Metabotropic group II glutamate receptors mediate cue-triggered increases in reward-seeking behaviour

Rationale Reward-associated cues can invigorate reward-seeking actions via Pavlovian-to-instrumental transfer (PIT). Glutamatergic neurotransmission mediates the appetitive effects of reward-associated cues. We characterized the expression of PIT and its mediation by metabotropic group II glutamate (mGlu(2/3)) receptor activity in female and male rats. Objectives Across the sexes, we used PIT procedures to determine (i) cue-triggered increases in instrumental responding for water reward (experiment 1) and (ii) the respective influences of the mGlu(2/3) receptor agonist LY379268 and thirst satiation on this effect (experiment 2). Methods Water-restricted female and male Sprague-Dawley rats learned to lever press for water. Separately, they learned that one of two auditory stimuli predicts free water (CS + vs CS -). On PIT test days, the CS + and CS - were presented independent of instrumental responding, and we measured effects on lever pressing under extinction (no water). In experiment 1, we characterized PIT across the sexes. In experiment 2, we measured PIT after systemic LY379268 administration (0, 0.3 and 1 mg/kg) and thirst satiation, respectively. Results Female and male rats showed similar PIT, with CS + but not CS - presentations potentiating water-seeking behaviour. LY379268 (1 mg/kg) attenuated CS + evoked increases in both water-associated lever pressing and conditioned approach to the water port. Thirst satiation attenuated both water-seeking and CS + evoked conditioned approach behaviour. Conclusions The sexes show similar cue-triggered increases in reward seeking, and thirst satiation suppresses both water-seeking and cue-triggered anticipation of water reward. Finally, across the sexes, mGlu(2/3) receptor activity mediates cue-triggered increases in reward seeking.

Automated summary

Across both sexes, there are similar cue-triggered increases in reward seeking behaviors, and thirst satiation suppresses both water-seeking behavior and the anticipation of water reward. The activity of mGlu(2/3) receptors plays a regulatory role in cue-triggered increases in reward seeking.