DEVELOPMENT OF PARVALBUMIN-IMMUNOREACTIVE NEURONS IN THE POSTNATAL HUMAN HIPPOCAMPAL FORMATION
Parvalbumin (PV) is a calcium-binding protein present in fast-spiking GABAergic neurons, such as basket and axo-axonic cells. Previous studies in non-human primates reported prenatal expression of PV in the temporal archicortex including entorhinal cortex and hippocampal formation. In contrast, PV-immunoreactivity was observed only postnatally in human entorhinal cortex, but no information is available regarding the hippocampal formation. Therefore, maturation of PV-immunoreactive interneurons were studied in the developing postnatal human hippocampal formation. At full-term birth, only few PV-immunoreactive neurons were visible in CA1-CA3a,b regions of Ammon’s horn, but not in CA3c. The first PV-immunoreactive cells in CA3c pyramidal layer appeared at the age of 1 month. Before the age of 6 months, no PV-immunoreactive neurons were detected in the dentate gyrus. Even at the age of 8 months, only a few PV-immunopositive cells were present in the dentate hilus. The numbers of the cells and their dendritic arborization in Ammon’s horn and in the dentate gyrus gradually increased with age. PV-immunoreactive axon terminals in CA1-CA3 and in the dentate granule cell layer were first detected at 1 year of age. Even at the age of 3 years, substantially less PV-immunoreactive axon terminals were present in the dentate gyrus than in Ammon’s horn, and the adult-like density of them could not be seen before the age of 8 years.Our results suggest long-lasting postnatal maturation of PV-immunoreactive interneurons that follows the maturation sequence of the subfields of the human hippocampal formation. Supported by: NAP 2.0 (2017-1.2.1-NKP-2017-00002), PTE EFOP-3.6.1.-16-2016-00004, 20765-3/2018/FEKUTSTRAT.