Postnatal development and laminar distribution of noradrenergic fibers in cat visual cortex

Previous studies have indicated that adrenergic receptors show significant changes either in laminar distribution or in number during the critical 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-containing afferents in visual cortex of kittens of various ages from birth to adulthood. In young kittens, less than 2 weeks of age, noradrenergic fibers were sparse, short and randomly oriented, and were concentrated in layer I and in deep cortical layers V and VI. By postnatal day 40, the fibers were present throughout all cortical layers and exhibited higher densities in layers I, II, III, V and VI, with a band of lower staining in layer IV. While tangential fibers predominated in layers I, V and VI, relatively straight radial fibers traversed layers II and III. After postnatal day 40, we did not find major changes in the laminar distribution of adrenergic fibers. This developmental laminar distribution pattern of adrenergic fibers resembles that of the beta-adrenergic receptors that we and others have studied in kitten visual cortex, but differs from that of alpha-adrenergic receptors.