bluuebunny/crossref_metadata_2025 huggingface dataset:
Genetic control of retinal ganglion cell projections
Authors: Lavail Jennifer H. , Nixon Ralph A. , Sidman Richard L.
Published: January 2005

We have assessed the effects of 15 pigmentation mutations on the development of retinal ganglion cell projections in mice in two ways: (1) by analyzing the pattern of innervation of the ipsilateral lateral geniculate nucleus as mapped in autoradiograms of brains of animals killed 12 days after intravitreal injection of 3H‐proline into one eye and (2) by determining the ratio of axonally transported radioactive protein in the contralateral and ipsilateral optic tracts after similar intravitreal injections. Analysis of the ratio of transported protein in the two optic tracts provides a new and useful assay of the degree of decussation in experimental animals. The effects of the mutations on eye pigmentation, whole eye melanin content and relative tyrosinase activity also were examined. The degree of ipsilateral innervation generally correlates with the degree of pigmentation of the retinal pigment epithelium and with tyrosinase activity. However, discrepancies have been found in ch and ce mutants. In these animals the pigment epithelium is well pigmented, and the area of ipsilateral innervation in the lateral geniculate nucleus is extensive, despite a high ratio of label in contralateral to ipsilateral optic tracts and low tyrosinase activity. Furthermore, mice heterozygous for the c2J allele have pigmentation and optic projections that are normal even though tyrosinase is reduced to 40% of normal. The few anomalous results suggest that alternative or additional factors may control optic axon projections.
Proliferative and degenerative events in the early development of chick dorsal root ganglia. II. Responses to altered peripheral fields
Authors: McMillan Carr Virginia , Simpson Sidney B.
Published: January 2005

Responses of chick embryo dorsal root ganglia to early wing bud amputation were examined histologically using tritiated thymidine (3H‐TdR) and autoradiography to analyze proliferation and the Feulgen procedure to visualize degenerating cells. Right wing buds were amputated at stage 15 or 16. At 4.5 to 9.5 days of incubation embryos were given a 1‐hour exposure to 3H‐TdR and fixed. Feulgen‐stained autoradiographs were examined for percentage of cells labelled (labelling index) or degenerating (degeneration index) in lateroventral (LV) and mediodorsal (MD) regions of brachial (G14‐16) and nonbrachial (G12, 13, 17) ganglia. The earliest response to amputation was a highly significant increase in degeneration indices of LV and MD regions of ipsilateral brachial ganglia at 5.5 days. Significant brachial LV responses were observed throughout the remainder of the experimental period. Two peaks occur in this response: at 5.5 days, corresponding to the peak seen in normal nonbrachial ganglia, and at 8.5 days, having no counterpart in normal development. In brachial MD regions significant degenrerative responses occur at most times examined. Significant responses also occur at 7.5 and 8.5 days in MD regions of nonbrachial ganglia. The presence of MD responses in our material indicates that maturation of at least some MD neurons occurs earlier than previously thought.

Significant labelling responses occur in brachial LV regions from 7.5 days on. Because other studies (Carr and Simpson, '78a) show that time is after the end of large‐scale neuronal production, this labelling response must be nonneuronal in nature. We conclude that this labelling is a secondary response to amputation, consequent to the greatly increased cellular degeneration.

Results of experiments involving addition of limb buds at the brachial level are also presented.
A regional specialization in the opossum's retina: Quantitative analysis of the ganglion cell layer
Authors: Hokoç Jan Nora , Oswaldo‐Cruz Eduardo
Published: January 2005

The distribution of ganglion cells in the opossum's retina was determined from flat‐mounted preparations stained with cresyl‐violet.

The retinal area is 109 mm2 (SD = 16 mm2). Maps of ganglion cell density were made from retinae of seven animals. in all maps iso‐density lines were approximately concentric, showing a slight elongation towards the nasal region. Cell density varied from 400 cells/mm2 at the extreme periphery to 2,900 cells/mm2 in the region of highest count, the are centralis. The center of this region lies 1.85 mm (26.3°) temporal to the center of the optic nerve head. The average total number of ganglion cells is 77,384 (SD = 10,173).

Based upon soma diameter histograms ganglion cells were classified into three groups, showing at area centralis peaks at 7 μm, 12 μm and 15 μm respectively. Cell soma diameter ranged from 6 μm to 21 μm, larger values being observed at the periphery.
Electron microscopic studies on the lamprey meninges
Authors: Nakao Taisuke
Published: January 2005

Lamprey meninges were revealed to consist of four layers. The I (outermost) layer was made up of densely packed collagen fibrils and microfibrils with fibrocytes interposed between them. It contained a vascular network (epidural vascular plexus). The II layer was a cellular layer, consisting of two parts: the outer, membranous and the inner, spongy part. The membranous part was composed of two sheets of type 1 cells which were held together by desmosomes, gap junctions and tight junctions. Continuous basal laminae were found on both the outer and the inner surface of the membranous part. The spongy part consisted of type 2 cells, collagen fibrils and microfibrils, which were loosely arranged. Type 2 cells were joined together with each other, or with type 1 cells, by gap junctions. These cells lacked a basal lamina covering. The III layer was a peculiar thick layer, being mostly occupied by fine filamentous matrix substance with scattered round cells, fibroblasts and microfibrils. The IV (innermost) layer was a thick fibrous one, consisting of two parts: the outer, vascular and the inner, loose part. The former consisted of a vascular network (perineural vascular plexus) and thick bundles of microfibrils which frequently contained a dense filamentous core. The latter was composed of loosely arranged collagen fibrils.

