The nicotinic α4 β2 receptor selective agonist, TC-2559, increases dopamine neuronal activity in the ventral tegmental area of rat midbrain slices

Abstract

The ability of α4 β2 nicotinic acetylcholine receptors to modulate dopaminergic (DA) cell activity in the ventral tegmental area (VTA) in rat midbrain slices was assessed using a selective α4 β2 receptor agonist, TC-2559 (( E)- N-methyl-4-[3-(5-ethoxypyridin)y1]-3-buten-1-amine). The selectivity of TC-2559 was characterized across 6 recombinant human nicotinic receptors ( α4 β2, α2 β4, α4 β4, α3 β4, α3 β2 and α7) stably expressed in mammalian cell lines. Using a fluorescent imaging plate reader and fluo-3 to monitor changes in intracellular calcium, TC-2559 was found to be at least 69 fold more potent on α4 β2 than on other heteromeric subtypes, with an efficacy of 33%. No activity on the homomeric α7 subtype was detected. TC-2559 also showed selectivity for α4 β2 over the α4 β4 and α7 subtypes expressed in Xenopus oocytes. When bath applied to VTA slices, TC-2559 increased the firing of DA cells in a dose-dependent manner, in the same concentration range that activates α4 β2 receptors in recombinant cell lines or oocytes. The effect of TC-2559 was blocked by 2 μM dihydro- β-erythroidine (an α4 β2-preferring antagonist), but not by 10 nM methyllycaconitine (an α7 antagonist). Glutamate receptor antagonists (6-cyano-7-nitroquinoxaline-2,3-dione and D(−)-2-amino-5-phosphonopentanoic acid) did not reduce TC-2559-induced responses, suggesting that the increase in DA cell firing induced by TC-2559 is caused by direct postsynaptic depolarisation via the activation of α4 β2 receptors and not by enhancement of glutamate release.