Exploring wanting and liking during positive human-animal interactions

Dopamine and opioids modulate the "wanting" and "liking" components of reward processes, yet their specific roles in social and human-animal interactions (HAIs) remain unclear.

In this pilot study, we aimed to disentangle the roles of dopamine and opioids during HAIs, contrasting them with food reward and novel object test scenarios. We investigated these neurotransmitter systems as proximate mechanisms for "wanting" and "liking" behaviours in domesticated pigs. Additionally, there is a significant knowledge gap on the optimal dosage for the dopamine D2/D3 receptor antagonist amisulpride and mu-opioid receptor antagonist naloxone.

We administered amisulpride orally and naloxone intranasally at three dosage levels to 30 female pigs using a within-subject design. Each treatment (drug × dose level) was administered prior to 10-min interaction sessions with a familiar human.

Both the high doses of amisulpride (800 mg) and naloxone (80 mg/ml) significantly increased pigs' latency to first contact with the human compared to pre-test, suggesting both systems modulate the motivation ("wanting") to interact. However, neither influenced the time pigs spent in contact with the human, contrary to our prediction that blocking opioids would decrease this behaviour as an indicator of the pleasurability ("liking") of the interaction.

These altered reward-related behaviours along with the absence of side-effects are the first indicators for the safe and effective use of amisulpride and naloxone to non-invasively study reward mechanisms in domesticated animals.