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R W Rhoades

Publications and source records attributed to R W Rhoades.

At least 199 records · Page 11Linked to original sources
PubMed1978

Functional properties of the corticotectal projection in the golden hamster.

Approximately 31% of the cells recorded in the hamster's superior colliculus could be activated by stimulation of the ipsilateral primary visual cortex. While cortically activated cells were encountered in all laminae of the colliculus where visual cells were isolated, the highest probability of driving visual cells was observed in the deeper laminae, that is, those ventral to the stratum opticum. Response latency, jitter (latency variability), latency shifts as a function of shock intensity, thresholds, and spike numbers did not vary as a function of depth in the colliculus. There was a clear correspondence between the visual fields of the best cortical stimulus points and the receptive fields of cortically activated cells recorded in the superficial laminae of the colliculus. However, there was considerably less retinotopic fidelity for the cortical areas from which cells isolated in the deeper laminae could be driven. This suggests a greater degree of convergence from relatively widespread cortical regions upon visual cells of the deeper laminae. The visal organization) of the cortically activated cells did not differ appreciably from the overall sample of visual cells recorded in the colliculus. Only 3 of the 159 cells tested were driven by stimulation of the contralateral visual cortex and two of these were responsive only at very long latencies.

Animals↗
PubMed1978

Directional selectivity in hamster superior colliculus is modified by strobe-rearing but not by dark-rearing.

Visual response properties of superior collicular neurons of normal hamsters were compared with those of animals reared from birth to adulthood in either total darkness or with stroboscopic illumination. Directional selectivity was markedly reduced only in the strobe-reared animals, thus demonstrating visual plasticity in a system that develops apparently normally without visual experience.

Action Potentials↗
PubMed1978

Receptive field characteristics of superior colliculus neurons and visually guided behavior in dark-reared hamsters.

Visual response properties of single neurons in the superior colliculus of golden hamsters reared from birth to adulthood in total darkness were compared to those of normal hamsters. Directional selectivity, speed preferences, and receptive field organization in dark-reared hamsters were essentially the same as those found in normally reared animals. Subtle neurophysiological effects of visual deprivation were indicated by the longer latencies of "on" responses to flashed spots of light in the dark-reared animals. Also, in the visually deprived animals three cells were encountered which changed their responses from phasic to tonic as the size of the visual stimulus was increased. In normally reared animals all cells responding to stationary stimuli showed only phasic responses regardless of spot size. Behaviorally, dark-reared animals could not be distinguished from normal animals on the basis of visual orienting and following tests. It was concluded that in the golden hamster visual experience during development has a minimal role in the induction or maintenance of the normal functional development of the superior colliculus.

Animals↗
PubMed1978

Relation of albinism and drugs to the visual evoked potential of the mouse.

The individual and combined influences of pentobarbital and chlorprothixene on the early components of the cortical visual evoked potential (VEP) were examined in the C57BL/6 mouse. Pentobarbital produced a large increase in latency, and chlorprothixene resulted in a smaller latency increase. When these agents were combined, their effects on the VEP latency were antagonistic. The effects of pentobarbital on VEP amplitude varied as a function of flash intensity, and this barbiturate anesthetic also produced qualitative VEP waveform changes. When the congenic albino (c/c) C57BL/6 was compared with the black (+/+) C57BL/6 mouse; pentobarbital anesthesia produced a decrease of latency with increasing stimulus intensity only in the c/c genotype, whereas VEP amplitudes were similarly affected by pentobarbital in both genotypes.

Albinism↗
PubMed1978

Modification of visual response properties in the superior colliculus of the golden hamster following stroboscopic rearing.

1. Visual response properties of superior collicular neurones were investigated in golden hamsters reared from birth to adulthood in a stroboscopic environment.2. In comparison to normally reared animals, there was a marked decrease in the incidence of directionally selective cells in the colliculus of the strobe-reared hamsters. This effect was apparent when directional selectivity was determined by either the null criterion or a statistical measure. The reduction in directionally selective cells was found in both superficial and the deep layers of the colliculus.3. Neurones in strobe-reared hamsters also exhibited a different speed preference distribution from that obtained for normal animals, in that more cells in the restricted hamsters responded only to slow velocities, and less were broadly tuned with regard to the speed of moving stimuli.4. In addition to the effects obtained in dynamic response properties, there were also changes in the static response properties of superior collicular neurones. These were an increase in the proportion of cells whose responses were not affected by changing the size of a stationary flashed stimulus, and a concomitant decrease in the number of cells demonstrating either partial or complete suppression when the size of a flashed stimulus exceeded the boundaries of the receptive field activating region. Furthermore, while all cells which responded to stationary stimuli in normal animals yielded only phasic responses to stimulus onset and/or offset, in the strobe-reared hamsters eight cells were encountered which responded in a sustained fashion to stationary spots.5. There was no indication of an increased responsivity in the restricted animals to strobe stimulation, even when a strobe rate identical to that employed in the rearing environment was employed.6. The results were interpreted as indicating a disruption of normal visual functional organization in the hamster's superior colliculus by an aberrant visual input during development.

