Firing properties of spherical bushy cells in the anteroventral cochlear nucleus of the gerbil.
In gerbils, spherical bushy cells (SBCs) encode low frequency sound signals into a temporal firing pattern. To investigate the support for the timing in this temporal code, we characterized the membrane electrical properties of visually identified SBCs in brainstem slices. A brief depolarizing subthreshold transient potential (TP) triggered, with relatively invariant latency, a single spike at the onset of a response to depolarizing current pulses. The activation of a subthreshold Na+-conductance, sensitive to blockade with tetrodotoxin, and a high threshold Ca2+-conductance, sensitive to blockade with Co2+ or Cd2+, accelerated the rising phase and amplified the TP. A K+-conductance, sensitive to blockade by 4-aminopyridine (4-AP, 50 microM), shaped the decay of the TP. Following a single spike, voltage-gated activation of transient and sustained K+-conductances suppressed any tendency to repetitively discharge. A reduction in either K+-conductance due to application of 4-AP or tetraethylammonium (TEA, 10 mM), converted the single spike mode to repetitive firing during the depolarizing pulses. A persistent, tetrodotoxin-sensitive Na+-conductance amplified steady-state depolarizing responses. A hyperpolarization-activated conductance, greatly decreased by extracellular Cs+ (3 mM) but resistant to Ba2+ (up to 1 mM), filtered the responses to hyperpolarizing current inputs. A depolarized membrane potential promoted repetitive firing in SBCs. This state, expected in pathophysiological conditions, would corrupt the temporal code.
Schwarz
D W
DW
The Rotary Hearing Center, Department of Surgery (Otolaryngology), University of British Columbia, Vancouver, Canada. dsch@unixg.ubc.ca
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D015761:4-Aminopyridine; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001309:Auditory Threshold / Q000187:drug effects / Q000502:physiology; D001464:Barium / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D048429:Cell Size; D017626:Cochlear Nucleus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D005849:Gerbillinae; D007473:Ion Channels / Q000187:drug effects*; D008857:Microscopy, Interference; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D019789:Tetraethylammonium; D013779:Tetrodotoxin
D007473:Ion Channels; D001464:Barium; D013779:Tetrodotoxin; D019789:Tetraethylammonium; D012964:Sodium; D015761:4-Aminopyridine; D011188:Potassium; D002118:Calcium