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Biomedical subjects

R W Rhoades

Publications and source records attributed to R W Rhoades.

At least 163 records · Page 9Linked to original sources
PubMed1984

Organization of the infraorbital nerve in rat: a quantitative electron microscopic study.

The normal organization of the rat's infraorbital (IO) nerve was studied using conventional electron microscopic (EM) methods. Just caudal to the infraorbital foramen, at the level of the anterior superior alveolar foramen, the nerve was composed of 18-25 fascicles which ranged from 575 to 87,923 micron2 in cross-sectional area. Complete axon counts from thin sections taken at this level demonstrated that the IO nerve contained an average of 19,740 (S.D. = 2054) myelinated and 13,319 (S.D. = 1159) unmyelinated axons. The average diameter (including the myelin sheath) for medullated fibers was 4.42 micron (S.D. = 1.76) and that for unmyelinated axons was 0.60 micron (S.D. = 0.16). The fiber diameter distributions for both myelinated and unmyelinated axons were essentially unimodal.

Animals↗
PubMed1984

A comparison of visual callosal organization in normal, bilaterally enucleated and congenitally anophthalmic mice.

Visual callosal connections were examined using the horseradish peroxidase (HRP) technique in normal, neonatal and adult C57BL mice, and in adults of this strain which were bilaterally enucleated within 12 h of birth. In addition, callosal connections were also delineated in two strains of congenitally anophthalmic mice, ZRDCT-an and orJ. Material from 129/J mice served as controls for the latter strain. In normal adults anterograde labelling and HRP labelled cells were visible primarily at the borders of area 17. In the 17-18a border region, labelled neurons were located primarily in layers II-III and V. In the medial striate cortex, a small number of labelled cells were present, primarily in lamina VI. Anterograde HRP labelling in the normal adults was also located primarily at the borders of area 17. At the 17-18a border, it was very heavy in layers V and VI, somewhat lighter in layer IV, and fairly dense in layers II-III and the lower half of lamina I. Labelling indicative of anterograde HRP transport was also visible in lowermost lamina V and layer VI across the entire mediolateral extent of area 17. In normals injected with HRP on postnatal day 2 and perfused 24 h later, callosal neurons were distributed throughout the dorsal posterior neocortex, primarily in layers V and VI. Only a very few labelled cells were visible in the supragranular laminae. In adult mice blinded at birth, the zone of callosal cells and terminals extended much further into area 17 than in normals, but aside from the anterograde labelling in layer VI and lowermost lamina V, the medial one-third of the striate cortex was still for the most part devoid of callosal cells and fibers. The laminar distributions of the labelled cells and anterograde transport in the blinded animals were the same as in the normal mice. In both strains of anophthalmic mice the pattern of callosal connections was unlike that in either the normals or neonatal enucleates. In the caudal "visual" cortex, callosal cells and anterograde transport indicative of terminal labelling were visible primarily in the 17-18a border area. Rostrally, however, they were both distributed in multiple (two-three) patches within area 17. Serial reconstructions demonstrated that these patches tended to be aligned in stripes which ran parallel to the 17-18a border. One of these was always located at the 17-18a border, and here the laminar distribution of labelled cells and anterograde labelling was the same as in the normals.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1984

Neonatal superior collicular lesions alter visual callosal development in hamster.

Visual callosal connections were examined using autoradiographic (ARG) and horseradish peroxidase (HRP) techniques in normal adult hamsters, and in adults subjected to ablation of the superficial tectal laminae at birth. Additional ARG and HRP experiments were carried out in hamsters 1-27 days of age in order to describe the normal development of this pathway. Neonatal collicular lesions, which deprived visual cortical neurons of a major terminal zone in the midbrain, substantially altered the visual callosal pathway. In the lesioned animals, the numbers of supragranular callosal cells in the 17-18a border region and lamina VI callosal neurons in medial area 17 were significantly greater than normal. The ARG experiments demonstrated additional clearcut abnormalities in the visual callosal pathway of the lesioned hamsters. First, the mediolateral extent of the supragranular callosal zone around the 17-18a border was increased. Secondly, dense label was visible over lower layer V and lamina VI throughout area 17. Finally, labelling in lamina I could also be observed across the entire mediolateral extent of area 17. Experiments in the developing hamsters suggested that some of the abnormalities observed in the lesioned animals may have resulted from the maintenance of normally transient developmental states. During the first postnatal week, both callosal cells and anterograde labelling were evenly distributed throughout the dorsal posterior neocortex, but only in the subplate region. During the second postnatal week, supragranular callosal cells were also labelled in both medial and lateral area 17, but from their first appearance, they were always most numerous in the 17-18a border region. At the same time callosal axons invaded the supragranular laminae, but only near the 17-18a border. By the end of the second postnatal week, the visual callosal pathway was very similar to that in the adult.

