Developmental changes in membrane excitability and morphology of neurons in the nucleus angularis of the chicken.
In order to understand how sound intensity information is extracted and processed in the auditory nuclei, we investigated the neuronal excitability in the nucleus angularis (NA) of the chicken (P0-5) and the chicken embryo (E16-21). In embryos, neurons fired basically in three patterns in response to current injections: the onset pattern (19 %), the tonic pattern (52 %) and the pause pattern (29 %). After hatching, neurons fired either in the tonic pattern (83 %) or in the onset pattern (17 %). In both pre- and post-hatch periods, multiple firing neurons (tonic and pause) increased the maximum rate of rise of the action potential 2.6-fold, the fall 3.9-fold, and the maximum firing frequency 4-fold, and shifted the threshold potential to be more negative. After hatching, the firing frequency of tonic neurons reached a maximum at about 650 Hz. Application of TEA (1 mM) reduced the firing frequency, broadened action potentials and reduced the maximum rate of fall, but the threshold current was not changed. Dendrotoxin-I (DTX, 100 nM) reduced the threshold current. Application of DTX induced the onset neuron to fire repetitively. Branching patterns of auditory nerve fibres (ANFs) in NA were visualized by labelling with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Di-I) placed within the cochlea. Di-I placed near the apex of the cochlea labelled the ventral part of the NA, and Di-I placed in the base labelled the dorso-lateral part. Tonic neurons labelled with biocytin extended dendrites in parallel with the projection of ANFs in the nucleus after hatching. ANF activity of a limited range of characteristic sound frequencies is thought to be extracted by tonic neurons and encoded into firing frequencies proportional to the strength of the input.
Fukui
Iwao
I
Department of Physiology, Faculty of Medicine, Kyoto University, Kyoto 606-8501, Japan.
Ohmori
Harunori
H
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002642:Chick Embryo; D002645:Chickens / Q000502:physiology*; D003056:Cochlear Nerve / Q000187:drug effects; D017626:Cochlear Nucleus / Q000166:cytology / Q000254:growth & development* / Q000502:physiology*; D004546:Elapid Venoms / Q000494:pharmacology; D004594:Electrophysiology; D066298:In Vitro Techniques; D008239:Lysine / Q000031:analogs & derivatives*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009412:Nerve Fibers / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D019789:Tetraethylammonium / Q000494:pharmacology
D004546:Elapid Venoms; D026902:Potassium Channel Blockers; D019789:Tetraethylammonium; C020273:dendrotoxin; C013411:biocytin; D008239:Lysine