To assess the functional state of ELK1 in relation to heroin exposure, we also measured levels of pELK1 in animals that self-administered the drug. While no changes in pELK1 were observed at the 1 hour time-point, we observed a significant increase in pELK1 relative to both total protein and total ELK1 protein at 24 hours after the last heroin session (pELK1/total protein: 201.31 ± 32.13%, p<0.05; F1,10= 6.03; pELK1/total ELK1: 158.14 ± 16.10%, p<0.05; F1,10= 6.50; Figure 5A.). Correlations to heroin intake revealed that at both time points, pELK1 negatively correlated to heroin intake (1 hour: r2=0.86, p<0.05; Figure 5B; 24 hours: r2=0.79, p<0.05; Figure 5C), indicating that high levels of heroin were associated with decreased active ELK1. These data support the notion that repeated heroin use dysregulates ELK1 expression relative to the overall history of drug exposure which may also account for individual differences observed in humans.
