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This chapter summarizes the findings on polysialic acid function in the adult brain. In particular, the roles of polysialic acid elucidated by analysis of NCAM knockout mice are described, together with descriptions of the role of polysialic acid in the circadian rhythm, long-term potentiation and memory, neurological diseases, and response to injury.

This chapter focuses on microglial cells. Microglial cell numbers are thought to make up 5% to 20% of the entire central nervous system (CNS) glial cell population. As a conservative estimate, assuming that microglia represent 10% of the total glial cell pool and knowing that there are at least 10 times as many glial cells as there are neurons in the CNS, it is apparent that there are at least as many microglia as there are neurons. The origin and lineage of microglia, methods for staining microglia, microglia and related cell types, and microglia in the normal adult and aging brain are discussed.

This chapter begins by outlining the structure-function organization of the adult paraventricular nucleus of the hypothalamus (PVH). It then reviews some highlights of what has already been learned about its pre- and postnatal development, with an eye toward providing a conceptual framework for broader experimental examination of molecular mechanisms underlying the progression from differentiated neuroepithelium to adult three-dimensional structure, axonal connections, and function. Topics discussed include what neuroepithelial region that generates the PVH, when PVH neurons are born, relationship between PVH and supraoptic nucleus development, and the relationship between developing PVH and pituitary.

This chapter narrates the beginning of the author's research on plasticity. He spent much of his time documenting how, on the level of experimental practice, technologies were being invented that enabled understanding the adult brain in embryogenetic terms. By that time, he was introduced to the nocturnal grounds of science. Alain Prochiantz said that science was neither (or not exclusively) about experimentation nor (or not exclusively) about truth, but instead about the work with ideas. Implicit in his lectures was the suggestion that the author's research questions were naïve. He wanted to make the author sensitive to other comprehensions of scientific practice.

This concluding chapter compares the work of Alain Prochiantz and Fred Gage—both of which presented the idea that some basic embryogenetic processes might continue in adult brains. While Prochiantz began to wonder whether homeoproteins could be plastic forces, Gage sought to invent a language that would allow thinking of the adult brain in terms of its embryogenesis. The background to Gage's conceptual innovation was very different from Prochiantz's. Gage had made a name for himself since the 1970s by grafting fetal brain tissue to mature brains to fight neurodegenerative diseases (mostly Parkinson's). He was interested in reintroducing, through cutting and pasting fetal tissue, the possibility of embryogenetic growth in diseased brains.

This chapter asserts that the overarching questions that had structured the work of the lab from its inception in 1989 to 2004–2005 was: Do homeoproteins transfer between cells? Is this transfer an important embryological process, one that organizes the cellular emergence of the brain, one that renders the adult brain plastic? The book's research had followed the emergence of these questions and the efforts to answer them. The the chapter states that the answers that concluded his work for the book were merely the beginnings of a new episode of the study done in the lab. The chapter enumerates the new or research positions of the people who had advanced the lab's experimental system.