bluuebunny/crossref_metadata_2025 huggingface dataset:
Intraocular grafts of fresh and freeze‐stored rat hippocampal tissue: A comparison of survivability and histological and connective organization
Authors: Jensen Steen , Sørensen Torben , Møller Anders G. , Zimmer Jens
Published: January 2005

Intraocular grafts of rat hippocampal tissue, grafted either directly from the immature donor brains (fresh) or after storage in liquid nitrogen at –196°C (freeze‐stored), were compared with regard to survivability and histological and connective organization. For direct grafting, pieces of hippocampal tissue from rat embryos (embryonic day 19, E21) and newborn rats (PO) were placed in the anterior eye chamber of adult rats immediately after dissection. For grafting after deep‐freeze storage, pieces of hippocampal tissue were taken from rat embryos (E16–E21) and newborn rats (PO), frozen at a cooling rate of 1°C/min in CO2 or N2 vapours after addition of the cryoprotective agent dimethylsolfoxide (DMSO), and stored in liquid nitrogen for 1 to 33 days before thawing and intraocular grafting. From 20 to 68 days after grafting, the recipient rats were sacrificed, their eyes sectioned, and the sections stained with thionine for cell bodies, Timm's sulphide silver method for hippocampal fiber systems and terminal fields, and acetylcholinesterase (AChE) for cholinergic fibers and AChE‐positive neurons.

When examining the 101 grafted eyes (34 grafted with fresh and 67 with freeze‐stored tissue) a significantly lower survival rate of the freeze‐stored tissue was found (28 vs. 88%). The survivability of the freeze‐stored tissue was age‐dependent with no survival at donor ages E16 and PO, while tissue from E18–E21 had a 50% survival rate. The grafts of the freeze‐stored tissue were also smaller and showed an increased tendency for fragmentation. When evaluating the structure of the grafts, the deep‐freeze storage was found primarily to have been harmful to the dentate granule cells and their precursors. The organization of intrinsic fiber connections followed the pattern known from lesion and intracerebral transplant studies. While demonstrating that immature brain tissue can survive deep‐freeze storage and subsequent intraocular grafting, the study also indicates that different schemes may have to be used to get optimal survival of different neuronal populations.
Elasmobranch oculomotor organization: Anatomical and theoretical aspects of the phylogenetic development of vestibulo‐oculomotor connectivity
Authors: Graf W. , Brunken W. J.
Published: January 2005

The oculomotor organization of two elasmobranch species, smooth dogfish (Mustelus canis) and little skate (Raja erinacea), was studied by investigating the extraocular muscle apparatus and the oculomotor motoneuron distribution.

The macroscopic appearance of the eye muscles was similar to any lateral‐eyed vertebrate species (e.g., goldfish, rabbit). The size of extraocular muscles was expressed by counting single muscle fibers and comparing cross‐sectional areas of the extraocular muscles. There were significant differences in the number of fibers in the six extraocular muscles in dogfish, but not in skate. Fiber sizes varied considerably; thus, the number of fibers did not relate to cross‐sectional areas. In the dogfish, no one pair of agonist‐antagonist extraocular muscles was larger than the others, suggesting that there was no preference for eye movements in a particular plane of space. However, the lateral rectus was more than twice the size of most of the other muscles. In the skate, cross‐sectional areas of the horizontal eye muscles were smaller than those of the vertical eye movers. This may indicate a reduced utilization of horizontal eye muscles, which may reflect the bottom‐dwelling habitat and mode of locomotion of the skate.

The distribution of the extraocular motoneurons was determined by injecting horseradish peroxidase (HRP) into single eye muscles. Medial rectus, superior rectus, and superior oblique motoneuron populations were located contralateral to their respective muscles. Lateral rectus, inferior rectus, and inferior oblique motoneurons were located ipsilateral to their muscles. This distribution is in contrast to almost all other vertebrates studied thus far, where medial rectus motoneurons are located ipsilateral to the muscle which they innervate. The oculomotor arrangement in elasmobranchs is likely to have consequences for the circuitry responsible for the production of conjugate compensatory eye movements in the horizontal plane.

We hypothesize that, in contrast to other vertebrates, the basic elasmobranch vestibulo‐ocular reflex pathway consists of three identically structured three‐neuron‐arcs connecting the three semicircular canals to their respective extraocular muscles. This innervation pattern may constitute a special feature of the elasmobranch brain or a phylogenetically older arrangement of eye movement pathways.
Autonomic nervous system innervation of thymic‐related lymphoid tissue in wildtype and nude mice
Authors: Bulloch Karen , Pomerantz William
Published: January 2005

