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(a) More active lever pressing during the final instrumental training session predicted more active lever pressing at test, specifically during presentations of the water-paired conditioned stimulus (CS +). (c) The rate of water cup entries during the first 10 s of each CS presentation was higher during CS + relative to CS- presentations, and this difference increased over the daily 44-min Pavlovian conditioning sessions. In (d-e), water cup entries/lever presses are shown as a difference score between responses during the 2-min CS and during the 2-min ITI immediately preceding each CS presentation. [Extracted from the article]

Rationale: Reward-associated cues can trigger incentive motivation for reward and invigorate reward-seeking behaviour via Pavlovian-to-instrumental transfer (PIT). Glutamate signaling within the basolateral amygdala (BLA) modulates cue-triggered increases in incentive motivation. However, the role of BLA metabotropic group II glutamate (mGlu2/3) receptors is largely unknown. Objectives: In Experiment 1, we characterized cue-triggered increases in incentive motivation for water reward using the PIT paradigm. In Experiment 2, we assessed the influence of intra-BLA microinjections of the mGlu2/3 receptor agonist LY379268 on this effect. Methods: Water-restricted male Sprague–Dawley rats learned to press a lever for water. Separately, they learned to associate one of two auditory cues with free water. On test days, rats could lever press under extinction conditions (no water), with intermittent, non-contingent CS+ and CS- presentations. In Experiment 1, rats were tested under baseline conditions. In Experiment 2, rats received intra-BLA microinjections of LY379268 (0, 3 and 6 μ g/hemisphere) before testing. Results: Across experiments, CS+, but not CS-, presentations increased water-associated lever pressing during testing, even though responding was reinforced neither by water nor the CS+. Intra-BLA LY379268 abolished both CS+ potentiated pressing on the water-associated lever and CS+ evoked conditioned approach to the site of water delivery. LY379268 did not influence locomotion or instrumental and Pavlovian response rates during intervals between CS presentations or during the CS-, indicating no motor effects. Conclusions: mGlu2/3 receptor activity in the BLA mediates cue-triggered potentiation of incentive motivation for reward, suppressing both cue-induced increases in instrumental pursuit of the reward and anticipatory approach behaviour. [ABSTRACT FROM AUTHOR]