title: Bilirubin facilitates depolarizing GABA/glycinergic synaptic transmission in the ventral cochlear nucleus of rats.
abstract: Excitotoxicity contributes to bilirubin-induced central nervous system injury; however, the mechanisms involved remain controversial. Previous studies from our lab have demonstrated that in juvenile rats bilirubin facilitates γ-aminobutyric acid (GABA)/glycinergic synaptic transmission through activation of presynaptic protein kinase A (PKA) in isolated neurons of the ventral cochlear nucleus (VCN). However, the descending mechanism and physiological effects of bilirubin-induced potentiation remain unclear. Here, whole-cell recordings show that 3×10(-6) M bilirubin increased the frequency of both spontaneous (sPSCs) and miniature (mPSCs) GABA/glycinergic postsynaptic currents in VCN neurons of postnatal day 12-14 (P12-14) rats. This action was dependent on the concentration and duration of exposure to bilirubin and was only partially suppressed by 10(-5) M bicuculline. The potentiation effect on mPSCs persisted in a Ca2+-free solution, but was fully occluded by pretreatment with 1,2 bis-(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM), an intracellular Ca2+ chelator. Following pretreatment of the neurons with BAPTA-AM, forskolin, a PKA activator, had no effect on the frequency or amplitude of mPSCs. This suggests that Ca2+ release from presynaptic stores is part of the descending pathway of PKA activation and is responsible for biliurbin-induced potentiation of cell activity. Using gramicidin-perforated patch recordings, the reversal potential of GABA-evoked currents (EGABA) was also investigated. The GABA response resulted in depolarization of 12 of 20 recorded VCN neurons from P12-14 rats. Therefore, potentiation of depolarizing GABA/glycinergic transmission by bilirubin may underlie bilirubin excitotoxicity, which may play a role in the hearing impairment observed among hyperbilirubinemic neonates.
authors: Department of Otorhinolaryngology, Affiliated Sixth People's Hospital of Shanghai Jiaotong University, 600 Yishan Road, Shanghai 200233, China.
authors: Chun-Yan
authors: CY
authors: Li
authors: Hai-Bo
authors: HB
authors: Shi
authors: Jian
authors: J
authors: Wang
authors: Hai-Bo
authors: HB
authors: Ye
authors: Ning-ying
authors: NY
authors: Song
authors: Shan-Kai
authors: SK
authors: Yin
mesh_terms: D000818:Animals; D001663:Bilirubin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D017626:Cochlear Nucleus / Q000166:cytology* / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D005998:Glycine / Q000378:metabolism*; D006309:Hearing / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D055369:Miniature Postsynaptic Potentials / Q000187:drug effects; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000187:drug effects*; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D005680:gamma-Aminobutyric Acid; D017868:Cyclic AMP-Dependent Protein Kinases; D001663:Bilirubin; D002118:Calcium; D005998:Glycine