Action Potentials↗
PubMed1978

Functional and anatomical consequences of neonatal visual cortical damage in superior colliculus of the golden hamster.

1. In normal hamsters the visual cortex sends a retinotopically organized projection to the ipsilateral superior colliculus. 2. Acute or chronic unilateral ablations of visual cortex in adult animals decrease the incidence of directionally selective cells encountered in the superficial laminae of the ipsilateral colliculus, but not in the deeper layers (those ventral to the stratum opticum). 3. Unilateral ablations of visual cortex in infant hamsters induce an aberrant crossed projection to the contralateral superior colliculus, confirming the finding of Mustari and Lund (58) in the rat. Horseradish peroxidase (HRP) experiments demonstrated that the cells whose axons comprise the normal as well as the anomalous projection are pyramidal neurons in layer V of cortex. 4. In adult hamsters that underwent early brain damage, about 13% of the cells in the colliculus could be activated by stimulation of the contralateral visual cortex. Only 1 unit (of the 159 cells tested) could be driven by similar stimulation in normal adult hamsters. This indicates that the anomalous crossed projection forms functional synapses in the contralateral tectum. 5. No cells (of the 113 tested) could be activated from the contralateral cortex in hamsters that sustained chronic ablations of visual cortex in adulthood; thus indicating that there is some limited time period during development when unilateral ablations of visual cortex induce an anomalous corticotectal pathway. 6. The visual response properties of superior collicular neurons in the neonatally brain-damaged animals were compared to those of normal hamsters, as well as to those with acute or chronic ablations of visual cortex sustained in adulthood. 7. There was no indication that the anomalous projection contributes to the organization of normal visual response properties in the superior colliculus of the neonatally brain-damaged animals. In fact, the incidence of directionally selective cells in these hamsters was found to be significantly lower than that of normals in both the superficial and deep laminae of the colliculus. 8. We conclude that while unilateral damage of visual cortex in the hamster induces an anomalous corticotectal projection that makes functional synapses, this aberrant input does not compensate for missing, normal corticotectal pathway in the organization of superior collicular response properties.

Animals↗
PubMed1977

Effects of single albino gene substitutions on the performance of mice in a compound avoidance-discrimination task.

Congenic C57BL/6J mice of the +/+, +/c and c/c genotypes were tested for motoric activity, active avoidance and visual discrimination performance in a variant of the Thompson-Bryant box. The three genotypes were observed to be identical in terms of motor activity, but differed greatly with regard to both avoidance and discrimination performance. On the avoidance portion of the task the c gene appeared to act in an additive fashion, with the +/+ mice being superior to the +/c mice, which were in turn superior to the c/c animals. Visual discrimination performance, however, indicated that the + allele operated in a dominant manner; here c/c mice were found to be inferior in performance when compared to either +/+ or +/c animals while no differences were observed between the two pigmented genotypes. Therefore, under the conditions of the present experiment, the albino gene shows incomplete dominance for active avoidance behavior and recessiveness for visual discrimination performance.

Animals↗
PubMed1977

Responses of visual, somatosensory, and auditory neurones in the golden hamster's superior colliculus.

