Neuroscience Online

Section I: Cellular and Molecular Neurobiology 10. Transport and the Molecular Mechanism of Secretion Part 1 of 5 Jack C. Waymire, Ph.D.

Introduction

As you learned in previous chapters, neurotransmission occurs through the secretion of neurotransmitter from a nerve ending to influence the postsynaptic cell. In this chapter the biological mechanisms of vesicle mediated synaptic transmission will be presented.

Within the last twenty years it has become apparent that all intracellular membrane trafficking is based on the same fundamental mechanisms. The same operations involved in the synthesis and transport of vesicles at the ER and Golgi apparatus in the soma are employed in a modified fashion during neurosecretion. The major difference is that vesicle trafficking during neurosecretion is regulated by Ca²⁺ influx whereas vesicle trafficking during the synthesis and transport of vesicles is not. Unregulated trafficking is termed constitutive. In both cases, however, trafficking is made up of a series of steps involving budding of vesicles, their docking with other organelles, and fusion with the membranes of these organelles. These processes are believed to be present during vesicle biogenesis when the ER generates vesicles that fuse with the Golgi apparatus, when the endosomes are trafficked to the lysosomes, and when vesicle membrane is recaptured from the nerve ending plasma membrane. There is a budding from their membrane origin, a movement to the destination point, and finally the docking of the vesicles with the target organelle where it attaches to and fuses with the organelle membrane.

This section will cover the life of a neurotransmitter vesicle beginning with its synthesis in the cell soma, transport to the nerve ending, recycling at the nerve ending. Vesicle proteins are eventually returned to the cell soma for reuse in the synthesis of new vesicles.

Figure 10.1 Five phases of neurotransmitter trafficking that will be discussed.

Click on the blocks marked on this Neuron (above) to see details,
or choose from the list below.