bluuebunny/crossref_metadata_2025_split huggingface dataset:
Organization of trigeminothalamic tracts and other thalamic afferent systems of the brainstem in the rat: Presence of gelatinosa neurons with thalamic connections
Authors: Fukushima Takanori , Kerr Frederick W. L. 
Published: January 2005

AbstractThalamic projections from trigeminal and certain other nuclei of the brainstem of the rat have been investigated using the technique of retrograde transport of horseradish peroxidase (HRP).The pattern of trigeminothalamic projections is very specifically related to the individual subnuclei of the complex. The Main Sensory Nucleus (MSN) provides profuse crossed connections to the ventrobasal thalamus (VB); these arise exclusively from medium and small‐sized neurons, but never from the large cells. In addition to these crossed connections, a small ipsilateral dorsal trigeminothalamic tract arises from the dorsal third of the most rostral part of the MSN; this is the only ipsilateral connection to VB found in the trigeminal complex.Subnucleus Oralis has no projections to the thalamus; it is suggested that it may be concerned primarily with reflex activation of the facial nucleus, with which it is co‐extensive in the rostro‐caudal axis.Subnucleus Interpolaris has a well‐defined crossed projection of moderate size which arises from the large, medium and some of the small neurons.Subnucleus Caudalis has a sparse output to the thalamus and differs in its projections from rostral to caudal. At the most rostral level, all layers (marginal, transitional gelatinosa and magnocellularis) contain neurons which project to the thalamus; particularly conspicuous in this respect are the marginal neurons, most of which are strongly labelled. The presence of gelatinosa neurons projecting to the thalamus emphasizes a point made in earlier reports, that these neurons do not form an homogeneous population. At caudal levels, the marginal neurons are the major source of thalamic projections, while connections to the thalamus form deeper lying neurons are infrequent.With a single exception, the medullary reticular nuclei contained no neurons with thalamic connections; a small number of reticulo‐thalamic neurons were found in the ventral pontine area.Marked labelling of the medial cuneate nucleus and moderate labelling of the gracilis and lateral cuneate nuclei occurred contralaterally to the injection site. A small number of medial cuneate and gracile neurons project to the ipsilateral thalamus. Projections from the solitary nucleus were always ipsilateral.The boundaries of individual subnuclei of the lateral sensory trigeminal complex in the rat have been redefined on the basis of cytological criteria; these are in good accord with the corresponding thalamic projection patterns.
Evidence for a critical period of neuronal trophism late in the development of the chick visual system
Authors: Ostrach Louis H. , Mathers Lawrence H. 
Published: January 2005

AbstractChick embryos and young hatchling chicks have undergone unilateral retinal ablation and the brains were subsequently prepared for modified Fink‐Heimer staining to detect degenerating axoplasm. Additional animals have been injected with tritiated proline or combinations of tritiated proline and tritiated fucose. In examining the patterns of degeneration and labelling produced, it appears that during the stage 40–44 period of embryonic life there is a critical period during which damage to retinal axons produces degeneration not only in the direct targets of the optic tract (primary centers), but also in a number of nuclei not projected to by the optic tract (secondary centers). By examining various survival times following retinal ablation and animals of varying embryonic and post‐hatch age, we have concluded that retinal ablation during the critical period causes a rapid and fulminant degeneration in the secondary centers because they are all targets of the projection from the optic tectum, itself a prime target of the optic projection. Presumably, interruption of the retino‐tectal projection during the critical period disrupts some as yet undefined trophic relationship between these two sets of neurons. Our studies show that the observed degenerative reaction in the secondary centers occurs most strongly in chick embryos between stage 40 and stage 44. This period coincides with the onset of synaptogenesis in the retino‐tectal system (Rager, '76a,b). We therefore hypothesize that during this period some property or influence is passing from the retinal to the tectal neurons such that interruption of this process leads to death of the tectal neurons.
Proliferative and migratory activity of glial cells in the partially deafferented hippocampus
Authors: Gall Christine , Rose Greg , Lynch Gary 
Published: January 2005

