NTRK2 and atrial fibrillation: However, expression levels of NGFr/TrkA, BDNF, TrkB and CALCRL was low (as compared to PBS injected IVD-AF tissues) or not observed in posterior/central AF tissue of healthy, uninjured IVDs that served as controls or NTG-101 injected IVDs (Figure 2, Figure 3, Figure 4 and Figure 5).