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PubMed1984

Altered somatosensory receptive fields in hamster colliculus after infraorbital nerve section and xylocaine injection.

The effects of acute infraorbital (i.o.) nerve section upon the responses of somatosensory cells in the rostral part of the deep layers of the hamster's superior colliculus were studied using standard extracellular single-unit recording and receptive field mapping techniques. In nine animals a given cell's receptive field was determined both before and after i.o. nerve section and, in all cases, new areas of sensitivity were unmasked within 15 min after the nerve was cut. In a given electrode penetration where the i.o. nerve was sectioned (n = 13), somatosensory cells recorded after the nerve was cut, as the electrode was being withdrawn from the colliculus, exhibited receptive fields considerably different from those of somatosensory cells isolated during the descent of the recording electrode. Seventeen deep-layer somatosensory cells (in eight hamsters) were tested before and after subcutaneous injections of xylocaine into their receptive fields. This manipulation unmasked new areas of cutaneous sensitivity for sixteen units. Of these, the new receptive fields of nine cells disappeared as sensitivity in the original receptive field returned; five ultimately retained both the new and old receptive fields; in two instances, sensitivity in the original receptive field never returned over the 3 h of testing. Control experiments (n = 7) demonstrated that the changes observed did not result from spontaneous alterations in receptive field borders, changes induced by variations in the level of general anaesthesia, or non-specific trauma associated with the xylocaine injections or the surgery required to expose the i.o. nerve.

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PubMed1984

Anatomical and functional organization of pathway from superior colliculus to lateral posterior nucleus in hamster.

A series of anatomical (autoradiographic and horseradish peroxidase, HRP) and electrophysiological experiments were carried out to determine the organization of the pathway from the superior colliculus (SC) to the lateral posterior nucleus (LP) in the hamster. Small, electrophoretic HRP deposits restricted to LP labeled numerous cells in both the ipsilateral and contralateral colliculus. Over 95% of the labeled cells were located in the lower one-half of the stratum griseum superficiale (SGS) and the upper stratum opticum (SO). A number of different morphological cell types contributed axons to the tecto-LP pathway. The receptive-field properties of antidromically activated tecto-LP neurons were delineated using extracellular single-unit recording techniques. Ninety-eight percent of the tecto-LP cells recorded were isolated in the SGS and SO. All tecto-LP cells responded more vigorously to moving than to flashed stimuli, one-third were directionally selective, and one-third exhibited some degree of speed selectivity. The responses of tecto-LP neurons did not differ appreciably from those of superficial layer collicular cells that could not be antidromically activated by LP shocks. Small pressure injections or electrophoretic deposits of [3H]leucine into sites with known retinotopy in the superficial collicular laminae were used to determine whether or not the tecto-LP projection in hamster was topographically organized. Injections anywhere in the SGS and SO yielded dense label in almost all of the caudal (LPc) and rostrolateral (LPrl) subnuclei of LP, ipsilaterally, and sparser labeling in these same subnuclei, contralaterally. No injection produced significant labeling in the rostromedial (LPrm) subnucleus. Our autoradiographic data gave no indication of any topographic order in the tecto-LP projection. Electrophysiological methods were also used to map the tecto-LP projection. Multiple stimulating microelectrodes were positioned at physiologically defined sites in the SGS, and single cells were recorded in LP, ipsilaterally. Threshold currents for activation of LP cells from different collicular sites were then compared with the angular separation of SC and LP receptive-field centers. No significant correlation between these two variables was noted, again indicating a lack of topographic organization in the tecto-LP projection. The receptive-field properties of individual LP neurons (n = 211) were also assessed and correlated with subnuclear location and responsivity to SC shocks.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Central projections of the normal and 'regenerate' infraorbital nerve in adult rats subjected to neonatal unilateral infraorbital lesions: a transganglionic horseradish peroxidase study.

