Evoked glutamate release probability is not influence by perinatal fentanyl exposure or environmental enrichment. A, Representative traces of EPSC responses to paired pulse stimulation. B, There were no differences in the PPR between groups before plasticity induction (n = 9–12 mice/group, 1 neuron/mouse). C, D, Within each group, there were no differences in baseline PPR compared with PPR post-LTP or LTD induction (n = 4–6 mice/group, 1 neuron/mouse). Data depict means and 95% confidence intervals.