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K V Fite

Publications and source records attributed to K V Fite.

At least 55 records · Page 3Linked to original sources
PubMed1982

Neural correlates of optokinetic nystagmus in the mesencephalon of Rana pipiens: a functional analysis.

The effects of lesions of the anuran mesencephalic retinal terminal fields on horizontal optokinetic nystagmus (OKN) were examined. Lesion sites which produced effects upon OKN responses were as follows: BOR, nBOR, peri-nBOR, the large-celled pretectal nucleus, and the dorsal tegmental gray and deep tectal layers. Transection of BOR generally resulted in an increase in saccadic frequently at the lower stimulus velocities. Lesions of nBOR produced a decrease in the frequency of both head and eye saccades in the middle to high range of stimulus velocities. The only lesions which totally abolished horizontal OKN were those located medical to nBOR, in the peri-nBOR region. Lesions of the large-celled pretectal nucleus and dorsal tegmental gray substantially reduced both head and eye saccades at all stimulus velocities. Small lesions in the deep tectal layers also depressed OKN frequency. These studies indicate that horizontal OKN may be mediated by a number of structures within the anuran mesencephalon.

Animals↗
PubMed1981

The accessory optic system of Rana pipiens: neuroanatomical connections and intrinsic organization.

The accessory optic system of Rana pipiens was investigated by autoradiographic, horseradish peroxidase, and Golgi techniques, revealing a complexity of neuroanatomical organization previously unrecognized. Retinal afferents project to the nucleus of the basal optic root (nBOR) via a primary bundle and more diffuse, medial bundle of optic axons, both of which contain large- and small-diameter fibers. At least six types of retinal ganglion cell contribute to the basal optic root (BOR), including giant ganglion cells, two intermediate-sized ganglion cell types, small ganglion cells, and two types of displaced ganglion cell. The major retinal projection is contralateral, but a small, ipsilateral component also exists. Afferents from neurons which are postsynaptic to the thalamic retinal terminal fields also reach nBOR. Four distinct cell types were identified within the terminal field of nBOR: stellate neurons (63%), amacrine cells (19%), elongate neurons (14%), and large ganglionic neurons (4%). Both stellate and amacrine cells appear to be intrinsic neurons, while elongate and ganglionic neurons constitute the efferent neuron population of nBOR. In addition, cells which lie medial to the terminal field, pyriform and commissural neurons, send dendrites into nBOR. Pyriform neurons project to the nucleus of the medial longitudinal fasciculus (nMLF) and cranial nerve nuclei III and IV, while commissural neurons project to the contralateral nBOR. Large reticular neurons of the nMLF also send dendrites into nBOR. Efferent projections from nBOR were observed in the large-celled pretectal nucleus and in nucleus lateralis profundus. A second major projection originates from the peri-nBOR region and is associated with the oculomotor system and with the nMLF. Efferent projections from the nMLF to the vestibular nuclei and to the rostral spinal cord were also observed, as well as projections which reach the brainstem from the large-celled pretectal nucleus, the posterior thalamic and anterior mesencephalic central gray.

Afferent Pathways↗
PubMed1981

Displaced ganglion cells and the accessory optic system of pigeon.

The central projection and retinal distribution of displace ganglion cells (DGC's) are described for the pigeon. Discrete, localized injections of horseradish peroxidase (HRP) into the nucleus of the basal optic root (nBOR) complex labeled as many as 4,800 DGC's in the contralateral retina. The greatest densities of DGC's were observed in the more peripheral regions of the middle and inferior temporal regions of the retina, with lowest densities occurring in the inferior nasal, red field, and foveal areas. Large HRP injections of the tectal lobes, which did not include the pretectal, accessory optic (nBOR), hypothalamic, or thalamic visual nuclei, labeled only ganglion cells within the ganglion cells layer. An HRP injection centered within the nucleus lentiformis mesencephali, also including portions of the optic tectum and optic tract, labeled only ganglion cells within the ganglion cell layer of the contralateral retina. DGC's thus appear to be the primary, if not exclusive, source of retinal afferents to the nBOR complex in pigeon. The observed retinal distribution of DGC's indicates that the areas of retina with the greatest density of cells in the receptor layer, inner nuclear layer, and ganglion cell layer are relatively devoid of DGC's. Since the nBOR complex projects directly upon the vestibulocerebellum and oculomotor nuclei, DGC's would thus appear to be involved in neural circuits that mediate oculomotor reflexes and visuomotor behavior.

Animals↗
PubMed1981

Bifoveal vision in anolis lizards.

