Release of Aromatic Amines From Brain Tissues of the Rat in Vitro1

Radioactive β‐hydroxylated phenylethylamines, DL‐octopamine and DL‐metara‐minol, as well as DL‐norepinephrine, were released from slices or minces of rat brain in vitro by electrical or ionic depolarizing stimuli. In contrast, labelled D‐amphetamine and p‐tyramine were poorly released and the release of urea was barely perceptible. Addition of unlabelled L‐norepinephrine to an incubating medium led to displacement of previously bound [3H]octopamine and [3H]metaraminol from a synaptosomal preparation. Pretreat‐ment of rats with intrathecal 6‐hydroxydopamine markedly decreased the ability of slices of their brains to release [3H]norepinephrine and [3H]octopamine. We suggest that certain phenolic β‐hydroxylated phenylethylamines may enter central, norepinephrine‐containing nerveendings, may be stored in presynaptic vesicles and may be released by nerve stimulation. Under certain circumstances such compounds may act as neurotransmitters with unknown post‐synaptic effects.