Cellular reaggregation in vivo: Modular patterns in intrastriatal grafts derived from fetal striatal primordia

This chapter discusses the cellular reaggregation. The process of reaggregation results eventually in crisp borders between cells of the patches (P) regions and cells of the nonpatch (NP) regions, judging, for example, by stains identifying the large cholinergic neurons, the enkephalin-immunoreactive medium-sized neurons, and the calbindin-D_28K-immunoreactive medium-sized neurons of the P regions. Moreover, available evidence suggests that appropriate tissue-specific afferent and efferent connections are made by neurons in the P regions. Tyrosine hydroxylase-immunoreactive fibers precisely innervate the P regions and are very rare in the NP regions. It is found that it is principally neurons in the P regions that innervate the pallidum of the host, suggesting that the specificity of cell–cell interactions in the transplants not only serves to reaggregate tissues of like type within the grafts but also favors the formation of appropriate connections with the host and discourages inappropriate connections.