Ased the number of BrdU+ CMs by 4.8 fold to 3.860.9 BrdU+ CMs/heart (p,0.05, n = 12) (Figure 5C). In order to assess whether the increased rate of BrdU incorporation was accompanied by an increase in the total number of cardiomyocytes in the heart, we used Tg(cmlc2:DsRed2nuc) Pentagastrin chemical information BTZ-043 zebrafish which express DsRed2 fluorescent protein in the nuclei of cardiomyocytes [22,23]. As evaluated by 2-way ANOVA, NGF significantly increased the time-dependent changes in cardiomyocyte numbers following AA exposure from 96?44 hpf (p,0.001, n = 15). More specifically, under basal conditions at 72 hpf, there were 256612 (n = 5) cardiomyocytes per heart. Following AA exposure (72?5 hpf), at 96 hpf there was a 24 decrease in cardiomyocyte numbers to 18766 (AA) per heart as compared to time-matched controls (p,0.01, n = 5; Figure 6A). In fish treated with AA subsequently exposed to NGF there was no significant evidence of regeneration at 96 hpf. By 120 hpf, the number of cardiomyocytes in the hearts of AA exposed zebrafish had decreased by 53 (118621 vs 252620 CMs/heart, p,0.01, n = 5; Figure 6B). By contrast, fish treated with AA and supplemented with NGF had a 102 greater number of cardiomyocytes (238617 CMs/heart, p,0.01, n = 5; Figure 6B). As shown in Figure 6C, at 144 hpf AA treatment caused a 63 reduction in total cardiomyocyte numbers compared to controls (AA vs control: 121630 vs 327630 CMs/heart p,0.01, n = 5). The addition of NGF after AA treatment rescued cardiomyocyteNGF Rescues Heart Failurecell numbers with a 142.3 increase to 293622 CMs/heart (p,0.01, n = 5). We next characterised the pattern of gene expression that accompanied the apparent regenerative actions of NGF in the zebrafish heart. On the basis of recent studies [10] we determined the level of expression of GATA4 and NKx2.5 mRNA within the zebrafish heart. In this model of HF, neither GATA4 nor Nkx 2.5 expression changed during the development of HF, and their expression was unaltered by the addition of NGF (data not shown). To determine whether NGF causes cardiomyocyte proliferation, wholemount immunohistochemistry was conducted on Tg(cmlc2:GFP) zebrafish exposed to control conditions (Egg water) or NGF (50 ng/ml) in the presence of BrdU from 76?00 hpf. Tg(cmlc2:GFP) zebrafish were exposed to NGF (50 ng/ml) continuously in Egg water from 76 hpf, a timepoint from the AA model from which NGF was added after AA was removed. Addition of NGF caused a 2.38 fold increase in BrdU+ cardiomyocytes (control vs NGF: 5.361.0 vs 12.663.0 BrdU+ CMs/heart, p,0.05, n = 8?0 per group; Figure 7A). To assess the relationship between increased numbers of BrdU+ cardiomyocytes in NGF treated fish and total cardiomyocyte numbers, Tg(cmlc2:DsRed2-nuc) zebrafish were exposed to NGF (50 ng/ml) continuously in Egg water from 76 hpf. The number 1527786 of cardiomyocytes in the heart were counted from confocal microscopy z-stacks of Tg(cmlc2:DsRed2-nuc) zebrafish on IMARIS. As determined by 2-way ANOVA, 11967625 zebrafish exposed to NGF caused a significant increase in cardiomyocyte numbers per heart compared to control fish raised in egg water from 96?68 hpf (p,0.05, n = 37?9). In detail, as shown in Figure 7B, by 120 hpf NGF induced a 14 increase in total cardiomyocytes (p,0.05, n = 9) from 227.766.7 CMs/heart (control) to 259.6610.2 CMs/ heart (NGF). At 168 hpf, NGF continued to be associated with a 14 increase in total cardiomyocytes compared to fish from egg water controls (control vs NGF: 25769.3 to 