Question: How does the organic cation transporter 3 (OCT3) play a role in the regulation of neurotransmission in the brain?

Context:
The organic cation transporter (OCT) 3 is widely expressed in various organs in humans, and involved in the disposition of many exogenous and endogenous compounds. Several lines of evidence have suggested that OCT3 expressed in the brain plays an important role in the regulation of neurotransmission. 
The organic cation transporter 3 (OCT3; synonymous: extraneuronal monoamine transporter, EMT, Slc22a3) encodes an isoform of the organic cation transporters and is expressed widely across the whole brain.
In agreement with this distribution, OCT3/Slc22a3-deficient mice show evidence of altered monoamine neurotransmission in the brain, with decreased intracellular content and increased turnover of aminergic transmitters.
CRT, taurine transporter (TauT/SLC6A6) and organic cation transporter (OCT3/SLC22A3) expressed at the BCSFB are involved in guanidinoacetic acid or creatinine efflux transport from CSF.
The organic cation transporter 3 (OCT3; synonymous: extraneuronal monoamine transporter, EMT, Slc22a3) encodes an isoform of the organic cation transporters and is expressed widely across the whole brain
The organic cation transporter 3 (OCT3; synonymous: extraneuronal monoamine transporter, EMT, Slc22a3) encodes an isoform of the organic cation transporters and is expressed widely across the whole brain. 
CRT may be a key factor facilitating blood-to-brain guanidinoacetate transport in patients deficient in S-adenosylmethionine:guanidinoacetate N-methyltransferase, the creatine biosynthetic enzyme, resulting in cerebral accumulation of guanidinoacetate. CRT, taurine transporter (TauT/SLC6A6) and organic cation transporter (OCT3/SLC22A3) expressed at the BCSFB are involved in guanidinoacetic acid or creatinine efflux transport from CSF.
Slc22a3) encodes an isoform of the organic cation transporters and is expressed widely across the whole brain.
CRT, taurine transporter (TauT/SLC6A6) and organic cation transporter (OCT3/SLC22A3) expressed at the BCSFB are involved in guanidinoacetic acid or creatinine efflux transport from CSF. Interestingly, BBB efflux transport of GCs, including guanidinoacetate and creatinine, is negligible, though the BBB has a variety of efflux transport systems for synthetic precursors of GCs, such as amino acids and neurotransmitters.
 The organic cation transporter (OCT) 3 is widely expressed in various organs in humans, and involved in the disposition of many exogenous and endogenous compounds. Several lines of evidence have suggested that OCT3 expressed in the brain plays an important role in the regulation of neurotransmission.
CRT, taurine transporter (TauT/SLC6A6) and organic cation transporter (OCT3/SLC22A3) expressed at the BCSFB are involved in guanidinoacetic acid or creatinine efflux transport from CSF.
Several lines of evidence have suggested that OCT3 expressed in the brain plays an important role in the regulation of neurotransmission.
The organic cation transporter 3 (OCT3; synonymous: extraneuronal monoamine transporter, EMT, Slc22a3) encodes an isoform of the organic cation transporters and is expressed widely across the whole brain.
OCT2-OCT-3 display differential tissue distribution: OCT1 is predominantly found in liver of humans, and liver and kidney in rodents; OCT2 is most strongly expressed in both human and rodent kidney, whereas is OCT3 primarily expressed in placenta, but also more widely detected in various tissues, including brain and lung.

Answer: Several lines of evidence have suggested that OCT3 expressed in the brain plays an important role in the regulation of neurotransmission.