The inner part of the I layer (inside the epidural vascular plexus) was considered to correspond to the true dura, and the II and IV layer to the arachnoid and pia in the meninges of higher animals, respectively. Characteristically the subarachnoid space was absent in lamprey meninges, and instead a peculiar “gelatinous” layer, III layer, was present between the II and IV layer.
Patterns of cell proliferation in the developing retina of the clawed frog in relation to blood supply and position of the choroidal fissure
Authors: Beach D. H. , Jacobson Marcus
Published: January 2005

The pattern of retinal vasculative is described and the position at which cell proliferation at the ventral retinal margin is maximal was shown to be at the point of entry of the ventral blood vessels. To test whether there is a causal relation between retinal blood supply and retinal cell production, surgical inversion of the eye, transplantations and excisions of retina were done to change the pattern of retinal vasculature. The growth pattern of inverted eyes was normal with respect to the internal axes of the eyes. After excision of part of the retina or after fusion of retinal fragments to form compound eyes, the pattern of retinal cell proliferation was not correlated with the distribution of retinal blood vessels, but was correlated with the position(s) of the choroidal fissure(s).
Substrate pathways which guide growing axons in Xenopus embryos
Authors: Katz Michael J. , Lasek Raymond J.
Published: January 2005

Optic axons from eyes transplanted to hindbrain and spinal cord (i.e., non‐optic areas) in Xenopus embryos reproducibly follow a particular pair of continous tracts, the external sensory tract and the internal sensory tract. The course of the external sensory tract may coincide with the course of the general somatic afferent tracts (i.e., the ascending and descending tracts of nerve V, the tract of Lissauer, and the Rohon‐Beard cell tracts). The course of the internal sensory tract parallels that of the external sensory tract but runs more medially. Transplanted optic axons follow the same tracts regardless of where along the neural axis the axons have entered the CNS. What kind of developmental cues guide these optic axons? It is unlikely that the guidance cues are organized as spatial coordinates, rather it appears that the optic axons of these two tracts are guided along pre‐existing substrate routes. We have called these routes substrate pathways. Substrate pathways may be a device normally used for organizing fiber tracts in the developing nervous system.
Differential projections of cortical sensorimotor areas upon the dorsal column nuclei of cats
Authors: Weisberg Julie A. , Rustioni Aldo
Published: January 2005

Cortical projections to the dorsal column nuclei (DCN) of cats arise from layer V pyramids throughout the sensorimotor cortex and also from the second somatosensory cortical area (SII). In this study, the relative contribution from various cortical areas to different portions within the DCN‐complex has been investigated in cats with restricted cortical lesions and using the Fink‐Heimer technique.

The sensorimotor cortex (areas 4, 3, 1, and 2) projects throughout most of the rostro‐caudal extent of the gracile nucleus. Densest projections arise from the upper bank of the cruciate sulcus containing mainly the hindlimb region (area 4), from the medial wall of the posterior sigmoid gyrus (mainly area 3a) and terminate in the rostral as well as in the clusters regions of the gracile nucleus. The contribution of cortico‐gracile projections from the hindlimb regions of areas 3b, 1 and 2 are much less conspicuous and terminate mainly in the rostral region of the nucleus. The nucleus z, the medullary relay for Ia fibers from the hindlimb, receives exceedingly sparse cortical projections. Dense projections to the cuneate n. arise from the cortical forelimb representation in the posterior sigmoid gyrus (areas 3a and 4) and laterally in the upper bank of the cruciate sulcus (area 4). The distribution pattern of cortical projections within the cuneate nucleus is however different from that within the gracile n. since (a) none of the lesioned cortical areas in the forelimb representation project to the clusters region, and (b) cortical projections terminate most densely in the base of the cuneate n., a medullary relay for Ia fibers from the forelimb. Sparse projections to the rostral region of the cuneate n. arise uniformly from all cytoarchitectonic areas of the forelimb representation. Cortical projections from SII are sparse and confined to the base and rostral region of the cuneate n.

The results provide further evidence for the origin of descending projections upon the DCN mainly from cortical regions related to movement control. Further, it is suggested that cortico‐DCN control is biased toward nuclear subdivisions related to cutaneous afferents from the hindlimb within the gracile n.‐nucleus Z complex but toward nuclear subdivisions related to deep and muscle afferents from the forelimb within the cuneate nucleus.
Restoration of visual cortical plasticity by local microperfusion of norepinephrine
Authors: Kasamatsu Takuji , Pettigrew John D. , Ary Marylouise
Published: January 2005

