Interactions of living astrocytes in vitro: evidence of the development of contact spacing.

We have studied the behaviour of living, process-bearing astrocytes in vitro, observing groups of cells at daily intervals for up to 7 days. Each cell initially formed two processes, appearing bipolar in shape, and with further time in culture, grew additional processes and appeared stellate. As their processes grew, the interactions between astrocytes underwent characteristic changes. While bipolar, the cells appeared to avoid making contact, lying parallel to each other. As they became stellate, the astrocytes made extensive contact with neighbours, gradually forming extended, contacting networks in which their somas were regularly spaced (as previously described). The interactions which led to the establishing of such arrays were also evident. If two cells were initially close or adjacent, they extended short processes to contact each other; then, as their processes grew, their somas moved apart, until they were separated by 60-120 microns. If two cells were initially well separated, each directed processes towards the other until contact was made, often with striking precision, and their somas then moved together, until they were separated by 60-120 microns. These behaviours of contact, separation, and approach caused astrocytes to form clusters, within which their somas appeared regularly spaced, and may represent the interactions which occur among astrocytes during normal development to produce the regularly spaced arrays of astrocytes described in earlier studies of intact central nervous tissue.