EN
Neurotrophins are important regulators of neuronal function in the developing and adult brain. We studied expression of TrkB receptors in the postnatally (P) developing brain of the opossum (Monodelphis domestica). The Western blot analysis showed presence of the full-length catalytical isoform of TrkB and three truncated kinase-lacking isoforms in the opossum brain. Expression of the fulllength TrkB receptor was present in the newborn opossum, whereas truncated forms of TrkB receptors were almost undetectable at this period. The level of the full-length TrkB protein gradually increased with a developing opossum brain, reaching maximum at P12–20. The highest levels of expression of the full-length TrkB correspond to the time of cortical layers generation. The level of truncated TrkB rapidly increased at P20 and started to dominate since P35 (when opossums open eyes). Immunohistochemical staining for TrkB receptors showed that the majority of labeled neurons were placed in the olfactory bulb, cerebral cortex, hippocampus, thalamus, hypothalamus, cerebellum and various brainstem structures. Interestingly, TrkB receptors were predominantly expressed in neurons. Lack of TrkB receptors in glial cells, especially astrocytes and oligodendrocytes, provides the evidence that TrkB receptors can play functionally different role in marsupials than in eutherians. Supported by the NSC grant No 2011/01/B/NZ4/01575.