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K V Fite
Publications and source records attributed to K V Fite.
Retinotopic organization of central optic projections in Rana pipiens.
The retinotopic organization of the anuran visual system has been investigated with the method of selective anterograde transport of horseradish peroxidase (HRP) following retinal lesions. The course of optic axons to specific structures was also confirmed by retrograde transport in the optic tract following HRP injections in the tectum and pretectum. As the optic nerve reaches the optic chiasm, the fibers from each of the four retinal quadrants appear as bands with the nasal (n) quadrant entering the chiasmal anterior pole, followed by ventral (v), temporal (t), and dorsal (d) quadrants. The preoptic nucleus is the first structure to be innervated, followed by the suprachiasmatic nucleus; both are innervated directly from fibers in the dorsal part of the optic nerve, which contains fibers from all the retinal quadrants. Each quadrant expands across the dorsoventral extent of the chiasm at the point where it enters. At this level the quadrants are arrayed along the rostrocaudal axis (as they are later in the marginal optic tract) in the sequence n-v-t-d. Optic fibers then spread across the chiasm, the nasal quadrant splits, taking up positions in the rostral and caudal margins of the optic radiation. Following the split in the nasal representation, the optic tract is transformed into topographically arranged sheets in the marginal optic tract. In the other retinorecipient nuclei, the sheet of optic axons is transformed back into the shape of the retinal hemisphere. Topographic maps of this kind display one of two possible orientations: (1) in the tectum and the nucleus lentiformis mesencephali (nLM), the temporal retina is represented in the anterior portion of the nucleus, whereas the nasal quadrant is found in the posterior portion; (2) in the thalamus, the retinotopic map is organized as a mirror-image reversal of that seen in the tectum and nLM (i.e., the nasal pole is anterior, whereas the temporal pole is in the posterior portion of the nucleus). Structures with this type of retinal map include the rostral visual nucleus, the corpus geniculatum, the nucleus of Bellonci, and the posterior thalamic nucleus. A third type of innervation occurs in the nucleus of the basal optic root (nBOR), which is the only mesencephalic visual nucleus not innervated by the marginal optic tract. The basal optic root is formed by the fibers exiting most caudally from the optic chiasm. All the retinal quadrants contribute to the basal optic root, but no evidence of retinotopy was found in nBOR.4+ target nuclei.
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Neurophysiological investigation of the pretectal nucleus lentiformis mesencephali in Rana pipiens.
Previous studies have demonstrated that the large-celled, optic pretectal nucleus lentiformis mesencephali (nLM) is essential for horizontal optokinetic nystagmus, yet little is known about its neurophysiology. In the present study, single-unit analysis of nLM utilized a large-field, patterned stimulus presented for 8 directions and 3 velocities of movement. All units localized in nLM were spontaneously active, motion sensitive, with response profiles that ranged from strongly directional and narrowly tuned to asymmetric and broadly tuned. Only about one-third of the units could be classified as directional, and no response bias for horizontal or temporal-to-nasal motion was observed. The majority of directional units showed greatest responsiveness at the lowest stimulus velocity, while the reverse occurred for many broadly tuned units. These low-velocity, highly directional units may be comparable to the 'retinal slip' neurons recently described in the large-celled pretectal nucleus of mammals. Directional information in the nLM of Rana pipiens thus appears to be represented in the activity of a large population of motion-sensitive units which includes both narrowly and broadly tuned individual response profiles. These results are consistent with the population-coding hypothesis recently advanced to account for directional coding in other sensorimotor systems, including primate motor cortex and superior colliculus.
Aging and sex-related changes in the outer retina of Japanese quail.
Age-related changes in the outer retina of Japanese quail 3 months to 3 years of age have been assessed with light and electron microscopy. A major difference was observed between males and females in the accumulation of lipofuscin in retinal pigment epithelial (RPE) cells. Females showed greater densities of lipofuscin granules, larger granules, and more lipofuscin per RPE cell than did males of comparable ages. In addition, a small but significant decrease (14-16%) in photoreceptor nuclear densities occurred in the temporal retina of both 1-year females and 3-year males. An overall correlation of -.77 between photoreceptor densities and amount of lipofuscin was observed, with a correlation of -.88 for females, alone. No male/female differences were observed with regard to age-related changes in height of RPE cells. Major differences in calcium metabolism and demand associated with egg-laying in females may underlie the observed sex-related differences that occur in the outer retina of this relatively short-lived, domestic species.
Anuran accessory optic system: evidence for a dual organization.