A study was undertaken to determine the source and terminal distribution of the autonomic nervous system (ANS) innervation of lymphoid tissue in the mediastinum of male and female B10 and Balb/c wildtype and syngeneic nude (nu/nu) mice. Acetylcholinesterase (AChE) histochemistry was used to localize this hydrolytic enzyme in neural tissue and glyoxylic acid fluorescent histochemistry was used to characterize catecholaminergic (CA) innervation. The thymus was innervated by AChE‐positive fibers of the vagus, the recurrent laryngeal, and the phrenic nerves. Catecholaminergic innervation was derived from the stellate ganglia and other small ganglia of the thoracic sympathetic nervous system chain. Whereas intrinsic AChE‐positive innervation of the thymus was evident at the cortico‐medullary boundaries and under the capsule, CA innervation was observed along the trabeculae with perivascular plexuses at the cortico‐medullary boundaries and interlobular septa. Free CA fibers were noted in the medulla and in the cortex, where they were often proximal to cortical autofluorescent (CAF) cells. The rudimentary thymus of the adult nude mouse received limited ANS innervation. Only a few CA or AChE‐positive fibers were evident, with the majority of fibers associated with the acinar cells of the gland. Mediastinal lymph nodes in male and female wildtype mice varied in their distribution and were frequently found clustered around nerves and ganglia. The intrinsic innervation of lymph nodes by AChE‐positive fibers was confined to the subcapsular marginal sinus, with a few vascular‐associated fibers in the parenchyma. Catecholaminergic perivascular plexuses were present in the hilar zone, whereas some free fibers were noted under the capsule and in the parenchyma. The mediastinal lymph nodes of male and female nude mice when compared to the lymph nodes of male and female wildtype mouse were found to be increased in number and in distribution. Clusters of these lymph nodes were found in close proximity to ANS tissue. The intrinsic innervation of the nude mediastinal lymph nodes was comparable to that present in the wildtype mouse tissue. The functional implication of these data is discussed with regard to nervous: immune system interactions.
Segmental variation in the arborization of identified neurons in the leech central nervous system
Authors: Gillon Jean W. , Wallace Bruce G.
Published: January 2005

Mechanosensory and motor neurons in the central nervous system of the leech have been examined by intracellular injection of horseradish peroxidase and electrophysiological mapping of their peripheral fields to determine how the arborizations of homologous cells are influenced by their segmental position. The branching patterns of annulus erector (AE) motoneurons in ganglia near the head and tail were found to be more extensive than those of cells in midbody ganglia. As in midbody ganglia, the peripheral fields of AE motoneurons in adjacent ganglia near the head and tail overlapped extensively, but the subfields innervated by individual branches of a single AE motoneuron showed little or no overlap. No AE motoneurons were found in the head ganglion or in the 20th and 21st free segmental ganglia. The branching pattern of touch‐sensitive mechanosensory cells showed a similar segmental variation; touch cells in ganglia near the head and tail had more extensive arborizations than those in midbody ganglia. The rostrocaudal position along the cord at which the branching pattern changed from that characteristic of midbody ganglia to one with a more extensive arborization differed for different types of neurons. These findings demonstrate that a cell's pattern of arborization is not determined by a simple segmental difference between ganglia and suggest that during development neurons respond individually to cues that vary along the length of the cord.
The interconnections of the inferior colliculi through their commissure
Authors: Aitkin L. M. , Phillips S. C.
Published: January 2005

Much is known of the sources and manner of termination of ascending and descending input to the inferior colliculus (IC) but its commissural connections are less well understood. Most studies of the commissure have utilized small lesions or tracer deposits; while all agree that commissural axons terminating in the IC do so in its superficial and dorsomedial sectors, it is not clear where projecting cell bodies are located in the IC.

The present study attempted total infiltration of the commissure of the cat IC with horseradish peroxidase (HRP) in an effort to label all neuronal somas whose axons cross in the commissure. The distribution of labeled cells after the brachium of the IC (BIC) was cut unilaterally and infiltrated with HRP was also examined to enable comparison of the locations and approximate proportions of cells projecting to the contralateral IC and medial geniculate body (MGB).

The cells giving rise to commissural axons form an array tilted dorsally from caudal to rostral that spreads mediolaterally through the central nucleus into the external nucleus of the IC, but largely excludes the dorsomedial sector at posterior levels. A similar distribution of labeled cells, but with reduced numbers, is found when large HRP deposits are made in the contralateral BIC. These results, in conjunction with those from studies of the terminations of commissural axons made by others, suggest that the interconnections of the inferior colliculi through their commissure are complementary, rather than reciprocal.
Cerebellar efferents in the lizard Varanus exanthematicus. I. Corticonuclear projections
Authors: Bangma G. C. , Donkelaar H. J. Ten
Published: January 2005

The organization of the cerebellar corticonuclear projections, i.e., the projections from the Purkinje cell layer to the cerebellar nuclei and the vestibular nuclear complex, was investigated with the horseradish peroxidase (HRP) technique in the lizard Varanus exanthematicus. After HRP slowrelease gels were implanted in the cerebellar nuclei or various parts of the vestibular nuclear complex, the following longitudinally oriented zones of labeled Purkinje cells could be distinguished: (1) a medial zone projecting to the medial cerebellar nucleus; (2) an intermediate zone projecting to the vestibular nuclear complex, especially the ventrolateral vestibular nucleus, but probably also the dorsolateral vestibular nucleus; (3) a caudolaterally located area of the cerebellar cortex projecting to the lateral cerebellar nucleus; and (4) the flocculus and the adjacent lateral part of the Purkinje cell layer with projections to the middle and caudal parts of the vestibular nuclear complex, i.e., the descending and ventromedial vestibular nuclei. All projections of the Purkinje cells appeared to be strictly ipsilateral. It can be concluded that in reptiles a longitudinal organization of cerebellar corticonuclear projections exists, which may be basic for terrestrial vertebrates.
The postnatal development of the tract of lissauer in the rat
Authors: Chung Kyungsoon , Coggeshall Richard E.
Published: January 2005

