Fig. 4. De novo expression of DA determinants during DA regeneration in the newt. (A) Time course of Msx-1/2 expression in the ventral diencephalon and mesencephalon following lesioning. Note the significant reduction in Msx1/2-expressing cells at 24 hours and the significant increase at 7 days. Mean±s.e.m.; ANOVA with Tukey post-hoc test; ^*, P<0.05. (B') Msx1/2 expression in control animals and (B'') 24 hours after sham lesion and after (B''') 24 hours and (B'''') 7 days in 6-OHDA lesioned animals. (C') Number of Nurr1⁺ cells in the TM 3, 8 and 13 days after lesioning. (C'') Proportion of Nurr1⁺ to TH⁺ cells in the TM. Note that at 8 days there are significantly more Nurr1⁺ than TH⁺ cells compared with controls, indicating that maturation of DA neurons occurs along the normal developmental pathway. Mean±s.e.m.; ANOVA with Tukey post-hoc test; ^**, P<0.005; ^***, P<0.001. (C''') An example of TH and Nurr1 double-positive cells in the TM of a control animal, illustrating the expression of Nurr1 in all TH⁺ neurons. Scale bars: 200 µm in A; 150 µm in B.