Multi-dimensional analyses of behavior in mice treated with morphine, endorphins and [des-tyrosine1]-gamma-endorphin.

An investigation was made as to the effects of an intracerebral injection of morphine, endorphins and [des-tyrosine1]-gamma-endorphin (DT gamma E) on spontaneous locomotor activity in mice. This was done by exploiting a newly devised multi-dimensional behavioral analyser with a capacitance system. This apparatus simultaneously recorded nine different degrees of behavior (1/1, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64, 1/128 and 1/256) according to the movement sizes in mice. Within 15 min after injection, gamma-endorphin (5 and 10 microgram), leucine-enkephalin (200 micrograms) and methionine-enkephalin (100 micrograms) produced a significant increase in the 1/1 size of movement. Fifteen to 30 min after injection, the movement patterns induced by morphine (40 micrograms) and DT gamma E (40 micrograms) became similar, although morphine (40 micrograms) caused a significant decrease in the 1/1 and 1/2 sizes of movement. beta-Endorphin (2 micrograms) significantly decreased most of the movement sizes for 30 min compared with saline-treated group. [D-alanine2]-methionine-enkephalinamide (20 micrograms) significantly decreased almost all the movement sizes within 15 min after injection. The significant alteration in the movement sizes induced by morphine and endorphins except for DT gamma E was antagonized by pretreatment with naloxone (1 mg/kg). These results strongly suggest the qualitative difference in the behavioral effects of each of the opioids and nonopioid.