Comparative Study of the Response to Light on the Sensory Motor Integration of Gill Lateral Cell Cilia in Bivalve Mollusc
Authors: Semple Danellie , Jean‐Pierre Johanne , Carroll Margaret A , Catapane Edward J 
Published: November 2023

Most bivalves have gill lateral cell (GLC) cilia that respond to serotonin, which is cilio‐excitatory and dopamine, which is cilio‐inhibitory. Crassostrea virginica and Mytilus edulis are two well‐studied bivalves whose GLC are innervated by serotonin and dopamine nerves. The motor aspects of GLC innervation have been well studied but the sensory side to the motor response of the cilia has not. Recently we found sensory cues, such as light, algae or crab extract applied to C. virginica mantle rim initiated an integrated response via the visceral/cerebral ganglia, between mantle rim sensory tentacles and the motor response of GLC cilia. Since in invertebrates, histamine is the neurotransmitter of photoreception, we tested histamine application to mantle rim and found it elicited the same sensory‐motor response as light had, decreasing cilia beating of GLC. In this study we tested effects of shining a spotlight (11 lumen, ¼ inch diameter) on mantle rim sensory tentacles of M. edulis and found it had a cilio‐excitatory effect on GLC cilia, opposite the cilio‐inhibitory effect we previously found in C. virginica. However, since C. virginica is nocturnal and M. edulis is not, the opposite responses to light may very well represent the appropriate motor response for each bivalve. In this study we also investigated effects of light on cerebral ocelli (eyespots) in both C. virginica and M. edulis. Cerebral ocelli are located near the cerebral ganglia. They have been rarely studied beyond a few histological/anatomical reports of their existence. We hypothesize cerebral ocelli are light sensitive and involved in a histamine‐mediated sensory‐motor integration response effecting GLC cilia. To test this we used animal preparations with intact gill to cerebral/visceral ganglia innervation and a spotlight (11 lumen, ¼ inch diameter) to stimulate cerebral ocelli. We found stimulating cerebral ocelli decreased beating of GLC cilia to zero in C. virginica, but increased cilia beating in M. edulis by over 300%. Again, opposite motor responses but consistent with the motor responses we observed when light was applied to mantle rim sensory tentacles. In both animals light induced sensory‐motor integration response of GLC was lost when cerebral ocelli were excised. We also treated cerebral ocelli with the histamine H2 receptor antagonist famotidine (10−9–10−3M) before light application and it, caused a statistically significant, dose‐dependent blockage of the motor response of GLC cilia. The study shows light induced sensory‐motor integration between mantle rim sensory tentacles and GLC cilia is also present in the bivalve M. edulis, and expands the existence of this sensory‐motor response to include the light‐sensitive cerebral ocelli of both bivalves. The study adds new knowledge of the physiological role of cerebral ocelli in a class of animals where it has not been well studied and further supports the hypothesis histamine is the sensory neurotransmitter for photoreceptor cells in both cerebral ocelli and mantle rim in these bivalves.

Support or Funding Information

This work was supported by grant 690340047 of PSC‐CUNY, grant 2R25GM06003 of the Bridge Program of NIGMS and a Carnegie Foundation award.