DOPAMINE REDUCES INTENSITY OF SEROTONIN-INDUCED SPAWNING IN THE ZEBRAMUSSEL DREISSENA-POLYMORPHA (PALLAS)

The effect of dopamine (DA) on serotonin (5-HT)-induced spawning in th e zebra mussel Dreissena polymorpha (Pallas) was tested. Administratio n of 1 mM DA with either 0.3 mM or 0.5 mM 5-HT significantly delayed s pawning and reduced its intensity in both males and females compared w ith 5-HT controls. In dose-response experiments, a minimal DA concentr ation of 0.3 mM was necessary to delay spawning and reduce male spawni ng intensity to levels below that of the 5-HT control. Mussels treated with 5-HT-DA or DA alone opened their valves initially, but after 1 h our most valves were closed and both inhalent and exhalent siphons app eared extended, squeezed, and narrow, with reduced aperture openings. Possible mechanisms for the observed reduction in spawning intensity a re discussed.