Influence of cardiac extracts on cultured ciliary ganglia

Inclusion of extracts of rat hearts in culture medium resulted in both a fibre outgrowth and maintenance of choline acetyltransferase (CAT) activity in explained chicken embryo ciliary ganglia. CAT activity was maintained in ganglia from 7- to 19-day-old embryos whereas fibre outgrowth was maximal in ganglia from 8- to 11-day-old embryos and as the embryo matured ganglia became less responsive, showing virtually no fibre response by 16 days. The fibre outgrowth response had an absolute dependence on serum in the medium and a pH optimum of 7.1--7.3. Maintenance of CAT was stimulated by, but not absolutely dependent on, the presence of serum in the medium and was insensitive to changes in the pH of the culture medium between 7.2 and 8.0 but was sensitive to decreases in pH below 7.2. Horse and fetal calf serum were equally effective in stimulating the cardiac extract medium-induced maintenance of CAT activity and induction of fibre outgrowth.