Gill lateral cell (GLC) cilia of Crassostrea virginica are innervated by a serotonin-dopamine innervation from their ganglia. Serotonin is an excitatory neurotransmitter causing GLC cilio -excitation, while dopamine (DA) causes cilio -inhibition. Manganism is a human neuropathology caused by chronic exposure to elevated environmental levels of manganese (Mn). Symptoms of Manganism are similar to Parkinson’s disease, but unlike Parkinson’s patients, those with Manganism are unresponsive to L-DOPA. The neurotoxic mechanism of Mn toxicity is unclear and successful clinical treatments for Manganism remain lacking. Recently, p-aminosalicylic acid (PAS) was reported a potentially effective treatment. While PAS had been used as an anti-inflammatory drug for tuberculosis, it also has strong chelating properties. Our lab previously showed placing C. virginica in artificial sea water (ASW) containing Mn impaired their DA system and prevented the cilio-inhibitory effect of DA on GLC. We also found this Mn neurotoxicity could be prevented and reversed by chelation, using various agents including taurine, carnosine, EDTA and PAS. Since chelation therapy targets metal removal from tissue, we were interested to determine effects of washing Mn exposed oyster tissue in reversing Mn neurotoxicity on the animal’s DA system. We hypothesize washing Mn from animals, by changing their water, would reduce tissue Mn levels and reverse the neurotoxic effects of Mn on the DA system. To test this, oysters were placed in containers of ASW containing 0.5mM of Mn for 3 days. Some Mn treated animals were then “washed” by placement in containers of ASW without Mn for 3 more days. Control animals were similarly treated, over the six-day period, in ASW without Mn. After the experimental period, controls, Mn treated, and Mn treated/washed animals had their gills excised and GLC cilia beating rates, in response to DA (10-5 - 10-3M) determined by stroboscopic microscopy. In control animals, applying DA to isolated gill decreased GLC cilia beating rates over 90%, from 16 to 1 beats/sec. In Mn treated animals, the DA response was severely impaired with beating rates decreasing only 20%, from 19 to 15 beats/sec. In Mn treated/washed animals the DA response was impaired to a lesser extent, with beating rates decreasing by 43%, from 15 to 8.5 beats/sec. The study demonstrates washing alone was slightly effective in reversing the neurotoxic effects of Mn on the oysters’ DA system. It is possible a longer or more intensive (changing the water several times a day) wash period may be more effective. We plan to continue the study by increasing the washing protocol. These findings are helpful in furthering the understanding of the mechanism of Mn neurotoxicity and demonstrates bivalve gill is a useful model to study regulatory mechanisms of cilia activity as well as the pharmacology of drugs affecting biogenic amines in nervous systems.
This work was supported in part by grants 2R25GM06003 of the Bridge Program of NIGMS, 0537231071 of the CSTEP Program of NYSED, P120A210054 of the MSEIP Program of the DoEd, and NIH grant K12GM093854-07A1 IRACDA Program of Rutgers University.