Abstract
Throughout the animal kingdom, the inhibitory neurotransmitter γ-aminobutyric acid (GABA) is a key modulator of physiological processes including learning. With respect to associative learning, the exact time in which GABA interferes with the molecular events of learning has not yet been clearly defined. To address this issue, we used two different approaches to activate GABA receptors during appetitive olfactory conditioning in the honeybee. Injection of GABA-A receptor agonist muscimol 20 min before but not 20 min after associative conditioning affects memory performance. These memory deficits were attenuated by additional training sessions. Muscimol has no effect on sensory perception, odor generalization, and nonassociative learning, indicating a specific role of GABA during associative conditioning. We used photolytic uncaging of GABA to identify the GABA-sensitive time window during the short pairing of the conditioned stimulus (CS) and the unconditioned stimulus (US) that lasts only seconds. Either uncaging of GABA in the antennal lobes or the mushroom bodies during the CS presentation of the CS-US pairing impairs memory formation, while uncaging GABA during the US phase has no effect on memory. Uncaging GABA during the CS presentation in memory retrieval also has no effect. Thus, in honeybee appetitive olfactory learning GABA specifically interferes with the integration of CS and US during associative conditioning and exerts a modulatory role in memory formation depending on the training strength.