Profiling the Effects of Repetitive Morphine Administration on Motor Behavior in Rats

Efficient repetitive clinical use of morphine is limited by its numerous side effects, whereas analgesic tolerance necessitates subsequent increases in dose to achieve adequate levels analgesia. While many studies focused on tolerance, the effect dosing non-analgesic effects has been overlooked. This study aimed characterize morphine-induced behavior and development progression behavioral tolerance. Adult male Sprague–Dawley rats were repetitively treated with subcutaneous for 14 days two groups (A: 5 mg/kg/day (b.i.d.) → 10 mg/kg/day; B: 20 mg/kg/day). Motor was assessed daily (distance traveled, speed, moving time, rearing, rotation) an open-field arena, before 30 min post-injections. Antinociception measured using tail-flick hot-plate assays. All parameters highly suppressed both first treatment day, followed a gradual manifestation as progressed. Animals high-dose group showed increased locomotor activity after treatment. excitatory phase converted inhibition when higher introduced. We suggest that exposure represent signature antinociceptive