living , mature organotypic cultures of chick dorsal root ganglion maintained in culture for 3 weeks were incubated in medium containing various levels of a precursor of porphyrin and heme formation , delta-aminolevulinic acid ( ala ) , ( 0.5 mm to 10 mm ) or a combination of ala ( 10 mm ) and a metal chelator , camg-edta ( 5 mm ) for up to 48 hours .
C2917401
precursor
C0002563
ala