I am looking into DNA methylation of mice as an aging marker along with other assays and recently I added brain IF to the list of assays. For this, I need to fix the brain by transcardial perfusion when I sacrifice a mouse. My concern is if this would affect DNA methylation states of tissues. Would this affect the DNA methylation? If so, what would be the best way to fix the brain without fixing other parts of mouse? Thank you in advance.