Effects of serotonergic agents on survival and hemolymph composition of the larval mosquitoAedes aegypti(Diptera: Culicidae, L.)in vivo: does serotonin regulate hemolymph acid–base homeostasis?

Abstract

SUMMARYThe role of serotonin in the regulation of larval Aedes aegyptihemolymph composition was investigated in vivo using two reuptake inhibitors (SSRIs), alaproclate HCl and 6-nitroquipazine maleate, and the receptor antagonist methiothepin mesylate. Larvae were placed in media differing in pH and salinity in the presence and absence of serotonergic agents. The toxicity of each agent was strongly influenced by ambient pH. For each agent, toxicity was negligible in acidic media, intermediate in neutral media and greatest in alkaline media. By contrast, toxicity of all agents was independent of salinity. No effects on mass-specific body water or hemolymph volume were observed whereas hemolymph osmotic pressure, Na+concentrations and pH differed significantly among treatments. 6-nitroquipazine caused a decrease in Na+ from 115±1.7 to 103±0.9 mmol l–1, and alaproclate caused alkalosis of the hemolymph from pH 7.55±0.026 to pH 7.72±0.044. Methiothepin decreased hemolymph osmotic pressure from 329±9.9 to 304±8.8 and showed the greatest overall toxicity. Control larvae excreted net base in pH 4 media (1.4 μmol g–1 h–1) and net acid in pH 7 (1.2 μmol g–1 h–1) and pH 11 (5.1μmol g–1 h–1) media. In pH 4 media,alaproclate and methiothepin caused a shift to net H+ excretion(1.1 and 1.5 μmol g–1 h1, respectively) whereas these agents did not influence acid excretion rates in pH 7 or pH 11 media. The hypothesis that serotonin is involved in hemolymph acid–base balance is discussed.