Activation of neuronal nicotinic receptors leads to downregulation of the EPP quantal content
Under control conditions, the quantal content (QC) was 46.8 ± 4.5. The bath application of nicotine (10 µM) decreased the QC of EPP significantly by 12.0 ± 4.4% (n = 5, 7 NMJs; Figure 2).
The nicotine-induced decrease in the number of ACh quanta released in response to stimulation of the motor nerve suggests the involvement of presynaptic cholinergic receptors. Using the antagonist of neuronal nicotinic ACh receptors (nNAChRs) DHβE (Moroni et al., 2006; Wonnacott, 2014), we obtained the data supporting this suggestion. Application of DHβE alone at a concentration of 1 μM did not change the QC of EPP (101.5 ± 1.3%; n = 6, 9 NMJs, Figure 2), however, after the pretreatment with DHβE, the inhibitory effect of nicotine on the quantal release of ACh was completely abolished (105.5 ± 6.6%; n = 6, 9 NMJs; Figure 2).