Seipel_2010_J.Neurochem_114_1659

Voltammetric analyses show that low (100-500 nM) doses of nicotine regulate striatal dopamine by inhibiting release evoked by a single stimulation to a greater extent than release evoked by high frequency stimulations. This frequency-dependent inhibition is because of nicotine desensitizing heteromeric beta2 subunit-containing nicotinic acetylcholine receptor (nAChR) subtypes. Surprisingly, a high dose of nicotine (2 muM; capable of interacting with additional nAChR subtypes) produced an inhibition of dopamine evoked by high frequency stimulation, an effect that was not seen with the low dose of nicotine or the beta2 antagonist, dihydro-beta-erythroidine hydrobromide. This inhibition was replicated by application of alpha7 nAChR antagonists methyllcaconitine citrate or alpha-bungarotoxin in conjunction with the low dose of nicotine or dihydro-beta-erythroidine hydrobromide. Blocking alpha7 receptor function alone produced a modest increase in dopamine evoked by single pulse stimulation while not affecting dopamine evoked by high frequency stimulation. The antagonist results were mimicked using selective alpha7 agonists PHA 543613 and PNU 282987. The frequency dependence of the low dose nicotine inhibition therefore requires functional alpha7 nAChRs, and may arise from differing levels of endogenous acetylcholine evoked by the stimulation.