Meeting Abstract

79.4  Sunday, Jan. 6  Insight into the neural encoding of water flow; morphological and functional heterogeneity in the lateral line neurons of larval zebrafish LIAO, James C.*; FETCHO, Joseph R.; Cornell University jl10@cornell.edu

Fishes detect water flow using clusters of directionally sensitive hair cells, which are distributed along the body surface as discrete neuromasts. Appropriately stimulated neuromasts provide excitatory input to bipolar posterior lateral line ganglion neurons (PLLGNs). We use optical and electrophysiological techniques to examine the intrinsic firing properties of PLLGNs, their connectivity and sensitivity to controlled hydrodynamic stimuli. In 5 day post-fertilization larvae there are at least 36 cells in a single PLL ganglion (44.8 ± 7.8), with an average cell circumference of 37.9 ± 1.0 µm. Confocal imaging of single PLLGNs was accomplished by either transient expression of a HUC-GFP construct or by electroporation with rhodamine dye. These results reveal that some PLLGNs send short axons to contact a single rostral neuromast while others project long axons to multiple caudal neuromasts. Extracellular recordings show that the PLLN fires to flow velocities above 2 mm/s, despite hair deflections occurring at lower flows. In vivo patch clamp recordings identified tonically firing cells (59.8 ± 3.8 Hz) in the absence of hydrodynamic stimuli. Firing frequency increased with depolarizing current injections (20-80 pA). When a jet of water is introduced along the body, high frequency spike bursts (222.9 ± 21.2 Hz) are superimposed onto the tonic background of single spikes. Phasically firing neurons are silent at rest, exhibit spikes only at the beginning of a depolarizing step, and do not fire consistently to hydrodynamic stimuli. These data shed insight into the morphological and functional heterogeneity underlying the mechanism for neural processing of hydrodynamic stimuli. All values are mean ± S.E., n= 4 fish.