Pharmacological Studies On Anti-nicotine Addiction Of α-Conotoxin TxIB,TxID And [S9K]TxID

Nicotinic acetylcholine receptors(nAChRs)are a superfamily of pentameric ligand gated ion channels,which are associated with nicotine addiction,alzheimer’s disease,pain and other diseases.The α6*nAChRs play an important role in the mediation of reward effect of nicotine.The α3β4 nAChR is predominantly distributed in some regions of the central nervous system,particularly in the medial habenula,which was involved with drug addiction.α-Conotoxin TxIB and TxID are novel peptides found in conus textile.TxIB is a specific antagonist of α6/α3β2β3 nAChR(IC50 is 28 nM).TxID is an antagonist of α3β4 nAChR with an IC50 of 12.5 nM,and it also blocks α6/α3β4 nAChR(IC50 is 94 nM),while[S9K]TxID,as the most selective analogue of TxID,can block α3β4 nAChR with an IC50 of 6.9 nM.Conditioned place preference model(CPP)was used to evaluate the effects of TxIB,TxID and[S9K]TxID on CPP expression and reinstatement.Locomotor activity was used to assess the effects of conotoxins on the locomotor activity in mice.Hot plate and tail flick were used to evaluate the effects of drugs on acute nicotine.Enzyme linked immunosorbent assay(ELISA)was used to evaluate the effects of TxIB on neurotransmitters in brain regions.The results showed that nicotine(0.5 mg/kg,s.c.)could successfully induce the CPP model.TxIB(0.01 nmol,0.1 nmol and 1 nmol,i.c.v.)could block CPP expression and reinstatement with a dose-dependent manner.TxID and[S9K]TxID(0.2 nmol,1nmol,5 nmol,20 nmol,i.c.v.)can both block the expression of CPP and inhibit the reinstatement dose-dependently.It is worth mentioning that the effective dose of[S9K]TxID is lower than TxID,and the blocking effect can be shown at 0.2 nmol.Neither TxIB nor[S9K]TxID(i.c.v.)mediated acute nicotine,while high-dose TxID showed an analgesic superposition effect with nicotine.Locomotor activity experiment showed that all kinds of doses of TxIB,TxID and[S9K]TxID had no effect on the locomotor activity in mice.ELISA experiment showed that TxIB(1 nmol)could inhibit the concentration of dopamine(DA),y-aminobutyric acid(GABA)and norepinephrine(NE)in the nucleus accumbens(NAc),hippocampus(HIP)and prefrontal cortex(PFC)which were increased by nicotine.However,TxIB could inhibit the increase of concentration of DA and NE in the ventral tegmental area(VTA),while the concentration of GABA was not obvious.In this study,the pharmacodynamics of three conotoxins were evaluated using animal models,which provided theoretical and experimental basis for the further development of anti-nicotine addiction drugs.