This study determined the numbers of axons in the tract of Lissauer of the S2 segment of rat spinal cord during postnatal development. One day after birth there were an average of 39 myelinated and 9,520 unmyelinated axons in this pathway. These numbers changed steadily to the 722 myelinated and 2,759 unmyelinated axons that characterize the adult. Thus there was a 20‐fold increase in myelinated axons but a threefold decrease in total axons in this pathway from birth to adulthood. The axonal changes occurred so long after the changes in the number of cells that give rise to these axons that the axonal changes were almost certainly not due to the death of their parent neurons. We do not yet understand the mechanisms that control axonal numbers in this pathway, but in our opinion these mechanisms are as important as those that control neuronal numbers in considerations of the development of the nervous system.
β‐Endorphin/ACTH immunocytochemistry in the CNS of the lizard Anolis carolinensis: Evidence for a major mesencephalic cell group
Authors: Khachaturian Henry , Dores Robert M. , Watson Stanley J. , Akil Huda
Published: January 2005

The immunocytochemical distribution of β‐endorphin and other proopiomelanocortin (POMC) peptides in the central nervous system of the lizard Anolis carolinensis was determined. Colchicine pretreatment was used to enhance perikaryal immunoreactivity. A major finding of this study is the localization of a previously undetected mesencephalic cell group which exhibits immunoreactivity to β‐endorphin, ACTH, and α‐MSH. The perikarya of these neurons are large, bipolar, and situated in the mesencephalic tegmental area. They appear to project to the mesencephalic central gray and other brainstem structures. In contrast, the immunoreactive parvicellular perikarya of the medial‐basal hypothalamus, corresponding to the POMC perikarya of the rodent arcuate nucleus, exhibit major rostral projections to various telencephalic and diencephalic structures. The exact extent of fiber projections and innervation patterns arising from either of these two groups is not clear at this time and will require further analyses. Scattered fiber immunoreactivity was also seen in the medial cerebral cortex and the striatal complex, regions which apparently are not innervated by β‐endorphin fibers in the rodent brain. Also, no immunoreactivity was seen to an antiserum to the 16K peptide of POMC. Other similarities and differences in the brain distribution of POMC in reptiles and mammals are discussed.
Cortical projections to the superior colliculus in the macaque monkey: A retrograde study using horseradish peroxidase
Authors: Fries W.
Published: January 2005

The topical and laminar distribution of corticotectal cells, as well as their size and morphology, were studied in the macaque monkey with the horseradish peroxidase (HRP) technique. After HRP injections restricted primarily to the superficial layers of the colliculus, labelled cells were found in visual cortex (areas 17, 18, and 19) and both in the frontal eye field (area 8) and the adjacent part of premotor cortex (area 6). The clustering of labelled cells in visual cortex indicated that each of the anatomically and functionally distinct visual areas has its own set of collicular projections. When intermediate and deeper layers of the colliculus were injected, labelled cells were found also in posterior parietal cortex (area 7) where they were concentrated mainly on the posterior bank of the intraparietal fissure, in inferotemporal cortex (areas 20 and 21), in auditory cortex (area 22), in the somatosensory representation SII (anterior bank of sylvian fissure, area 2), in upper insular cortex (area 14), in motor cortex (area 4), in premotor cortex (area 6), and in prefrontal cortex (area 9). In the motor and premotor cortex, labelled cells formed a continuous band which appeared to stretch across finger‐hand‐arm‐shoulder‐neck representation. Similarly, the cluster of labelled cells in area 2 may correspond to the finger‐hand representation of SII. The cortical regions not containing labelled cells were the somatosensory representation SI (areas 3, 1 and 2) and the infraorbital cortex.

Labelled cells were restricted to layer V of all cortical areas except in the primary visual cortex, where labelled cells were found in both layer V and layer VI. The size spectrum of corticotectal cells ranged from 14.8 μm (average diameter) in area 17 to 27.8 μm in area 6, comprising cells as small as 8 μm and as large as 45 μm. Labelled cells in posterior parietal (area 7), in auditory (area 22), and in motor cortex (area 4) were small and distributed over only a narrow range of sizes. Those in premotor cortex (area 6) were often large and had a wide range in size distribution. The differences in size and morphology of corticotectal neurons suggest that they do not form a uniform class of neurons.
Role of nerve growth factor in the adult dorsal root ganglia neuron and its response to injury
Authors: Rich Keith M. , Yip Henry K. , Osborne Patricia A. , Schmidt Robert E. , Johnson Eugene M.
Published: January 2005

The response of dorsal root ganglia (DRG) neurons to NGF deprivation and to axotomy was examined in adult guinea pigs. The success of NGF deprivation by means of an autoimmune approach was monitored by the measurement of serum antibody titer levels against guinea pig NGF with the standard bioassay for NGF activity. That the antibody produced NGF deprivation was confirmed by histologic evidence of neuronal atrophy and apparent cell loss in sections of the superior cervical ganglia (SCG) and by marked decreases (65–80%) of SCG neurotransmitter‐synthesizing enzyme activity levels. By using the autoimmune approach a new source of guinea pigs was found which consistently produced high titers of cross‐reacting anti‐NGF antibodies.