Using a newly developed technique of continuous microperfusion, we obtained further evidence in support of our hypothesis that the neocortical catecholamines (CAs), particularly norepinephrine (NE), are responsible for a high level of cortical plasticity. We used the visual cortical changes in ocular dominance which follow a brief monocular deprivation as a simple and reliable index of cortical plasticity. Local perfusion of kitten visual cortex with 1 mg/ml (4.0 mM) 6‐hydroxydopamine (6‐OHDA) prevented the effects of monocular deprivation in kittens, thus replicating the results we had obtained using intraventricular injections (Kasamatsu and Pettigrew, '76b, '79). Locally perfused NE at a concentration of 10−2 mg/ml (48.6 μM) restored visual cortical plasticity in animals which were no longer susceptible to brief monocular lid‐suture. These numbers refer to the concentration of solutions in the cannula/minipump system. The effective concentrations at the site of recording (about 2 mm away) are probably much lower than these. This effect of NE perfusion was seen both in kittens which had received prior 6‐OHDA treatment as well as in older animals which had outgrown the susceptible period. In the kittens we obtained a nearly complete shift in ocular dominance toward the open eye and in the older animals a decrease in binocularity was obtained. The changes were found only in the local region of visual cortex perfused with either NE or 6‐OHDA, while nearby cortical regions in the same animals were unaffected. There were no obvious changes in receptive field properties of individual neurons other than ocularity, and externally perfused NE did not itself reduce binocularity in normal animals: the effects of NE described above only occurred when the animal's visual experience was simultaneously altered. These results support the view that NE plays an important role in cortical plasticity.
Connections of areas 3b and 1 of the parietal somatosensory strip with the ventroposterior nucleus in the owl monkey (Aotus trivirgatus)
Authors: Lin Chia‐Sheng , Merzenich Michael M. , Sur Mriganka , Kaas Jon H.
Published: January 2005

Anatomical tracers were injected into electrophysiologically defined sites in somatosensory cortical Area 3b (SI proper) and Area I (posterior cutaneous field) of owl monkeys after these cortical subdivisions had been extensively explored in microelectrode mapping experiments. These mapping experiments revealed that both Areas 3b and 1 contain complete and separate representations of the body surface (Merzenich et al., '78). Restricted injections of the retrograde tracer, horseradish peroxidase (HRP), into either Area 3b or Area 1 labeled neurons within a band of cells in the ventroposterior nucleus (VP). The location of the labeled band in VP varied with the location of the injection site in both representations, and the labeled region of VP was overlapping for injections in corresponding body parts in the two representations. Neurons projecting to the hand and foot cortical representations were in architectonically identified subnuclei. Because injections into either Area 3b or Area 1 labeled over half of the neurons in the appropriate regions of VP, it appears that some neurons in VP project to both cortical representations. Finally, injections of HRP combined with the anterograde tracer, 3H‐proline, indicate that VP neurons are reciprocally interconnected with both Areas 3b and 1.
Somatostatin neurons and their projections in dog diencephalon
Authors: Hoffman Gloria E. , Hayes Terry A.
Published: January 2005

Immunocytochemical localization of the tetradecapeptide somatostain was performed in dog brain using the unlabeled antibody enzyme method. A large population of immunoreactive neurons was seen in the periventricular areas of the preoptic area and anterior hypothalamus. This field of neurons extended into the paraventricular nucleus, arcuate nucleus and tuberal areas surrounding the ventromedial nuclei. Fibers from the periventricular somatostatin cells projected into the median eminence, the third ventricle, the pars nervosa of the hypophysis, the organum vasculosum of the lamina terminalis, the medial preoptic area and the interstitial nucleus of the stria terminalis. The tuberal cells projected to the ventromedial nucleus and the cells of the arcuate nucleus terminated within the arcuate nucleus as well as within the contact zone of the median eminence. These findings suggest that somatostatin can exert hormonal effects via the vasculature or the cerebrospinal fluid, or transmitter and/or neuromodulatory effects via contacts with other neurons.
Sulfide silver stainability of a type of bouton in spinal cord motoneuron neuropil: An electron microscopic study with Timm's method for demonstration of heavy metals
Authors: Daa Schrøder Henrik
Published: January 2005

Spinal cord motoneuron neuropil (cervical and lumbar enlargements) has been studied at the ultrastructural level after fixation with glutaraldehyde and staining with uranyl acetate and lead citrate. Based on the appearance of the synaptic specializations, different types of boutons were identified and correlated with the classification of bouton types based on osmicated tissue.

The sulfide silver method for histochemical demonstration of heavy metals was applied to the same region. The localization of reaction products (silver grains) was predominantly in the terminals. Within the bouton, the grains were mainly in the specialized region of the synaptic contact, and the presynaptic network has also labelled, but to a lesser degree. All stained boutons had the same type of paramembranous synaptic specialization, but not all of the boutons with this type of specialization were stained. The stained boutons are interpreted as a fraction of the ‘F’ boutons.
Determinants of cell shape and orientation: A comparative Golgi analysis of cell‐axon interrelationships in the developing neocortex of normal and reeler mice
Authors: Lord M. C. Pinto , Caviness V. S.
Published: January 2005

