Shahroud University of Medical siences Shahroud Journal of Medical Sciences 2423-6594 11 3 2025 08 15 Impact of Circadian Disruption on CART mRNA Expression in Nucleus Accumbent: Insights from Constant Light Exposure and Wheel-Running Activity in Rats 8 16 eng Fahimeh Mohseni Department of Addiction, School of Medicine, Shahroud University of Medical Sciences, Shahroud, Iran; Neuroscience Research Center, Shahroud University of Medical Sciences, Shahroud, Iran... fahime.mohseni123@gmail.com Afsaneh Vahedifar Student Research Committee, School of Medicine, Shahroud University of Medical Sciences, Shahroud, Iran.. mohamadi.sh@shmu.ac.ir Shima Mohammadi Neuroscience Research Center, Shahroud University of Medical Sciences, Shahroud, Iran; Department of Neuroscience, School of Medicine, Shahroud University of Medical Sciences, Shahroud, Iran.. shimamohamadi1365@gmail.com Kia Garmabi Student Research Committee, Kermanshah University of Medical Sciences, Kermanshah, Iran.. Kiakdot@gmail.com Atefeh Bakhtazad Cellular and Molecular Research Center, Deputy of Research and Technology, Iran University of Medical Sciences, Tehran, Iran; Department of Neuroscience, School of Advanced Technologies in Medicine, Iran University of Medical Sciences, Tehran, Iran. bakhtazad.atefeh@gmail.com Behzad Garmabi 2 Neuroscience Research Center, Shahroud University of Medical Sciences, Shahroud, Iran;Department of Neuroscience, School of Medicine, Shahroud University of Medical Sciences, Shahroud, Iran.. behzad.garmabi@gmail.com 2025 04 13 2025 08 04 Background: Cocaine Amphetamine Related Transcript (CART) is expressed in the nucleus accumbens (NAc), a region that serves as extra-SCN circadian oscillators. This study examined whether CART mRNA in the NAc follows a diurnal rhythm and how circadian disruption affects its expression. Methods: Rats (n=28) were monitored for 30 days in a 12:12 light-dark cycle (LD). On day 30, 14 rats were sacrificed (7 in the morning, 7 in the evening). The remaining rats (n=14) were exposed to constant light (LL) from day 30 to day 60 and then sacrificed (7 in the morning, 7 in the evening). CART mRNA levels were measured via real-time PCR. Results: In the LD group, CART mRNA was higher in the evening than in the morning (P-value<0.001). In the LL group, evening levels remained elevated but were reduced compared to LD (P-value<0.01). Morning mRNA levels in the LL group were lower than in LD (P-value<0.05). Conclusions: Constant light exposure downregulated CART mRNA, suggesting impaired circadian regulation in the NAc. This disruption may alter neurochemical signaling, affecting behavioral and mood-related processes. The findings highlight CART’s role in circadian coordination and its susceptibility to rhythm disturbances, which could influence mood and activity patterns.