Neural regulation of cholinesterase in newt skeletal muscle. III. Regulation in vitro by proteins from chick embryo brains

Abstract Triceps muscles of newts ( Notophthalmus viridescens ) lose AChE activity and show characteristic changes of various molecular forms of AChE after denervation in vivo or when maintained in organ culture (Rathbone et al., '79b). We examined the ability of nerve explants or homogenates from various sources to prevent the changes in total activity and molecular forms of AChE when added to the cultured muscles. These included dorsal root (sensory) ganglia from larval and adult Ambystoma tigrinum , from Plethodon cinereus and from chick embryo (10‐20 days in ovo). Sympathetic ganglia and brain homogenates offered the best combination of AChE‐maintaining activity and ready availability as a source from which to purify the active factor(s). The extracts of chick embryo brains (CBE) when added to newt triceps in organ culture both maintained total AChE activity and prevented alterations in the activity of the various molecular forms of AChE that normally occur after denervation or in organ culture. The active factor(s) were heat labile, trypsin sensitive but RNAase insensitive and had an apparent molecular weight of <20,000 daltons. Nerve growth factor, bovine serum albumin and RNA from chick embryo brains were all ineffective in maintaining the AChE activity of the muscles. The brain extracts also contained material of molecular weight >50,000 daltons that enhanced the loss of AChE from the muscles. It is concluded that embryonic chick brain extract is a plentiful source of neurotrophically active material from which a factor, most likely a small protein, can be purified for examination of the physiological role of putative neurotrophic factor.