Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, SAL) is a tetrahydroisoquinoline derivative, detected in humans. Salsolinol can be formed in the mammalian brain by three different mechanisms: (1) via the nonenzymatic Pictet–Spengler condensation of dopamine and aldehydes producing salsolinol as two racemic isomers (R or S). (2) By the nonenzymatic condensation of dopamine and pyruvate yielding 1-carboxyl-tetrahydroisoquinoline, followed by decarboxylation and reduction, which produces (R)-salsolinol. (3) By selective synthesis of (R)-salsolinol from dopamine and acetaldehyde, the level of which is increased after ethanol intake. Apart from that salsolinol has also been detected in certain beverages and foodstuff, including soy sauce, cheese. Only the (R) enantiomer of Salsolinol and occur in the human brain, cerebrospinal fluid (CSF) and intraventricular fluid (IVF), and the (S) enantiomer was not detected. Salsolinol was also found to be involved in neurotoxicity processes altering the normal function and survival of dopamine neurons. It has been proposed, that salsolinol participated in the etiopathogenesis of Parkinson’s disease. Salsolinol could inhibit various enzymes, for example, monoamine oxidase and tyrosine hydroxylase and recently was revealed, that (R)-SAL and (S)-SAL were agonists of the μ-opioid receptor. (S)-SAL is a more potent agonist than the (R)-SAL stereoisomer, it was suggested that an opioid action of SAL or its enantiomers is involved in the rewarding effects of ethanol.

PET imaging using 2-[11C]thymidine (dThd) was developed as a measure of tumor proliferation and cancer response to treatment. The drug was tested on patients with brain tumors. A PET image is a result of the metabolic processes for delivery, uptake, and retention in DNA by the tumor and degradative metabolism in the whole patient. 2-[11C]Thymidine is metabolized to [C11]CO2, which rapidly crosses the blood-brain barrier and distributes throughout the brain. 2-[11C]Thymidine itself is poorly transported by the blood-brain barrier, however, it may intercalate into DNA.