Journal of Neuroscience, Vol 16, 137-147, Copyright © 1996 by Society for Neuroscience
Axonal transport and distribution of synaptobrevin I and II in the rat peripheral nervous system
JY Li, L Edelmann, R Jahn and A Dahlstrom
Department of Anatomy and Cell Biology, University of Goteborg, Sweden.
Synaptobrevin, a membrane protein of synaptic vesicles that plays a key
role in exocytosis, occurs in two closely related isoforms, synaptobrevin I
and II. We have analyzed the axonal transport of both isoforms in sciatic
nerve and spinal roots. When fast axonal transport was interrupted by
crushing, the proteins accumulated continuously proximal to the crush.
Accumulation also was observed distal to the crush, but to a lesser extent
(47 and 63% of the proximal accumulation for synaptobrevin I and II,
respectively). Immunoelectron microscopy revealed that, proximal to the
crush, synaptobrevin I and II were associated with small clear vesicles
reminiscent of typical synaptic vesicles. Distal to the crush, membranes
positive for synaptobrevin I or II were more heterogeneous, including
larger membrane profiles that may represent endosomes. In spinal cord,
synaptobrevin I and II were colocalized in many terminals. However,
labeling for synaptobrevin I was more intense whereas labeling for
synaptobrevin II was stronger in dorsal than in ventral horn terminals.
Motor endplates contained only synaptobrevin I. In the sciatic nerve,
synaptobrevin I was present predominantly in large, myelinated axons,
whereas synoptobrevin II was virtually absent but abundant in small- and
medium-sized axons. Lumbar sympathectomy, ventral rhizotomy, and
double-labeling studies confirmed that synaptobrevin I is present
predominantly in motor neurons whereas synaptobrevin II is present in
adrenergic and sensory neurons. We conclude that synaptobrevin I and II are
transported bidirectionally by fast axonal transport and are expressed
heterogeneously in different neurons in the peripheral nervous system of
the adult rat, suggesting that these isoforms have special functional roles
in different sets of neurons.