title: Developmental profiles of the intrinsic properties and synaptic function of auditory neurons in preterm and term baboon neonates.
abstract: The human fetus starts to hear and undergoes major developmental changes in the auditory system during the third trimester of pregnancy. Although there are significant data regarding development of the auditory system in rodents, changes in intrinsic properties and synaptic function of auditory neurons in developing primate brain at hearing onset are poorly understood. We performed whole-cell patch-clamp recordings of principal neurons in the medial nucleus of trapezoid body (MNTB) in preterm and term baboon brainstem slices to study the structural and functional maturation of auditory synapses. Each MNTB principal neuron received an excitatory input from a single calyx of Held terminal, and this one-to-one pattern of innervation was already formed in preterm baboons delivered at 67% of normal gestation. There was no difference in frequency or amplitude of spontaneous excitatory postsynaptic synaptic currents between preterm and term MNTB neurons. In contrast, the frequency of spontaneous GABA(A)/glycine receptor-mediated inhibitory postsynaptic synaptic currents, which were prevalent in preterm MNTB neurons, was significantly reduced in term MNTB neurons. Preterm MNTB neurons had a higher input resistance than term neurons and fired in bursts, whereas term MNTB neurons fired a single action potential in response to suprathreshold current injection. The maturation of intrinsic properties and dominance of excitatory inputs in the primate MNTB allow it to take on its mature role as a fast and reliable relay synapse.
authors.affiliation: Department of Physiology.
authors.forename: Sei Eun
authors.initials: SE
authors.lastname: Kim
authors.affiliation: Department of Physiology.
authors.forename: Seul Yi
authors.initials: SY
authors.lastname: Lee
authors.affiliation: Department of Pediatrics, University of Texas Health Science Center, San Antonio, Texas 78229.
authors.forename: Cynthia L
authors.initials: CL
authors.lastname: Blanco
authors.affiliation: Department of Physiology, Center for Biomedical Neuroscience, and kimjh@uthscsa.edu.
authors.forename: Jun Hee
authors.identifier: http://orcid.org/0000-0003-0207-8410
authors.initials: JH
authors.lastname: Kim
mesh_terms: D000818:Animals; D001306:Auditory Pathways / Q000502:physiology; D001640:Bicuculline / Q000494:pharmacology; D001933:Brain Stem / Q000254:growth & development* / Q000473:pathology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005260:Female; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D018684:Glycine Agents / Q000494:pharmacology; D008297:Male; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D010215:Papio; D047928:Premature Birth / Q000473:pathology*; D011810:Quinoxalines / Q000494:pharmacology; D013331:Strychnine / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D050598:Vesicular Glutamate Transport Protein 1 / Q000378:metabolism
chemical_list: D018691:Excitatory Amino Acid Antagonists; D058787:GABA-A Receptor Antagonists; D018684:Glycine Agents; D008869:Microtubule-Associated Proteins; D011810:Quinoxalines; D050598:Vesicular Glutamate Transport Protein 1; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; D013331:Strychnine; D001640:Bicuculline
keywords: MNTB; auditory brainstem; calyx synapse; development; nonhuman primate; synaptic transmission