Experiments were designed to examine the response of the sensory neuron to injury while chronically deprived of NGF. Total neuronal counts in the sixth lumbar DRG 98 days after sciatic nerve crush showed no difference between NGF‐deprived and control ganglia. Measurement of the size spectrum of DRG neurons showed evidence of atrophy of the NGF‐deprived neurons in both the uninjured and axotomized side compared to respective controls. The mean volume of uninjured sensory neurons measured in the NGF‐deprived guinea pigs was decreased 27.7% (P <0.05) compared with that of control guinea pigs.

The degree of regeneration 6 days following a nerve crush was the same in NGF‐deprived sensory neurons and in controls when measured by the “pinch test” and by isotope‐labeled axonal transport studies. The long‐term regenerative response was analyzed with various histologic and morphometric techniques studying the sural nerve 98 days after sciatic nerve crush. No differences between control and NGF‐deprived guinea pig sural nerves were noted at the light microscopic and ultrastructural levels. These studies demonstrated an unimpaired regenerative capability of sensory neurons deprived of NGF compared with controls.
Morphology of Golgi‐Cox‐impregnated barrel neurons in rat SmI cortex
Authors: Simons Daniel J. , Woolsey Thomas A.
Published: January 2005

Golgi‐Cox‐impregnated neurons in the barrel cortex of the rat were studied qualitatively and quantitatively. Adult rat brains were sectioned perpendicular to or parallel to the cortical representation of the large facial vibrissae at 125 μm. Cortical laminar and barrel boundaries were identified from the Nissl counterstain. Over 200 well‐impregnated neurons in cortical layers I–IV were selected for classification and further detailed study. Three broad classes of neurons were recognized: (1) pyramidal cells with conical somata, a stout apical dendrite, and spines; (2) class I nonpyramidal cells having small spherical somata and spiny dendrites; and (3) class II nonpyramidal cells having larger ellipsoid somata and smooth or beaded dendrites. The class I cells were further subdivided into “star pyramids” (cells with an apical dendrite) and spiny stellate cells (cells in which all dendrites were of similar length). The class II cells also were subdivided into multiform cells (with multiple dendrites radiating from the soma) and bipolar cells (with two principal dendritic trunks arising from the superficial and deep aspects of the soma). The position of these various cell types in the superficial cortical laminae was mapped in sections normal to the pia. Numerous examples of the class I and class II neurons were drawn with respect to the barrels in layer IV and the extent of their processes noted. Finally, approximately 250 barrel‐related class I and II neurons were studied quantitatively using a computer‐microscope and digitizing tablet.

The density of the Golgi‐impregnated neurons corresponds to the pattern of cell density seen with the Nissl counterstain. The various cell types arc not uniformly distributed as a function of cortical depth. Cells with apical dendrites were found principally in the supragranular layers and star pyramids in the superficial one‐half of layer IV. Spiny stellate cells are concentrated in layer IV and the smooth cells are present in greatest number in deep layer III and deeper layer IV. On the basis of these distributions we suggest that layer IV be subdivided into two sublaminae. The class I and class II neurons can be distinguished according to quantitative criteria which apply in either plane of section used. Class I neurons have smaller projected somal areas, more proximal dendritic branching, and shorter dendrites when class I and II neurons are measured in three dimensions. For neurons with somata in layer IV there is a pronounced tendency for the dendrites to be confined to one or two cortical barrels depending on the exact location of the soma in a barrel. This finding is true for both the class I and class II cells although the class I neurons had more tightly confined processes, particularly with respect to the vertical axis of the cortex. These results are discussed in relation to similar findings in mice and to functional studies of the rodent barrel cortex.
Development of synaptic organization in the tangential vestibular nucleus: A quantitative electron microscope study
Authors: Peusner Kenna D.
Published: January 2005

The objective of the present study is to quantify the developmental changes in the total synaptic pattern of one part, the soma, of one particular cell type, the principal cells of the tangential vestibular nucleus. The term “synaptic space” is defined and quantified. Intermediate stages in the development of synaptic organization are compared.

The findings show that the synaptic space available to the full complement of afferents is constant throughout development, while specific terminals in the afferent population change their synaptic space allotments. The synaptic‐junction covering is invariant for small terminals at intermediate stages of development with set proportions between “active” and “non‐active” zones of the synaptic surfaces. However, the spoon endings and the postsynaptic target cells are covered by synaptic junctions in variable amounts.

