Katherine V. Fite - US grants

Our recent research has provided evidence concerning the major nervous system components and circuits which appear to be involved in mediating a visuomotor response which occurs in all vertebrates, optokinetic nystagmus (OKN). In the present proposal, a series of studies are described which will expand and refine our knowledge of the organization and interconnectivity of these neural structures, particularly their relationships with other brain regions involved in sensory-motor integration and the generation of motor response patterns. Ultimately, we are concerned with developing a detailed understanding of the fundamental organizational and functional framework within the nervous system which guides and controls a variety of visually guided behaviors in vertebrates. A thorough understanding of the neuroanatomical and physiological properties of these visual areas should precede, or at least, accompany, studies concerning the function roles of these regions. Anurans are eminently suited for investigations of visuomotor behaviors and their neural substrates. Impairment of these neural systems, which are found in all vertebrates, including Man, may lead to a wide variety of neurological disorders, from congenital nystagmus and oculomotor apraxia, to a variety of oculomotor and vestibular abnormalities for which adequate nerual models have yet to be described.

A series of studies are proposed to investigate age-related alterations in the outer retina of the Japanese quail, which is a relatively short-lived, highly visual species with a cone-rich retina. Baseline morphological data will be estabished with regard to the choriocapillaris, Bruch's membrane, retinal pigment epithelium, photoreceptors, and integrity of the posterior blood- retinal barrier, all of which may show substantial alterations with increasing age. A variety of experimental manipulations will include tests of the following hypothesis: (1) that the effects of a short-duration, moderate-to-high intensity light exposure will have differential effects in the outer retina depending upon age, pigmentation (melanin) of the retinal pigment epitheliam and lipofuscin/age pigmentatin levels of the pigment epithelial cells; (2) that the phagocytic capability or activity of the pigment epithelial cells will vary with age and light-exposure history, and that such effects may be differentially expressed in the central vs. peripheral retina and effect the cone vs. rod photoreceptor shedding processes differentailly; (3) that dietary manipulations which include vitamin-E deprived (-E) vs. vitamin-E deprived Vitamin-A enriched (-E+A) will have differential effects on the accumulatin of age-related pigments in the retinal pigment epithelial cells. Further, that vitamin-E enriched (+E) diet may provide a protective effect against potentially damaging light exposure. By experimentally uncoupling the normally occuring relationship between retinal pigment epithelial concentrations of age-related pigments, both the phagocytic potential and the effects of ligh-damage upon the pigment epithelium can be assessed in young vs. aged animals, Japanese quail should prove to be an excellent laboratory species for experimental studies of aging in the vertebrate retina, since its offers all of the major advantages of a short-lived, highly visual diurnal species, with a pigmented retina of the avascular type, characterized by a large proportion of cones as well as rod photoreceptors. The studies proposed should have major relevance for age-related changes that occur in the human macula, particularly those associated with senile macular disease which is one of leading causes of visual disability and blindness in people 65 years of age and older. At present, a major need exists for laboratory species with many of the characteristics seen in the human retina, but which age rapidly, as does the quail.

The central visual pathways of amphibians have been chosen as a model system for investigation of the neural substrates of visuomotor behaviors mediated via mesencephalic circuits. In recent years, increased attention has been directed toward the pretectual and accessory optic pathways and their associated correlates of visually guided behaviors in anurans, including optokinetic nystagmus, visual orientation and prey-acquisition behaviors. Our recent studies have utilized neuropharmacological and microiontophoretic analyses as well, demonstrating that neuropharmacologic manipulation of accessory optic and pretectal optic systems can provide a powerful tool with which to elucidate the physiological interactions which occur both within and between these two extratectal optic circuits. The studies proposed in this application are presented within the context of our current knowledge and previous work concerning the accessory opticpretectal circuitry and with regard to relevant histochemical observations: (1) singleunit analysis of the effects of cholinergic drugs in the pretectal nucleus lentiformis mesencephali and the extent to which visually responsive units may be modulated by simultaneous microiontophoresis of cholinergic agonists or antagonists, (2) GABAnergic effects on visual neuronal responses on nLM and the accessory optic nucleus, nBOR, as well as the effects of accessory optic deafferentation on visual responses in the pretectal nLM. These studies will advance our knowledge concerning the functional organization of the accessory optic and pretectal optic nuclei including the neuropharmacologic mechanisms and neuromodulatory processes which ultimately affect visuomotor responses mediated through these extratectal optic systems.