1. The response characteristics of visual, somatosensory, and auditory neurones in the golden hamster's superior colliculus were investigated.2. As has been noted for other mammalian species, a distinct difference between the functional organizations of the superficial and deeper layers of the superior colliculus was observed.3. Neurones in the superficial layers were exclusively visual, with small receptive-fields, and generally did not show response decrements with repeated stimulation. The sizes of the receptive-fields did not vary appreciably as a function of retinal eccentricity.4. In the deeper layers, visual receptive-fields were large, or could not be accurately delimited, and response habituation was often evident. In addition, many cells in the deeper layers of the colliculus responded only to somatosensory stimuli. Far fewer cells, which appeared to be confined to the caudal portions of the colliculus, responded to auditory stimuli. Polymodal cells were also encountered.5. Selectivity to opposing directions of movement was tested for ninety-four visual cells. Using a ;null' criterion, 27.7% of these cells were judged to be directionally selective. A distribution of the preferred directions of these cells showed a significant preference for movement with an upper-nasal component. With a statistical criterion, 60.6% of these cells were considered to show a significant asymmetry in responding to movement in opposing directions.6. Directional selectivity was also tested for ninety-two cells following acute, unilateral, lesions of the visual cortex. For the eighty cells recorded, homolateral to the ablated cortex, 27.5% were judged as directionally selective using the statistical criterion, while 12.5% were selective with the ;null' criterion. Of the twelve cells isolated in the colliculus, contralateral to the lesions, seven were judged as directionally selective with the statistical, and three with the ;null' criterion.7. The effects of visual cortical lesions upon directional selectivity appeared to be confined to cells in the superficial layers of the colliculus. It was suggested that directional selectivity of many cells in the superficial layers of the tectum of the hamster is organized cortically.8. A clear spatial correspondence was observed for the receptive-fields of visual, somatosensory, and auditory neurones.9. As has been suggested for other species, the hamster's superior colliculus appears to play an important role in orienting the animal toward visual, somatosensory, and auditory stimuli.

Action Potentials↗
PubMedDate not supplied

Effects of angiotensin II on visual neurons in the superficial laminae of the hamster's superior colliculus.

Superficial layer superior colliculus (SC) neurons were recorded extracellularly with multibarreled recording/ejecting micropipettes. Angiotensin II was delivered via micropressure ejection during visual stimulation (n = 215 cells), or during electrical stimulation of either the optic chiasm (OX; n = 150 cells) or visual cortex (CTX; n = 42 cells). Application of angiotensin II decreased visual responses of SC cells to 43.8% +/- 30.7% (mean +/- S.D.) and reduced responses to electrical stimulation of the OX and CTX to 58.6% +/- 34.1% and 43.8% +/- 30.7% of control values, respectively. Angiotensin II enhanced responses by at least 30% in only 6 cells (1.5%). Of the 35 neurons tested with both OX and CTX stimulation, the correlation of evoked response suppression by angiotensin II was highly significant (r = 0.69; P < 0.001). This suggests that the suppressive effects of angiotensin II were common to both pathways. To test whether the inhibitory effects of angiotensin II were presynaptic or postsynaptic, Mg2+ ions were ejected iontophoretically to abolish synaptic responses, and the neurons were activated by iontophoresis of glutamate and then tested with angiotensin II. Angiotensin II reduced the glutamate-evoked responses to an average 29.1% +/- 21.1% of control values (n = 9 cells). This suggest that the site of action of angiotensin II is most likely postsynaptic. To identify which receptors were involved in these effects, angiotensin II was ejected concurrently with the AT1 antagonist Losartan (DUP753) or with either of two AT2 antagonists, CGP42112A or PD123177. Losartan antagonized the action of angiotensin II in 65.6% of the cells tested (n = 99) and CGP42112A and PD123177 had antagonistic effects in 58% (n = 65) and 60% (n = 5), respectively. Both classes of antagonists were tested in 29 cells; and there was no significant correlation between their effectiveness. These results suggest that both AT1 and AT2 receptors may independently mediate the suppressive effects of angiotensin II, and that collicular neurons may have either or both receptor subtypes.

Angiotensin I↗
PubMedDate not supplied

Effects of neurotensin on visual neurons in the superficial laminae of the hamster's superior colliculus.

Autoradiography with 125I-neurotensin in normal and enucleated hamsters was used to define the distribution of receptors for this peptide in the superficial layers of the superior colliculus (SC). Neurotensin binding sites were densely distributed in the stratum griseum superficiale (SGS), and results from the enucleated animals indicated that they were not located on retinal axons. The effects of neurotensin on individual superficial layer cells were tested in single-unit recording experiments. Neurotensin was delivered via micropressure ejection during visual stimulation (n = 75 cells), or during electrical stimulation of either the optic chiasm (OX; n = 47 cells) or visual cortex (CTX; n = 29 cells). In comparison with control values, application of neurotensin decreased visual responses of all SC cells tested to 54.1 +/- 34.9% (mean +/- standard deviation; range of decrement 7.5 to 100%; nine cells showed no effect or an increase in visual activity, which for four of these was > or = 30%). Neurotensin application also reduced responses to electrical stimulation of either OX or CTX, respectively, to 65.8 +/- 36.5% of control values (range of decrement 2.6 to 97.4%; 12 neurons showed a weak increment < or = 30%) and 68.0 +/- 38.5% (range of decrement 3.3 to 100%; five cells showed no effect or an increment, in one case > or = 30%). Of the 25 neurons tested with both OX and CTX stimulation, the correlation of evoked response suppression by neurotensin was highly significant (r = 0.70; P < 0.001). This suggests that the suppressive effects of neurotensin were common to both pathways. To test whether the inhibitory effects of neurotensin were presynaptic or postsynaptic, Mg2+ ions were ejected iontophoretically to abolish synaptic responses, and the neurons (n = 16) were activated by iontophoresis of glutamate and then tested with neurotensin. Neurotensin reduced the glutamate-evoked responses to an average 59.3 +/- 37.9% of control values (range 2.3 to 92.5%; one cell showed an increment > 30%). This result suggests that the site of action of neurotensin is most likely postsynaptic.

