One rat study noted that ingestion of Codonopsis resulted in attenuation of the memory-impairing effects of scopolamine as well as alcohol (30g/kg) in mice and rats, and was thought to be secondary to a bioactive in the n-butyl alcohol fraction which was shown to increase the density of muscarinic cholinergic receptors in the brain; no binding or alterations in affinity were noted.[12]
Currently, other studies that note interactions with the cholinergic system have found increased tension in the smooth muscle tissue of the stomach, which was partially blocked by Atropine.[13]
Possibly something related to acetylcholine receptors may contribute, but the evidence is currently subpar
Codonopsis alkaloids were found to suppress cell growth of the neural cell line PC12. Cell growth was suppressed by up to 15% at the concentration of 30ug/mL under the influence of NGF at 2ug/mL; in this study, 100ug/mL of Codonopsis was required to be equally effective as 50ug/mL NGF in suppressing proliferation (to 80% of control).[14]
Codonopsis alkaloids have been found to, in vitro, enhance NGF-induced neuronal outgrowth in PC12 cells. Although it alone failed to enhance neurite length, 2ug/mL enhanced NGF-induced growth from 7.0+/-3% to 52.0+/-8%; 742% the growth of NGF alone.[14] Synergism were noted to be statistically significant at 10ug/mL, and missed statistical significance at 3ug/mL.[14] These benefits appeared to be mediated via MAPK (the pathway mediated by NGF[15]), as incubation with the inhibitor PD98059 suppressed growth.[14] In Schwann cells (RSC 69) it was found that the signalling via MAPK is p38 and ERK dependent,[16] where concentrations of 10-100ug/mL for 16 hours significantly increased proliferation of cell nuclear antigen (up to 120% at 60ug/mL) and increased Schwann cell proliferation around 350% of control at 20-40ug/mL and increased cell migration in a dose-dependent manner coupled with increased MMP9 and uPA, which may be downstream of an increase in FGF-2.[16] The authors hypothesized that the increase of neuronal proliferation and migration could aid nerve regeneration.[16]
Too preliminary to draw conclusions, but some bioactives in Codonopsis (alkaloids in structure) appear to enhance neuronal differentiation in vitro.