Is there such thing as "half-life" of dopamine? If a dopamine is released at T=0 and binds to receptor D2, what determines the time when the concentration of this neurotransmitter bound to the receptor reaches half of the original concentration? In other words, when will the effect of neurotransmitter on the intercell signalling fall in half? **Is there any time estimate of how quickly the brain thinks that neurotransmitter has "fulfilled its purpose" and is to be re-uptaken?** Or is this process completely random? Thank you for your input!

**The half life of dopamine in the extracellular space is of the order of 200 milliseconds.**

Yavich,L. (2007) Site-Specific Role of Catechol-O-Methyltransferase in Dopamine Overflow within Prefrontal Cortex and Dorsal Striatum. J. Neurosci. 27:10196-10202

In Figure 1 of this paper the authors present values for the half-life (τ) of dopamine elimination from extracellular space in the caudate nucleus and prefrontal cortex of mice as:

caudate nucleus: 0.2 +/- 0.03 sec

prefrontal cortex: 1.92 +/- 0.22 sec

Apparently this is because dopamine is usually inactivated when the presynaptic cell takes it back up using the dopamine transporter, but in the prefrontal cortex uptake is instead via a lower affinity norepinephrine transporter on neighbouring neurones. Thus the value of 200 milliseconds seen in the caudate nucleus is probably more typical.