We also examined the possibility that our antibiotic treatment regimen may have been stressful and thereby altered function of the hypothalamic-pituitary-adrenal (HPA) stress axis. As serum levels of corticosterone, the primary serum glucocorticoid in mice, can affect behavioral responses to cocaine25 we measured serum levels of control and antibiotic-treated mice. From these analyses we see that treatment with antibiotics via the drinking water for two weeks did not alter peak (afternoon) serum levels of corticosterone (Fig. 2c – two-tailed t-test: p = 0.68; t = 0.42), which was the time of day when behavioral testing was performed. This indicates that any behavioral changes seen in our antibiotic-treated animals were not likely due to gross dysregulation of the HPA stress axis.
