Substance P-like immunoreactivity in human prenatal hippocampal formation.

Presence and localization of substance P-like immunoreactive neuronal structures in human hippocampal formation during prenatal stages of ontogenesis are reported. In fetuses at 16 and 17 weeks of gestation immunoreactivity is very scarce and represented only by sporadic fibres in Ammon's horn and the entorhinal area. In specimens at 25 and 26 weeks of gestation, more or less intensely labelled perikarya of different morphology are easily detectable in deep layers of Ammon's horn and the hilus of fascia dentata. Immunoreactive beaded fibres are also present at this stage. The possibility of the existence of a substance P-containing extrinsic projection to Ammon's horn is pointed out.