VISUAL CORTICOPONTINE PROJECTIONS IN THE GUINEA-PIG - AN AUTORADIOGRAPHIC STUDY

The goal of this study is to characterize the anatomical organization of the visual cortical output to the basal pontine nuclei in the guine a pig. Data from the Literature show that guinea pigs exhibit differen t optokinetic oculomotor behaviors with respect to rats and rabbits. N amely, they present a fast rise in eye movement velocity at stimulus o nset and a better performance in monocular horizontal stimulation. Pos sible differences in the visual corticopontocerebellar pathway might e xplain these peculiarities. The pontine projections from the primary v isual cortex were studied with the method of the anterograde axonal tr ansport of [H-3]leucine. The terminal labeling forms prominent patches , ipsilaterally to the cortical injection, throughout the rostrocaudal extent of the pontine nuclei, predominantly in the dorsolateral regio n. At the intermediate rostrocaudal level, some foci of labeling are f ound ventrolaterally as well. Sparse fields are present also in the me dial pontine nuclei and in the nucleus reticularis tegmenti pontis, bu t only when the injection site extends to secondary visual areas, eith er lateral or medial. The present description of the corticopontine pr ojections in guinea pigs is in substantial agreement with the projecti ons previously described in rats, with a few differences, namely: (1) the recipient area extends more caudally; (2) secondary visual areas p roject to the nucleus reticularis tegmenti pontis.