BIOCHEMICAL PHARMACOLOGY OF FEEDING BEHAVIOR IN THE BLACK BLOW FLY, PHORMIA REGINA MEIGEN (BIOGENIC AMINES, INSECT, HPLC)
Abstract
HPLC with electrochemical detection was used to determine the levels of octopamine, dopamine and 5-hydroxytryptamine (5-HT) in the brains of control and drug-treated blow flies, Phormia regina Meigen. Parallel studies, carried out to assess the effects of the drugs on fly feeding behavior, measured the mean acceptance threshold (MAT): the minimum concentration of sucrose to which the average fly will respond by proboscis extension when its tarsi contact the solution. In saline-injected flies, all three amines were at levels of approximately 2 pmols/brain. Thirty min after injection with d-amphetamine (12 ug/fly), brain octopamine was depleted by 85%, while dopamine and 5-HT were depleted by 70%. Reserpine (5 ug/fly), 24 h after injection, caused 70% depletion of brain dopamine and greater than 90% depletion of octopamine and 5-HT. With either drug, the time course of amine depletion closely matched the time course of the increase in MAT observed in drug-treated flies. These results suggest that CNS pools of octopamine, dopamine, and 5-HT are important in governing blow fly responsiveness to food stimuli. Blow flies pretreated with either amphetamine (12 ug/fly) or saline, were injected again with a 50 ug dose of octopamine, dopamine, 5-HT, or saline. In flies pretreated with amphetamine, brain levels of octopamine rose 40-fold, brain dopamine rose 45-fold, and brain 5-HT rose 20-fold after injection with octopamine, dopamine, and 5-HT respectively. Octopamine partially reversed the rise in MAT observed in amphetamine-treated flies. Dopamine and 5-HT had no significant effect on MAT. These results suggest that brain octopamine plays a key role in the positive modulation of blow fly responsiveness. Low levels of N-acetyloctopamine (NAOA) were discovered in the blow fly brain. NAOA, N-acetyldopamine (NADA), and NA-5-HT (all at 10 ug/fly) were pharmacologically active in the tarsal-taste test. By 10 min after injection, NAOA and NADA caused MAT to rise while NA-5-HT caused MAT to fall below that of controls. Brain levels of NAOA, NADA, and NA-5-HT were elevated in flies injected with the respective NA-amine. Brain levels of free amines were not affected by any of the NA-amines. These results provide the first evidence that NA-amines are pharmacologically active and suggest that N-acetylation may represent a process other than inactivation of the biogenic amines.
Degree
Ph.D.
Subject Area
Entomology
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