In this study, the results in PD mice indicated that Bifidobacterium breve A1 prevented the decrease in spine density and kept it at the same level as in the control group (* p < 0.01) vs. Control + Saline († p < 0.05): Between MPTP + Saline and MPTP + Bifidobacterium breve A1, Bifidobacterium breve A1 had no effects on the levels of hippocampal cAMP-adenylyl cyclase (AC)–cyclic AMP in the PD and control mice (* p < 0.01 vs. Control + Saline) [65]. This evidence concerns the gene CAMP and Parkinson disease.