Octopamine in leeches—II. Synthesis, release and reuptake of octopamine by the ventral nerve cord of Erpobdella octoculata

Abstract

1. Octopamine was synthesized by the ventral nerve cords of E. octuculata during in vitro incubation in radiolabelled tyrosine and tyramine. Trace amounts of dopamine were also synthesized from tyrosine and tyramine. 2. In vitro uptake of 3H-octopamine revealed the presence of a sodium sensitive and a sodium insensitive component which was linear up to 10.54 μM. The sodium sensitive component showed at least one component that was fully saturated at 1.54 μM octopamine, possessed a K m of approximately 4 × 10 −7 M and a V max of 15.5 mM/10 ventral nerve cord ganglia/min. 3. Release of preloaded 3H-octopamine from ventral nerve cords was by a calcium-dependent process. A high-potassium-induced calcium-dependent release was also demonstrated. 4. Hydroxymandelic acid production was decreased in the presence of iproniazid phosphate suggesting the presence of a monoamine oxidase. 5. The synthesis, release, reuptake and metabolism of octopamine are discussed in the light of octopamine as a central transmitter in the leech.