AbstractThe proliferative response of the glial cell population of the adult rat hippocampus deafferented by unilateral lesion of the entorhinal cortex was studied using 3H‐thymidine autoradiography. Two experimental paradigms were used, involving: (1) intraventricular 3H‐thymidine injection at a number of post‐lesion intervals with sacrifice six hours later and (2) intraventricular injection at 30 hours post‐lesion with sacrifice at 6, 96, or 192 hours later.The first increase in the number of labeled glial cells was obtained at 20 hours post‐lesion and was confined to areas of degenerating axons. By 30 hours a large and uniformly dense proliferative response was observed throughout the ipsilateral, and medial aspects of the contralateral, hippocampus encompassing both deafferented and intact regions. Cell division continued through 50 and 65 hours post‐lesion particularly in directly deafferented regions, but diminished to control levels by 80 hours. Although oligodendroglia and astrocyte‐like cells were sometimes found to have incorporated the label the most common proliferative element within the hippocampus corresponded to previous light microscopic descriptions of “microglial” cells. The experiments using thymidine injection given at the peak proliferative period followed by survival periods of varying lengths indicated that a progressive redistribution of labeled nuclei occurred resulting in an accumulation of labeled cells in the zones of deafferentation. Multiple division of cells within these areas as well as the migration of nuclei from non‐deafferented regions was found to contribute to this effect. The possible involvement of glial proliferation with other morphological effects of deafferentation, including the sprouting response of intact afferents, is discussed.
Evidence for two organizational plans within the somatic sensory‐motor cortex of the rat
Authors: Donoghue John P. , Kerman Karen L. , Ebner Ford F. 
Published: January 2005

AbstractPrevious electrophysiological mapping of somatic sensory (SI) and motor (MI) cortex in the rat has shown that these functional regions are completely overlapping in the hindlimb (HL) area. Partially separate in the forelimb area, and completel separate in the face area. The present studies were designed to show how the sensory and motor thalamic relay nuclei priject onto separate or overlapping subdivisions of SI and MI cortex. The experimental sequence involved physiological mapping of one subdivision of SI or MI cortex and then injecting horseradish peroxidase (HRP) as a retrograde cell marker to back‐fill the thalamic neurons that project to the identified area of cortex. The central issue was to compare the projection of the lemniscal‐recipient ventrobasal nucleus (VB) and the cerebellar‐recipient ventrolateral nucleus (VL) to the hindlimb and face subdivision of SI and MI cortex. Various authors, however have divided the ventral nucleus differently using Nisslstained transverse sections through the thalamus. Therefore, tritiated amino acids were also injected into the deep cerebellar nuclei and the distribution of cerebellar fiber terminals in the ventral nucleus was used as another criterion to identify the border between VB and VL.Following HRP injections in physiologically identified HL cortex, labelled neurons were present in both VB an VL. Face area SI injections back‐filled cells in VB (but not VL), while face area MI injections back‐filled cells in VL (but not VB). Neurons in the intralminar nuclei and the posterior nuclear complex were labelled after all injections.These results demonstrate that SI and MI cortex in the rat shows a combiation of overlapping and separated plans of organization. Other species, in which both the anatomical an physiological information is available, show other organizational plans. In the Virginia opssum, for example, overlap is present in all subregions of SI and MI cortex. While the Rhesus monkey shows separation of these areas. The result suggest that different mammals have evolved different degrees of separation of SI and MI cortex. Our results predict that in every case where there is evidence of sensory and motor overlap, there will be anatomical convergence of VB and VL projections to htat single cortical area.
Ultrastructural development of Rohon‐Beard neurons: Loss of intramitochondrial granules parallels loss of calcium action potentials
Authors: Lamborghini Janet E. , Revenaugh Marsha , Spitzer Nicholas C. 
Published: January 2005

