Figure 6.

The adenosine A_2AR-mediated inhibition of the nicotine-induced [³H]DA release mainly depended on α6β2-containing nicotinic ACh receptors (nAChRs). (A) Western blot analysis revealed specific bands for the different major nAChR subunits in pre-synaptic membrane preparations, with the molecular weight indicated on the right of each excerpt. (B) Quantification of the density of the different subunits obtained from three (α4, α7 and β2) and four (α6) rats under three different protein loads to ensure that the signal is not saturated (maximum = 100% = saturated signal). (C) Time course displaying the averaged [³H]DA release induced by nicotine (30 nM) in the absence or in the presence of either the α6 subunit antagonist α-CTX (30 nM), the α7 subunit antagonist α-BTX (100 nM) or the β2 subunit antagonist DHβE (100 nM). (D) Time course displaying the averaged [³H]DA release, induced by nicotine (30 nM) in the presence of α-CTX (30 nM), when combined with either the A_2AR agonist CGS (30 nM) or the A_2AR antagonist ZM (100 nM). (E) Bar graph summarizing the sensitivity of 30 nM nicotine-stimulated [³H]DA release under the difference conditions tested in (C) and (D). Data are mean ± SEM of nine experiments performed in duplicate. *P < 0.05, **P < 0.01 and ***P < 0.001 versus 0 FR% (i.e. no change in baseline); ^$$$P < 0.001 between nicotine alone (blue bar) and nicotine with antagonists of nicotinic acetylcholine receptors; n.s., not significant. Note that neither CGS nor ZM affected the non-α6 subunit-containing nAChR-induced release of [³H]DA, suggesting that it is these α6 subunit-containing nAChRs that are modulated by A_2ARs to control striatal dopamine release.