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Bulbus arteriosus of the bivalve mollusc Mercenaria mercenaria : Morphology and pharmacology
Author(s) -
Deaton Lewis E.,
Felgenhauer Bruce E.,
Duhon Daniel W.
Publication year - 2001
Publication title -
journal of morphology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.652
H-Index - 74
eISSN - 1097-4687
pISSN - 0362-2525
DOI - 10.1002/jmor.1064
Subject(s) - anatomy , ventricle , ductus arteriosus , biology , aorta , lumen (anatomy) , fmrfamide , medicine , neuropeptide , microbiology and biotechnology , biochemistry , receptor
We examined the morphology and pharmacology of the bulbus arteriosus of the marine bivalve mollusc Mercenaria mercenaria. The bulbus arteriosus is an organ of unknown function associated with the posterior aorta and the ventricle. It is composed of connective tissue interspersed with muscle bundles. In contrast to the lumen of the ventricle, which has an extensive trabecular network, the lumen of the bulbus arteriosus has no trabeculae. No valve is present in the posterior aorta connecting the lumina of the ventricle and the bulbus arteriosus. Scattered neuronal profiles are present in the wall and the axonal processes contain vesicles that may contain neurosecretory products. We did not, however, find synapses or evidence of vesicular release into the lumen of the bulbus arteriosus. The bulbus arteriosus contains acetylcholine, 5‐hydroxytryptamine (5HT), and the molluscan neuropeptides FMRFamide (phenyl‐alanyl‐methionyl‐arginyl‐phenylalaninylamide) and FLRFamide (phenylalanyl‐leucinyl‐arginyl‐phenylalanylamide). The isolated bulbus arteriosus contracts tonically in response to mechanical stress and exposure to 5HT or FMRFamide, while acetylcholine relaxes it. We surmise that the bulbus arteriosus probably functions as a mechanism for regulating the relative amounts of hemolymph pumped into the anterior and posterior aortae by the ventricle and that the bulbus arteriosus may be a neurohemal site. J. Morphol. 250:185–195, 2001. © 2001 Wiley‐Liss, Inc.