DEVELOPMENT AND REGULATION OF ALPHA-ADRENOCEPTORS IN KITTEN VISUAL-CORTEX

Alpha-1 and alpha-2 adrenergic receptors were localized in developing cat visual cortex by using [H-3]prazosin and [H-3]rauwolscine, respect ively as selective ligands. The effects of neuronal input on the devel opment of the two receptor subtypes were also studied in animals with lesions at various sites within the central visual pathways. Binding d ensities for both ligands increased during the first few postnatal wee ks and declined thereafter. For both receptor subtypes, the highest co ncentration of binding sites was found in the subplate zone of the cor tex in neonatal animals. Both ligands showed their highest concentrati ons in cortical layer IV beginning at postnatal day 30 and in the supe rficial cortical layers in adulthood. However, the developmental redis tribution of alpha-1 receptors began at earlier ages than that of the alpha-2 sites. The alpha-1 sites were still concentrated in the subpla te zone up to 60 days postnatal, while the alpha-2 sites in this regio n disappeared much earlier. Receptor. binding densities were also exam ined in animals with quinolinic acid lesions within cortex, lesions of the lateral geniculate nucleus and lesions of the optic tract. The re sults indicate that both alpha-adrenoceptor subtypes were mainly locat ed on cortical cells, and that the absence of neuronal activity during development resulted in a reduction of the binding density for both s ubtypes in the visual cortex. An additional major reduction in alpha-2 but not alpha-1 binding sites was observed following the lateral geni culate nucleus lesion, suggesting that the development of alpha-2 rece ptors is also dependent on input from the lateral geniculate nucleus. Removal of the lateral geniculate nucleus early in life resulted in a significant increase in alpha-1 receptors in the subplate region, indi cating that receptor densities in this zone may be negatively regulate d by the lateral geniculate nucleus afferents. These results show that adrenergic receptors reorganize during postnatal cortical development with a strong temporary concentration in the subplate zone. The reorg anization process is heavily influenced by cortical inputs.