Development of full-length Trk B-immunoreactive structures in the prefrontal and visual cortices of the macaque...

Distribution and morphological changes of cells containing the signal transducing neurotrophin receptor, full-length Trk B (fl-Trk B), were investigated in the prefrontal cortex (area FD) and the primary visual cortex (area OC) of the macaque monkey between embryonic day 140 and the adult stage. In area FD at the adult stage, fl-Trk B immunoreactivity was mainly observed in the pyramidal cells in layers II/III, V and VI. Small numbers of granule cells in layer IV were immunopositive. Bipolar and multipolar cells in layer II were rarely immunoreactive. At embryonic day 140, the number of fl-Trk B immunoreactive pyramidal cell was high, and gradually decreased until the adult stage. In layer IV, the number of fl-Trk B-ir cells was also high at embryonic day 140, and decreased remarkably from postnatal day 7 to the adult stage. On the other hand, in area OC at the adult stage, cells in layers II/III, IV, V and VI were fl-Trk B immunopositive. From embryonic day 140 until adulthood, the cells in layer IVc were fl-Trk B immunoreactive. The strongest fl-Trk B immunoreactivity in areas FD and OC occurred at postnatal month 6, coinciding with the time of the synapse overproduction. These findings suggest that ligands of fl-Trk B, such as BDNF and NT4/5 may be involved in the development and maintenance of the monkey cerebral cortices.