Long term (2-to 3-week) cultures of superior cervical ganglia (SCG) were established from rats and rat embryos ranging in age from 15 days of gestation (E15) to 279 days postnatal (P279). Cultures were grown on a collagen substratum and fed a serum-containing medium with added nerve growth factor. Radial outgrowth of neurites was measured as a function of time for up to 2 to 3 weeks. Computer-aided analysis generated estimates of onset time, initial rate, and subsequent changes in the rate of

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... owth of these neurites. The explants from perinatal rats showed the fastest growth onset time (5 to 13 hr), fastest initial rate of growth (370 to 660 pm/d), and a decline in growth rate during the first 2 weeks in culture. The outgrowth from these perinatal explants was composed of many small fascicles. Neurites from the prenatal explants (El5 to E20) began to grow within 22 hr in uitro. Their rate of growth was lower initially (150 to 300 pm/d) but increased to equal the perinatal explant initial rate before again falling to an intermediate level (200 to 300 pm/d). The outgrowth from prenatal explants contained fewer larger fascicles. Postnatal explants had low initial rates of growth (70 to 176 pm/d) but exhibited an increasing growth rate in vitro, again approaching an intermediate rate of 200 to 250 pm/d after 2 to 3 weeks. Neurite outgrowth from the postnatal explants was delayed by an amount roughly correlated with the age of the animal from which they had come (up to 68 hr for P49). The initial rate of growth also decreased with advancing postnatal age but reached an asymptote of about 50 to 150 pm/d at about P30. The outgrowth was initially sparse but became denser with time in culture. Thus, in a culture system in which medium composition and growth substratum are held constant, marked differences can be observed in pattern, latency, initial rate, and subsequent changes in rate of neurite extension among SCG explants from different ages of rats and rat embryos. 503