AbstractWe have examined the ultrastructure of the cell body of a vertebrate spinal neuron, the Rohon‐Beard cell of Xenopus laevis, at four stages during its development (Nieuwkoop and Faber stages: 22, 29/30, 37/38 and 42). At this time it has attained its electrical excitability and the action potential mechanism in the cell body is maturing through a sequence of stages in which the inward current is carried by Ca++ (stages 20–25), later by Ca++ and Na+ (stages 25–40), and finally by Na+ (stages 40–51) (Spitzer and Baccaglini, '976; Baccaglini and Spitzer, '77). There is a change in the abundance and distribution of the organelles in the perikaryon during this period, characteristic of other developing neurons. Mitochondria and Golgi apparatus become localized progressively more in the interior of the cells, and rough endoplasmic reticulum progressively more to the periphery where it often appears in orderly tiers parallel to the plasma membrane. The mitochondria contain dense intramitochondrial granules which are known in other cells to contain concentrations of divalent cations. The number of granules declines over the course of the developmental period studied.The presence of the intramitochondrial granules was examined quantitatively because electrophysiological data indicate that the amount of Ca++ entering the cells in early stages should raise the internal Ca++ concentration by several orders of magnitude, and that Ca++ is rapidly sequestered (Baccaglini and Spitzer, '77). A minimum of 200 mitochondrial profiles from at least four Rohon‐Beard cells were scored for the presence of dense intramitochondrial granules at each stage studied. In stage 22 Rohon‐Beard cells 75 ± 5% (mean ± SD, n = 4) of the mitochondrial profiles scored contained granules; in stage 29/30, 56 ± 10% (n = 7); in stage 37/38, 3 ± 3% (n = 5); and in stage 42, 0.5 ± 0.25% (n = 4). Therefore, dense intramitochondrial granules, an indication of calcium accumulation in mitochondria, decrease in parallel with the loss of the Ca++ component of the inward current of the action potential in Rohon‐Beard neurons.
Efferent projections from temperature sensitive recording loci within the marginal zone of the nucleus caudalis of the spinal trigeminal complex in the cat
Authors: Burton H. , Craig A. D. , Poulos D. A. , Molt J. T. 
Published: January 2005

AbstractThe efferent projections from nucleus caudalis of the spinal trigeminal complex in cats were studied with retrograde and anterograde axonal transport techniques combined with localization of recording sites in the thalamus and marginal zone of nucleus caudalis to innocuous skin cooling. Results showed brainstem projections from nucleus caudalis to rostral levels of the spinal trigeminal complex, to the ventral division of the principal trigeminal nucleus, the parabrachial nucleus, cranial motor nuclei 7 and 12, solitary complex, contralateral dorsal inferior olivary nucleus, portions of the lateral reticular formation, upper cervical spinal dorsal horn and, lateral cervical nucleus. Projections to the thalamus included: a dorsomedial region of VPM (bilaterally) and to the main part of VPM and PO contralaterally. Neuronal activity was recorded in the dorsomedial region of VPM to cooling the ipsilateral tongue. HRP injections in this thalamic region retrogradely labeled marginal neurons in nucleus caudalis. These results show that marginal neurons of nucleus caudalis provide a trigeminal equivalent of spinothalamic projections to the ventroposterior nucleus in cats.
Horizontal ampullary nerve fiber projections to the crista angustarum in the crista ampullaris
Authors: Dunn Robert F. 
Published: January 2005

AbstractIndividual nerve fibers were traced on consecutive serial 1‐μm‐thick cross‐sections to determine their position of origin within the horizontal ampullary nerve trunk (HANT) and the site at which they penetrated the basilar lamina of the horizontal crista in the guitarfish, Rhinobatos productus. Of the 132 fibers successfully traced, 87.1% followed an anatomical projection pattern consistent with the dynamic response characteristics of the nerve fibers. That projection pattern was: from the peripheral HANT region to the ipsilateral slope; from the central HANT region to the crest; and from the intermediate HANT region both to the ipsilateral slope and the crest of the horizontal crista. The 12.9% of “error” fibers not following this projection pattern were also consistent with the functional neurophysiological data. The terms crista bulbus and crista angustarum were introduced to designate specific anatomical regions of the dumb‐bell shaped crista ampullaris.
“Extra” optic fibers exclude normal fibers from tectal regions in goldfish
Authors: Meyer Ronald L. 
Published: January 2005