Application of horseradish peroxidase (HRP) to the proximal stump of the transected infraorbital (IO) nerve in the orbit was employed in normal adult rats to demonstrate the ganglionic representation of and brainstem innervation by the trigeminal (V) branch which supplies primarily the mystacial vibrissae. In the V ganglion, somal clusters resembling the barrels or barreloids which comprise the central representations of the whiskers were not visible. In the trigeminal brainstem nuclear complex (TBNC), however, barrel-like aggregates of HRP-labeled terminals could be clearly seen throughout subnucleus interpolaris and, to a lesser extent, in the principal sensory nucleus, subnucleus caudalis and the first cervical segment. In adult rats subjected to neonatal IO nerve section and vibrissae follicle cauterization, transganglionic HRP transport from the 'regenerate' IO nerve indicated an almost exclusive projection to the marginal layer of the medullary and rostral cervical dorsal horn.

Animals↗
PubMed1983

Neonatal enucleation alters functional organization in hamster's lateral posterior nucleus.

In normal hamsters, somatosensory cells comprise 23% of all the units recorded in the lateral posterior nucleus (LP), and such cells tended to be clustered in the ventral part of this nucleus. In animals subjected to removal of both eyes within 12 h of birth, 59% of all LP cells responded to tactile stimuli, and these neurons were distributed evenly throughout the nucleus. This altered sensory organization is consistent with the prior observation that superficial layer collicular cells, whose axons comprise a major input to LP, were responsive to somatosensory stimulation in hamsters which were enucleated at birth.

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PubMed1983

Reorganization of trigeminal primary afferents following neonatal infraorbital nerve section in hamster.

The infraorbital nerve was sectioned and the ipsilateral whisker follicles were cauterized in hamsters within 12 h of birth. Sixty to ninety days later application of HRP to the proximal stumps of the ipsilateral lingual, inferior alveolar, mylohyoid and auriculotemporal nerves resulted in increased numbers of labeled somata in trigeminal ganglion regions which contain primarily infraorbital cell bodies in normal animals. The labeled central processes of mandibular nerves also occupied portions of the brainstem trigeminal complex normally innervated by infraorbital axons. These findings represent the first anatomical demonstration of trigeminal primary afferent plasticity.

Afferent Pathways↗
PubMed1983

Complex somatosensory receptive fields of cells in the deep laminae of the hamster's superior colliculus.

Responses to separate and simultaneous application of noxious and innocuous tactile stimuli were examined for neurons recorded from the deep layers of the hamster's superior colliculus. Forty-four percent of the units isolated were responsive only to innocuous, primarily cutaneous, stimuli; 10% were activated only by noxious stimulation; and 15% were characterized as having a wide dynamic range. The remaining 31% of the somatosensory cells recorded had complex receptive field properties which have not heretofore been described for tectal neurons in any species. Ten percent of all somatosensory cells had no excitatory receptive fields, but their spontaneous discharges could be suppressed by low threshold and/or noxious stimulation of discrete portions of the body. In 18% of the units which we recorded, innocuous and noxious stimuli had opposing effects upon cellular activity. Most of these neurons had small receptive fields in which innocuous tactile stimuli yielded excitation and larger fields, often including most of the body surface, where noxious stimulation suppressed both spontaneous activity and the responses normally elicited by appropriate tactile stimulation. Finally, a very small number of units (3% of all somatosensory cells recorded) had multiple receptive fields in which low threshold stimulation produced opposing effects on spontaneous activity. Somatosensory units were recorded in all of the deep laminae, but cells with complex response characteristics were isolated primarily in stratum griseum profundum.

Animals↗
PubMed1982

Indirect visual cortical input to the deep layers of the hamster's superior colliculus via the basal ganglia.

Anterograde and retrograde tracing techniques were employed to delineate the organization of a visual cortical input to the deep layers of the hamster's superior colliculus which may be mediated by links in the striatum and substantia nigra. Autoradiographic experiments showed that areas 17, 18a, and the cortex medial to area 17 (areas 18b and 29) all projected to the dorsocaudal part of the ipsilateral striatum. This projection was organized so that the rostrocaudal axis of the visual cortex was represented along the antero posterior axis of the striatum. Large posterior neocortical injections which included all of these areas also revealed a weak, crossed corticostriatal pathway. Such injections also demonstrated clear discontinuities in the terminal distribution of the visual corticostriatal projection, similar to those which have been noted after injections of tracers into the motor and premotor cortices. Retrograde tracing experiments showed that the cells of origin of the visual cortical projections to the striatum were medium-sized pyramidal neurons located primarily in the upper portion of lamina V. Anterograde transport of [3H]-leucine and HRP showed that the portion of the striatum heavily innervated by the visual cortex projected to the part of substantial nigra, pars reticulata immediately adjacent to the cerebral peduncle. Injections in the rostral striatum labeled more medial portions of this nucleus. The cells of origin of the striatonigral pathway measured between 13 and 20 micrometers in diameter and they were located primarily in the dorsal and lateral parts of the striatum. Anterograde tracing after substantia nigra, pars reticulata injections revealed a projection to both superior colliculi. The uncrossed pathway terminated primarily as a series of patches throughout the mediolateral and rostrocaudal extents of the lower stratum griseum intermediale and stratum album intermedium. Labeling was also visible in the lateral portion of the stratum griseum profundum. The crossed nigrotectal pathway terminated primarily in the rostrolateral stratum griseum profundum. The cells of origin of the nigrocollicular pathway were fusiform or multipolar cells and were located primarily adjacent to the cerebral peduncle throughout the rostral half of the substantias nigra, par reticulata.

