Research reportProtracted cocaine withdrawal produces circadian rhythmic alterations of phosphorylated GSK-3β in reward-related brain areas in rats

Protracted cocaine withdrawal can extend for months and contribute to cocaine seeking and relapse. However, no previous studies have reported the manifestation of protracted withdrawal from chronic cocaine in rats. Glycogen synthase kinase 3β (GSK-3β) can phosphorylate PER2, CRY2, Rev-erbα, and BMAL1 in mammals. The circadian rhythmic expression of GSK-3β in reward-related brain areas is unclear. We examined rodent behaviors and circadian disturbances of GSK-3β expression during 30 days of protracted cocaine withdrawal. The behavioral tests included open field, elevated plus maze, weight gain, and sucrose preference tests performed 3, 10, and 30 days after stopping cocaine. At these three assessment points, we collected brain samples every 4 h for 24 h to examine the circadian rhythmic expression of GSK-3β. Decreased locomotor activity, weight loss, decreased sucrose consumption on day 3, and increased time spent in the open arms of the elevated plus maze on day 10 after cocaine administration were found. Blunted circadian rhythms of phosphorylated GFK-3β (pGSK-3β) persisted for at least 30 days in all examined brain areas, with the exception of 10 days in the suprachiasmatic nucleus (SCN) and nucleus accumbens (NAc). The expression of pGSK-3β decreased in the SCN and increased in the NAc and ventral tegmental area persisted for at least 30 days, whereas in the prefrontal cortex decreased during withdrawal for 10 days but then reversed to abnormally high levels with protracted withdrawal. These long-lasting changes disrupted circadian rhythms and produced abnormal levels of phosphorylated GSK-3β protein in reward-related brain circuits, which may play a role in protracted cocaine withdrawal and contribute to relapse.

Research highlights▶ Protracted cocaine withdrawal including decreased locomotor activity, weight loss and sucrose consumption was found after cocaine administration. ▶ Blunted circadian rhythms of pGSK-3β persisted in most examined brain areas after cocaine withdrawal. ▶ Expression of pGSK-3β increased in the nucleus accumbens and ventral tegmental area after cocaine withdrawal. ▶ Expression of pGSK-3β decreased in the suprachiasmatic nucleus and prefrontal cortex decreased during cocaine withdrawal.