Differential conduction velocity regulation in ipsilateral and contralateral collaterals innervating brainstem coincidence detector neurons.
Information processing in the brain relies on precise timing of signal propagation. The highly conserved neuronal network for computing spatial representations of acoustic signals resolves microsecond timing of sounds processed by the two ears. As such, it provides an excellent model for understanding how precise temporal regulation of neuronal signals is achieved and maintained. The well described avian and mammalian brainstem circuit for computation of interaural time differences is composed of monaural cells in the cochlear nucleus (CN; nucleus magnocellularis in birds) projecting to binaurally innervated coincidence detection neurons in the medial superior olivary nucleus (MSO) in mammals or nucleus laminaris (NL) in birds. Individual axons from CN neurons issue a single axon that bifurcates into an ipsilateral branch and a contralateral branch that innervate segregated dendritic regions of the MSO/NL coincidence detector neurons. We measured conduction velocities of the ipsilateral and contralateral branches of these bifurcating axon collaterals in the chicken by antidromic stimulation of two sites along each branch and whole-cell recordings in the parent neurons. At the end of each experiment, the individual CN neuron and its axon collaterals were filled with dye. We show that the two collaterals of a single axon adjust the conduction velocities individually to achieve the specific conduction velocities essential for precise temporal integration of information from the two ears, as required for sound localization. More generally, these results suggest that individual axonal segments in the CNS interact locally with surrounding neural structures to determine conduction velocity.
Virginia Merrill Bloedel Hearing Research Center, and Departments of Otolaryngology-Head and Neck Surgery, and Physiology and Biophysics, University of Washington, Seattle, Washington 98195.
Armin H
AH
Seidl
Edwin W
EW
Rubel
Andrés
A
Barría
D000818:Animals; D001369:Axons / Q000502:physiology; D001933:Brain Stem / Q000166:cytology*; D002642:Chick Embryo; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D018756:GABA Antagonists / Q000494:pharmacology; D021621:Imaging, Three-Dimensional; D066298:In Vitro Techniques; D008297:Male; D008959:Models, Neurological; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010852:Picrotoxin / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology
D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D010852:Picrotoxin; D011810:Quinoxalines; D014633:Valine; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; C056639:2-amino-5-phosphopentanoic acid
conduction velocity regulation; myelin plasticity; sound localization