Neurotransmitter synthesis in the nervous system of the mollusc Hermissenda

1. Biochemical and histochemical analysis of the circumesophageal ganglia of the nudibranch mollusc Hermissenda crassicornis revealed four putative neurotransmitters: acetylcholine, dopamine, serotonin and histamine. 2. Acetylcholine was synthesized and accumulated within the neuropile where all known synaptic interactions occur. 3. Histochemical staining demonstrated that acetylcholinesterase is almost entirely localized in the neuropile region. 4. Degradation of ACh was increased by perfusing the preparation with seawater containing high K⁺. 5. Study of the enzymes involved in the metabolism of the above-mentioned neurotransmitters revealed that choline-acetyltransferase had much higher specific activity than either tyrosine or tryptophan hydroxylases. 6. The temperature optimum found for the CAT was 20°C, while tryptophan and tyrosine hydroxylase showed an increase in their activity up to 30 and 35°C respectively. 7. AChE was found to have high activity throughout the temperature range tested (0-35°C).