Subsecond Regulation of Synaptically Released Dopamine by COMT in the Olfactory Bulb.

In the olfactory bulb (OB), odors are encoded by glomerular activation patterns. Dopaminergic short axon neurons (SACs) form an extensive network of lateral connections that mediate cross talk among glomeruli, releasing GABA and DA onto sensory nerve terminals and postsynaptic neurons. DA neurons are ∼10-fold more numerous in OB than in ventral tegmental areas that innervate the striatum. We show that OB has abundant expression of the DA catalytic enzyme catechol-O-methyl-transferase (COMT), but negligible expression of the dopamine transporter. Using optogenetics and fast-scan cyclic voltammetry, we show that inhibition of COMT increases DA signals ∼2-fold. Thus, in contrast to the striatum, which has the brain's highest proportion of DAergic synapses, the DA catalytic pathway involving COMT predominates over re-uptake in OB.