The retinas of 14 ecologically diverse species of Anolis lizards have been examined neuroanatomically. Both central and temporal foveas were observed in each eye of all species: however, the two foveas differed with regard to a number of structural and morphological characteristics. All central foveas were deep and convexiclivate, while temporal foveas were shallower and more variable both in shape and retinal location across species. Central foveas had higher cell densities and a broader foveal clivus than did temporal foveas both within and across species. As eye size increased across species, densities of receptor nuclei per visual degree2 (vis. deg.2) increased more rapidly than did ganglion cell densities/vis, deg.2 in the central fovea. In contrast, both cell types increased at approximately the same rate in the temporal fovea as eye size increased. Several of these relationships have been previously reported for diurnal birds of prey, which are also bifoveate. of stomach contents revealed that Anolis species which feed upon small prey items have temporal foveas with a relatively deep clivus. Foveal characteristics may influence both species typical foraging behaviors and the type of prey which can be effectively utilized by a given species.

Animals↗
PubMed1981

Retinal dystrophy associated with a postnatal amelanosis in the chicken.

Melanin pigmentation changes were studied in a mutant (delayed amelanotic) line of chickens characterized by a postnatal, spontaneous cutaneous amelanosis and a high incidence of blindness. Cutaneous pigment loss was accompanied by destruction of the choroidal melanocytes throughout the orbit. The presence of blindness appeared to be correlated with the histopathologic finding of severe degenerative changes in the pigment epithelium and neural retina first seen near the base of the pecten and progressing radially in irregular patterns.

Animals↗
PubMed1980

Optokinetic nystagmus in the domestic pigeon. Effects of foveal lesions.

Using both binocular and monocular viewing conditions, optokinetic nystagmus (OKN) frequency-velocity functions were measured before and after ophthalmic laser-produced retinal lesions. With binocular viewing conditions, the range of effective pattern velocities and the upper velocity threshold increased by 20--30 degrees/sec in subjects with both foveas lesioned, and by 12 degrees/sec in a subject with only a single foveal lesion. Subjects with parafoveal lesions showed no change in postlesion binocular OKN response functions. Prelesion monocular OKN functions were obtained for both temporal-to-nasal (T-N) and nasal-to-temporal (N-T) directions of pattern movement. T-N OKN functions were similar to those obtained with binocular viewing but N-T movement elicited OKN over a much narrower range of stimulus velocites. Lesions of the foveal area appeared to have little effect on N-T OKN functions, although an increase in N-T upper velocity thresholds was obtained from at least one eye in 4 of 5 animals. Thus, lesions of the foveal and parafoveal area do not impair, and may actually facilitate, OKN in the pigeon.

Animals↗
PubMed1979

Optokinetic nystagmus and the accessory optic system of pigeon and turtle.

Optokinetic nystagmus (OKN) response functions were obtained in pigeon (Columba livia) and turtle (Chrysemys picta) before and after electrolytic lesions of the accessory optic nuclei (AON). Postlesion retinal input to the AON was evaluated using standard autoradiographic techniques. Bilateral destruction of AON in both pigeon and turtle did not abolish OKN, but was correlated instead with a reduction in OKN frequencies at high pattern velocities. A difference was observed between species with respect to the effects of partial lesions. Incomplete destruction of AON produced no observable change in OKN response functions in pigeon, but correlated with reduced OKN response functions in turtle. These results suggest that the AON mediate a portion of OKN in both pigeon and turtle, particularly at high pattern velocities, but are not essential for its occurrence.

Animals↗
PubMed1978

Wavelength discrimination in the leopard frog: a reexamination.

A reexamination of wavelength discrimination using a 2-choice paradigm and both chromatic-chromatic and chromatic-achromatic stimulus pairs has reaffirmed the positive tendency of Rana pipiens to approach short wavelengths. In addition, a strong avoidance of long wavelengths was observed and an interaction of these two opposite response tendencies was demonstrated. Thus, the percent choice frequency for a short-wavelength stimulus depends upon the stimulus with which it is paired. A positive phototaxis appears to influence response to some short-wavelength stimuli when they differ in brightness from an achromatic stimulus, but not with wavelengths above 471 nm.

Animals↗
PubMed1977

Specific projection of displaced retinal ganglion cells upon the accessory optic system in the pigeon (Columbia livia).

In the pigeon, the nucleus of the basal optic root, a component of the accessory optic system, projects directly upon the vestibulo-cerebellum. This nucleus receives a prominent projection composed of large-diameter retinal axons, known as the basal optic root. The cells of origin of this tract were identified using horseradish peroxidase (donor:hydrogen-peroxide oxidoreductase, EC 1.11.1.7) as a retrograde marker. Injections of horseradish peroxidase confined primarily to the basal optic root nucleus labeled displaced ganglion cells of the contralateral retina. Cell sizes were 18-30 micronm and the dendrites of these cells were confined to the first stratum of the inner plexiform layer. Approximately 3700 displaced ganglion cells were labeled after injections of horseradish peroxidase into basal optic root. In contrast, no displaced ganglion cells were labeled after injections of horseradish peroxidase into the optic tectum, which labeled only cells in the ganglion cell layer proper. These findings indicate that displaced ganglion cells constitute a unique population of retinal neurons that give rise to a bisynaptic pathway directed to the cerebellum via the nucleus of the basal optic root. These displaced ganglion cells may play a major role inoculomotor reflexes.

