POSTNATAL-DEVELOPMENT OF H-3 RAUWOLSCINE BINDING-SITES IN THE DORSAL LATERAL GENICULATE-NUCLEUS AND THE STRIATE CORTEX OF THE TREE SHREW (TUPAIA-BELANGERI)

Noradrenaline has been shown to play an important role within the visual system of the brain. analyze the postnatal development of alpha2-noradrenergic receptors in the visual system of tree shrews, we localized and quantified binding sites for the antagonist [H-3]-rauwolscine by in vitro-autoradiography in the dorsal lateral geniculate nucleus and the striate cortex at different postnatal ages. At birth, the dorsal lateral geniculate nucleus is only slightly labeled by [H-3]-rauwolscine. During the postnatal period, the number of binding sites increases to reach a maximum around postnatal day 20. Since the young tree shrews open their eyes at approximately day 19, it appears that this high concentration of alpha2-adrenoceptors is related to eye opening. In the adult animal, [H-3]-rauwolscine labeling shows a laminated pattern in the dorsal lateral geniculate nucleus. Laminae 1, 2, and 3 are more strongly labeled than laminae 4, 5, and 6. In the striate cortex, the pattern of [H-3]-rauwolscine-binding sites changes dramatically during the early postnatal period. Immediately after birth, there is only one layer, located within the subplate zone, which is labeled. From postnatal day 5 onwards, all cortical layers which can be distinguished on histologically stained sections reveal [H-3]-rauwolscine-binding sites, but in layer IV, which is known to receive major inputs from the dorsal lateral geniculate nucleus, there is very little labeling during the first two postnatal weeks. In this layer, a large number of [H-3]-rauwolscine-binding sites occurs between postnatal day 15 and 20, that is slightly before and around the time of eye opening. From this time onwards, the pattern of [H-3]-rauwolscine binding in the striate cortex is very similar to that in the adult, where all layers are labeled although to different degrees. Since around postnatal day 20, maximal numbers of [H-3]-rauwolscine binding sites are present in the dorsal lateral geniculate nucleus and a large number of these binding sites also emerges in layer IV of the striate cortex, alpha2-noradrenergic receptors are probably important for processes related to the opening of the eye and/or for the visual system to function.