This volume is a collection of articles written by Nobel Laureate Rita Levi-Montalcini and published from 1942 to 1995. Studies described in the first part set the stage for the discovery of a protein molecule which became known as the Nerve Growth Factor (NGF), described in detail in the second part. The NGF synthesized in minute amounts in all vertebrate tissues, plays an essential role in the differentiation and survival of several nerve cell populations in the peripheral and central nervous system. The discovery of the NGF was defined by the Nobel Foundation as a milestone in developmental neurobiology, and the author was awarded in 1986 with this prestigious award. Studies pursued in subsequent years and still in progress, have unveiled other fundamental properties of the NGF, described in the third part of this volume.

A host of environmental factors regulate the embryonic development of neurons. In adults, the survival of neurons, the regeneration of damaged axons, and plastic changes in axonal arborization are also controlled by a complex array of environmental cues. An important category of regulatory influences involves target-derived hormone-like peptides act ing on neuronal cell surface receptors. Nerve growth factor (NGF) was the first such factor to be characterized (LEVI MONTALCINI and HAMBURGER 1953) and has served as the model against which all similar factors are compared. A number of factors with properties similar to NGF have been described with activities toward differing populations of neurons. Many of these factors have been characterized only poorly at the biochemical level. However, several factors have been charac terized to the extent that molecular clones are available and complete amino acid sequences are known. These include: three structurally related factors, NGF itself (SCOTT et al. 1983), brain-derived neurotrophic factor (BDNF) (LEIBROCK et al. 1989), and neurotrophin-3 (NT-3) (MAISONPIERRE et al. 1990; HOHN et al. 1990); ciliary neurotrophic factor (CNTF) (LIN et al. 1989) and a second set of structural homologs; acidic and basic fibroblast growth factors (aFGF, bFGF) (ABRAHAM et al. 1986; JAYE et al. 1986). Investigators have cloned the receptors for NGF (JOHNSON et al. 1986; RADEKE et al. 1987) and FGF (LEE et al. 1989).

A fundamental problem in neuroscience is the elucidation of the cellular and molecular mechanisms underlying the development and function of the nervous system. The complexity of organization, the heteroge neity of cell types and their interactions, and the difficulty of controlling experimental variables in intact organisms make this a formidable task. Because of the ability that it affords to analyze smaller components of the nervous system (even single cells in some cases) and to better control experimental variables, cell culture has become an increasingly valuable tool for neuroscientists. Many aspects of neural development, such as proliferation, differentiation, synaptogenesis, and myelination, occur in culture with time courses remarkably similar to those in vivo. Thus, in vitro methods often provide excellent model systems for investigating neurobiological questions. Ross Harrison described the first culture of neural tissue in 1907 and used morphological methods to analyze the cultures. Since that time the technique has been progressively modified and used to address an ever widening range of developmental questions. In recent years a con vergence of new or improved cell culture, biochemical, electrophysiol ogical, and immunological methods has occurred and been brought to bear on neurobiological questions. This volume is intended not to be comprehensive but rather to highlight some of the latest findings, with a review of previous important work as well, in which combinations of these methods are used.