Animals↗
PubMed1975

A comparative study of deep avian foveas.

The foveas of nine avian species, initially selected for the presence of a deep fovea and representing a wide range of eye sizes and ecological habits, were studied with quantitative light microscope techniques. Considerable variation was observed in the location and configuration of the avian foveas, although they appeared to be 'convexiclivate' in shape when compared with the fovea of the rhesus monkey. Comparisons of foveal cell densities (receptor nuclei and ganglion cells) across species showed an increase in the average number of cells/visual degree2 with increasing eye size; similarly, an increase occurred in receptor nuclei relative to ganglion cell density. Thus, smaller eyes showed a coarser retinal grain and a lower 'concidence ratio' of receptors to ganglion cells than was found in the largest eyes. There appeared to be no relationship between receptor densities/mm2 and (a) eye size, (b) depth of foveal clivus, or (c) width of foveal clivus. However, a negative correlation was generally observed between the width of the foveal clivus and eye size. Two foveas were seen in the red-tailed hawk, goshawk, sparrow hawk, and least tern. The central fovea was more differentiated, with greate densities of both receptor nuclei and ganglion cells than was observed in the emporal fovea of the same species. Further conclusions, particularly with respect to potential visual acuity, await quantitative measurements of foveal cone densities across species.

Animals↗
PubMedDate not supplied

GABAergic visual pathways in the frog Rana pipiens.

Gamma-aminobutyric acid (GABA) is the most prevalent inhibitory neurotransmitter in the vertebrate brain. It can exert its influence either as GABAergic projection pathways or as local interneurons, which play an essential role in many visual functions. However, no GABAergic visual pathways have been studied in frogs so far. In the present study, GABAergic pathways in the central visual system of Rana pipiens were investigated with double-labeling techniques, combining immunocytochemistry for GABA with Rhodamine microspheres for retrograde tracing. Three GABAergic visual pathways were identified: (1) a retino-tectal projection, from retina to the contralateral optic tectum (OT); (2) an ipsilateral projection from the nucleus of the basal optic root (nBOR) to the pretectal nucleus lentiformis mesencephali (nLM); and (3) a second-order pathway from the nucleus isthmi (NI), bilaterally, to the optic tectum. These results indicate that GABA is involved in both first-order (retina to optic tectum) as well as second-order (nucleus isthmi to optic tectum) visual projections in Rana pipiens, and may play a major role in mediating visuomotor reflexs such as optokinetic nystagmus or other visually guided behaviors.

Animals↗
PubMedDate not supplied

Distribution of GABA-like immunoreactive neurons and fibers in the central visual nuclei and retina of frog, Rana pipiens.

Immunocytochemistry was used to study the distribution of gamma-aminobutyric acid (GABA) throughout the central visual nuclei and retina in Rana pipiens. In the retina, GABA immunoreactivity (both somata and fibers) was observed in all layers except the outer nuclear layer (ONL). Contrary to earlier reports, about 30% of total neurons within ganglion cell layer (GCL) expressed GABA immunoreactivity. Double-labeling studies indicated that about half of the GABA-containing perikarya in the GCL were retinal ganglion cells (RGCs). In the diencephalon, intensely labeled GABA-immunoreactive neurons and nerve fibers were observed within the neuropil of Bellonci (nB) and corpus geniculatum (CG), while only immunoreactive puncta were found in the rostral visual nucleus (RVN). In the pretectal region, the posterior thalamic nucleus (nPT) contained the most intensely labeled GABA immunoreactive perikarya and nerve fibers in the entire brain. Lightly immunoreactive perikarya were also found in the large-celled nucleus lentiformis mesencephali (nLM), as well as in the pretectal gray, which contains neurons postsynaptic to the retinal terminal zones within nLM. In the optic tectum (OT), both immunoreactive perikarya and fibers were found within superficial layers 8 and 9, whereas only densely packed immunoreactive perikarya were evident in the deep tectal layers (i.e. 2, 4, 6). The nucleus of the basal optic root (nBOR) contained a small number of lightly labeled GABA-immunoreactive perikarya, mostly located in the dorsal half of the nucleus. A large number of perikarya within the nucleus isthmi (NI) were also immunostained.

Animals↗