Neuromodulation in the chemosensory system of mosquitoes - neuroanatomy and physiology

The impact of mosquito vectored disease on global public health is overwhelming. Mosquitoes depend on chemosensory capability for blood-feeding and as such have a highly developed chemosensory system, which consists of peripheral and central components. The repertoire of mosquito behaviors during their life cycle are modified by external and internal factors. The main goal of this thesis is to describe some factors that modulate odor-associated behavior, focusing on biogenic amines, neuropeptides, and physiological state change. I generated a detailed distribution map of serotonin, one of the major biogenic amines in the central and peripheral chemosensory system of Aedes aegypti. The arborization pattern of serotonin-immunoreactive (SI) neurons in the central chemosensory neuropil included the antennal lobe (AL), subesophageal ganglion, tritocerebrum and higher brain centers. In addition, I found SI fibers in the peripheral chemosensory organs: the antennae, the maxillary palps and the labia. Furthermore, to investigate the affects of the gonotrophic and circadian state of mosquitoes on serotonin, dopamine and octopamine levels in the heads of female Ae. aegypti, I used high-performance liquid chromatography coupled with electrochemical detection. Changes in the titer level of these biogenic amines are correlated to flight activity and physiological status of this mosquito. The neuropeptides in the mosquito AL are a highly diverse class of neurochemicals described by matrix assisted laser desorption ionization time-of-flight mass spectrometry of a single AL. I isolated and identified a total of 26 neuropeptides belonging to 10 gene families. Additionally, the cellular distribution of four major families of neuropeptides revealed distinct localization patterns of each of these families in the AL and to other olfactory-associated neuropil areas in the brain. Finally, I employed single sensillum recording to investigate the modulation of odorant receptor neurons housed in the antennal sensilla trichodea after a blood meal. Three functional classes of short blunt-tipped type II sensilla displayed a higher sensitivity after blood feeding to the host and oviposition-associated cues, indole and three phenolic compounds. This study indicates modulation of olfactory behavior occurs at the peripheral level post blood-meal, which may be associated with the physiological status of the mosquitoes.