Animals↗
PubMed1982

The intercollicular pathway in the golden hamster: an anatomical study.

The intercollicular pathway of the hamster was studied by means of a combination of horseradish peroxidase (HRP), autoradiographic, and double-labeling (nuclear yellow-HRP) techniques. Small deposits of HRP marked significant numbers of cells in the contralateral colliculus only when the injection site included the laminae ventral to the stratum opticum. Anterior deposits labeled many more neurons than injections into the caudal part of the tectum. Of the cells labeled by our injections, 18.2% were located in the superficial collicular laminae (stratum griseum superficiale and stratum opticum), and the remainder (81.8%) were in the deep layers. A wide variety of morphological cell types contributed axons to the intercollicular projection, and in a given animal the loci of the labeled neurons were generally symmetrical with the injection site. Small deposits of [3H]-leucine resulted in contralateral labeling only when the injection included the deep collicular laminae. The transported label was most dense in the stratum griseum intermediale and stratum griseum profundum, and its location was generally homotopic with the injection site. Experiments in which collicular HRP deposits were combined with large cervical spinal or pontine reticular injections of Nuclear Yellow indicated that intertectal neurons did not, in most cases, contribute axon branches to the spinal or pontine reticular projections of the colliculus. Receptive field data obtained at the time of the HRP and/or [3H]-leucine deposits demonstrated that the collicular representations of the ipsilateral and at least 45 degrees of the contralateral hemifields were encompassed by intercollicular connections. This was also true for the somatosensory representation of the entire head and a portion of the neck.

Animals↗
PubMed1982

Altered organization of intercollicular pathway in bilaterally enucleated hamsters.

Autoradiography and the horseradish peroxidase technique were used to examine the intercollicular pathway in normal hamsters and in animals subjected to removal of one or both eyes at birth. The topographic organization of the intercollicular pathway and the numbers and laminar distributions of intertectal cells were the same in all groups. The laminar distributions of commissural fibers were also quite similar in the normal and unilaterally enucleated hamsters. In the bilateral enucleates, however, intertectal axons innervated the superficial gray and optic layers much more densely than in either of the other two groups.

Animals↗
PubMed1982

Effects of neonatal cortical lesions upon retinocollicular projections in the hamster.

Autoradiography and anterograde horseradish peroxidase transport were used to examine retinocollicular projections in normal hamsters and in animals subjected to ablation of the ipsilateral, posterior neocortex at 1, 3, 6, 10, or 120 days of age. The crossed retinotectal projections of all groups were quite similar. There did, however, appear to be a slight increase in the density of the projection to the lower portion of the stratum griseum superficiale in the neonatally brain-damaged hamsters. The uncrossed pathway, on the other hand, was quite abnormal in the neonatally lesioned animals. In normals, the ipsilateral retinocollicular projection consisted almost entirely of a series of patches along the stratum griseum superficiale-stratum opticum border in the rostral one-third of the colliculus. Only a few axons from the ipsilateral eye were observed in the caudal two-thirds of the tectum and these could only be visualized when horseradish peroxidase was used as the tracer. In all of the neonatally brain-damaged hamsters both autoradiography and horseradish peroxidase tracing demonstrated that the ipsilateral retina densely innervated the entire rostrocaudal extent of the colliculus. Retrograde tracing experiments demonstrated that the portion of the temporal retina which gave rise to the uncrossed retinocollicular projection in the normal hamsters was also the source of the expanded projection in the neonatally brain-damaged animals; and, further, that the numbers and areal distributions of ipsilaterally projecting retinal and retinocollicular ganglion cells were similar in the two groups. These findings suggest that, at least in the hamster, normal inputs from the two eyes may not be a sufficient condition for the development of the largely complementary pattern of collicular innervation by the two retinae.

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