Katalia Koves
Semmelweis University of Medicine, Hungary
Title: Basic research about the neural connections between the eye and the neuroendocrine system
Biography
Biography: Katalia Koves
Abstract
Ample evidence indicates that both retinofugal (classical visual and the retinohypothalamic pathway) and retinopetal connections (centrifugal visual system) are found between the eye and the central nervous system. The most important retinofugal connection is the classical visual pathway. Scharrer hypothesized that photic stimuli from the eye are conjucted not only to the main visual centers, but also to some hypothalamic neurons and then to neuroendocrine effector cells. He called this system as photoneuroendocrine. The anatomical basis of this system is the retinohypothalamic tract. The main retinorecipient area of the hypothalamus is the suprachiasmatic nucleus which regulates biological rhythms (biological clock). More than hundred years ago, Cajal and Dogiel described termination pattern of the fibers deriving from the avian central nervous system. However, the location of nerve cell bodies was not known at that time. In the last century many data accumulated about these neurons not only in lower vertebrates but in mammals as well. The structures where the neurons give rise to the centrifugal visual fibers in mammals are the following: The pretectum, midbrain, dentate gyrus, hippocampus, olfactory
tubercle, habenula, indusium griseum, and the hypothalamus. The centrifugal visual fibers enter the optic nerve layer, then reach the inner plexiform layer and terminate in the inner nuclear layer of the retina in the vicinity of the amacrine cells. A series of neuropeptides and neurotransmitters have been described in the origin of the centrifugal visual system i.e., luteinizing
hormone releasing hormone, pituitary adenylate cyclase activating polypeptide, vasoactive intestinal polypeptide, serotonin, histamine and leu-enkephalin. Several hypotheses exist on the function of this system. Centrifugal visual system arising from the histaminergic mammillary neurons modifies the sleep/wake cycle. Hallucinogenic drugs through the limbic system may
cause disturbance of visual function and result in seeing visual hallucinations or distorted images.