Patterns of dendritic development in the neocortex of normal and reeler E15‐17 mouse embryos are studied in Golgi impregnations. Interactions between dendrites and axon‐rich strata appear to be critical determinants of dendritic morphology in both genotypes. Firstly, axon‐dendrite proximity appears to stimulate dendritic sprouting, elongation and branching. Secondly, the position of the axon‐rich strata with respect to the differentiating cell appears to determine the direction of dendritic growth and thereby the ultimate configuration of the dendritic arbor. With regard to specific cell configuration, a multipolar form is generated when the cell is embedded in an axon‐rich zone. A monopolar or bipolar configuration is achieved when the cell lies in the axon‐poor cortical plate and addresses an axon‐rich stratum with one or both radially extended migratory processes. Such variations in the configuration of neurons with polar dendritic systems may be observed uniquely in the mutant cortex be cause axon‐rich zones are stratified anomalously at multiple levels in the cortical plate. As a consequence, polar dendritic systems develop from either the superior, the inferior or both somatic poles of postmigratory cells. Pyramidal cells may, therefore, develop a normal upright or an abnormal “upside‐down” disposition. Regardless of the orientation of the polar dendritic system, the axon emerges from the inferior aspect of the cell suggesting that there has been no rotation of the original migratory axis of the cell.
Visual thalamocortical connections in sheep studied by means of the retrograde transport of Horseradish‐Peroxidase
Authors: Karamanlidis A. N. , Saigal R. P. , Giolli R. A. , Mangana O. , Michaloudi H.
Published: January 2005

In order to study the visual thalamocortical connections in the sheep, horseradish peroxidase (0.3‐0.5 μ1 of a 30% solution) has been injected in the gyri marginalis, ectomarginalis medius pars medialis, ectomarginalis medius pars lateralis and ectosylvius caudalis. The results show that: (1) the dorsal lateral geniculate nucleus (LGNd) projects to the former three gyri. Dorsal parts of the LGNd project to caudal areas, whereas its ventral parts project to rostral areas of these gyri; medial parts of the LGNd project to the gyrus ectomarginalis medius pars lateralis, while lateral parts project to the gyrus marginalis; (2) the medial interlaminar nucleus (MIN) or pars geniculata pulvinaris of Rose ('42b) projects to the caudal part of the gyrus marginalis and to the gyrus ectomarginalis medius pars lateralis; (3) the pulvinar proper of Rose (PUL) projects to the caudal part of the gyrus ectosylvius caudalis whereas the rostral part of this gyrus receives input from the medial geniculate body.

In relation to Rose's cytoarchitectonic study of the cortex of sheep (1942a) the present study has shown that the LGNd projects to both the area striata (gyrus marginalis + gyrus ectomarginalis medius pars medialis) and area occipitalis (gyrus ectomarginalis medius pars lateralis) of Rose, that the gyrus marginalis and the area occipitalis receive a second projection (from the MIN), and that the PUL projects beyond the area occipitalis to the area parietalis of Rose.
The retinothalamic pathways in Siamese cats
Authors: Cooper Michael Lee , Pettigrew John D.
Published: January 2005

By injecting one lateral geniculate nucleus with large amounts of horseradish peroxidase (HRP), we have determined the retinal distributions of contra‐ and ipsilaterally projecting retinothalamic ganglion cells in the Siamese cat. In accord with the data of others, we observe that large numbers of temporal ganglion cells, which normally send axons ipsilaterally, instead misproject to the contralateral thalamus. However, in contrast to the expectations raised by previous work, we do not find the Siamese defect to be a simple 20° shift of the naso‐temporal decussation line. Rather, there is intermingling of the crossed and uncrossed retinothalamic populations in the temporal retina, with a gradual increase in the proportion of ipsilaterally projecting ganglion cells as one moves temporally. Thus, the Siamese abnormality represents not only a temporal displacement of the retinothalamic decussation line, but also a smearing of the normally rather sharp division between regions of ipsilateral and contralateral projection.

Cell size measurements and anterograde transport of H3‐proline confirm the HRP finding and suggest differential effects of the Siamese abnormality according to ganglion cell class. In particular, it appears that the large ganglion cells tend to misproject to a greater degree than the rest of the retinothalamic population.
The striate projection zone in the superior temporal sulcus of Macaca mulatta: Location and topographic organization
Authors: Ungerleider Leslie G. , Mishkin Mortimer
Published: January 2005

In the rhesus monkey, the caudal portion of the superior temporal sulcus (STS) receives a direct projection from lateral striate cortex, the striate area representing central vision. The present study was undertaken to determine whether STS also receives a direct projection from areas of striate cortex representing peripheral vision, with the intent of defining the entire striate projection zone in STS as well as providing information regarding a possible topographic organization within this secondary visual area. A series of five rhesus monkeys was prepared with unilateral lesions of lateral, posterior, or medial striate cortex, such that, collectively, the lesions in the series included all of striate cortex with little or no invasion of prestriate cortex. The monkeys were sacrificed seven days after surgery and their brains were processed by the Fink‐Heimer procedure. An analysis of the distribution of terminal degeneration within STS indicated: (1) All areas of striate cortex project to a restricted region along the caudal portion of STS. The ventral limit of this region can be demarcated by an imaginary line connecting the ventral tips of the lunate and intraparietal sulci; from this limit the region extends dorsocaudally for approximately 12 mm to the point at which STS frequently bifurcates, sending one spur forward into the inferior parietal lobule. (2) Within this portion of STS there is an orderly mapping of the visual field; progression from central vision to the far periphery is represented by a progression down the posterior bank of STS and continuing along the entire floor, or insula‐like portion, of the sulcus. (3) Projections from striate cortex to STS terminate predominantly in layer IV and the deep part of layer III. (4) There is a distinctive pattern of myelination contained within the striate projection zone of STS. These anatomical findings concerning the striate projection zone of STS. in the rhesus monkey are remarkably similar to those that have been described for the middle temporal visual area (MT) in New World monkeys, and thus support earlier proposals that the two areas are homologous.
Projections of the nucleus of the basal optic root in the pigeon: An autoradiographic and horseradish peroxidase study
Authors: Brecha Nicholas , Karten H. J. , Hunt S. P.
Published: January 2005

