Techniques for the production and purification of single nerve cells.

Rationale for single-cell analysis The human brain has approx. IO’O nerve cells and the vast population of neurons presents a formidable challenge to the biologist attempting to understand how the nervous system works. Three approaches have generally been used. The first is to try to localize the tissue constituent by making it in some way visible in histological sections, e.g. by staining, by using fluorescent dyes or by radioactive labelling followed by autoradiography. Procedures of this sort have become increasingly sophisticated, as exemplified by the development of the whole field of immunohistology, where specific monoclonal antibodies may be used. The second major approach is to separate component parts, e.g. cell bodies, glia, myelin, nuclei, synaptosomes, synaptic vesicles etc., and study them in isolation. While studies of this kind have many advantages, they can suffer from certain drawbacks, such as the possibility of changes occurring in the constituents caused by the elaborate separation of fractionation procedures employed. The third, and possibly the oldest approach, is the subject of this contribution. It consists of the direct quantitative microchemical analysis of identified samples obtained under controlled conditions from specific sites in the nervous system. The originators of direct quantitative histochemistry were Kai Linderstrtam-Lang and Heinz Holter in the early 1930s. Their classical studies involved producing serial frozen sections from the gastric mucosa (Holter & Linderstrtam-Lang, 1935), staining and chemically analysing alternate sections and then making a correlation between the distribution of pepsin and several specific cell types. David Glick (Glick, 1938) and Alfred Pope (Pope, 1952) were among the first to apply the original Lang-Holter methodology to the nervous system, and it became evident that original procedure had to be modified if it was to be applied generally, because adjacent systems in the nervous system can be very dissimilar in cellular composition. In recent years many studies have attempted to characterize biochemically the individual cells within nervous tissue, the most prominent developers being Lowry, Giacobini and Hyden (see Osborne, 1974). There are various procedures for isolating defined components of the nervous system by dissection and analysing them with suitable biochemical methods, some of which I shall deal with briefly. Detailed information on microbiochemical procedures and their application are described elsewhere (Lowry, 1963: Lowry & Passonneau, 1972: Osborne, 1974; Giacobini, 1975; Glick, 1977: Wu, 1978).