The findings are important to the fields of neuroembryology and neural plasticity, for the system provides a useful basis to measure the influence of factors in the local environment and the role of formation of synaptic connections in the competition for synaptic space. This study will assist investigators to probe the mechanisms operating in the selection of competing afferents for the limited amount of surface area available under the changing conditions of maturation and aging in the central nervous system.
The distribution of filipin‐sterol complexes in photoreceptor synaptic membranes
Authors: Cooper Nigel G. F. , McLaughlin Barbara J.
Published: January 2005

The polyene antibiotic filipin, which binds to membrane sterols, has been used to investigate the relative distribution of cholesterol at photoreceptor synaptic junctions in the chick retina. Following anesthesia and aldehyde perfusion fixation, the retina is removed and immersed in fixative solution containing the filipin for 36–48 hours. The retinas are then processed for freeze‐fracture. Electron microscopy of freeze‐fracture replicas demonstrates that the filipin‐sterol complexes are not evident between intramembrane particles of the presynaptic and postsynaptic particle arrays that are present at ribbon and basal junctions. In contrast, the synaptic vesicle fusion zone of ribbon junctions contains large numbers of filipin‐sterol complexes which are observed merging with the free margins of the presynaptic particle array. There is a scarcity of such complexes, however, around the free margins of basal junction presynaptic particle arrays. These latter sites do not contain a vesicle fusion zone. Particle‐poor areas of membrane that surround postsynaptic particles arrays of ribbon and basal junctions also do not contain filipin binding sites. The nonsynaptic membrane of photoreceptor terminals contains large numbers of filipin‐sterol complexes, less tightly packed than in the synaptic vesicle fusion zone. Coated vesicle fusion sites in the presynaptic membrane contain groups of intramembrane particles but the filipin‐sterol complexes are excluded from these sites. The observations suggest that synaptic membrane domains which interact with cytoskeletal components, such as clathrin and pre‐ and postsynaptic densities contain less cholesterol than other domains such as the synaptic vesicle fusion zones.
Prenatal and postnatal development of retinogeniculate and retinocollicular projections in the mouse
Authors: Godement Pierre , Salaün Josselyne , Imbert Michel
Published: January 2005

The development of retinal projections to the dorsal lateral geniculate nucleus (dLGN) and superior colliculus (SC) has been studied in fetal and neonatal mice of the pigmented C57BL/6 strain, using the anterograde transport of tritiated proline and horseradish peroxidase (HRP).

Retinal efferents are present contralaterally just beyond the chiasm at E14. By E16 they have grown into both dLGN and SC. Ipsilateral fibers are limited to the proximal optic tract at E16; their growth into dLGN and SC is delayed until E18‐birth.

During the first 2 postnatal days, an early population of ipsilateral fibers invades the dLGN. Most of these fibers grow in or around the mediodorsal sector of the dLGN, i.e., the future binocular segment. Fibers are also present, but at lower densities, in the ventral half of the nucleus and thereafter become dispersed or are lost, without at any stage becoming dense. Some denser labeling is also present ipsilaterally in the outer rim of dLGN, just below the optic tract, and later disappears.

On the third postnatal day, the ipsilateral fibers establish a deep and denser projection along the medial and dorsal borders of dLGN; this projection overlaps part of the crossed projection, which at this age extends to the whole nucleus. The segregation of each projection starts on the fourth postnatal day, when crossed fibers begin to disappear from the small region of uncrossed projection. This process goes on for another 4 days. During this period, the ipsilateral fibers withdraw from the deepest layer of dLGN, and their terminal density increases gradually; by the eighth postnatal day, both projections are already well separated.

Dense crossed projections first appear near the surface of the SC at birth. Prior to this, retinal fibers course throughout neurons of the collicular plate and underneath the pia.

The uncrossed fibers invade the SC between birth and P3. They are located preferentially in the anterior and medial aspect of the SC. Subsequently, there occurs a diminution in the laminar and tangential extent of these projections, simultaneously with an intensification of the ipsilateral input to several small, longitudinally oriented clusters located deep to the crossed projections.
Ganglion cells in retinae transplanted to newborn rats
Authors: Perry V. H. , Lund R. D. , McLoon S. C.
Published: January 2005

Cells projecting out of retinal transplants placed over the tectum of newborn rats were studied by labelling with horseradish peroxidase 1 month or more after transplantation. Using this technique, it was found that only cells with the dendritic characteristics of ganglion cells were labelled and, furthermore, that the major classes of ganglion cells seen in normal retinae were also present in the transplants. The cell body size histograms of ganglion cells in normal and transplanted retinae compared closely with each other.

Dendritic trees were closely confined by the limits of the inner plexiform layer, and if that layer was folded or distorted, they were themselves frequently abnormal. While axons usually coursed over the surface of the retinal transplants, they quite often followed an anomalous course crossing the individual layers.

