Neurochemical regulation of Aedes aegypti salivary gland function

Abstract

The salivary gland of hematophagous arthropods is critical for blood meal acquisition, blood vessel localization, and secretion of digestive enzymes. Thus, there is significant interest in the regulation of salivary gland function and mechanisms driving the secretion of saliva and digestive proteins. We aimed to gain a broader understanding of the regulatory role of aminergic, cholinergic, and octopaminergic neuromodulators to saliva and protein secretion from the female A. aegypti salivary gland. Quantification of saliva after injection with neuromodulators showed that dopamine, serotonin, and pilocarpine increased the secretory activity of the salivary gland with potency rankings dopamine = serotonin > pilocarpine. No change in saliva secretion was observed with octopamine or ergonovine, which indicates the A. aegypti salivary gland may be regulated by dopaminergic, serotonergic, and cholinergic systems, but are not likely regulated by octopaminergic or tryptaminergic systems. Next, we studied the regulatory control of dopamine-mediated salivation. Data indicate extracellular calcium flux, but not neural function, is critical for dopamine-mediated salivation, which suggests epithelial transport of ions and not neuronal control is responsible for dopamine-mediated salivation. For regulation of protein secretion, data indicate dopamine or serotonin exposure facilitates amylase secretion, whereas serotonin but not dopamine exposure increased apyrase concentrations in the secreted saliva. General immunoreactivity to anti-rat D1-dopamine receptor antibody was observed, yet immunoreactivity to the anti-rat D2-receptor antibody was identified in the proximal regions of the lateral lobes and slight immunoreactivity in the distal portion of the lateral lobe, with no expression in the medial lobe.