The efferent projections of the nBOR complex, have been studied with both anterograde autoradiographic and retrograde horseradish peroxidase (HRP) techniques. The nBOR complex includes three distinct subdivisions: the nucleus of the basal optic root (nBOR), the nBOR pars dorsalis (nBORd) and the nBOR pars lateralis (nBORl).

Unilateral injections of 3H‐leucine or 3H‐proline/3H‐leucine mixtures into the nBOR complex have demonstrated prominent bilateral projections upon (1) the vestibulocerebellum, (2) the inferior olivary complex, (3) the oculomotor nuclear complex, (4) the nucleus interstitialis, contralateral projections upon (5) the contralateral nBOR complex and ipsilateral projections upon (6) a pretectal nucleus, the nucleus lentiformis mesencephali, pars magnocellularis.

Unilateral injections of HRP confined to folia IXc, d and paraflocculus of the cerebellum, the contralateral nBOR complex or the nucleus lentiformis mesencephali resulted in retrograde labeling of predominantly medium and large size cells within the entire nBOR complex. Unilateral injections of HRP within the inferior olive resulted in retrograde labeling of small, spindle‐shaped cells within nBOR and nBORd. Unilateral injections of the oculomotor complex which included the trochlear nucleus resulted in retrograde labeling of small cells within the ipsilateral nBORd and predominantly medium and large cells in the contralateral nBOR.

The displaced ganglion cells of the retina give rise to a prominent and distinct projection upon the nBOR complex (Karten et al., '77). The nBOR complex in turn projects upon the oculomotor nuclear complex, the nucleus interstitialis and the vestibulocerebellum, regions which have been implicated in oculomotor function. These findings strongly suggest that the displaced ganglion cells and the accessory optic system have a major influence upon oculomotor reflexes including eye and head movements.
Ontogeny of the retina and optic nerve in Xenopus laevis. II. Ontogeny of the optic fiber pattern in the retina
Authors: Grant Philip , Rubin Eric
Published: January 2005

The ontogeny of optic fiber patterns within the Xenopus laevis retina has been studied in silver‐stained serial sections and whole mounts. Ganglion cell axons (“pioneers”) appear much earlier than previously recognized, at Nieuwkoop‐Faber ('56) Stage 28. Fibers fasciculate into bundles as they arise in the retina and reach the chiasma by NF Stage 32. Because the retina grows in rings at its margins, ganglion cell axons differentiate at the periphery and join the nearest fiber bundles (fascicles) to reach the optical disc. A radial fascicle pattern develops by Stage X (Grant et al., '80) within the optic fiber layer of the retina and acts as a template of pathways that lead all later appearing fibers out of the retina. Since the retina grows asymmetrically along its dorso‐ventral axis, the fascicle pattern develops asymmetrically, with dorsal quadrant fascicles forming an arcuate pattern in contrast to shorter, thicker ventral quadrant fascicles.

The growth pattern of the retina and the “principle” of fiber following suggest that ‘positional information’ is acquired by ganglion cells according to a system of polar coordinates (MacDonald, '77). A radial distance “r” from the center is determined temporally by ganglion cell birthday and an angular value “TH” is given by the angular position of the fascicle followed by its axons to the optical disc. Wedges of ganglion cells send their axons into a common fascicle which retains its integrity as it leaves the retina at the optic disc. This pattern of optic fiber development suggests a model for retino‐topic ordering of the optic fiber projection in Xenopus, with the fascicle acting as the “pattern‐forming unit of connectivity.”.
Cells of origin of the afferent fibers to the median eminence in the rat
Authors: Wiegand S. J. , Price J. L.
Published: January 2005

The cell bodies of origin of axons terminating in the median eminence have been identified by retrograde axonal transport of horseradish peroxidase (HRP) or 125I‐wheat germ agglutinin (WGA). The tracers were injected into the median eminence by pressure and under direct visual control, using a ventral surgical approach. The retrogradely labeled cells are exclusively located within the hypothalamus. The most heavily labeled cells are parvocellular neurons in the arcuate nucleus, the periventricular area, the medial part of the paraventricular nucleus, and the rostral paraventricular nucleus; a few cells are also located in the rostral part of the preoptic area immediately lateral and dorsal to the organum vasculosum of the lamina terminalis (OVLT). Less heavily labeled cells are found in the magnocellular neurosecretory nuclei, including the lateral parts of the paraventricular and rostral paraventricular nuclei, the supraoptic nucleus, and the accessory magnocellular nuclei.

