VGLUTs define subsets of excitatory neurons and suggest novel roles for glutamate

Exocytotic release of the excitatory neurotransmitter glutamate depends on transport of this amino acid into synaptic vesicles. Recent work has identified a distinct family of proteins responsible for vesicular glutamate transport (VGLUTs) that show no sequence similarity to the other two families of vesicular neurotransmitter transporters. The distribution of VGLUT1 and VGLUT2 accounts for the ability of most established excitatory neurons to release glutamate by exocytosis. Surprisingly, they show a striking complementary pattern of expression in adult brain that might reflect differences in membrane trafficking. By contrast, VGLUT3 is expressed by many cells traditionally considered to release a different classical transmitter, suggesting novel roles for glutamate as an extracellular signal. VGLUT3 also differs from VGLUT1 and VGLUT2 in its subcellular location, with somatodendritic as well as axonal expression.