Physiological Study of the Neurotoxic Actions of Manganese on Dopamine Cell Signaling in Crassostrea virginica, Downstream of D2‐Like Receptor Activation

Abstract

Dopamine and serotonin are important neurotransmitters in invertebrates and have been well studied in bivalves with respect to gill and heart. Lateral gill cell cilia of Crassostrea virginica are controlled by a reciprocal dopaminergic‐serotonergic innervation from their ganglia. Dopamine slows down and stops beating of gill lateral cell cilia while serotonin accelerates cilia beating rates. Previously we found that dopamine postsynaptic receptors involved in controlling gill lateral cell cilia are D2‐like (D2DR). The D2DR signaling pathway involves steps that include inhibition of adenylyl cyclase and activation of phospholipase C (PLC). While the effects of dopamine on cAMP levels in oyster gill is well known, the activation of PLC by dopamine D2DR signaling has not been well studied. PLC activation increases cellular inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 and DAG are both second messengers. IP3 binds to IP3 receptors and increase cytoplasmic calcium levels. High cytoplasmic calcium levels have been shown to slow down gill lateral cell cilia beating. DAG activates protein kinase C. Manganese is a neurotoxin causing Manganism in people, a Parkinson's‐like syndrome. The dopamine induced cilio‐inhibition of gill lateral cell cilia activity in C. virginica is disrupted by manganese. Earlier work of our lab showed the site of action of manganese is the D2DR receptor. We hypothesize IP3 and DAG would be cilio‐inhibitory but not be effected by manganese treatments. We studied this by conducting acute experiments testing the effects of IP3, a DAG analog, a DAG kinase inhibitor, and manganese on gill lateral cell cilia beating. Ciliary activity of gill lateral cells was measured by stroboscopic microscopy and expressed as beats/min ± sem. The results showed that IP3, the DAG analog and the DAG kinase inhibitor each produced a dose dependent (10−6 – 10−4 M) decrease in gill lateral cell cilia beating. Acute treatments with 500 μM of manganese did not reduce the effectiveness of IP3 and the DAG analog to reduce cilia beating. This study provides new knowledge of the physiological actions of the PLC, IP3 and DAG components of the D2DR pathway on gill lateral cell cilia of C. virginica and demonstrates that manganese did not affect those aspects of the D2DR pathway. The study also provides a foundation to further study the physiological roles of PLC in bivalve gill as well as the neurotoxic actions of manganese on the physiology of the D2‐like receptors in the gill.Support or Funding InformationSupported in part by a Carnegie Foundation award.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.