I am attempting to determine whether I can combine two different data sets. The first data set was collected from adult C57BL/6J mice at PND 160-PND 189 (5-6 months), and the second data set was collected from adult C57BL/6J mice at PND 115-PND 140 (3-4 months). I administered an acute restraint stress to both sets of mice, and am examining mRNA expression levels of stress neuropeptides and pro-inflammatory factors in the brain 24 hours after the stress exposure. Aside from the differences in ages, the experimental paradigm was kept identical for both cohorts of mice. The literature generally indicates that mice are considered "young adults" from about PND 90-PND 182 (3-6 months). However, one large scale analysis (Shoji 2016, Mol Brain) suggests that there are behavioral differences even between mice within this "young adulthood" age group (2-3 months, 4-5 months, and 6-7 months). I was wondering if anyone has come across differences in mRNA/protein expression levels across young adult mice of different ages, and whether you would recommend that I keep my two datasets separate based on this.