Regulation of glutamatergic and GABAergic neurotransmission in the chick nucleus laminaris: role of N-type calcium channels.
Neurons in the chicken nucleus laminaris (NL), the third order auditory nucleus involved in azimuth sound localization, receive bilaterally segregated (ipsilateral vs contralateral) glutamatergic excitation from the cochlear nucleus magnocellularis and GABAergic inhibition from the ipsilateral superior olivary nucleus (SON). Here, I investigate the voltage-gated calcium channels (VGCCs) that trigger the excitatory and the inhibitory transmission in the NL. Whole-cell recordings were performed in acute brainstem slices. The excitatory transmission was predominantly mediated by N-type VGCCs, as the specific N-type blocker omega-Conotoxin-GVIA (omega-CTx-GVIA, 1-2.5 microM) inhibited excitatory postsynaptic currents (EPSCs) by approximately 90%. Blockers for P/Q- and L-type VGCCs produced no inhibition, and blockade of R-type VGCCs produced a small inhibition. In individual cells, the effect of each VGCC blocker on the EPSC elicited by activation of the ipsilateral input was the same as that on the EPSC elicited by activation of the contralateral input, and the two EPSCs had similar kinetics, suggesting physiological symmetry between the two glutamatergic inputs to single NL neurons. The inhibitory transmission in NL neurons was almost exclusively mediated by N-type VGCCs, as omega-CTx-GVIA (1 microM) produced a approximately 90% reduction of inhibitory postsynaptic currents, whereas blockers for other VGCCs produced no inhibition. In conclusion, N-type VGCCs play a dominant role in triggering both the excitatory and the inhibitory transmission in the NL, and the presynaptic VGCCs that mediate the two bilaterally segregated glutamatergic inputs to individual NL neurons are identical. These features may play a role in optimizing coincidence detection in NL neurons.
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Department of Anatomy and Neurobiology, Northeastern Ohio Universities Colleges of Medicine and Pharmacy, 4209 State Route 44, Rootstown, OH 44272, USA. ylu@neoucom.edu
D000818:Animals; D001306:Auditory Pathways / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000378:metabolism*; D002642:Chick Embryo; D002645:Chickens; D017626:Cochlear Nucleus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D007839:Functional Laterality / Q000187:drug effects / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism*; D009433:Neural Inhibition / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D012249:Rhombencephalon / Q000166:cytology / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D020866:omega-Conotoxin GVIA