Animals↗
PubMedDate not supplied

Neonatal administration of the neurotoxin 5,7-dihydroxytryptamine results in synaptic reorganization in the superficial gray layer of the hamster's superior colliculus.

Neonatal subcutaneous administration of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) to hamsters results in a marked depletion of serotonin (5-HT) in cortex and an increase in the concentration of this amine in the superior colliculus (SC). To determine whether this increase was associated with an alteration in the synaptic organization of 5-HT-containing axons in the superficial gray layer of the SC, immunocytochemistry was combined with electron microscopy. In normal adult hamsters, only 4.0% of 500 5-HT-immunoreactive profiles make synaptic contacts in the superficial gray layer of the hamster's SC. In 5,7-DHT-treated animals, examination of 400 individual profiles indicated that 25.5% of 5-HT-positive profiles made synaptic contacts (P < 0.05). Given the recently demonstrated effect of 5-HT on retinotectal transmission in this species, the present results suggest that the functional organization of the SC may also be markedly altered in animals that sustain neonatal 5,7-DHT administration.

5,7-Dihydroxytryptamine↗
PubMedDate not supplied

Projection status of calbindin- and parvalbumin-immunoreactive neurons in the superficial layers of the rat's superior colliculus.

Immunocytochemistry and retrograde labeling were used to define the thalamic projections of calbindin- and parvalbumin-containing cells in superficial layers of the rat's superior colliculus (SC). Quantitative analysis revealed that 90.8 +/- 2.2% (mean +/- standard deviation) of the calbindin-immunoreactive neurons in the stratum griseum superficiale (SGS) projected to the dorsal lateral geniculate nucleus (LGNd) and that 91.3 +/- 4.3% of calbindin-immunoreactive neurons in the stratum opticum (SO) projected to the lateral posterior nucleus (LP). In contrast, only 17.3 +/- 2.5% of parvalbumin-immunoreactive neurons in the SGS were found to project to the LGNd and 16.5 +/- 3.1% of the parvalbumin-immunoreactive SO cells were retrogradely labeled after LP injections. Few of the parvalbumin-immunoreactive neurons in either the SGS (7.2 +/- 2.5%) or the SO (9.2 +/- 2.5%) were GABA positive. The retrograde-labeling results suggest that parvalbumin-immunoreactive neurons in the rat's SO and SGS may either be primarily interneurons or have descending projections, while calbindin-containing cells are primarily thalamic projection neurons. These results are consistent with data from other rodents, but almost exactly the opposite of data that have been reported for the cat for these same populations of SC projection neurons. Such interspecies differences raise questions regarding the functional importance of expressing one calcium-binding protein versus another in a specific neuronal population.

Animals↗
PubMedDate not supplied

Increased serotonin in the developing superior colliculus affects receptive-field size of retinotectal afferents but not that of postsynaptic neurons.

Administration of a single subcutaneous dose of 5,7-dihydroxytryptamine (5,7-DHT) to newborn hamsters results in a significant increase in the density of serotoninergic (5-HT) fibers in the superficial layers of the superior colliculus (SC) and marked abnormalities in the uncrossed retinotectal projection when these animals reach adulthood (Rhoades et al., 1993). The present study was undertaken to determine whether elevation of 5-HT in the developing SC altered the visual representation in SC. Multi-unit recordings from SC cells demonstrated that the overall organization of the visual map in the superficial SC laminae was normal and that the receptive-field sizes for unit clusters were unchanged in the 5,7-DHT-treated animals. However, when a combination of CNQX and MK-801 was directly applied to the SC to block postsynaptic activity, the receptive fields of unit clusters (presumably retinotectal axon terminals) in the 5,7-DHT treated animals were significantly larger than those in the normally reared hamsters. These results are consistent with the conclusions that elevation of 5-HT levels in the developing SC reduces the postnatal refinement of the crossed retinotectal axons, and that mechanisms operating within the SC may act to maintain normal sizes for the receptive fields of its constituent neurons.

5,7-Dihydroxytryptamine↗