Abstract The information emerging from the studies demonstrates adrenergic system and nociceptin/orphanin FQ (N/OFQ) play a crucial role on appetite regulation but there is no information for their interaction. The purpose of this study was to examine the effects of intracerebroventricular (ICV) injection of prazosin (a1 receptor antagonist), yohimbine (a2 receptor antagonist), metoprolol (b1 adrenergic receptor antagonist), ICI 118,551 (b2 adrenergic receptor antagonist) and SR59230R (b3 adrenergic receptor antagonist) on N/OFQ-induced hyperphagia by 3-h fooddeprived neonatal broiler chicken. In experiment 1, chicken injected with saline, prazosin (10 nmol), N/OFQ (16 nmol) and co-injection of prazosin ? N/OFQ. In experiment 2, ICV injection of saline, yohimbine (13 nmol), N/OFQ (16 nmol) and yohimbine ? N/OFQ applied to the birds. In experiment 3, injections were saline, metoprolol (24 nmol), N/OFQ (16 nmol) and metoprolol ? N/OFQ. In experiment 4, the birds received ICV injection of saline, ICI 118,551 (5 nmol), (C) N/OFQ (16 nmol) and co-administration of ICI 118,551 ? N/OFQ. In experiment 5, chicken injected with saline, SR59230R (20 nmol), N/OFQ (16 nmol) and SR59230R ? N/OFQ. Then, cumulative food intake was recorded until 120 min after injection. According to the results, ICV injection of N/OFQ significantly increased food intake (P\0.001). The effect of N/OFQ significantly amplified by co-injection of N/OFQ ? b2 adrenergic receptor antagonist (P\0.001). Also, administration of b1 or b3 adrenergic receptor antagonist had no effect on N/OFQ-induced hyperphagia (P[0.05). These results suggest that the effect of N/OFQ on cumulative food intake is mediated via b2 adrenergic receptors in neonatal chicken.

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