POSTNATAL-DEVELOPMENT AND LAMINAR DISTRIBUTION OF NORADRENERGIC FIBERS IN CAT VISUAL-CORTEX

Previous studies have indicated that adrenergic receptors show signifi cant changes either in laminar distribution or in number during the cr itical period of kitten visual cortex development. In order to further investigate the postnatal development of this neurotransmitter system , especially in relation to the critical period, we used a polyclonal antibody against dopamine-beta-hydroxylase to localize noradrenaline-c ontaining afferents in visual cortex of kittens of various ages from b irth to adulthood. In young kittens, less than 2 weeks of age, noradre nergic fibers were sparse, short and randomly oriented, and were conce ntrated in layer I and in deep cortical layers V and VI. By postnatal day 40, the fibers were present throughout all cortical layers and exh ibited higher densities in layers I, II, III, V and VI, with a band of lower staining in layer IV. While tangential fibers predominated in l ayers I, V and VI, relatively straight radial fibers traversed layers II and III. After postnatal day 40, we did not find major changes in t he laminar distribution of adrenergic fibers. This developmental lamin ar distribution pattern of adrenergic fibers resembles that of the bet a-adrenergic receptors that we and others have studied in kitten visua l cortex, but differs from that of alpha-adrenergic receptors.