Table 3. Effect on the expression of α6- and β3-containing nAChRs by chronic nicotine exposure.

Change	Species/cells	Treatment/dose	Brain region	Subtype	Reference
Upregulation	Rat	Injection; 6.0 mg kg−1 per day; 2 weeks	NAcc; SC	α6β2*	97
		Injection; 1.5 mg kg−1 per day; 18 day	NAcc; VTA/SN; CPu; Thal	α6*	103
	Mouse	Injection; 0.4 mg kg−1 per h; 10 day	VTA/SNc	α6*	102
		Injection; 2 mg kg−1 per h; 10 day	VTA/SNc; mHb; SC	α6*	102
		Oral; 300 μg ml−1; 2 weeks	Str	α6(nonα4)β2*	107
	HEK tsA201 cell	Incubation; 100 μm; overnight	—	α6β2* α6β2β3*α6β4; α6β4β3*	100
		Incubation; 30 μm; 24 h	—	α6β2*	101
	Neuro-2a cell	Incubation; 50 μm; 24 h	—	α6β2β3*	102
No change	Monkey	Oral; 650 μg ml−1; 6–8 months	NAcc	α6β2*	109
		Oral; 650 μg ml−1; 8 months	VPu; DPu	α6β2*	110
		Oral; 650 μg ml−1; 3–6 months	NAcc	α6β2*	111
	Rat	Injection; 6.0 mg kg−1 per day; 2 weeks	Str; SC	β3*	105
			SC	α6*
	Neuro-2a cell	Incubation; 50 μm; 24 h	—	α6β2*	102
Downregulation	Rat	Oral; 650 μg ml−1; 6 months	CPu; AcbC; AcbSh; SNPC; VTA	α6β2*	113
		Injection; 6.0 mg kg−1 per day; 2 weeks	Str	α6*	105
		Injection; 6.0 mg kg−1 per day; 2 weeks	Str; DLG; VLG	α6*	106
		Oral; 100 μg ml−1; 2 weeks	Str	α6β2*	107
		Oral; 25 μg ml−1; 2–3 months	NAcc	α6β2*	114
	Mouse	Oral; 300 μg ml−1; 1–6 weeks	Str	α6*	104
		Oral; 300 μg ml−1; 2 weeks	Str	α6β2*	107
		Injection; 0.125–4.0 mg kg−1 per h; 10 day	DLG; NAcc; Str; OT; VLG	α6β2*	108
	Monkey	Oral; 650 μg ml−1; 6 months	Str	α6*	112

Abbreviation: AcbC, core of nucleus accumbens; AcbSh, shell of nucleus accumbens; CPu, caudate putamen; DLG, dorsolateral geniculate; DPu, dorsal putamen; HEK, human embryonic kidney; NAcc, nucleus accumbens; Neuro, neuroblastoma; OT, olfactory tubercle; SC, superior colliculus; SN, substantia nigra; SNPC, pars compacta of substantia; Thal, thalamus; VLG, ventrolateral geniculate; VTA, ventral tegmental area mHb.