It appears, therefore, that this transplantation procedure has relatively little impact on the ability of ganglion cells to develop many of their characteristic morphological features. Whether the different functional responses of the various ganglion cell classes are also preserved after transplantation is a matter for further investigation.
The development of the nucleus isthmi in Xenopus laevis. I. Cell genesis and the formation of connections with the tectum
Authors: Udin Susan Boymel , Fisher Mark D.
Published: January 2005

The nucleus isthmi (NI) of the amphibian relays visual input from one tectum to the other tectum and thus brings a visual map from the eye to the ipsilateral tectum. This isthmotectal visual map develops slowly; it is first detected electrophysiologically at stages 60–62, the age at which the eyes begin their dorsalward migration and the region of binocular overlap begins to increase in extent. During this critical period of life, normal binocular visual input is required for establishment of normal topographic isthmotectal projections. In this study, we have used anatomical methods to trace cell birth, cell death, and formation of connections by the nucleus isthmi during the critical period.

Tritiated thymidine labelling demonstrates that cells in the nucleus isthmi are generated throughout most of tadpole life (stages 29–62). Most cells conform to an orderly ventrodorsal gradient starting from stage 29 and extending to stage 56; later cells are inserted at apparently random locations in the nucleus. We have re‐examined the hypothesis of Tay and Straznicky (1980) that the order of cell genesis in the NI and tectum could help establish proper isthmotectal connections, and we find that a timing mechanism does not explain the two‐dimensional topography of the isthmotectal map but that timing may aid in proper mediolateral positioning of isthmotectal axons at the points where they first enter the tectum.

Horseradish peroxidase labelling was used to investigate whether anatomical projections from tectum to NI and from NI to tectum are present prior to the onset of eye migration. The results show that there are tectoisthmotectal projections by stage 52. Moreover, isthmotectal axons grow into as yet monocular tectal regions prior to the onset of eye migration. At stage 60, when binocular overlap begins, isthmotectal axons are visible throughout the tectum but are densely branched only at the rostral tectal margin, the location where they are predicted to occur on the basis of electrophysiological maps.
The onset and development of descending pathways to the spinal cord in the chick embryo
Authors: Okado Nobuo , Oppenheim Ronald W.
Published: January 2005

The ontogenetic development of afferent (supraspinal and propriospinal) as well as efferent (ascending) fiber connections of the spinal cord was examined following the injection of horseradish peroxidase (HRP) or wheat germ agglutinin HRP (WGA‐HRP) into the cervical and lumbar spinal cords (or brains) of embryos ranging in age from 4 to 14 days of incubation. A few cells were first reliably retrogradely labelled in the pontine reticular formation on embryonic day (E) 4 and E5 following the injection of WGA‐HRP into the cervical and lumbar spinal cord, respectively. Propriospinal projections to the lumbar spinal cord, originating from brachial spinal cord, were found by E5, and from the cervical spinal cord by E5.5. Ascending fibers arising from neurons in the lumbar spinal cord could be followed to rostral mesencephalic levels in E5 embryos. Thus, the earliest supraspinal, propriospinal, and ascending fiber connections appear to be formed almost simultaneously. Retrogradely labelled cells were found in the raphe, reticular, vestibular, interstitial, and hypothalamic nuclei in E5.5 embryos following lumbar injections of WGA‐HRP. Except for neurons in cerebellar nuclei, all the cell groups of origin that project to the cervical spinal cord of posthatching chicks were also retrogradely labelled by E8. There was a delay in the time of appearance of the projections from various regions of the brain stem to the lumbar versus the cervical spinal cord, ranging from 0.5 to 7 days, but typically of about 3 days duration. A large number of cells located in the ventral hypothalamic region, just dorsal to the optic chiasma, were found to be labelled following cervical HRP injection between E6 and E10. These cells may represent transient projections that are present only during embryonic stages since no labelled cells were found in this region in the newly‐hatched chick.
Evidence for proctolin‐like substances in the central nervous system of the leech hirudo medicinalis
Authors: Li C. , Calabrese R. L.
Published: January 2005

The distribution of proctolin‐like immunoreactive (PLI) cells was mapped in the central nervous system of the leech Hirudo medicinalis. In segmental ganglia, PLI cells can be divided into two groups: cells that stain repeatedly in every successive ganglion, and cells that stain only in specific segmental ganglia. The number of PLI cells, therefore, ranged from eight to 20 cells per ganglion. One bilateral pair of PLI cells (cells PLI‐1) was further characterized morphologically by Lucifer yellow and horseradish peroxidase cell injections. Cell PLI‐1 conforms in soma position, morphology, and physiological properties with cell 101, which has been previously classified as an inhibitory motoneuron to the flattener muscles.

