Activity-dependent regulation of neurotransmitter synthesis refers to the ability of some nerve cells to change the amount of neurotransmitter synthesized in response to activity. Study of this regulation is prompted by the belief that it is important not only for maintaining a source of neurotransmitter but also for adaptive changes that take place in certain nerve cells during learning and memory. A basic postulate necessary for neurotransmitter synthesis regulation to be a mechanism for learning and memory is that increased neurotransmitter synthesis acts to increase neurotransmitter secretion and, as a consequence, synaptic strength. It has not been technically possible thus far to demonstrate a causal relationship between activity-dependent regulation of neurotransmitter synthesis and an increase in neurotransmitter secretion. Nonetheless, activity-dependent regulation of neurotransmitter synthesis remains a candidate for the cause of neuroplastic changes that underlie learning, memory, and neuroplasticity. Neurotransmitters...