Cholinergic mechanisms in the central nervous system of the sipunculoid Physcosoma japonicum

Acetylcholine (ACh) content of the central nervous system in the sipunculid P. japonicum was estimated by application of extracts from the nervous tissue to dental retractor of the sea urchin using ACh solutions with known concentration as a standard. It was shown that the nervous tissue contains 46 (from 41 to 51) microng of ACh (calculated as cation) per 1 g of wet material. In the presence of the nervous homogenate from Physcosoma, 880 micronM of ACh are hydrolyzed by 1 g of wet tissue per 1 hour. The content of ACh and the activity of cholinesterase are comparable with those in the brain of molluscs, arthropods and mammals. Anticholinesterase drugs (physostigmine and neostigmine) evoked spontaneous contractions of the proboscis retractor when applied to the nervous cord and enhanced the response of this muscle to electrical stimulation of this cord. Cholinolytics (arpenal and pentaphen) also caused spontaneous muscle contractions, but prevented the increase in muscular activity in response to electrical stimulation in presence of physotigmine. The data obtained suggest cholinergic nature of the transmission in the central nervous system of sipunculids.