Influence of transmitter type on projections formed by brain transplants

Brain transplants placed adjacent to the hippocampus in the developing rat brain have been used to probe the mechanisms underlaying the formation of specific terminal fields. In recent experiments we have analyzed the capacity of transplants which use different transmitter types to survive and innervate the hippocampus. A cavity was placed in the entorhinal occipital cortex of 3 day old rat pups. Transplants were placed in the cavity three to six days later when all degeneration products had been removed and the level of neurotrophic factors had increased. Septal or striatal tissues survived and innervated the hippocampus forming terminal fields like those of the native septal input. Fibers from transplants of the raphe area also innervated the hippocampus and these formed normal raphe-like projections though the density of innervation was greater. Thus it appears that the outgrowth pattern from transplants is related at least iN part to a property related to transmitter type.