Bulbus arteriosus of the bivalve mollusc Mercenaria mercenaria: Morphology and pharmacology

Abstract

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.

Physiological–biochemical properties of blue mussel Mytilus edulis adaptation to oil contamination

“…In the future, special attention should be paid to the biogenic amines FMFR since concentrations of these neurotransmitters grow under stress conditions (Yamagishi et al 2004). Also, one cannot exclude a contribution of acetylcholine to controlling cardiac activity, as it is one of the main inhibitory neurotransmitters (Deaton et al 2001). At least, heavy metals have influenced external cholinergic control of heart activity in invertebrates, resulting in a decrease in hemolymph circulation (Bini et al 2006).…”