Serotonergic responses of the siphons and adjacent mantle tissue of the zebra mussel, Dreissena polymorpha.
Bivalve siphons have important functional roles in nutritional physiology, defense, and reproductive mechanisms, yet little is known about their neuromuscular control. In the present study, tension measurements and video observations of siphons and adjacent mantle tissue were used to investigate responses to serotonin (5-HT). 5-HT caused relaxation at 10(-6) M and 10(-5) M, contraction or biphasic responses at 10(-4) M and 10(-3) M, and siphon opening at 10(-4) M and 10(-3) M. Responses were slow and lasted 5-10 min after much shorter (20 s) applications of 5-HT. The relaxation phase was enhanced in high potassium medium. Contractile responses could be mimicked by alpha-1-methyl-5-HT and 2-methyl-5-HT but not by 8-OH-DPAT. The responses were not affected by methiothepin, TFMPP, 1-(1-naphthyl)piperazine, metergoline, NAN-190, mianserin, cyproheptadine, and ketanserin. The pharmacology of the 5-HT receptor(s) mediating these siphon/mantle responses is, therefore, different from previously described 5-HT receptors involved in spawning. The siphon/mantle contains previously undescribed longitudinal muscle fibers in the mantle and circular muscle fibers around the siphons. Serotonergic innervation of the siphon margins and mantle tissue was observed by immunohistology. The presence of 5-HT in the siphon/mantle tissue and the responsiveness of these preparations to 5-HT suggest that 5-HT may be a physiological regulator of mantle and siphon movements in the zebra mussel.
Ram
J L
JL
Department of Physiology, Wayne State University, Detroit, MI 48201 USA. jeffram@med.wayne.edu
Moore
D
D
Putchakayala
S
S
Paredes
A A
AA
Ma
D
D
Croll
R P
RP
D000818:Animals; D049872:Bivalvia / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009132:Muscles / Q000187:drug effects* / Q000502:physiology; D012701:Serotonin / Q000494:pharmacology*
D012701:Serotonin