Genesis of Visual Connections in the Rhesus Monkey
The basic afferent connections of the visual system in the rhesus monkey are laid down before birth, although the process of segregation of terminals and synaptogenesis continue into postnatal period. Autoradiographic studies show that projections subserving each eye initially overlap in the dorsal lateral geniculate nucleus (LGd) and in the cerebral cortex of fetal monkeys. In the LGd, retinal terminals originating from each eye become segregated from each other during the middle of the 165-day gestational period. In the cortex, axons representing each eye are intermixed in layer 4 until three weeks before birth when ocular dominance stripes first begin to emerge. This process of segregation in the distribution of geniculocortical afferents is not completed until the second postnatal month. Cortical efferents also begin to develop at the end of the first half of gestation. Corticogeniculate terminals appear characteristically wedge-shaped and topographically organized by midgestation.
Considerable rearrangement of axon terminals is visible in the mature monkey if one eye is enucleated by intrauterine surgery at critical prenatal stages. Thus, when one eye is enucleated during the first third of gestation and the animal survives until the second postnatal month, the LGd is devoid of laminae and the remaining eye projects diffusely throughout the nucleus. Transneuronally transported tracers indicate that ocular dominance stripes fail to develop in the visual cortex. Thus, it appears that both the development of cellular laminae in the LGd as well as the segregation of afferent connections in both the LGd and cortex may depend on competition between projections subserving the two eyes.
KeywordsVisual Cortex Rhesus Monkey Primary Visual Cortex Ocular Dominance Lateral Geniculate Body
Unable to display preview. Download preview PDF.
- Brodmann, K. (1905). Beitrage zur histologischen lokalization der Grosshirnrinde Dritte Mitteilung: Die Rinderfelder niederen Affen. J. Psychol. Neurol. (Leipzig) 9:177–226.Google Scholar
- Giordano, D. L., and T. J. Cunningham (1978). Naturally occurring neuron death in the superior colliculus of the postnatal rat. Anat. Rec. 190:402 (abstract).Google Scholar
- Goldman, P. S. (1979). Prenatal development of cortico-striatal connections in the rhesus monkey: transformation from diffuse to patterned projections (submitted).Google Scholar
- Hendrickson, A., and P. Rakic (1977). Histogenesis and synaptogenesis in the dorsal lateral geniculate nucleus (LGd) of the fetal monkey brain. Anat. Rec. 187:602 (abstract).Google Scholar
- Price, J. L., G. F. Moxley, and J. E. Schwob (1976). Development and plasticity of complementary afferent fiber systems in the olfactory cortex. Exp. Brain Res. Suppl. 1:148–154.Google Scholar
- Rakic, P. (1975). Timing of major ontogenetic events in the visual cortex of the rhesus monkey. In: Brain Mechanisms in Mental Retardation. N. A. Buchwald and M. Brazier (eds.).Google Scholar
- Rakic, P. (1977c). Effects of prenatal unilateral eye enucleation on the formation of layers and retinal connections in the dorsal lateral geniculate nucleus (LGd) of the rhesus monkey. Neuroscience Absts. 3:573 (abstract).Google Scholar
- Rakic, P. (1979a). Genetic and epigenetic determinants of local neuronal circuits in the mammalian central nervous system. In: Neurosciences. Fourth Study Program. F. O. Schmitt and F. G. Worden (eds.), MIT Press, Cambridge, Massachusetts, pp. 109–127.Google Scholar
- Rakic, P. (1979b). Mode of genesis of central visual connections revealed by orthograde axonal flow and transneuronal transport of radioactive tracers following unilateral eye injection in temporarily exteriorized monkey fetuses (submitted).Google Scholar
- Ramón y Cajal, S. (1911). Histologie du Système Nerveux de l’Homme et des Vertébrés Paris, Maloine Reprinted by Consejo Superior de Investigaciones Cientificus, Madrid, 1955, Vols. I and II.Google Scholar
- Shatz, C., and P. Rakic (1978). Prenatal development of efferent projections from the visual cortex in the rhesus monkey. Neurosc. Absts. 4:654 (abstract).Google Scholar
- Swindale, N. V. (1979). How ocular dominance stripes may be formed (this volume).Google Scholar