The observationofthe avt-egfp transgenic embryo led us to identify
the AVT neuronal populations with two different origins: the
telencephalon-derived and the OT-derived populations. The onset
of these two populations occurred at different stages from 2 dpf to
4 dpf, and they subsequently migrated and converged on a distinct
region of the forebrain. The results from assessing the sections of
embryos and juveniles confirmed that the telencephalon-derived
and the OT-derived populations develop to the POA and VH populations
of AVT neurons, respectively. Little information about the
development of AVT neurons is known in vertebrates, excepting
zebrafish. Eaton et al. used in situ hybridization and demonstrated
that AVT-expressing neurons are detected in the VH and POA at
24 h and 48 h postfertilization of zebrafish embryo, respectively,
and the avt gene transcription in these two regions are separately
regulated by different genes [22]. The period from fertilization to
hatching differs between the medaka and zebrafish [23], however,
our results are consistent with zebrafish in that the AVT expression
in this distinct brain region occurs in the embryo during early
developmental stages.