Identification of the Nicotinic Receptor Subtypes Expressed on Dopaminergic Terminals in the Rat Striatum

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Fig. 1.
Immunoprecipitation analysis of the subunit content of α6β2* and α4(nonα6)β2* nAChR subtypes immunopurified through affinity column from striatal extracts and labeled with 2 nm³H-Epi. The results are expressed as percentage of total ³H-Epi binding present in the solution before immunoprecipitation. Each data point is the mean ± SEM of five determinations performed in triplicate.
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Fig. 2.
Inhibition of ¹²⁵I-Epi binding to native immunoimmobilized α6β2* (a) and α4(nonα6)β2* (b) nAChRs by several nicotinic ligands, including nicotine (Nic), acetylcholine (ACh), cytisine (Cyt), dihydro-β-erythroidine (DHBE),d-tubocurarine (dTC) (a, b), α-CntxMII (c), and MLA (d). The curves were obtained by fitting three or four separate experiments using the LIGAND program (Munson and Rodbard, 1980).
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Fig. 3.
a, b,³H-WIN-35,428 (a) and³H-Epi binding (b) in rat striatal membranes obtained from control and 6-OHDA lesioned rats.c, Immunoprecipitation of nAChR subunits in 2% Triton X-100 extracts from control and 6-OHDA lesioned striata. Each value represents the mean ± SEM of three separate experiments. Statistical analysis according to Mann–Whitney U test, **p < 0.01.

Table 1.

Affinity of nicotinic agonists and antagonists for immunoimmobilized nAChR subtypes

K_d and K_i values were derived from curves of ¹²⁵I-Epi saturation and competition binding, respectively, to α6β2* or α4(nonα6)β2
↵* immunoimmobilized receptors. Curves obtained from three or four separate experiments were fitted using a nonlinear least-squares analysis program. For both α-conotoxin MII and methyllycaconitine, a two-site model was statistically significant (F test), whereas for d-tubocurarine and cytisine the data were better fitted with a one-site model. Numbers in parentheses represent percentage of coefficient of variation.