The identification and distribution of major biogenic amines in the central nervous system of Aedes triseriatus (Say) (Diptera: Culicidae) and studies on their regulation of adult mosquito behavior
The major biogenic amines of the insect nervous system (dopamine, octopamine, and serotonin) were identified and quantified by high performance liquid chromatography in the brain and thoracic ganglia of female Aedes triseriatus mosquitoes. Octopamine was quantitatively dominant in both tissues while dopamine and serotonin were found in smaller but generally similar amounts. Noradrenaline was not found in measurable quantities. Amine levels in the brain and thoracic ganglia increased significantly between days 1-14 of adult life while total protein content remained unchanged. No statistically significant circadian changes in brain amine levels were observed. When brains were divided by region (midbrain, optic lobes, subesophageal ganglion), octopamine was more abundant in the optic lobes, relative to the distribution of dopamine and serotonin;Biogenic amine concentrations were depleted in A. triseriatus when administered a single oral dose (approximately 4 [mu]g) of [alpha]-methyl tyrosine (AMT) or [alpha]-methyl tryptophan (AMTP). AMTP treatment selectively lowered the brain concentration of serotonin through the 14 days monitored following treatment. During the first week, serotonin levels in AMTP-treated mosquitoes were approximately 10% of control levels. Administration of AMT significantly depleted dopamine through 14 days post-treatment; dopamine was reduced by 50% in AMT-treated mosquitoes during the first week. Octopamine concentration was also lowered by AMT (determined on Day 3 post-treatment), but not to the degree of dopamine depression. Treatment with AMT or AMTP elicited statistically significant decreases in the spontaneous, circadian flight-activity of A. triseriatus for several days but flight activity of treated mosquitoes returned to control levels prior to evidence of amine pool repletion. Amine reductions did not alter the circadian pattern of flight activity;Host-seeking ability (evaluated with an olfactometer) was not altered by treatment with either AMT or AMTP. However, bloodfeeding success was significantly reduced by either oral administration or injection of AMTP. AMTP-treated mosquitoes responded positively when placed in close proximity to a host (rabbit) but fewer mosquitoes fed to repletion or fed at all. Those that fed to repletion took longer to do so. No differences were observed between control and AMT-treated mosquitoes. These observations suggest that serotonin plays a role in modulating bloodfeeding behavior in A. triseriatus.