Height-dependent difference in the expression of naloxone-induced withdrawal jumping behavior in morphine dependent rats.

Opiate withdrawal syndrome may motivate opiate seeking and taking. Thus, development of an effective medical treatment for these symptoms is a primary research goal and strongly relies on improved experimental models. Opiate withdrawal syndrome is characterized by several behavioral signs such as wet dog shake, teeth chattering, sniffing, scratching, chewing, diarrhea, rearing, ptosis and jumping. The goal of present study was to evaluate the impact of the cylindrical chamber height on the expression of jumping behavior in morphine dependent rats. Adult male Wistar rats were rendered dependent on morphine by subcutaneous (s.c.) injection of morphine sulfate (10 mg/kg) with an interval of 12 h for 9 days. On day 10, 2 h after morphine injection, rats were injected with naloxone (1 mg/kg, i.p.). Naloxone-induced jumping was monitored during a period of 30 min in a clear cylindrical Plexiglas test chamber with the floor covered by woodchip. The chambers had the same diameter (35 cm), but the heights of chambers were different (30, 40, 50, 60, 70 and 80 cm). Incidence and frequency of jumping decreased with increasing the height of the test chambers (P<0.05). Altogether, these findings highlight the possibility of detecting height-dependent difference in the expression of naloxone-induced jumping behavior in morphine dependent rats.