3-pyr-Cytisine

3-pyr-Cytisine is a partial agonist of α4β2 receptor with Ki values of 0.91, 119 and 1100 nM for α4β2, α3β4 and α7 receptors, respectively [1].

The alpha-4 beta-2 nicotinic receptor (α4β2 receptor) is a nicotinic acetylcholine receptor participated in learning and is widely expressed in the central nervous system. Also, α4β2 receptor has the highest affinity for nicotine.

3-pyr-Cytisine is an α4β2 receptor partial agonist. In cells expressed α4β2 receptor, 3-pyr-Cyt reduced the agonist response by ACh, which relayed on the intrinsic activity of 3-pyr-Cyt and 3-pyr-Cyt concentration [1]. In PC12 cells, 3-pyr-Cyt significantly induced release of norepinephrine (NE) in a time-, dose- and Ca2+-dependent way. Also, 3-pyr-Cyt inhibited nicotine-induced NE release and increased the mRNA levels of tyrosine hydroxylase (TH), which is necessary for catecholamine biosynthetic [2].

In the tail suspension test, mice treated with 3-pyr-Cyt (0.6 mg/kg) spent significantly less time immobile in a dose-dependent way. In the forced swim test, mice treated with 3-pyr-Cyt (0.3, 0.6 or 0.9 mg/kg) were significantly less immobile in a dose-dependent way, which suggested that 3-pyr-Cyt exhibited antidepressant-like effects in a dose-dependent way [1].

References:
[1].  Mineur YS, Eibl C, Young G, et al. Cytisine-based nicotinic partial agonists as novel antidepressant compounds. J Pharmacol Exp Ther, 2009, 329(1): 377-386.
[2].  Turcanu DS, Kirtok N, Eibl C, et al. Nicotinic receptor partial agonists alter catecholamine homeostasis and response to nicotine in PC12 cells. Neurosci Lett, 2012, 516(2): 212-216.

Cytisine-based nicotinic partial agonists as novel antidepressant compounds.[Pubmed:19164465]

J Pharmacol Exp Ther. 2009 Apr;329(1):377-86.

Nicotine and other nicotinic agents are thought to regulate mood in human subjects and have antidepressant-like properties in animal models. Recent studies have demonstrated that blockade of nicotinic acetylcholine receptors (nAChRs) including those containing the beta2 subunit (beta2(*)), results in antidepressant-like effects. Previous studies have shown that cytisine, a partial agonist at alpha4/beta2(*) nAChRs, and a full agonist at alpha3/beta4(*) and alpha7 nAChRs, has antidepressant-like properties in several rodent models of antidepressant efficacy; however, it is not clear whether more selective partial agonists will also be effective in these models. We tested cytisine and two derivatives, 5-bromo-cytisine (5-Br-Cyt) and 3-(pyridin-3'-yl)-cytisine (3-pyr-Cyt) for their ability to act as a partial agonist of different nAChR subtypes and to show antidepressant-like activity in C57/BL6 mice in the tail suspension, the forced-swim, and the novelty-suppressed feeding tests. 3-pyr-Cyt was a partial agonist with very low efficacy at alpha4/beta2(*) nAChRS but had no agonist effects at other nAChRs normally targeted by cytisine, and it was effective in mouse models of antidepressant efficacy. Animals showed dose-dependent antidepressant-like effects in all three behavioral paradigms. 5-Br-Cyt was not effective in behavioral tests when administered peripherally, probably because of its inability to penetrate the blood-brain barrier, because it efficiently reduced immobility in the tail suspension test when administered intraventricularly. These results suggest that novel nicotinic partial agonists may provide new possibilities for development of drugs to treat mood disorders.

Activation and inhibition of mouse muscle and neuronal nicotinic acetylcholine receptors expressed in Xenopus oocytes.[Pubmed:20100906]

J Pharmacol Exp Ther. 2010 May;333(2):501-18.

Transgenic mouse models with nicotinic acetylcholine receptor (nAChR) knockouts and knockins have provided important insights into the molecular substrates of addiction and disease. However, most studies of heterologously expressed neuronal nAChR have used clones obtained from other species, usually human or rat. In this work, we use mouse clones expressed in Xenopus oocytes to provide a relatively comprehensive characterization of the three primary classes of nAChR: muscle-type receptors, heteromeric neuronal receptors, and homomeric alpha7-type receptors. We evaluated the activation of these receptor subtypes with acetylcholine and cytisine-related compounds, including varenicline. We also characterized the activity of classic nAChR antagonists, confirming the utility of mecamylamine and dihydro-beta-erythroidine as selective antagonists in mouse models of alpha3beta4 and alpha4beta2 receptors, respectively. We also conducted an in-depth analysis of decamethonium and hexamethonium on muscle and neuronal receptor subtypes. Our data indicate that, as with receptors cloned from other species, pairwise expression of neuronal alpha and beta subunits in oocytes generates heterogeneous populations of receptors, most likely caused by variations in subunit stoichiometry. Coexpression of the mouse alpha5 subunit had varying effects, depending on the other subunits expressed. The properties of cytisine-related compounds are similar for mouse, rat, and human nAChR, except that varenicline produced greater residual inhibition of mouse alpha4beta2 receptors than with human receptors. We confirm that decamethonium is a partial agonist, selective for muscle-type receptors, but also note that it is a nondepolarizing antagonist for neuronal-type receptors. Hexamethonium was a relatively nonselective antagonist with mixed competitive and noncompetitive activity.