Differential modulation of behavioral responses by [D-Ala2, NMePhe4, Gly-ol]enkephalin, [D-Ala2] deltorphin II and [D-Pen2, L-Pen5]enkephalin in the mouse.

The effects of [D-Ala2, NMePhe4, Gly-ol]enkephalin (DAMGO), a mu-selective opioid receptor agonist, [D-Ala2]deltorphin II (DELT) and [D-Pen2, L-Pen5]enkephalin (DPLPE), delta-selective opioid receptor agonists, on different behavioral responses were investigated in mice by multidimensional behavioral analyses. DAMGO (0.1 and/or 0.3 microgram) produced a marked increase in circling, rearing and grooming within 15-30 min after the start of behavioral measurements. DELT (0.3, 1.0 and/or 3.0 micrograms) produced a significant increase in linear locomotion and circling within 15-30 min after the start of behavioral measurements, whereas DPLPE (10.0 micrograms) increased only circling. The behavioral effects of DAMGO, DELT or DPLPE were almost completely antagonized by beta-funaltrexamine (2.5 and 5.0 micrograms) or naltrindole (3.0 and 10.0 mg/kg). These results suggest that opioid peptides selective for receptor types elicit different behavioral responses in mice. Moreover, the different behavioral effects between DPLPE and DELT may be due to the delta opioid receptor subtypes such as delta-1 and delta-2.