A locust bioassay (O'Shea and Adams, Science 213:567–569, 1981) was used to detect the presence of proctolin‐like bioactivity. Extracts of leech ganglia when applied to the extensor tibial is muscle of the locust leg induced a proctolin‐like response similar to the responses induced by proctolin standards. This work extends the finding of proctolin‐like substances to the annelid phylum.
Derivation of cerebellar golgi neurons from the external granular layer: Evidence from explantation of external granule cells in vivo
Authors: Hausmann Beate , Mangold Ulrich , Sievers Jobst , Berry Martin
Published: January 2005

The present report provides evidence to challenge the traditional view that cerebellar Golgi cells are derived from the ventricular neuroepithelium, postulating instead that they originate from external granule cells. Supporting evidence for this assertion comes from three sources: (1) Typical Golgi cells are found in ectopic granule cell colonies, both outside the cerebellum (in the subarachnoid space) and also within the cerebellar cortex between fused folia. Because ectopic granule cell colonies are derived from external granule cells, which become displaced after treatment with 6‐hydroxydopamine (6‐OHDA), it was assumed that the ectopic Golgi cells also stem from such displaced external granule cells. (2) In order to demonstrate that Golgi cell precursors migrate from the external granular layer into the Purkinje cell plate, the development of the cerebellar cortex was studied over the period of Golgi cell genesis. On E19 the external granular layer in the rat is subdivided into an outer proliferative and an inner subproliferative zone. At the inner margin of the external granular layer, and in the marginal zone, radially oriented, darkly staining cells are present that exhibit all the characteristics of migrating neurons possessing a leading process oriented toward the Purkinje cell plate, a somatic cilium, and a close association with radial glia fibers. In later stages, these cells are also found deep to the Purkinje cell plate. Because Golgi cells arise during the period between E19 and postnatal day 2 in the rat (Altman and Bayer, 1977, 1978) and as the basket cells, the first neurons of proven origin from the external granular layer, are not produced before the second postnatal day (Altman, 1972), the earlier migrating neurons are presumed to be Golgi cells. (3) Available data from cell kinetic 3H‐thymidine studies show that there is no unequivocal evidence for Golgi cell genesis from the ventricular neuroepithelium, because, at the time of Golgi cell birth, ventricular and external granular stem cell populations are proliferating, and with the present methods it is not possible to decide which of these are the precursors of Golgi cells. Thus, taken together, the findings of this study show that Golgi cells are more likely to arise from the external granular layer than from the ventricular neuroepithelium. This concept would unify cerebellar histogenesis by proposing that projection neurons arise from the ventricular neuroepithelium, whereas all interneurons of the cerebellar cortex are descendants of the external granular layer.
The three‐dimensional morphology of afferent terminal fields in the rat dentate gyrus: Periodic variation
Authors: King Michael A. , Reep Roger L. , Hunter Bruce E. , Walker Don W.
Published: January 2005

The laminated afferent terminal fields in the rat dentate gyrus molecular layer exhibit differential histochemical staining properties. Dependent variables (e.g., field geometries, stain intensity) based on this organization can allow evaluation of the effect of independent variables upon the integrity of each afferent, but anatomically justifiable procedures for matching measurement regions across animals are necessary. We describe such a procedure and a serendipitous observation on the normal organization of the terminal fields. From a 10 × 10 mediolateral × anteroposterior array of measurement points per animal, it was determined that each afferent field, and the total molecular layer, exhibits periodic variation in width relative to the granule cell layer. Thus, to reduce statistical variability, either a high dependent variable sampling rate, or sampling within a region of naturally low variability, is suggested. Evidence for such a region is presented, and possible consequences of this novel topology of afferentation are discussed.
Postnatal development of the ipsilateral retinocollicular projection and the effects of unilateral enucleation in the golden hamster
Authors: Insausti R. , Blakemore Colin , Cowan W. Maxwell
Published: January 2005

Anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) was used to study the normal development of the ipsilateral retinocollicular projection in golden hamsters, and to examine the effect of enucleation of the other eye at birth. In neonatal animals there were retinal fibers and sparsely distributed granular labeling in the superficial layers of the ipsilateral superior colliculus over its entire areal extent. Differences in the uncrossed projections of normal and enucleated animals first became clear at day 5. In normal animals, retinal fibers withdrew from the superficial layers of the superior colliculus, and the projection became concentrated in the stratum opticum, where denser clumps of label in the rostral part of the superior colliculus were first seen at day 5. In enucleated animals, the retinal projection persisted in the most superficial layers, and the density of labeling was higher than in normals. The very sensitive WGA‐HRP technique showed retinal fibers extending to the caudal pole of the superior colliculus at all ages: even in normal animals more than 2 weeks of age some fibers reached as far as the inferior colliculus. When the shrunken size of the superior colliculus in the enucleated animals was taken into account, the total areal distribution of the ipsilateral projection was similar in normal animals and enucleates. The major difference between the two groups was in the higher density of ipsilateral labeling, especially in the caudal part of the superior colliculus, and in its more superficial laminar distribution in the enucleated animals.
The spinal terminations of single, physiologically characterized axons originating in the pontomedullary raphe of the cat
Authors: Light Alan R.
Published: January 2005

