Amphetamine and Reserpine Deplete Brain Biogenic Amines and Alter Blow Fly Feeding Behavior

: HPLC with electrochemical detection was used to determine the levels of p‐hydroxyphenylethanolamine (octopamine), 3,4‐dihydroxyphenylethylamine (dopamine), and 5‐hydroxytryptamine (5‐HT) in the brains of control, reserpine, and d‐amphetamine‐treated blow flies, Phormia regina Meigen. Parallel studies were carried out to assess the effects of the two drugs on fly feeding behavior, measured as mean acceptance threshold: the minimum sucrose concentration to which the average fly in a population will respond by proboscis extension when its tarsi contact the solution. In saline‐injected control flies, all three amines were found at levels of approximately 2 pmol/brain. Thirty minutes after injection with d‐amphetamine (12 μg/fly), brain octopamine was depleted by 85%, whereas dopamine and 5‐HT were depleted by 70%. Reserpine (5 μg/fly) caused 70% depletion of dopamine and >90% depletion of both octopamine and 5‐HT 24 h after injection. However, the effect of reserpine was much slower in onset (hours versus minutes) and more persistent (days versus hours) than was the effect of d‐amphetamine. With either drug, the time course of amine depletion closely matched the time course of the increase in feeding threshold observed in drug‐treated flies. These results suggest that CNS pools of the biogenic amines, octopamine, dopamine, and 5‐HT are important in governing blow fly responsiveness to food stimuli.