Influence of Dendritic Morphology on Axonal Competition.pdf

Influence of Dendritic Morphology on Axonal Competition Arjen van Ooyen 1 , David J. Willshaw 2 and Ger J. A. Ramakers 1 (1) Netherlands Institute for Brain Research, Meibergdreef 33, 1105 AZ, Amsterdam, The Netherlands (2) Institute for Adaptive and Neural Computation, Division of Informatics, University of Edinburgh, 2 Buccleuch Place, Edinburgh EH8 9LW, UK Neurocomputing 32-33 (2000) 255-260 Abstract The development of nerve connections involves competition among axons for survival promoting factors, or neurotrophins, which are released by the axons’ target cells. We have extended our model of axonal competition [11] to study the influence of the target’s dendritic tree on competition. We show that spatial separation of innervating axons on the target’s dendrites mitigates competition and permits the coexistence of axons. The model accounts for the finding that in many types of neurons a positive correlation exists between the size of the dendritic tree and the number of innervating axons surviving into adulthood [6, 8]. Our results emphasize the importance of postsynaptic dendritic morphology in the development of specific patterns of nerve connections. Keywords: competition; neurotrophins; dendrites; morphology 1 Introduction The development of connections between neurons and their target cells often involves an initial stage of superinnervation followed by elimination of axons [7]. Competition among innervating axons for target- derived neurotrophins, which are taken up by the axons via specific receptors at their terminals [1] and which affect the growth and branching of the axons, is thought to be involved in the elimination of axons [9]. In many types of neurons, a positive correlation exists between the complexity of the dendritic tree and the number of innervating axons surviving into adulthood [6, 8]. In the ciliary ganglion of adult rabbits, for example, neurons that lack dendrites are innervated by a single axon, whereas neurons with many dendrites are