(-)-Cytisine.
A Nicotinic Channel Agonist and a Partial Agonist of beta2 Subunit.
(-)-Cytisine is an alkaloid, which is occurring naturally in several types of plants as well as in animals feeding on them (see an example in reference #1).
(-)-Cytisine is a potent and selective agonist of neuronal nAChR. It acts as a partial agonist at beta2-containing nAChR. EC\50\s differ for different subunits composed channels; for recombinant human channels expressed in Xenopus oocytes the following EC\50\ values were reported: 25 μM, 39 μM, 67 μM, 72 μM, 2.6 μM 0.9 μM and 71 μM for alpha2beta2, alpha2beta4, alpha3beta2, alpha3beta4, alpha4beta2, alpha4beta4 and alpha7 respectively.
However, in beta2 containing channels, the response to acetylcholine is largely reduced when applied in combination with (-)-Cytisine. Therefore, when applied in vivo it exerts a compound effect of both activating certain nAchRs and inhibiting the effect of Ach on others.
For example, (-)-Cytisine was found to have antidepressant-like effects in several animal models of antidepressant efficacy. This was probably achieved by inhibiting the effect of Ach on alpha2beta4 channel in the basolateral amygdale.
In another study, the effects of (-)-Cytisine were compared to nicotine; rats were trained to discriminate nicotine from saline and it was confirmed that (-)-Cytisine had a nicotine-like discriminative effect, but it was much less potent than nicotine itself.
Ion Channel Modulators; Nicotinic Acetylcholine Receptor Channel Activators
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