CLARK, T.M.*; HIRSCHLER, A.; LAWECKI, J.L.; Indiana Univ. South Bend; Indiana Univ. South Bend; Indiana Univ. South Bend: Actions of the serotonin-selective reuptake inhibitor alaproclate in the larval mosquito: does serotonin regulate hemolymph pH?

Larval Aedes aegypti survive well in water ranging from pH 4 to pH 11, and from dilute water to salt solutions of 3% or more. Serotonin is known to hormonally stimulate excretory system and midgut transport in insects. The physiological significance of this regulation in the larval mosquito was investigated using the serotonin-selective reuptake inhibitor alaproclate. Larvae were exposed in vivo to alaproclate in waters varying in pH and salinity, within their tolerable range of each of these parameters. Survival of alaproclate exposure was found to be strongly dependent on pH whereas no salinity-dependent effects were detected. Alaproclate enhanced survival in acid waters, but caused significant mortality in neutral and alkaline waters. Alaproclate did not alter either total body water or hemolymph volume, but increased hemolymph osmotic pressure and hemolymph chloride concentrations. Alaproclate caused a transient alkalosis at three hours followed by recovery to an acidotic condition at twenty four hours of exposure. Failure to alter water balance and hemolymph volume, and the lack of interaction with ambient salinity, indicates that the hormonal role of serotonin is not regulation of water balance or stimulation of diuresis in larval mosquitoes. Instead, the primary role of peripheral serotonin appears to be regulation of hemolymph pH. This is quite different from its known actions in the Hemipteran Rhodnius prolixus indicating significant functional plasticity among insects in the endocrine regulation of excretory system function. Supported by NRICGP #35302-8371 to TMC.