Structure and function of synapses

Calcium promotestransmitterexocytosisatmultiple stages. There are several pools of neurotransmitter vesicles in the nerve ending, which differ by their maturity (e g., amount of transmitter stored) and their availability for immediate exocytosis. One effect of calcium consists in the recmit- 

The very fast release of neurotransmitter (1 milliseeond after presynaptie exeitation) is due to the exoeytosis from pre-attached vesieles. This is effeeted via S5maptotagmin, which binds and directly responds to calcimn. Besides the proteins mentioned, there is a somewhat distressing multitude of additional proteins also participating in neurotrans- 

Direct agonists and antagonists will directly bind to the postsynaptic receptor and either activate or competitively block it. 

Within the presynaptie neuron, synthesis, breakdown, or vesicular accumulation of the transmitters may be altered. This may lead to short-term release and long-term depletion of neurotransmitter. These mechanisms are relevant to cocaine and mechanistically similar dmgs of abuse. Dmgs that act according to any of these mechanisms are usually referred to as indirect agonists or antagonists, respechvely. 

We will see examples of all of these mechanisms in subsequent chapters. 

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Bodian, D. Synaptic diversity and characterization by electron microscopy. In G. D. Pappas and D. P. Purpura (eds.), Structure and Function of Synapses. New York Raven Press, 1972, pp. 45-65. 

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