Neural mechanisms of target ranging in FM bats: physiological evidence from bats and frogs.
Echolocating bats assess target range by the delay in echo relative to the emitted sonar pulse. Earlier studies in FM bats showed that a population of neurons in auditory centers above the inferior colliculus (IC) is tuned to echo delay, with different neurons tuned to different echo delays. A building block for delay-tuned responses is paradoxical latency shift (PLS), featuring longer response latencies to more intense sounds. PLS is first created in the IC, where neurons exhibit unit-specific quantum increase in response latency with increasing sound level. Other IC neurons display oscillatory discharges whose period is unit-specific and level tolerant, indicating that this is attributable to cell's intrinsic properties. High-threshold inhibition of oscillatory discharge produces PLS, indicating that oscillatory discharge is a building block for PLS. To investigate the cellular basis of oscillatory discharges, we performed whole-cell patch-clamp recordings from IC neurons in leopard frogs (which also exhibit oscillatory discharges and PLS). These recordings show that IC neurons are heterogeneous displaying diverse biophysical phenotypes; each phenotype (and cell) has its own membrane time constant, input resistance, and strengths of I(h), I(kir), I(kv)--these intrinsic properties give rise to cell-specific resonance which can be observed through current and afferent stimulations.
Feng
Albert S
AS
Department of Molecular and Integrative Physiology, Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. afeng1@illinois.edu
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001307:Auditory Perception / Q000502:physiology*; D001683:Biological Clocks / Q000502:physiology; D002685:Chiroptera / Q000502:physiology*; D004455:Echolocation / Q000502:physiology*; D007245:Inferior Colliculi / Q000502:physiology*; D011898:Ranidae / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D011984:Sensory Receptor Cells / Q000502:physiology
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