Retrogradely labeled cells are not found in the ventromedial hypothalamic nucleus, except for a few lightly labeled cells in the posterior division of the nucleus. However, if the injected tracer spreads into the arcuate nucleus, labeled cells are present throughout the ventromedial nucleus. Labeled cells are not found in other parts of the hypothalamus, including lateral and posterior portions of the preoptic area, the anterior hypothalamic area, and the suprachiasmatic nucleus, or in catecholaminergic cell groups of the midbrain, pons, and medulla.

Control injections of HRP into the posterior pituitary and the ventromedial nucleus produce patterns of cell labeling which are very distinct from that seen with injections into the median eminence. Following injections into the posterior pituitary, the cells of the magnocellular neurosecretory nuclei are all heavily labeled, but small cells in the parvocellular neuronal groups are not labeled. Direct injections into the ventromedial nucleus resulted in labeled cells in widespread parts of the hypothalamus, as well as in the bed nucleus of the stria terminalis and the lateral septum, in parts of the amygdaloid complex and the subiculum, and in several cell groups in the midbrain, pons, and medulla.
Afferents to oculomotor nuclei from area “y” in Macaca mulatta: An anterograde degeneration study
Authors: Stanton Gregory B.
Published: January 2005

Electrolytic lesions were placed in the dentate and interpositus nuclei of the monkey M. mulatta and the resulting anterograde degeneration was stained with the Wiitanen or Nauta‐Laidlaw techniques. Two of 19 lesions produced preterminal degeneration in the oculomotor nuclei. In both cases the lesions also damaged vestibular area “y” subjacent to the rostral pole of the dentate nucleus. The course and terminal distribution of anterograde degeneration to the oculomotor nuclei was the same in both cases. Degenerating fibers were found in lateral parts of the ipsilateral MLF, and preterminal degeneration was found in the ipsilateral abducens and trochlear nuclei and the dorsal subdivision of the oculomotor nucleus. Degenerating fibers were also traced from the crossed brachium conjunctivum to the contralateral paramedian subdivision of the oculomotor nucleus. These fibers appeared to course in dorsomedial parts of the brachium. Lesions of the dentate and interpositus nuclei which did not damage area “y” produced no anterograde axonal degeneration in the MLF or the oculomotor nerve nuclei. The results are discussed with regard to previous reports of cerebello‐oculomotor fibers originating in the dentate and interpositus nuclei. The results suggest that area “y”, rather than the cerebellar nuclei, projects principally to oculomotor neurons that control vertical eye movements.
Interactions among lumbar motoneurons on opposite sides of the frog spinal cord: Morphological and electrophysiological studies
Authors: Erulkar S. D. , Soller R. William
Published: January 2005

Light and electron microscopy have been used to study the projections of dendrites from motoneurons in lumbar segments of the spinal cord of the frog following administration of horseradish peroxidase to cut ventral roots. Processes originating from motoneurons crossed to the opposite side of the spinal cord via the anterior commissure and made contact with dendrites and motoneuronal somata. Typically, in segments 6 to 8 the crossing dendrites showed irregular enlargements in diameter.

Electrophysiological recordings were obtained both extracellularly from ventral roots and intracellularly from motoneuronal somata. In Ringer's solution containing 1 mM calcium, stimulation of a lumbar ventral root elicited population responses with early and late components in the ventral root of the opposite side of the same segment. Only the early, short latency component remained in calcium deficient Ringer's solution. In calcium‐containing Ringer's solution, intracellular recording from an antidromically activated motoneuron showed an action potential with a short latency; this response was followed by excitatory postsynaptic potentials (epsps) from which action potentials could be generated. Contralateral ventral root stimulation also elicited in the same motoneuron a short latency action potential that was rarely followed by epsps. The short latency responses, that were elicited by stimulation of ventral roots of either side persisted in calcium‐deficient Ringer's solution, but the epsps were abolished. Contralaterally elicited short latency responses were eliminated by section of the anterior commissure.

We believe that electrically mediated crossed interactions among lumbar motoneurons may serve as a means of coordinating muscle groups of opposite sides that are used in movements that require bilateral synchronization, such as jumping and swimming.
Supraependymal macrophages of third ventricle of hamster: Morphological, functional and histochemical characterization in situ and in culture
Authors: Bleier Ruth , Albrecht Ralph
Published: January 2005

Supraependymal cells (SECs) of the young hamster's third ventricle have been examined by scanning and transmission electron microscopy. Of special interest were cells with the surface morphology and ultrastructure of macrophages, which were found in largest numbers in 12–15‐day‐old females and males. In the ciliated areas SECs are generally smooth and rounded; in nonciliated areas, they frequently have surface ruffles, blebs and microprocesses. SECs were frequently seen to be dividing or fusing. The macrophage‐like cells are characterized by prominent Golgi zones and numerous large vacuoles, and frequently contain inclusions in their cytoplasm which resemble intraventricular cell processes, cytoplasmic protrusions from ependymal cells and cellular debris. We have demonstrated that supraependymal macrophage‐like cells phagocytose latex beads injected into the ventricles of the brain.

Supraependymal cells from 12‐day‐old hamsters were grown in tissue culture. Phagocytic, cytochemical and surface ultrastructural studies were then done sequentially on the same population of cells. These studies revealed the cells to be actively phagocytic as well as strongly esterase positive and peroxidase negative, consistent with their classification in the macrophage/monocyte category. The surface ruffles, ridges and microprocesses were also characteristic of the SECs seen in situ with scanning electron microscopy and of the macrophages cultured from the peritoneum and peripheral blood of the same hamsters.

