Table 2.

The function and anatomic location of nicotinic acetylcholine receptors (nAChR) associated with the habenula.

Receptors/subunit	Anatomic location	Function	Reference
Nicotinic acetylcholine receptors (nAChR)	Ligand-gated ion channels formed by a pentameric arrangement of alpha and beta subunits to create distinct muscle and neuronal receptors.	Neuronal communication; converts neurotransmitter binding in to membrane electrical depolarization; binds the addictive drug nicotine.	Hogg et al. (2003)
α2	IPN, hippocampus.	Involved in withdrawal symptoms after chronic nicotine treatment.	Salas et al. (2009), Lotfipour et al. (2013)
α3	Pineal gland, mitral cells in the olfactory bulb, thalamus, MHb.	Necessary for nicotine-induced hypolocomotion (or sedation) and nicotine-induced seizures. Necessary for normal development of the peripheral nervous system.	Xu et al. (1999a)
α4	Hippocampus, cortex, MHb, IPN.	Necessary for tolerance, reward and sensitization.	Tapper et al. (2004), Salas et al. (2004a)
α5	Moderately expressed in the MHb. Also expressed in the IPN, VTA, cerebral cortex and in area CA1 of the hippocampus.	Involved in withdrawal symptoms after chronic nicotine treatment.	Fowler et al. (2011), Frahm et al. (2011), Salas et al. (2009), Morel et al. (2013), Bailey et al. (2010)
α6	VTA. Usually expressed with the β3 subunit.	Important for addiction, reward and dopaminergic transmission.	Wang et al. (2013), Brunzell (2012)
α7	Hippocampus, cortex	Forms homopentamers. May be involved in schizophrenia-related behaviors.	Freedman (2014), Young and Geyer (2013)
β2	Ubiquitously expressed, usually with the α4 subunit.	Essential for nicotine self-administration in mice.	Picciotto et al. (1998)
β3	MHb, VTA. Usually expressed with the α6 subunit.	Important for dopamine release, addiction, and reward.	Cui et al. (2003)
β4	MHb, pineal gland and mitral cells in the olfactory bulb.	Implicated in nicotine withdrawal.	Salas et al. (2004b)