ENDOGENOUS SYNAPTOGENESIS IN THE DEAFFERENTED DENTATE GYRUS DOES NOT EXCLUDE SYNAPSE FORMATION BY EMBRYONIC ENTORHINAL TRANSPLANTS

After partial deafferentation postsynaptic sites are reinnervated by l ocal sprouting of remaining axons. We have investigated whether this p rocess is sufficient to prevent new synapses being formed by transplan ted embryonic tissue. We find that after unilateral entorhinal ablatio n endogenous sprouting by local axons is unable to reinnervate all the postsynaptic sites in the denervated outer dentate molecular layer. A xons from embryonic entorhinal tissue transplanted adjacent to the den ervated area are able to reclaim a further proportion of the denervate d postsynaptic sites. Thus, after a large lesion, endogenous sprouting is insufficient to preclude reinnervation by axons from embryonic tra nsplants. (C) 1997 Elsevier Science B.V.