Opioid receptor function in social attachment in young domestic fowl

Opioid systems are implicated in social attachment processes. This research sought to determine the functional contribution of each opioid receptor in modulating social attachment/separation distress. Following ICV administration of opiate probes, 7-day-old cockerels were isolated from conspecifics for a 3 min test period under either a mirror or no-mirror condition. Vocalizations served as the measure of separation-stress. Opioid receptor probes included: the μ agonist DAMGO (0.02, 0.19, 1.95 nmol), the μ antagonist CTOP (0.009, 0.09, 0.9 nmol), the δ agonist SNC80 (0.3, 1.0, 3.0 μmol), the δ antagonist naltrindole (0.2, 2.2, 22.2 nmol), the κ agonist U50, 488 (1, 30, 100 nmol), the κ antagonist norBNI (1.3, 13.6, 136.1 nmol), the NOP agonist N/OFQ (0.01, 0.1, 1.0 nmol), and the NOP antagonist UFP-101 (0.1, 1.0, 10.0 nmol). DAMGO attenuated separation distress vocalizations. No other drug probe enhanced or attenuated distress vocalizations. Further, the non-selective opiate antagonist naloxone (0.3, 8.3, 27.5 nmol) did not exacerbate distress vocalizations. These results suggest that only the μ receptor modulates social attachment in young domestic fowl.