Abstract
It was found previously that transection of one branch of the bifurcate axon of a giant serotonergic neuron of Aplysia causes a proportionate decrease in the export of transmitter storage vesicles from the cell body, despite the ability of the remaining branch to transport all of the vesicles normally exported (Aletta and Goldberg, 1982). We report here evidence that this down-regulation is achieved by a decrease in the production of vesicles, rather than a slowing of the processing of vesicles for export from the cell body. Counts of serotonergic vesicles in the cell body show that the size of the somal pool of vesicles is not increased at a time when their rate of export has been halved. Also, transection of one or both branches of the axon decreases the amount of 3H-fucose incorporated during a short period into a putative vesicle membrane glycoprotein but not into other glycoproteins. The results indicate that axotomy should be a useful technique for studying the mechanism of regulation of the synthesis of a secretory organelle. It was also previously shown that transection of one branch of the axon far from the cell body does not impair the ability of the injured branch to transport serotonergic vesicles, yet the majority of vesicles that would normally enter that branch are nevertheless rerouted into the uninjured branch. We have studied quantitatively the partitioning between the 2 branches, after one has been transected distally, of 6 fucosyl glycoproteins, including the putative vesicle glycoprotein and a glycoprotein whose transport moderately increases after transection.(ABSTRACT TRUNCATED AT 250 WORDS)