Cholinergic modulation of persistent inward currents is mediated by activating muscarinic receptors of serotonergic neurons in the brainstem of ePet-EYFP mice.

Abstract

Persistent inward currents (PICs) play important roles in regulating neural excitability. Results from our previous studies showed that serotonergic (5-HT) neurons of the brainstem expressed PICs. However, little is known about cholinergic (ACh) modulation of PICs in the 5-HT neurons. The whole-cell patch-clamp recordings were performed in the brainstem slices of ePet-EYFP mice to investigate the electrophysiological properties of PICs with cholinergic modulation. PICs in 5-HT neurons were activated at -51.4 ± 3.7mV with the amplitude of -171.6 ± 48.9 pA (n = 71). Bath application of 20-25μM ACh increased the amplitude by 79.1 ± 42.5 pA (n = 23, p < 0.001) and hyperpolarized the onset voltage by 2.2 ± 2.7mV (n = 23, p < 0.01) and half-maximal activation by 3.6 ± 2.7mV (n = 6, p < 0.01). Muscarine mimicked the effects of ACh on PICs, while bath application of nicotine (15-20μM) did not induce substantial change in the PICs (n = 9). Muscarine enhanced the amplitude of PICs by 100.0 ± 27.4 pA (n = 28, p < 0.001) and lowered the onset voltage by 2.8 ± 1.2mV (n = 28, p < 0.001) and the half-maximal activation by 2.9 ± 1.4mV. ACh-induced increase of amplitude and hyperpolarization of onset voltage were blocked by 3-5μM atropine. Furthermore, the muscarine-induced enhancement of the PICs was antagonized by 5μM 4-DAMP, the antagonist of M3 receptor, while the antagonists of M1 (Telenzepine, 5μM) and M5 (VU6008667, 5μM) receptors did not significantly affect the PIC enhancement. This study suggested that ACh potentiated PICs in 5-HT neurons of the brainstem by activating muscarinic M3 receptor.