Individual axon morphology and thalamocortical topography in developing rat somatosensory cortex
Article first published online: 6 DEC 1998
Copyright © 1996 Wiley-Liss, Inc.
Journal of Comparative Neurology
Volume 367, Issue 1, pages 36–53, 25 March 1996
How to Cite
Catalano, S. M., Robertson, R. T. and Killackey, H. P. (1996), Individual axon morphology and thalamocortical topography in developing rat somatosensory cortex. J. Comp. Neurol., 367: 36–53. doi: 10.1002/(SICI)1096-9861(19960325)367:1<36::AID-CNE4>3.0.CO;2-K
- Issue published online: 6 DEC 1998
- Article first published online: 6 DEC 1998
- Manuscript Accepted: 18 OCT 1995
- NIH. Grant Numbers: NS07351, NS30109
- NSF. Grant Number: BNS 90-22168
- Human Frontiers. Grant Number: RG 55/94B
- axon arbors;
- ventral posterior nucleus
The morphology of individual thalamocortical axons in developing rat primary somatosensory cortex was studied using lipophilic tracers. Anterograde labeling with lipophilic dyes demonstrated a topographical organization of thalamocortical projections exiting the thalamus as early as embryonic day (E)16; retrograde labeling studies demonstrated topography of these projections as they reached the cortex as early as E18. At E17, axons course tangentially within the intermediate zone and turn or branch near the deepest layer of cortex (layer VIb), suggesting the presence of guidance cues in this region. Axons appear to grow and branch progressively within layers VIb and VIa during the following days; axons in the intermediate zone may give rise to radially directed branches. Individual axons appear to grow steadily and progressively into the cortex, with the leading front of axons at the transition zone between the cortical plate (CP) and the differentiating cortical layers. At birth (PO), thalamocortical axons extend radially through layers VIa and V and emit branches within these layers; some axons reach the CP. By P1, layer IV has begun to differentiate and axons begin to form a few simple branches in the vicinity of the layer IV cells. Over the ensuing week, axons generate more branches within layer IV, but the tangential extent of individual axon arbors does not exceed the width of a barrel. By P7, individual axons overlap within barrel clusters, and individual axons span the width of a cluster. These observations indicate that thalamic afferents develop by progressive growth of arbors that remain spatially restricted, rather than by overbranching and retracting arbors. © 1996 Wiley-Liss, Inc.