A new attempt to assess the effect of learning processes on the cholinergic system: studies on fruitflies and honeybees.

The effect of training on the functioning of the cholinergic system was investigated in fruitflies and in honeybees. Drosophila were submitted to a passive avoidance conditioning of the proboscis extension response (PER). Flies had to learn to suppress the sugar-induced PER to avoid an aversive quinine reinforcement. In a yoked control group, the punishment was administered with no relation to the response displayed. Honeybees underwent a five-trial olfactory conditioning of the PER elicited by an antennal gustatory stimulation. In the control group, olfactory and gustatory stimulations were unpaired to prevent a learning process from developing. Immediately at the end of the learning session, acetylcholinesterase (AChE) activity was individually measured on the whole animal for Drosophila and on the head for the honeybee in experimental and in control groups. In fruitflies and honeybees, the AChE rate did not differ between the experimental group and its respective control group. Moreover, no significant correlation could be found individually between the learning performance and the AChE rate in either Drosophila or in honeybees. This experiment did not reveal any modulatory effect of the learning acquisition level on the AChE activity in insects as was previously reported in honeybees.