AbstractA small group of selected optic fibers were surgically deflected from one tectum into the other, thus creating a novel additional projection originating from a small area of ipsilateral retina. The normal fibers to this “recipient” tectum were also severed so that both the deflected and the normal fibers regrew into this tectum at about the same time. The reinnervation pattern was analyzed by autoradiography and electrophysiologic mapping. Both techniques showed that the deflected fibers and the “normal” fibers failed to intermix. The deflected fibers typically formed several well‐defined patches of innervation in roughly the appropriate region of denervated recipient tectum. The normal fibers filled in the remaining uninnervated tectal areas and were completely or nearly completely excluded from the patches occupied by the deflected fibers. This segregation was often quite sharp having an apparent average overlap less than 25–50 μm. The electrophysiology indicated that the projections of both deflected and normal fibers were retinotopically organized but that the mapping by the normal fibers was compressed. This compression, an apparent consequence of being squeezed onto a smaller than normal region of tectum, was similar to that previously observed following ablations of part of the tectum. The negligible surgical damage in the present experiment, however, excludes the kind of cytochemical reorganization previously suggested to produce compression. The findings also provide evidence for a competitive type of interaction between optic fibers.
Proprioceptive reflex connections of head musculature and the mesencephalic trigeminal nucleus in the carp
Authors: Luiten P. G. M. 
Published: January 2005

AbstractThe location of the sensory cells concerned with the proprioception of respiratory and extraocular musculature in the carp was studied by retrograde transport of horseradish peroxidase. Sensory cell labeling after intramuscular HRP injection was exclusively found in the trigeminal‐facial‐anterior lateral line ganglion complex. The muscles innervated by the trigeminal system are represented in the more rostral ganglion areas, the muscles innervated by the facial system in the more caudal ganglion parts. Nearly all labeled cells were situated on the ipsilateral side. Sensory cells labeled after extraocular muscle injection were also found all over the V‐VII ganglion, however, to a considerable degree also on the contralateral side. All muscle injections failed to give mesencephalic trigeminal cell labeling. The results of intranerve HRP injections in peripheral trigeminal nerve branches strongly suggests a perioral mechanoreceptive function for the mes.V neurons. A bisynaptic proprioceptive reflex model is described for respiratory musculature consisting of a sensory cranial ganglion component connected to the descending trigeminal nucleus, which on its turn links the proprioceptive ganglion cells to the trigeminal and facial motorneurons. Monosynaptic proprioceptive reflex circuits are discussed on neurophysiological grounds.
The cerebellar projection of the vestibular nerve in the cat
Authors: Korte Gary E. , Mugnaini Enrico 
Published: January 2005

AbstractThe projection of the vestibular nerve to the cerebellum of the cat was examined with silver degeneration methods after complete lesions of the vestibular ganglion. The majority of the primary vestibular afferents were traced to the cortex of the ipsilateral nodulus and uvula, relatively fewer entering the ipsilateral flocculus. Fibers were not traced to the paraflocculus, lingula or lateral cerebellar nucleus. A sparse projection to the ipsilateral fastigial nucleus may exist, but it remains equivocal until confirmed with additional methods. Light microscopic examination of plastic sections confirmed these observations and showed further details of the organization of the primary vestibular projection to the nodulus and uvula. These results show that the region of the cerebellum densely innervated by primary vestibular afferents is smaller than previously believed.
The origin, distribution and synaptic relationships of substance P axons in rat spinal cord
Authors: Barber Robert P. , Vaughn James E. , Randall Slemmon J. , Salvaterra Paul M. , Roberts Eugene , Leeman Susan E. 
Published: January 2005