Single myelinated axons were recorded in the dorsolateral funiculus of the cat and physiologically characterized as descending from the midline medulla or midline pons. Following further physiological characterization (e.g., conduction velocity, adequate stimulus, receptive field, activation by stimulation of periaqueductal gray), the axons were Labeled with horseradish peroxidase that was iontophoretically ejected from the recording micro‐pipette. Histochemical reaction allowed visualization of the stained axons and their arborizations in the spinal gray matter. The conduction velocities of the sampled axons ranged from 7.3 to 117.2 m/second with a mean of 35.5 m/second. However, unmyelinated axons could not be sampled with the technique employed here. Descending axons could be divided into two groups: (1) those which terminated in laminae I, II, V, and X, and (2) those which terminated in laminae V, VII, and X. Axons from both groups had myelinated parent axons, were activated by periaqueductal gray stimulation, and responded to noxious pinch of their receptive field Terminal collaterals from both groups of axons were generally transversely oriented. These results suggest heterogeneous functions for these descending axons which may include modulation of nociceptive input to higher centers.
The ultrastructure and synaptic connections of the spinal terminations from single, physiologically characterized axons descending in the dorsolateral funiculus from the midline, pontomedullary region
Authors: Light Alan R. , Kavookjian Anahid M.
Published: January 2005

Single axons descending in the spinal, dorsolateral funiculus which were directly activated by stimulating in or near nucleus raphe magnus (nRM) in the rostral medulla were iontophoretically injected with horseradish peroxidase (HRP).

Labeled axons and terminal arborizations in the spinal cord were demonstrated by diaminobenzidine histochemistry following fixation. Sections were processed for electron microscopy and embedded between coverslips. Following examination with the light microscope, selected boutons were sectioned in ultrathin series and examined with the electron microscope. Two arborization patterns were observed with the light microscope. One terminated dorsally in laminae I, II, V, and X, while the other terminated ventrally in laminae V, VII, and X.

At the ultrastructural level, boutons predominantly contacted dendrites and occasionally contacted cell somas. Ventrally projecting axons had boutons characterizable as Gray's type I. Some dorsally projecting axons also had Gray's type I boutons, while other axons had Gray's type II boutons. Thus, these descending axons may be heterogeneous in function. No differences in physiological characteristics were found between axons with Gray's type I boutons versus axons with Gray's type II boutons.
The differential projection of two cytoarchitectonic subregions of the inferior parietal lobule of macaque upon the deep layers of the superior colliculus
Authors: Lynch J. C. , Graybiel A. M. , Lobeck L. J.
Published: January 2005

Parietotectal projections were studied in the macaque monkey in experiments designed to compare the distribution of fibers originating in two cytoarchitecturally distinct regions within the inferior parietal lobule: the inferior bank of the intraparietal sulcus (area POa of Seltzer and Pandya, '80) and the adjoining part of area PG (von Bonin and Bailey, '47) on the convexity of the hemisphere, here called PGc. A dense fiber projection from POa to the intermediate and deep layers of the superior colliculus was observed by both anterograde autoradiographic and anterograde horseradish peroxidase methods. In contrast, only faint labeling was seen in the superior colliculus following injections of tritiated amino acids into area PGc on the convexity. In a second set of experiments, injections of horseradish peroxidase were placed in the intermediate and deep layers of the superior colliculus so that the cells of origin of the parietotectal projections could be identified. Many retrogradely labeled neurons were observed in POa, whereas very few labeled neurons were present in any other subdivision of the inferior parietal lobule or in the superior parietal lobule. These findings demonstrate that area POa has a prominent direct efferent projection to a major premotor region of the brainstem oculomotor system and suggest that by virtue of its parietotectal connection, this sulcal subdivision may have functional properties not shared with other subdivisions of the inferior parietal lobule.
Peripheral nerve grafts to the frog optic tectum: A morphological study of foreign axon regeneration in the central nervous system
Authors: Kaplan Elliot I. , Clemente Carmine D.
Published: January 2005

The proximal stump of a transected mandibular nerve was grafted onto the rostrodorsal surface of the optic tectum in adult Rana pipiens to investigate the morphologic characteristics of nonspecific axonal regeneration in a highly organized region of central nervous system (CNS). Within the first 3 weeks postgraft surgery (WPS), the nerve‐tectum interface became firmly established. Concomitant with this was an invasion of the host tectum by a small number of fine “pioneerlike” axons from the nerve. By 6 WPS there developed a concerted instreaming of a large number of peripheral fibers. Once within the CNS, the foreign axons distributed themselves throughout the rostrocaudal extent of the tectum, but primarily its dorsal aspect within superficial layers 8 and 9.

Presence of intact optic fibers at the time of mandibular fiber invasion served somewhat to restrict the regenerating aberrant axons in their course through layer 9. This restriction could be avoided by removal of the optic input either before or during peripheral ingrowth. However, once peripheral fibers had entered and established themselves in the host environment, no subsequent manipulation of the retinotectal projection had any effect.

The aberrant growth pattern, which appeared remarkably stable after 6 WPS, consisted of a plexus of medium‐ and fine‐caliber peripheral axons. Many of these fibers had numerous branches and “en passant” varicosities, the latter encompassing a variety of shapes and sizes. Terminal swellings and arborizations were also found.

When comparing the regeneration of optic and mandibular nerve fibers in the tectum, two distinctions were made. Whereas optic axons revealed a fascicular and layered organization, mandibular axons showed a highly segregated and disordered growth pattern. These characteristic differences were maintained even when the two fiber systems were allowed to coregenerate into the same target tectum. Thus, each of the two groups of axons interacts with the tectal substrate in a distinct manner, apparently independent of the other.