Place memory formation in Drosophila is independent of proper octopamine signaling

The biogenic amines play a critical role in establishing memories. In the insects, octopamine, dopamine, and serotonin have key functions in memory formation. For Drosophila, octopamine is necessary and sufficient for appetitive olfactory memory formation. Whether octopamine plays a general role in reinforcing memories in the fly is not known. Place learning in the heat-box associates high temperatures with one part of a narrow chamber, and a cool, strongly preferred temperature with the other half of the chamber. The cool-temperature-associated chamber half could provide a rewarding stimulus to a fly, and thus a place memory is composed of an aversive and rewarded memory component. The role of octopamine in place memory was thus tested. Using a mutation in the tyramine beta hydroxylase (TβH[M18]) and blocking of evoked synaptic transmission in the octopamine (and tyramine) neurons labeled with a tyramine decarboxylase-2 (TDC2) gene regulatory elements we found that reinforcement of place memories is independent of normal octopamine signaling. Thus, reinforcing mechanisms in Drosophila have specialized systems in the formation of specific memory types.