AbstractSubstance P positive (SP+) immunoperoxidase reaction product has been localized in light and electron microscopic preparations of rat lumbar spinal cord using an immunocytochemical method. SP+ reaction product was found to be highly concentrated in dorsal horn laminae I, II, portions of III, Lissauer's tract, s small nucleus in the dorsal part of the lateral funiculus, and in a longitudinal bundle of fibers just ventral to the central canal. Moderate accumulations of SP+ reaction product were observed in portions of laminae III‐V, lamina X and in a narrow zone bordering fasciculus gracilis which expanded in its ventral aspect to include nucleus cornucommissuralis dorsalis and nucleus dorsalis. Remaining portions of the spinal gray matter exhibited extremely sparse staining. Light microscopic observations indicated that SP+ product was concentrated in fine axons and collaterals, which displayed densely‐stained varicosities and terminal puncta. These varicosities and puncta were closely associated with neurons and blood vessels.Dorsal rhizotomy produced a marked reduction in the number of SP+ fibers in Lissauer's tract, dorsal horn laminae I‐III and the nucleus of the dorsolateral funiculus. However, dorsal root fibers were not the only source of SP+ structures in these regions since some SP+ fibers remained following dorsal root resections. In addition, this residual population of SP+ fibers did not appear to be altered by a combination of dorsal rhizotomy and ipsilateral transverse hemisection of the spinal cord. In conjunction with the results of other investigators, this finding suggests that the SP+ fibers which remain after dorsal rhizotomy are derived from local circuit interneurons of the spinal cord.Electron microscopic observations revealed that certain axons and axon terminals contained concentrations of SP+ product which were associated with large, granular vesicles, while lesser amounts were in the terminal cytoplasm and associated with the exterior surfaces of small, agranular synaptic vesicles. SP+ terminals formed axodendritic, axosomatic and axoaxonal synapses, but the deposition of SP+ product often was not concentrated precisely at the “active sites” of these synaptic junctions. Some SP+ axons also made rudimentary contacts with astrocytic processes including those surrounding blood vessels. Since many of the SP+ terminals are similar in several respects to neuroendocrine terminals, it is possible that substance P may be released at several different types of non‐synaptic sites as well as at conventional synaptic junctions. Thus our findings suggest that substance P could participate in a variety of neural functions ranging from those which are limited to synaptic junctions to those which are more generally distributed via an involvement of axonal plexuses as well as the glial, vascular and ventricular systems.
The organization of the second somatosensory area (SmII) of the grey squirrel
Authors: Nelson R. J. , Sur M. , Kaas J. H. 
Published: January 2005

AbstractMicroelectrode mapping methods were used to determine the organization of the second somatosensory representation, SmII, in grey squirrels. A systematic representation of the contralateral body surface was found in lateral parietal cortex adjoining the first somatosensory representation, SmI (Sur et al., '78a). The representation of the body in SmII was found to be much less distorted than in SmI. Under our recording conditions, almost all recording sites were activated from strictly contralateral body locations. The most important finding was that the basic orientation of the body representation in SmIi is “erect” rather than “inverted.” This orientation allows SmII and SmI to be adjoined along a common border representing the top of the head and face. This type of border has been called congruent (Allman and Kaas, '75; Kaas, '77), and it may have significance in the development of sensory representations.
The environment of axonal migration in the developing chick retina: A scanning electron microscopic (SEM) study
Authors: Suburo Angela , Carri Nestor , Adler Ruben 
Published: January 2005

AbstractWe have made a SEM study of the basal intercellular spaces of the retina in chick embryos of different developmental stages. Since this is the environment where optic axons grow, the structural characteristics of this region might play some role in the orientation of axonal migration towards the choroid fissure. The basal region of undifferentiated retinas is formed by the vitreal expansions of neuroepithelial cells. In pre‐axonal stages, the intercellular spaces between these expansions do not show any preferential orientation towards the fissure. The growth cones of ganglion cell axons appear in an apicobasal direction and turn towards the fissure immediately beneath the vitreal surface. Fasciculation is an early event during development and, in the more advanced stages, the vitreal expansions from retinal cells are placed in rows following the same orientation as the axon bundles. These observations are discussed in relationship to current hypotheses on axonal migration and orientation.