Degree of hyperinnervation of area dentata by locus coeruleus in the presence of septum or entorhinal cortex as studied by sequential intraocular triple transplantation.

In situ area dentata receives a sparse noradrenergic innervation from locus coeruleus. Embryonic area dentata co-transplanted with locus coeruleus to the anterior eye chamber receives an abundant ingrowth of nerves from the noradrenergic neurons of the locus graft. We sought to identify restrictive forces acting on coeruleo-dentate axons by arranging for the innervation of area dentata transplants by either entorhinal cortex or septal nuclei transplants prior to locus coeruleus transplantation. The noradrenergic hyperinnervation was not inhibited when locus coeruleus transplants were placed on the opposite side of area dentata from the entorhinal or septal transplant. Noradrenergic innervation of area dentata was restricted when the locus coeruleus transplant was placed in contact with the septal transplant. This inhibitory interaction seemed to take place between the septal and locus coeruleus transplants rather than in the area dentata neuropil. This type of interaction points towards one means by which axonal growth may be inhibited during development or in the adult.