The accessory optic system of Rana pipiens consists of lateral and medial fascicles of the basal optic root (BOR1, BORm) and a single terminal nucleus, nBOR. The present study provides new evidence that these two fascicles differ not only in their trajectories but in fiber spectra and innervation patterns as well. BOR1 contains a substantially higher percentage of large, myelinated axons than does BORm, and the mean diameter of axons in BOR1 is greater than that of BORm. BOR1 innervates the entire terminal field of nBOR, while BORm innervates only the central and mediodorsal portions of nBOR. The ventrolateral portion of nBOR is uniquely innervated by BOR1 and contains several types of neurons not found in the central and medial regions of nBOR which are innervated by both fascicles. Cytoarchitectural analysis of nBOR with Golgi techniques has revealed a number of similarities between the anuran nBOR and the mammalian medial terminal nucleus (MTN) with regard to cellular morphology, dendritic geometry, and retinofugal arborization patterns. In frog, nBOR appears comparable to the ventral subdivision of the mammalian MTN, while the peri-nBOR region, which contains neurons postsynaptic to nBOR, may represent a more primordial version of the mammalian dorsal MTN.
Enhanced integumental and ocular amelanosis following the termination of cyclosporine administration.
The Smyth delayed amelanotic line of chickens display symptoms commonly associated with human vitiligo. Administration of the immunosuppressive compound, cyclosporine, significantly delayed the mean age of onset and incidence of integumental pigment losses in this mutant line of vitiliginous chickens. Associated ocular pathology was also less severe in treated chicks. Termination of cyclosporine administration resulted in enhanced integumental and choroidal amelanosis, choroidal inflammation, and chorioretinal damage beyond that observed in nontreated controls. These results suggest that withdrawal of cyclosporine in treatment of this spontaneous autoimmune disease may exacerbate associated symptoms.
Microiontophoresis and single-unit analysis of cholinergic drugs in the optic tectum of frog.
Microiontophoresis of acetylcholine (ACh), atropine, or curare was accompanied by single-unit analysis of visual neuronal responses in the optic tectum of Rana nigromaculata. In 71% of the units tested, ACh enhanced responses to visual stimuli, while atropine suppressed visual responses. Twenty-two percent of the remainder showed no ACh- or atrophin-induced effects and were recorded within 125 microns of the pial surface. The majority of ACh-enhanced, atropine-suppressed units were recorded from visually responsive units localized in the postsynaptic cellular layer 8. The iontophoretic effects of curare were considerably more varied, with approximately equal numbers of units showing an increase (33%), a decrease (35%) or no change (32%) in visually activated responses. The specific effects of curare were also related to the depth from which unit recordings were obtained. These findings indicate that ACh functions as a modulatory neurotransmitter in the frog optic tectum, with a predominantly muscarinic mode of action at postsynaptic levels.
Effects of cyclosporine in spontaneous, posterior uveitis.
Cyclosporin A (CsA) was administered to chicks of the Smyth delayed-amelanotic (SDA) line from day of hatch to 4, 8 or 12 weeks of age. Animals were evaluated at 8, 12, 16 or 20 weeks with regard to major features of the SDA-line disorder, including extent of feather and choroidal amelanosis, choroidal inflammation, and histopathology of the retinal pigment epithelium and outer retina. A suppression and delay in the onset of both amelanosis and ocular histopathology occurred during CsA administration. However, a rebound enhancement of symptoms occurred 4-8 weeks after withdrawal of CsA that was closely associated with the duration of CsA treatment. These results indicate that CSA may yield therapeutic effects during the period of treatment, but its withdrawal may lead to more severe symptoms that would have occurred without treatment.
The pretectal nucleus lentiformis mesencephali of Rana pipiens.
