Neurotrophin receptor Ntrk2b function in the maintenance of dopamine and serotonin neurons in zebrafish

Neurotrophins and their receptors have highly conserved evolutionary lineage in vertebrates including zebrafish. The NTRK2 receptor has two isoforms in zebrafish, Ntrk2a and Ntrk2b. The spatio-temporal expression pattern of bdnf and ntrk2b in the zebrafish brain was studied using in situ hybridization. The robust and corresponding expression pattern of ntrk2b to bdnf suggests that ntrk2b is the key receptor for bdnf in the zebrafish brain, unlike its duplicate isoform ntrk2a. To study ntrk2b function, two different genetic strategies, the TILLING mutant and morpholino oligonucleotides (MO), were used. Specific subsets of the dopaminergic and serotonergic neuronal populations were affected in the mutants and morphants. The mutant showed anxiety-like behavior both in larval and adult stages. Our results consistently indicate that BDNF/NTRK2 signaling has a significant role in the development and maintenance of aminergic neuronal populations. Therefore, the ntrk2b-deficient zebrafish is well suited to study mechanisms relevant for psychiatric disorders attributed to a dysfunctional monoaminergic system.