Histamine Mediates the Response to Light in the Sensory Motor Integration of Gill Lateral cell Cilia in the Bivalve Mollusc, Crassostrea virginica

Gill lateral cells of Crassostrea virginica are innervated by serotonin and dopamine nerves from their ganglia.  Most bivalves have lateral cell cilia that respond to serotonin and dopamine, with serotonin being the neurotransmitter that increases beating rates and dopamine being the neurotransmitter that decreases beating rates.  The motor aspects of gill lateral cell innervation have been well studied, but not the sensory side.  There is limited information about sensory inputs.  Our previous work found that C. virginica can sense and adjust gill lateral cell cilia beating to the presence of food, crab extract and light, as well as a variety of chemical cues including histamine when applied to the mantle rim.  Shining light on the mantle rim or applying histamine decreased gill lateral cell cilia beating rates, but did not alter cilia beating rates when applied directly to gill.  In many invertebrates histamine is a neurotransmitter involved in photoreception.  We hypothesize that in C. virginica, histamine is the neurotransmitter of mantle rim photoreceptors.  To test this we used whole animal preparations in which the innervation of the gill from the cerebral and visceral ganglia is intact and tested the actions of a histamine H2 antagonist, famotidine, on the response to light.  Cilia beating was measured by stroboscopic microscopy.  An eleven lumen, ¼ inch diameter spotlight source was used to stimulate the mantle rim in the vicinity of the siphons.  Stimulating the mantle rim with light decreased cilia beating in the gill.  Adding the H2 antagonist famotidine caused a dose-dependent blockage of this action over the range of 10^-9 - 10^-3.  The study further demonstrates the sensory-motor integration of beating of lateral cilia involving the sensory mantle rim and visceral/cerebral ganglia, supporting the hypothesis that histamine is the sensory neurotransmitter in mantle photoreceptor cells. This work was supported by grants 2R25GM06003 of the Bridge Program of NIGMS, 0516041071 of NYSDOE and 0622197 of the DUE Program of NSF.