The pretectal nucleus lentiformis mesencephali (nLM) of Rana pipiens was investigated with autoradiographic, horseradish peroxidase (HRP), and Golgi techniques. Retinal afferents to nLM originate primarily from the central retina. The primary projection is contralateral with a small ipsilateral component. Following optic nerve transection and HRP impregnation, contralateral retinal afferents show a restricted, dense core of HRP label in the superficial portion of the nucleus with sparser HRP label in the surround. Ipsilateral retinal afferents arborize throughout nLM, except in the dense-core region. Additional afferents to nLM originate from the ipsilateral tectum, the nucleus rotundus, the mesencephalic pretectal gray, the contralateral nLM, and the nucleus of the basal optic root. Afferents from the accessory optic system arborize only in the dense-core region, following HRP injections into the nucleus of the basal optic root, while afferents from the mesencephalic pretectal gray arborize in all parts of nLM except the dense core. Afferents from the tectum and anterior thalamus appear to arborize throughout the nucleus without discernible pattern. The lamination of afferent terminals in nLM was correlated with Nissl-stained cytoarchitectural material in which the majority of large neurons cluster around the dense core of nLM. Three types of neurons occur in nLM: large neurons (25-micron dia.), fusiform neurons (12.5-micron dia.), and stellate neurons (10-micron dia.). Additionally, two cell groups outside nLM which send dendrites into the nucleus were observed: cells of the posterior lateral nucleus and cells of the posterior thalamic pretectal gray. Both large and fusiform neurons project to the deep layers of the optic tectum as well as to the ventral rhombencephalon superficial to the abducens nucleus. While a small number of fusiform neurons project to the nucleus of the basal optic root, the stellate neurons appear to be intrinsic to nLM. The anuran nLM strongly resembles the nucleus of the optic tract in mammals in terms of the site of origin of its retinal afferents, lamination of afferent terminations, its central connections, and its demonstrated involvement in horizontal optokinetic nystagmus.
Retinal pigment epithelial correlates of avian retinal degeneration: electron microscopic analysis.
The delayed amelanotic (DAM) strain of domestic chicken is characterized by an early, developmental onset of choroidal inflammation and destruction of both feather and choroidal melanocytes. Secondarily, retinal pigment epithelial (RPE) cells in the peripapillary region develop abnormalities, and a series of progressive histopathological changes ensues which includes reduction and ultimate loss of RPE-melanin granules and RPE-cell atrophy. The earliest sign of RPE-cell abnormality is a dramatic alteration in the distribution of intracellular melanin granules. Apical processes also show a lessening of contact with photoreceptor outer segments, leading in more advanced stages to their retraction and development of retinal detachments. Other progressive alterations in RPE cells include disorganization and loss of basal infoldings; size reductions and density increases in both mitochondria and myeloid bodies from early to advanced stages; appearance of large macrophages in the subretinal space; Loss of intercellular junctional complexes; and progressive reduction in the density of melanin granules. These abnormalities appear to spread in a cell-by-cell, radial pattern, until widespread areas of the retina become severely pathologic and atrophic. The DAM chorioretinal disorder appears to show many of the histopathologic features which characterize experimentally induced uveitis and other ocular diseases which may result from hypersensitivity to, or autoimmune reaction against, pigments of the uveal tract.
Development of the avian accessory optic system: effects of embryonic optic lesions.
Representative cross-sections of the nuclei ectomammillaris (EM) from both normal and optically lesioned chick embryos (45 h of incubation, stage 12), were analyzed and compared on days 6, 8, 10, 12, 14 and 16 of incubation. An identifiable EM is clearly present at 8 days, in both normal and lesioned embryos, and increases in cell number and area up to embryonic day 12. However, embryos with partial or complete unilateral optic ablations demonstrate an apparent acceleration in cell death rate when compared with normals, from days 12-16, when a relatively mature and stable form of EM is apparently reached. Thus, early optic lesions do not affect the morphology of EM until day 12. These data also indicate that embryonic ipsilateral pathways to EM may persist and even expand when one eye primordium is removed or partially lesioned.
The accessory optic system and temporal correlates of visuomotor orientation.
Surgical transection of the basal optic root in Rana pipiens leads to substantial increases in prey-orientation latencies for stimuli presented in the contralateral visual field. In general, the greater the reduction in retinal innervation of nBOR, the greater the postoperative increase in prey-orientation latencies. The results support Herrick's earlier suggestion that the accessory optic system may be substantially involved in early activation and temporal modulation of visuomotor behaviors mediated via mesencephalic circuits.
Pretectal and accessory-optic visual nuclei of fish, amphibia and reptiles: theme and variations.
The organization of the accessory optic and pretectal circuits is surveyed in a variety of poikilotherms and the conclusion drawn that a common organizational pattern exists. This pattern consists of the presence of three optic pretectal nuclei located rostrocaudally in lateral-superficial, central and dorsomedial (or periventricular) positions. Furthermore, a well-defined basal optic tract and ventrolaterally placed terminal field at the level of the oculomotor nucleus appears to be a consistent feature among bony fish, amphibians and reptiles. The possible role of these circuits in in visuomotor behaviors is discussed.
Behavioral and central visual correlates of inherited retinal degeneration in the domestic chicken (Gallus domesticus).
