Synthesis of acetylcholine by excitatory motoneurons in central nervous system of the leech

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Abstract
The synthesis of acetylcholine (ACh) and other transmitters by the cell bodies of functionally identified neurons in leech segmental ganglia was studied. Choline acetyltransferase, the synthetic enzyme for ACh, was detected in excitatory motor neurons but not in mechanosensory cells or Retzius cells. The ability of motor neurons to synthesize ACh was demonstrated by their accumulation of 3H-ACh following incubation of segmental ganglia with 3H-choline. 3H-ACh was not detected in the other cell types. When eserine was included in 3H-choline incubations, the amount of 3H-ACh in motor neurons increased several fold and small amounts of 3H-ACh (1% that in motor cells) appeared in extracts of sensory and Retzius cells. In addition to 3H-ACh, segmental ganglia synthesized 3H-5-HT [5-hydroxytryptamine], 3H-GABA, 3H-dopamine and 3H-octopamine from exogenous, labeled precursors. None of these labeled transmitters was detected in identified neurons except 3H-5-HT, which was found in Retzius cells. These results provide biochemical evidence that excitatory motor neurons in the leech are cholinergic but leave open the identity of the sensory transmitter(s).