ZFIN ID: ZDB-PUB-150512-4
A Convergent and Essential Interneuron Pathway for Mauthner-Cell-Mediated Escapes
Lacoste, A.M., Schoppik, D., Robson, D.N., Haesemeyer, M., Portugues, R., Li, J.M., Randlett, O., Wee, C.L., Engert, F., Schier, A.F.
Date: 2015
Source: Current biology : CB   25(11): 1526-34 (Journal)
Registered Authors: Engert, Florian, Randlett, Owen, Robson, Drew, Schier, Alexander, Schoppik, David
Keywords: none
MeSH Terms:
  • Animals
  • Animals, Genetically Modified
  • Escape Reaction/physiology*
  • Interneurons/physiology*
  • Zebrafish/physiology*
PubMed: 25959971 Full text @ Curr. Biol.
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ABSTRACT
The Mauthner cell (M-cell) is a command-like neuron in teleost fish whose firing in response to aversive stimuli is correlated with short-latency escapes [1-3]. M-cells have been proposed as evolutionary ancestors of startle response neurons of the mammalian reticular formation [4], and studies of this circuit have uncovered important principles in neurobiology that generalize to more complex vertebrate models [3]. The main excitatory input was thought to originate from multisensory afferents synapsing directly onto the M-cell dendrites [3]. Here, we describe an additional, convergent pathway that is essential for the M-cell-mediated startle behavior in larval zebrafish. It is composed of excitatory interneurons called spiral fiber neurons, which project to the M-cell axon hillock. By in vivo calcium imaging, we found that spiral fiber neurons are active in response to aversive stimuli capable of eliciting escapes. Like M-cell ablations, bilateral ablations of spiral fiber neurons largely eliminate short-latency escapes. Unilateral spiral fiber neuron ablations shift the directionality of escapes and indicate that spiral fiber neurons excite the M-cell in a lateralized manner. Their optogenetic activation increases the probability of short-latency escapes, supporting the notion that spiral fiber neurons help activate M-cell-mediated startle behavior. These results reveal that spiral fiber neurons are essential for the function of the M-cell in response to sensory cues and suggest that convergent excitatory inputs that differ in their input location and timing ensure reliable activation of the M-cell, a feedforward excitatory motif that may extend to other neural circuits.
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