Prenatal nicotine exposure alters the nicotinic receptor subtypes that modulate excitation of parasympathetic cardiac neurons in the nucleus ambiguus from primarily α3β2 and/or α6βX to α3β4

Abstract

Nicotinic receptors play an essential role in central cardiorespiratory function, however, the types of nicotinic receptors responsible for activating cardiac vagal neurons in the nucleus ambiguus that control heart rate are unknown. This study tests whether α-conotoxin MII and α-conotoxin AuIB sensitive nicotinic receptors are involved in augmentation of glutamatergic neurotransmission and changes in holding current in cardiac vagal neurons, and whether exposure to nicotine in the prenatal period alters these responses. The nicotinic agonist cytisine significantly increased the holding current and amplitude of glutamatergic mEPSCs. In unexposed animals α-conotoxin MII (100 nM) significantly reduced the increase in mEPSC amplitude and change in holding current evoked by cytisine. However, in animals prenatally exposed to nicotine, α-conotoxin MII blunted but did not block the increase in mEPSC amplitude but blocked the increase in holding current evoked by cytisine. In unexposed animals, α-conotoxin AuIB (10 μM) blocked the cytisine evoked increase in mEPSC amplitude and inhibited but did not abolish the increase in holding current. In contrast, in animals exposed to nicotine, α-conotoxin AuIB blunted the increase in mEPSC amplitude, and completely abolished the cytisine evoked increase in holding current. These data demonstrate that the prenatal nicotine exposure alters the nicotinic receptors involved in excitation of cardiac vagal neurons.