On the basis of cellular morphology, cytochemical staining characteristics and functional response to exposure to foreign particles both in situ and in cell culture, we have demonstrated that supraependymal cells of the third ventricle of the hamster are phagocytes that resemble cells of the macrophage/monocyte line. It is suggested that they constitute a resident macrophage system of the ventricles of the brain.
Organization of the motoneurons innervating the pelvic muscles of the male rat
Authors: Schrøder Henrik Daa
Published: January 2005

The cytoarchitecture of the motoneuron pool of the male rat was studied at the lumbo‐sacral transition area, particularly in L6. In the latter segment a dorso‐medial (DM), ventral (V), dorso‐lateral (DL), and retrodorso‐lateral group (RDL) could be defined. The DL group was associated with a prominent longitudinal dendrite bundle and the DM group with smaller transverse bundles. Morever, close soma‐somatic apposition was found between neurons in these columns.

Because L6gives rise to n. pudendus and contributes to n. ischiadicus, horseradish peroxidase (HRP) was applied to the cut n. ischiadicus and in other experiments injected into the pelvic muscles. Neurons in RDL were labeled following exposure of n. ischiadicus to HRP. Injections in m. levator ani resulted in labeled neurons in the V group, mainly below L6. Injections in m. sphincter urethrae resulted in labeled neurons in the DL group as well as neurons immediately cranial to this column. Musculus ischiocavernosus injections resulted in transport of HRP to neurons in the DL group, primarily in its medial part, and to more cranially located neurons. In addition, some neurons in the V group in L6were labeled. Following injections in m. bulbocavernosus and m. sphincter ani, labeled neurons were found primarily in the DM group, and to a lesser extent in the V group.

Histochemical investigations with staining methods for the localization of acetyl cholinesterase (AChE) and heavy metals (the Timm method) demonstrated that part of the neuropil of DL and of DM were different from the rest of the motoneuron neuropil. In the DL group the area with the diverging staining patterns corresponded to the region of the dendrite bundle. The experimental data indicated and the ultrastructural studies demonstrated that the histochemical differences could be correlated with differences in the composition of the populations of boutons.

The comparison of the cytoarchitectural and histochemical data with the results obtained by the aid of the retrograde HRP tracing technique established that mm. sphincter urethrae, ischiocavernosus, bulbocavernosus, and sphincter ani were each innervated by two populations of neurons that were situated in separate areas which had different histochemical properties, and which thus probably have different compositions of their afferent inputs.

The daulity in the motoneuron pool that innervates the pelvic muscles might be a reflection of the dual influence on these muscles. As all other striated muscles the pelvic muscles are under voluntary control. However, they are also tightly linked to the function of the pelvic viscera and thus under influence of the autonomic nervous system.
Reciprocal synapses between hair cells and first order afferent dendrites in the crista ampullaris of the bullfrog
Authors: Dunn Robert F.
Published: January 2005

Reciprocal synapses were found between afferent dendrites and hair cells of the crista ampullaris in the vestibular system of the bullfrog. The reciprocal synapse consisted of two components forming a dual synaptic complex between a single hair cell and a single dendritic process such that the receptor cell was both presynaptic and postsynaptic to the afferent dendrite. The first component, a typical afferent synaptic complex, consisted of a synaptic sphere surrounded by a single layer of clear vesicles, and was located within the hair cell. In addition, 3–4 arciform structures were located between the sphere and the plasma membrane of the hair cell. The second component of the reciprocal synapse, located approximately 1.5 μm from the first, was recognized by a localized accumulation of clear membrane vesicles within the neuronal process and a short membrane profile within the cytoplasm of the adjacent hair cell. Additional characteristic features included continuity of the arciform structures with the plasma membrane of the hair cell, and within the neuronal process, a greatly reduced number of vesicles when compared with the efferent axonal terminal. This latter was important in distinguishing a first‐order afferent dendritic process from an efferent neuronal process. The possible functional significance of these reciprocal synapses has been discussed in terms of the two components having an opposite effect on the membrane polarization of the hair cell.
Goldfish retinotectal system: Continuing development and synaptogenesis
Authors: Marotte L. R.
Published: January 2005

The development of the retina and tectum in goldfish was studied using light and electron microscopy. Soon after hatching the retina is well differentiated in that all the layers of the adult retina are present. The tectum at this time lacks the characteristic layered structure of the adult and innervation in the stratum opticum is extremely sparse, being confined mainly to the rostral region. The retina grows rapidly and retinal layers increase in thickness. This continues into adulthood. Optic innervation of the tectum increases and in fish 19 mm in body length the adult pattern of layers seen by silver staining and by electron microscopy is recognizable. At this time the optic nerve contains large number of unmyelinated axons. The thickness of tectal layers continues to increase over the entire size range of fish studied, well into adulthood. Synaptic densities in the layer of optic termination also change. Density falls in the rostral region as the fish increase in size. In the caudal region there is an initial decrease followed by a small increase. Total numbers of synapses in the main layer of optic termination increase both rostrally and caudally over the entire range of fish studied. Optic and nonoptic fibers contribute to this. The optic nerve at this stage is almost completely myelinated. The continuing growth of both the retina and tectum, including synaptogenesis, may provide a basis for the remarkable regeneration and plasticity shown by this system.
Cell responses evoked by tooth pulp stimulation above the marginal layer of the cat's trigeminal nucleus caudalis
Authors: Dawson N. J. , Hellon R. F. , Hubbard J. I.
Published: January 2005

