title: NAD+ Attenuates Bilirubin-Induced Hyperexcitation in the Ventral Cochlear Nucleus by Inhibiting Excitatory Neurotransmission and Neuronal Excitability.
abstract: Nicotinamide adenine dinucleotide (NAD+) is an important molecule with extensive biological functions in various cellular processes, including protection against cell injuries. However, little is known regarding the roles of NAD+ in neuronal excitation and excitotoxicity associated with many neurodegenerative disorders and diseases. Using patch-clamp recordings, we studied its potential effects on principal neurons in the ventral cochlear nucleus (VCN), which is particularly vulnerable to bilirubin excitotoxicity. We found that NAD+ effectively decreased the size of evoked excitatory postsynaptic currents (eEPSCs), increased paired-pulse ratio (PPR) and reversed the effect of bilirubin on eEPSCs, implicating its inhibitory effects on the presynaptic release probability (Pr). Moreover, NAD+ not only decreased the basal frequency of miniature EPSCs (mEPSCs), but also reversed bilirubin-induced increases in the frequency of mEPSCs without affecting their amplitude under either condition. Furthermore, we found that NAD+ decreased the frequency of spontaneous firing of VCN neurons as well as bilirubin-induced increases in firing frequency. Whole-cell current-clamp recordings showed that NAD+ could directly decrease the intrinsic excitability of VCN neurons in the presence of synaptic blockers, suggesting NAD+ exerts its actions in both presynaptic and postsynaptic loci. Consistent with these observations, we found that the latency of the first postsynaptic spike triggered by high-frequency train stimulation of presynaptic afferents (i.e., the auditory nerve) was prolonged by NAD+. These results collectively indicate that NAD+ suppresses presynaptic transmitter release and postsynaptic excitability, jointly weakening excitatory neurotransmission. Our findings provide a basis for the exploration of NAD+ for the prevention and treatment of bilirubin encephalopathy and excitotoxicity associated with other neurological disorders.
authors.affiliation: Department of Otorhinolaryngology, The Sixth People's Hospital, Shanghai Jiao Tong University Shanghai, China.
authors.forename: Min
authors.initials: M
authors.lastname: Liang
authors.affiliation: Department of Otorhinolaryngology, The Sixth People's Hospital, Shanghai Jiao Tong University Shanghai, China.
authors.forename: Xin-Lu
authors.initials: XL
authors.lastname: Yin
authors.affiliation: Programs in Neurosciences and Mental Health, SickKids Research Institute and Department of Physiology, University of Toronto Toronto, ON, Canada.
authors.forename: Lu-Yang
authors.initials: LY
authors.lastname: Wang
authors.affiliation: Med-X Research Institute and School of Biomedical Engineering, Shanghai Jiao Tong University Shanghai Shanghai, China.
authors.forename: Wei-Hai
authors.initials: WH
authors.lastname: Yin
authors.affiliation: Department of Otorhinolaryngology, West China Hospital, Sichuan University Chengdu, China.
authors.forename: Ning-Ying
authors.initials: NY
authors.lastname: Song
authors.affiliation: Department of Otorhinolaryngology, The Sixth People's Hospital, Shanghai Jiao Tong University Shanghai, China.
authors.forename: Hai-Bo
authors.initials: HB
authors.lastname: Shi
authors.affiliation: Department of Otorhinolaryngology, The Sixth People's Hospital, Shanghai Jiao Tong University Shanghai, China.
authors.forename: Chun-Yan
authors.initials: CY
authors.lastname: Li
authors.affiliation: Department of Otorhinolaryngology, The Sixth People's Hospital, Shanghai Jiao Tong University Shanghai, China.
authors.forename: Shan-Kai
authors.initials: SK
authors.lastname: Yin
keywords: bilirubin encephalopathy; evoked EPSCs (eEPSCs); hyperexcitation; miniature excitatory postsynaptic currents (mEPSCs); nicotinamide adenine dinucleotide (NAD+); patch-clamp recording; spontaneous spike; ventral cochlear nucleus