281.4611.3 CMs/ hear.Ased the number of BrdU+ CMs by 4.8 fold to 3.860.9 BrdU+ CMs/heart (p,0.05, n = 12) (Figure 5C). In order to assess whether the increased rate of BrdU incorporation was accompanied by an increase in the total number of cardiomyocytes in the heart, we used Tg(cmlc2:DsRed2nuc) zebrafish which express DsRed2 fluorescent protein in the nuclei of cardiomyocytes [22,23]. As evaluated by 2-way ANOVA, NGF significantly increased the time-dependent changes in cardiomyocyte numbers following AA exposure from 96?44 hpf (p,0.001, n = 15). More specifically, under basal conditions at 72 hpf, there were 256612 (n = 5) cardiomyocytes per heart. Following AA exposure (72?5 hpf), at 96 hpf there was a 24 decrease in cardiomyocyte numbers to 18766 (AA) per heart as compared to time-matched controls (p,0.01, n = 5; Figure 6A). In fish treated with AA subsequently exposed to NGF there was no significant evidence of regeneration at 96 hpf. By 120 hpf, the number of cardiomyocytes in the hearts of AA exposed zebrafish had decreased by 53 (118621 vs 252620 CMs/heart, p,0.01, n = 5; Figure 6B). By contrast, fish treated with AA and supplemented with NGF had a 102 greater number of cardiomyocytes (238617 CMs/heart, p,0.01, n = 5; Figure 6B). As shown in Figure 6C, at 144 hpf AA treatment caused a 63 reduction in total cardiomyocyte numbers compared to controls (AA vs control: 121630 vs 327630 CMs/heart p,0.01, n = 5). The addition of NGF after AA treatment rescued cardiomyocyteNGF Rescues Heart Failurecell numbers with a 142.3 increase to 293622 CMs/heart (p,0.01, n = 5). We next characterised the pattern of gene expression that accompanied the apparent regenerative actions of NGF in the zebrafish heart. On the basis of recent studies [10] we determined the level of expression of GATA4 and NKx2.5 mRNA within the zebrafish heart. In this model of HF, neither GATA4 nor Nkx 2.5 expression changed during the development of HF, and their expression was unaltered by the addition of NGF (data not shown). To determine whether NGF causes cardiomyocyte proliferation, wholemount immunohistochemistry was conducted on Tg(cmlc2:GFP) zebrafish exposed to control conditions (Egg water) or NGF (50 ng/ml) in the presence of BrdU from 76?00 hpf. Tg(cmlc2:GFP) zebrafish were exposed to NGF (50 ng/ml) continuously in Egg water from 76 hpf, a timepoint from the AA model from which NGF was added after AA was removed. Addition of NGF caused a 2.38 fold increase in BrdU+ cardiomyocytes (control vs NGF: 5.361.0 vs 12.663.0 BrdU+ CMs/heart, p,0.05, n = 8?0 per group; Figure 7A). To assess the relationship between increased numbers of BrdU+ cardiomyocytes in NGF treated fish and total cardiomyocyte numbers, Tg(cmlc2:DsRed2-nuc) zebrafish were exposed to NGF (50 ng/ml) continuously in Egg water from 76 hpf. The number 1527786 of cardiomyocytes in the heart were counted from confocal microscopy z-stacks of Tg(cmlc2:DsRed2-nuc) zebrafish on IMARIS. As determined by 2-way ANOVA, 11967625 zebrafish exposed to NGF caused a significant increase in cardiomyocyte numbers per heart compared to control fish raised in egg water from 96?68 hpf (p,0.05, n = 37?9). In detail, as shown in Figure 7B, by 120 hpf NGF induced a 14 increase in total cardiomyocytes (p,0.05, n = 9) from 227.766.7 CMs/heart (control) to 259.6610.2 CMs/ heart (NGF). At 168 hpf, NGF continued to be associated with a 14 increase in total cardiomyocytes compared to fish from egg water controls (control vs NGF: 25769.3 to 281.4611.3 CMs/ hear.