In cats anesthetized with urethane, all‐or‐nothing, synaptically evoked recordings were made from 80 separate units in the descending spinal tract of the trigeminal nerve above the left trigeminal nucleus caudalis, at depths not exceeding 50 μm from the surface of the medulla. The units were excited by the left upper (21), left lower (25), either (28), or only on simultaneous stimulation of both (six) canine tooth pulps. There was no somototopic distribution.

The latency of responses ranged from 4 to 82 msec. For the group of 28 units excited by upper and lower tooth pulps, there was close matching of response latencies from the two teeth.

An abrupt decrease in latency upon increasing stimulation strength (“jumping”), and a gradual increase in latency during repetitive stimulation at a frequency between 1 and 20 Hz (“drifting”) was characteristic of most, but not all, responses. Units evoked by stimulation of the inferior dental or infraorbital nerves had similar characteristics.

Stimulation of a tooth pulp at threshold for a particular unit was used to test the excitability of that unit after suprathreshold stimulation of the same or a different canine tooth pulp. Stimulation of the upper left canine tooth pulp was generally only facilitatory, while stimulation of the lower left canine tooth pulp was initially facilitatory and later inhibitory. Stimulation of the upper or lower right canine tooth pulps did not excite but could inhibit units excited by the left canine tooth pulps.

There was a significant correlation between the frequency at which a unit would follow repetitive stimulation and the duration of the inhibition generated by the first of a pair of stimuli. Long inhibition was associated with poor frequency following.
Corticocortical neurons projecting to the medial and lateral banks of the middle suprasylvian sulcus in the cat: An experimental study with the horseradish peroxidase method
Authors: Kawamura Koki , Naito Jumpei
Published: January 2005

Corticocortical afferents to both cortical walls of the cat middle suprasylvian sulcus (MSs area) were investigated by means of retrograde axonal transport of horseradish peroxidase (HRP).

The visual cortex (V‐I and V–II) projects to the medial wall of the MSs, the projection from V–II being heavier. The auditory cortex (A‐I, A‐II, and Ep), including cortical walls of the dorsal part of the anterior and posterior ectosylvian sulci, sends fibers to the lateral wall of the MSs. Connections from the first auditory area (A‐I) are heavier than from the second (A‐II). In the rostral part of the MSs, both the medial and lateral walls receive fibers from the somatosensory (S‐I and S‐II) cortex. A larger number of association fibers appear to arise from S‐II than S‐I. Although the MSs as a whole apparently receives various kinds of sensory inputs, there seems to be a parcellation of the MSs area such that the areas receiving cortical association fibers from the visual, auditory, or somatosensory cortical areas also receive thalamic projections from those parts of the thalamus receiving sensory connections of the same modality.

The cells of origin of the association fibers were mostly pyramidal, the majority located in layer III (e.g., 80% in the visual cortex and 74% in the auditory cortex), some in layer V, and a few in other layers. Most (76–79%) of the labeled cell bodies were of 15–20 μm diameter. Smaller (8–15 μm) and larger (20–26 μm) cells constituted less than 15% in each case. The mean diameters were 17.0 ± 2.8 μm (SD) in the visual cortex and 17.7 ± 3.2 μm (SD) in the auditory cortex.
Growth of a limb spinal nerve: An ultrastructural study
Authors: Prestige M. C. , Wilson Margaret A.
Published: January 2005

A quantitative study of the delivery of nerve fibers to the developing limb has been made. Electron microscope (EM) sections of SN 9 in Xenopus were taken at close intervals between dorsal root ganglion and limb‐bud. Numbers and types of axons in each section were counted. Counts declined steadily with distance from the ganglion towards the base of the limb. This is largely due to some axons not having grown the full distance at the time of fixation. The slope corresponded with an outgrowth velocity of 0.5 mm a day, without branching. Distally, at stages 50 and 51, but not at stages 49 or 54, the decline was reversed, and a peak of axon number was found. This is strong evidence for axon branching in this region. Since this took place at least one stage before SN 9 bifurcated, and since the bifurcation was distal to the branching when it did appear, it is suggested that axon branching at a nerve bifurcation might be part of a trial‐and‐error mechanism for pathway selection. Observations were made on the sheath surrounding the nerve, and on its assembly. Initially, axons grow out naked and not parallel; Schwann cells migrate after the growing front. Processes of these cells collect individual axons, and transfer them inwards to form the primitive parallel fibre bundle, enclosed by a family of Schwann cells. Myelination later occurs in a similar manner: Schwann‐cell processes extend into a bundle of naked axons and eventually encircle a single transitional axon, with one Schwann cell eventually containing many such axons. Finally comes the stage of promyelin, in which a single Schwann cell encircles a single axon. Myelin whorls are then formed from this complex.