundle pass to the medial parts of the tegmental reticular nucleus and of some of the tegmental fields, the dorsal part of the medial accessory nucleus of the inferior olivary complex, and to the ventral horn of the cervical spinal cord. Ascending projections of the stratum griseum profundum terminate in several nuclei of the pretectum, the magnocellular nucleus of the medial geniculate complex and several intralaminar nuclei of the thalamus, and in the fields of Forel and zona incerta in the subthalamus.

The strata grisea profundum and intermediale each have projections to homotopic areas of the contralateral superior colliculus, to the pretectum, and to the central lateral and suprageniculate nuclei of the thalamus. However, the stratum griseum intermediale has few or no descending projections.