Loss of TH+ neurons following LPS injection normally takes 2–3 weeks (Meredith et al., 2008). However, stereological analysis revealed a significant decrease in TH+ neurons in the SN of shNurr1 lentivirus-injected mice compared to shCtrl-injected animals after only 7 days of LPS treatment (Fig. 1A and B). Interestingly, a pathological morphology of TH+ neurons with reduced or absent processes and alterations in the size and shape of the cells was observed more often in the shNurr1 groups (Supp Fig. 2E and Fig. 1B). In addition, pathological TH+ cells were observed close to activated microglia (Fig. S2F). The accelerated loss of TH+ neurons following Nurr1 knockdown required LPS injection, as it was not observed in buffer (PBS)-injected animals (Fig. 1C and D). In addition, LPS injection was associated with detection of caspase-3 cleavage, suggesting that loss of TH+ cells was due to cell death rather than to loss of TH expression (Fig. S2G) (Sakurada et al., 1999). Reduction of Nurr1 expression in the SN also resulted in exaggerated expression of inflammatory mediators in response to LPS injection, including iNOS, TNFα and IL1β (Fig. 1E–G).
