DAGO ([D-Ala2,N-Me-Phe4,Gly-ol]enkephalin) specifically reverses apomorphine-induced increase in rearing and grooming behaviors in the mouse.

The effects of intracerebroventricular injections (10 microliters) of the mu-selective opioid peptide DAGO on apomorphine (0.1, 0.56, 1.0 and/or 3.0 mg/kg)-induced motor activity were investigated in the mouse using multi-dimensional behavioral analyses. A lower dose (0.1 mg/kg) of apomorphine failed to significantly affect motor activity, whilst higher doses (0.56, 1.0 and 3.0 mg/kg) of the drug produced a marked increase in linear locomotion, circling, rearing and/or grooming behaviors. DAGO (0.003 and 0.01 micrograms) did not significantly affect different behaviors. DAGO (0.01 micrograms) antagonized the apomorphine (1.0 mg/kg)-induced increase in behaviors such as rearing and grooming. However, DAGO (0.003 or 0.01 micrograms) did not affect behaviors induced by a 3.0 mg/kg dose of apomorphine. Furthermore, the effects of DAG]O on apomorphine-induced behaviors were fully reversed by treatment with the mu-selective alkylating agent beta-FNA (beta-funaltrexamine) (5.0 micrograms). These results suggest that mu opioid receptors play a principal role in the apomorphine-induced increase in rearing and grooming behaviors.