A major objective of the research proposed is to further advance our basic knowledge of the organization of central visual pathways, including the optic nerve, the relationship of cell groups in the optic chiasm to the divergence of the optic tracts, and the innervation of multiple central targets. A major focus is upon two major extratectal nuclei, the accessory optic nucleus and pretectal nucleus lentiformis mesencephali and their interrelationship. These studies are relevant to understanding how the retina innervates multiple targets in more complex species, as well. The proposal addresses the following questions: 1, to what degree are retinal axons within the optic nerve organized by morphological type; 2, what is the nature of the spatial transformations of retinal axons within the optic nerve and chiasma; 3, at what point do retinal axons separate into fascicles bound for specific target destinations; 4, what is the relationship of these optic fascicles to cell groups of the hypothalamus in the immediate vicinity of the optic chiasm; 5, how are axons arranged within each of the optic- tract fascicles; and 6, how are the different arrangements of axons, i.e., retinal topography, morphological type of axon and central target destination interrelated? A second major objective is to further clarify the dual organization of the accessory optic system and its interrelationship with the pretectal nucleus lentiformis mesencephali. Ultrastructural techniques will be used to examine central-retinal vs. peripheral-retinal innervation of the basal optic nucleus via medial and lateral fascicles of the basal optic root, respectively. An ultrastructural analysis of the efferent projection from the accessory optic nucleus to the pretectal nucleus lentiformis mesencephali is also proposed. %%% For more than 50 years, the amphibian visual system has been the focus of a broad range of investigations that have provided a major source of knowledge about the basic organization of the vertebrate visual system, particularly the retina and subcortical visual pathways. Evolutionarily, amphibians are among the oldest vertebrates which possess the major retinal projections which occur, generally, in vertebrates.

Non-Technical Summary IBN 95-13884 PI: K. Fite Finding Food: Neuroethological Aspects of Foraging This is a proposal for partial support for a conference that integrates functional (adaptive ecological) and mechanistic approaches to the study of how animals forage. That is, how do animals locate, capture and identify sources of essential nutrition. The unique feature of this conference is that it brings together scientist who seek to answer this fundamental question from the perspectives of 1) sensory mechanisms, 2) neural processes, 3) cognitive and learning processes, and 4) behavioral ecology. This conference will be an exemplary forum that will provide young as well as experienced investigators a view of how contemporary science attacks an age-old question in Animal Behavior, how do organisms find the sources of ingested energy necessary to sustain life.

An expanding research and clinical literature indicates that a strong association exists between light stimulation and a variety of affective, behavioral, and cognitive functions. At present, little is known about the neural circuitry whereby environmental light stimulation may influence the serotonin system, one of the oldest and most widespread neurochemical systems in the brain. Recently, the existence of a direct retinalpathway to the large, serotonergic dorsal raphe nucleus (DRN) of the brainstem has been described in a number of different vertebrate species. The DRN has widespread projections to the forebrain and contains the greatest proportion of serotonergic neurons in the brainstem. Several neuroanatomical studies conduct by the PI indicate that the retinal-DRN project is substantially large in diurnal than in nocturnal species. At present, the functional correlates of this direct optic pathway to the DRN are unknown.

Several exploratory studies are proposed to investigate the functional correlates of optic input to the DRN and serotonergic system using Mongolian gerbils, a highly visual diurnal rodent with a well-developed retinal-DRN projection. Major research objectives include the following: (1) Experiments utilizing the 2-deoxyglucose (2-DG) metabolic technique should reveal whether visual stimulation alters 2-DG uptake in the DRN, and if so, where the greatest uptake occurs. Several kinds of visual stimulation will be presented: (a) exposure to a sustained, high-intensity stimulus, (b) exposure to a flashing light presented at different flash frequencies, (c) exposure to a large-field, random-dot moving pattern presented at different velocities. Experimental animals will be compared with controls exposed only to dim illumination. The effects of electrical stimulation of the optic nerve on 2-DG uptake in the DRN also will be investigated. (2) A second set of experiments will involve application of 5-HT microdialysis techniques in the gerbil DRN to determine whether extracellular 5-HT varies in the DRN over the 24-hour, light:dark cycle. In addition, experiments will be conducted to determine whether a 30-minute presentation of high intensity light stimulation presented at different times of the 24-hour light:dark cycle will alter baseline, extracellular 5-HT levels, particularly in regions of the DRN where optic terminal occur with highest density.

These studies should contribute substantially advances in fundamental knowledge about this direct optic pathway to the serotonin system and facilitate a variety of future experiments to determine the effects of DRN stimulation on efferent target structure such as the intergeniculate leaflet, superior colliculus, and visual cortex, all of which receive serotonergic projections from DRN.