Effect of circadian rhythm disturbance on morphine preference and addiction in male rats: Involvement of period genes and dopamine D1 receptor

Highlights • Constant light exposure for one month reduced the concentration of melatonin in the plasma of wistar rats. • Constant light up-regulated the mRNA level of Per1, Per2 and dopamine D1 receptor in the striatum. • Constant light up-regulated the mRNA level of Per2 and dopamine D1 receptor in the prefrontal cortex. • Exposure to constant light led to greater preference for oral morphine consumption. • Rats exposed to constant light had more severe morphine withdrawal syndrome.