SNAP-25 requirement for dendritic growth of hippocampal neurons

Structure and dimension of the dendritic arbor are important determinants o f information processing by the nerve cell, but mechanisms and molecules in volved in dendritic growth are essentially unknown. We investigated early m echanisms of dendritic growth using mouse fetal hippocampal neurons in prim ary culture, which form processes during the first week in vitro. We detect ed a key component of regulated exocytosis, SNAP-25 (synaptosomal associate d protein of 25 kDa), in axons and axonal terminals as well as in dendrites identified by the occurrence of the dendritic markers transferrin receptor and MAP2, Selective inactivation of SNAP-25 by botulinum neurotoxin A (BoN TA) resulted in inhibition of axonal growth and of vesicle recycling in axo nal terminals, In addition, dendritic growth of hippocampal pyramidal and g ranule neurons was significantly inhibited by BoNTA, In contrast, cleavage of synaptobrevin by tetanus toxin had an effect on neither axonal nor dendr itic growth, Our observations indicate that SNAP-25, but not synaptobrevin, is involved in constitutive axonal growth and dendrite formation by hippoc ampal neurons. (C) 1999 Wiley-Liss, Inc.