Cholinesterase inhibitors induce growth cone collapse and inhibit neurite extension in primary cultured chick neurons.

Cholinesterase inhibitors are commonly prescribed medicines in neurological and anesthesiological clinical practices at relatively high doses. Recent studies report that cholinesterases, originally described as neurotransmitter degradation enzymes, are expressed in the developing central nervous systems. They are hypothesized to play an important role during the establishment of neuronal cytoarchitecture. In this study, the effects of several clinically utilized cholinesterase inhibitors on one potential aspect of neuronal development were examined using a primary culture system of chick central and peripheral neurons. Three cholinesterase inhibitors, physostigmine, neostigmine, and edrophonium, suppressed the activity of the leading edges of the extending axons (the nerve growth cones) dose dependently. Filopoda and lamellipodia of nerve growth cones were collapsed by the exposure to the cholinesterase inhibitors. This action was quick, mostly within 5 min, and partly irreversible. The lowest concentration that could induce statistically significant growth cone collapse was 10(-5) M for physostigmine, 10(-4) M for neostigmine, and 10(-2) for edrophonium, respectively. The ED50 values for the growth cone collapsing activity were approximately, 10(-3) M for physostigmine. 10(-2.5) M for neostigmine, and 10(-2) M for edrophonium both in dorsal root ganglion culture and in retinal culture. Even though the result of this in vitro study cannot be applied directly to the in vivo situation, physicians should consider the potential detrimental effects of cholinesterase inhibitors to growing and regenerating nervous tissues.