Table 1. Curve-fit parameters for chronic nicotine-induced changes (up- or down-regulation) of nAChR expression.

Parameters are derived from curve fits performed in Figures 2 (for α6β2* nAChR; left column) and 3 (for α4β2* nAChR; right column).

Region	[125I]α-CtxMII binding sites (α6β2* nAChR)		Cytisine-sensitive [125I]-epibatidine binding sites (α4β2* nAChR)
	ED50 (nM) / mg/kg/h	Max % change	ED50 (nM) / mg/kg/h	Max % change
OT	0.128 ± 0.057	−28.8 ± 13.4*	0.258 ± 0.130	71.1 ± 23.5
nAcc	0.136 ± 0.110	−23.9 ± 9.6*	.446 ± 0.212	89.5 ± 33.3
Str	0.241 ± 0.129	−22.0 6.7*	0.255 ± 0.170	47.2 ± 19.9
opt	ns	ns	ns	ns
OPTN	ns	ns	ns	ns
DLG	0.066 ± 0.045	−22.4 ± 6.7*	ns	ns
VLG	0.061 ± 0.047	−23.2 ± 6.2*	ns	ns
SCsg	ns	ns	ns	ns
fCX	nd	nd	0.339 ± 0.189	73.6 ± 25.7
inCX	nd	nd	0.208 ± 0.193	93.2 ± 29.9
orbCX	nd	nd	0.218 ± 0.116	71.8 ± 22.9
outCX	nd	nd	0.287 ± 0.160	61.4 ± 23.1
SCdl	nd	nd	ns	ns
Th	nd	nd	ns	ns
Overall for regions with changes	0.108 ± 0.040	−24.1 ± 1.2	0.293 ± 0.027	+72.5 ± 5.9

nd = not determined for reasons of undetectable binding; ns = un-measurable change by treatment. Two-way ANOVA was performed to determine the effects of Region and Dose on α6β2* nAChR downregulation following chronic nicotine treatment levels. Both factors significantly affected expression (F[7,56] = 591, p < 0.001 and F[6,56] = 6.33, p < 0.001, respectively), confirming that expression of α6β2* nAChR varies across brain regions, and is significantly affected by chronic nicotine treatment. No Region × Dose interaction was seen, however (F[7,42] = 0.86, p < 0.727), demonstrating that the dose dependence of α6β2* nAChR downregulation is generally similar for each region. Results were further analyzed to calculate the nicotine treatment dose dependence on binding site densities for each brain region as described in the Methods. Significant and similar extents of downregulation were observed for five of the eight brain regions. The means ± SEM for the maximum percentage decreases shown are significantly less than zero as determined by t-test for that parameter calculated from the non-linear least-squares curve fits. Accordingly, a mean ED₅₀ downregulation nicotine dose was calculated for those five brain regions. Expression of α4β2* nAChR was generally upregulated, in contrast to the effects recorded for α6β2* nAChR. Two-way ANOVA showed that both Region (F[12,91] = 104, p < 0.001) and Dose (F[6,91] = 3.08, p = 0.006) significantly affected expression of this receptor population. Again, no Region×Dose interaction was observed (F[12,72] = 0.27, p =1). Results were further analyzed to calculate the nicotine treatment dose dependence for the increase in binding site densities as described in the Methods. Significant upregulation was detected in seven of the fourteen regions analyzed. The means ± SEM for the maximum percentage decreases shown are significantly greater than zero as determined by t-test for that parameter calculated from the non-linear least-squares curve fits. Mean ED₅₀ values for nicotine-induced upregulation were also calculated for these regions. By t-test, the ED₅₀ values for α6β2* nAChR downregulation are significantly different from the ED₅₀ values for the α4β2* nAChR upregulation (t=5.23, degrees-of-freedom = 12; p < 0.001). Regions of interest are labeled as follows: Regions of interest are labeled as follows: DLG, dorsolateral geniculate nucleus; fCX, frontal cortex; in CX, inner layers of cortex; nAcc, nucleus accumbens; opt, optic tract; OPTN, olivary pretectal nucleus; orbCx, orbital cortex; outCx, outer layers of cortex; OT, olfactory tubercle; SCdl, superior colliculus (deep layers); SCsg, superior colliculus (superficial grey); Str, striatum; Th, thalamus; VLG, ventrolateral geniculate nucleus.