Papers of the Week

Opioid use disorder is a public health problem that includes symptoms such as withdrawal syndrome and opioid-induced hyperalgesia. Currently, drugs to treat side effects of opioids also have undesirable effects, which lead to limitations. This study investigated the effect of a treatment with cannabidiol in morphine-induced hyperalgesia and withdrawal behavior in morphine-dependent rats. Male and female rats were submitted to a morphine-induced physical dependence protocol consisting of a twice daily treatment with morphine (filtered solution, dose of 7.89 mg/kg, 1 ml/kg, s.c.) for 10 days. Nociception was measured using the hot plate test and morphine-induced thermal hyperalgesia was equally achieved following 7-10 days of morphine administration in male and female rats. Repeated treatment with cannabidiol (30 mg/kg) was sufficient to prevent thermal hyperalgesia in male and female rats. Subsequently, rats received an acute administration of naloxone (2 mg/kg. s.c.), 90 min after the morphine treatment on day 11, the number of withdrawal behaviors was scored. Rats that received treatment exclusively with morphine presented significant withdrawal behaviors compared to control (Water). Morphine-dependent female rats showed a prevalent stereotyped behavior of rearing, whereas male rats had teeth chattering behavior as the most preeminent. Treatment with cannabidiol on day 11 partially attenuated withdrawal behavior in morphine-dependent male rats, with mild effects in female rats (high withdrawal responders only). Altogether, our data provide evidence of an anti-hyperalgesic effect of cannabidiol in rats. Male and female rats treated chronically with morphine exhibited withdrawal behaviors in different ratios, and cannabidiol treatment attenuated withdrawal behavior in a sex-dependent manner.