A developmental, posthatch loss of cutaneous and ocular melanocytes in the mutant DAM (delayed amelanotic) chicken is accompanied by severe retinal degeneration. Using a food-location task, increased ocular pigment loss was associated with increased latency of response, both developmentally in young DAMS, and among adults with differing degrees of amelanosis. Analysis of optic nerve fiber composition in normals and DAMs showed a reduction in the small diameter optic axon population in severely amelanotic DAMs. With increasing severity of ocular amelanosis among animals, reduction in the density of anterogradely transported horseradish peroxidase (HRP) reaction product was seen first in retinorecipient thalamic nuclei, subsequently in the optic tectum, and ultimately in the accessory optic nucleus. An inverse relationship was also observed between the density of HRP reaction product occurring in retinal terminal fields and density of HRP label seen in the optic tracts of the same animal. No changes in either the volume or extent of central visual nuclei were apparent in partially sighted and blind DAMs.
Optokinetic nystagmus in progressive retinal degeneration.
Optokinetic nystagmus (OKN) was studied in both normally pigmented and delayed amelanotic (DAM) strains of domestic chicken. The DAM line is characterized by postnatal feather and ocular depigmentation accompanied by progressive retinal degeneration that occurs, initially and most severely, in the central retina. A close association exists between the extent of ocular pigment loss and relative reduction in OKN responsiveness in DAMs. The directional asymmetry of OKN responses, which normally occurs with monocular temporal-to-nasal (T-N) but not to nasal-to-temporal (N-T) stimulation, was altered in relation to the extent of ocular amelanosis among DAMs. In particular, T-N OKN responses were progressively reduced as amelanosis of the central retina increased in severity. In DAMs with moderate to severe reductions in T-N responsiveness, relatively little reduction occurred in N-T responsiveness. The central retina, therefore, appears to play a major role in mediating responses to T-N stimulation, whereas the peripheral retina mediates both directions of response. Optokinetic nystagmus also provides a useful index of the extent of retinal degeneration and the progressive loss of retinal pigment epithelium and photoreceptors which occurs in this mutant strain.
Photomechanical responses of visual receptors in the retina of the bullfrog (Rana catesbeiana).
All photoreceptor types in the bullfrog (Rana catesbeiana) retina exhibit changes of position within the receptor layer, depending upon the state of retinal adaptation, and the season in which the displacement was measured. The most light-adapted position of each photoreceptor type following monochromatic adaptation was not related specifically to the lambda-max of its own photopigment. In general, however, the response profiles were similar for photoreceptors having the same lambda-max. The red rod, accessory member of the double cone, green rod and the miniature cone showed similar response profiles, while the single cone and the principal member of the double cone showed similar patterns of movement as a function of adapting wavelength. The response profiles for the short and middle lambda-max photoreceptors obtained in summer months appeared similar to the action spectrum of the retinal pigment epithelium (RPE) as previously described by Liebman and co-workers. Seasonal differences were also found. The observed photomechanical response profiles may be determined by complex interactions between adjacent photoreceptors, as well.
Progressive cytologic changes during the development of delayed feather amelanosis and associated choroidal defects in the DAM chicken line. A vitiligo model.
Newly hatched Gallus domesticus chicks of the delayed amelanotic (DAM) line have phenotypically normal down pigmentation. Functioning pigment cells are present in the down plumage, choroid, and retinal pigment epithelium. However, histologic and ultrastructural studies reveal that after hatching regenerating feather melanocytes synthesize melanosomes with abnormal, irregularly shaped surfaces and pigmented extensions. Eventually retraction of melanocytic dendrites and clumping of pigment occurs concomitantly with intracellular compartmentalization of the abnormal melanosomes. Melanocyte degeneration is accompanied by the appearance of mononuclear leukocytes (MNLs) in the pulp of the regenerating feathers. Concurrently, melanocytes cease to migrate into the regenerating feather epithelium, and the result is amelanosis. Changes in choroidal melanocytes are first evident as swelling of cell bodies and associated dendrites. Ultrastructurally, the choroidal melanocytes demonstrate increased cytoplasmic material, melanosomal irregularities, retraction of dendrites, melanosome compartmentalization, and eventual necrosis. Concurrently, MNLs arrive and remove the pigment from the choroid. The authors conclude that a basic melanocyte defect precedes the arrival of immunocytes in the delayed cutaneous and choroidal amelanosis in the genetic DAM vitiligo model of the chicken.