Neonatal septal implants: development of afferent lamination in the rat dentate gyrus

The technique of tissue implantation into neonatal rats was used to assess mechanisms underlying the development of afferent lamination in the rat hippocampal formation. Septal nuclei, dissected from the brains of rat embryos (E17-E20), were implanted into the occipital or entorhinal cortex of 2--3 day old neonates that simultaneously received fimbrial transections to remove hippocampal innervation by native septal efferents. As visualized with acetylcholinesterase (AChE) histochemistry, the distribution of enzyme activity in implant-innervated hippocampi is qualitatively identical to the pattern in unoperated animals. Fibers from septal implants placed into the entorhinal cortex, appear to interact with commissural/associational afferents and produce altered laminar zones in the dentate gyrus.