Role of μ- and δ-opioid receptors in the nucleus accumbens in turning behaviour of rats

The role of mu-, delta(1)- and delta(2)-opioid receptors in the nucleus accumbens in pivoting was investigated in freely moving rats. Unilateral injections of the mu-opioid receptor agonist, [D-Ala(2).N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO, 1 and 2 mug) and the delta(2)-opioid receptor agonist, deltorphin II (1 and 2 mug), but not the delta(1)-opioid receptor agonist, [D-Pen(2.5)]-enkephalin (DPDPE, 1 4 mug), into the shell or the core of the nucleus accumbens significantly induced contraversive pivoting. The pivoting induced by DAMGO (2 mug) and deltorphin II (2 mug) was inhibited significantly by the mu-opioid receptor antagonist, D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH2 (CTOP, 0.1 and 1 mug), and the delta(2)-opioid receptor antagonist, naltriben (NTB, 0.1 and 1 mg/kg. i.p.), respectively. The DAMGO (2 mug)- or deltorphin II (2 mug)-induced pivoting was also inhibited significantly by co-administration of the dopamine D-1/D-2 receptor antagonist, cis(Z)-flupentixol (1 and 10 mug). The pivoting induced by unilateral injections of a mixture of dopamine D-1 (SKF 38393, 5 mug) and D-2 (quinpirole, 10 mug) receptor agonists into the shell was significantly inhibited by cis(Z)-flupentixol (1 and 10 mug) or NTB (1 and 3 mg/kg, i.p.). but not CTOP (1 mug) or delta1-opioid receptor antagonist, (E)-7-benzylidene-naltrexone (1 mg/kg, i,p.). The contraversive pivoting elicited by the cholinergic agonist, carbachol (5 mug), into the core was inhibited by co-administration of the muscarinic M-1 antagonist, pirenzepine (1 mug), but not cis(Z)-flupentixol (1 mug). The results suggest that unilateral activation of mu- or delta(2)-opioid, but not delta(1)-opioid, receptors in the core and/or shell of the nucleus accumanism elicits contraversive pivoting that requires intact dopamine D-1/D-2 receptors in the shell, but not intact muscarinic M-1 mechanism in the core. The study also shows that delta(2)-opioid, but not mu- and delta(1)-opioid, receptors in the core and/or shell modulate the shell-specific, dopamine D-1/D-2 receptor mechanisms involved in the production of pivoting. (C) 2004 Elsevier Ltd. All rights reserved.