of Drosophila melanogaster

established to be modulated by various neuromodula-tors. Serotonin (5-HT) showed dose-dependent re-sponses in direct application within semi-intact preparations. At 1 nM, HR decreased by 20 % while it increased at 10 nM (10%) and 100 nM (30%). The ef-fects plateaued at 100 nM. The action of 5-HT on the heart was examined with an intact Central Nervous System (CNS) and an ablated CNS. The heart and aorta of dorsal vessel pulsate at different rates at rest and during exposure to 5-HT. Splitting the heart and aorta resulted in a dramatic reduction in pulse rate of both the segments and the addition of 5-HT did not produce re-gional differences. The split aorta and heart showed a high degree of sensitivity to sham changes of saline but no significant effect to 5-HT. Larvae-fed 5-HT (1 mM) did not show any significant change in HR. Since 3,4-methylenedioxymethamphetamine (MDMA) is known to act as a weak agonist on 5-HT receptors in verte-brates, we tested an exogenous application; however, no significant effect was observed to dosage ranging from 1 nM to 100 lM in larvae with and without an intact CNS. In summary, direct application of 5-HT to the larval heart had significant effects in a dose-dependent manner while MDMA had no effect