9cRA is more effective than atRA against 6-OHDA –mediated neurodegeneration in VM TH neurons. (A) Primary VM neuronal cultures were treated with either 6-OHDA (100 μM) or saline for two hours and then were treated with either 9cRA or atRA (50 nM). 9cRA, compared to atRA, is more potent in protecting against 6-OHDA –mediated loss of TH cells). (B) 9cRA (50 nM) is significantly effective than atRA (50 nM) to increase survival of TH cells after lesioning with 6-OHDA (100 μM). The density of TH (+) cells was normalized to the cell density in the non-6-OHDA and non-9cRA (vehicle) -treated group. More TH neurons survived after treatment with 9cRA+ 6-OHDA, compared to atRA + 6-OHDA (*p<0.001).