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COMPARISON OF LEVELS OF ADENOSINE 3′,5′‐MONOPHOSPHATE IN HIGHLY PURIFIED AND MIXED PRIMARY CULTURES OF NEURONS AND NON‐NEURONAL CELLS FROM EMBRYONIC CHICK SYMPATHETIC GANGLIA

Primary cultures containing ≥99% neurons, ≥99% non‐neuronal cells (glia), or both cell types were prepared from the sympathetic ganglia of 12‐day chick embryos. Levels of cyclic AMP in the non‐neuronal cells (∼14 pmol/mg protein) were approximately 3‐fold higher than levels in the neurons (∼4 pmol/mg protein). Mixed cultures had concentrations of cyclic AMP which fell between the values measured for pure neuronal and pure non‐neuronal cultures. The measured cyclic AMP values of mixed cultures were indistinguishable from values predicted by summing the expected contributions of the neurons and non‐neuronal cells. Thus, contact between the neurons and non‐neuronal cells in these mixed cultures did not appear to alter the level of cyclic AMP in either cell type. Neuronal‐glial interactions, such as the specific neuronal stimulation of non‐neuronal cell proliferation, occurred independently of any changes in the level of cyclic AMP in the mixed cultures. Cell density was varied in both pure and mixed cultures, and both cyclic AMP concentrations and amounts of [3H]thymidine incorporation into DNA were measured. The cyclic AMP content of the non‐neuronal cells varied inversely with cell density. [3H]Thymidine incorporation was independent of cell density in both neuronal and non‐neuronal cultures. Parallel density‐dependent decreases in cyclic AMP concentration and [3H]thymidine incorporation were observed in mixed cultures as cell density was increased. The data suggest that there is no relationship between changes in rate of non‐neuronal cell proliferation and cyclic AMP levels in these cultures.