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Tm2 & L4: Major ‘OFF-Pathway’ Elements in the Drosophila Motion Circuit

Matthias Meier1*, Etienne Serbe1* and Alexander Borst1
  • 1 Max Planck Institute for Neurobiology, Circuits Computations Models, Germany

In flies, motion detection is known for long to be well described by an algorithmic model, the so-called ‘Reichardt detector’. In order to discover the neural circuit corresponding to this model, genetic silencing of specific neurons in Drosophila identified two first-order interneurons of the lamina, L1 and L2, as providing input to the motion detection circuit (Rister et al, 2007; Joesch et al, 2010; Clark et al, 2012), and the T4/T5 cells as conveying the directional output onto the tangential cells (Schnell et al, 2012). The signals from L1 and from L2 have been proposed to feed into two, functionally distinct motion detection circuits, one processing increments (L1, ‘ON’), the other decrements (L2, ‘OFF’) of local luminance (Joesch et al, 2010; Eichner et al, 2011; Joesch et al, 2013). Interestingly, a recent anatomical study revealed that Tm2, a medulla neuron postsynaptic to L2, receives additional input from an anterior column via L4 (Takemura et al, 2011). This wiring directionality could implement, as one out of several alternatives, specific motion sensitivity for the detection of front-to-back motion. To investigate this hypothesis, we genetically silenced L4 and Tm2 while recording from two classes of lobula plate tangential cells, the HS- and VS-cells, sensitive to horizontal and vertical motion, respectively. We used gratings and edges of both polarities (ON- and OFF-edges) moving along all 4 cardinal directions to probe for specific deficits with respect to motion direction or to contrast polarity. Blocking L4 and Tm2 by several different driver lines led to a similar phenotype. In all cases, we found no specific reduction of the response to front-to-back motion. However, the response was impaired most strongly for OFF-edges, no matter in what direction they were moving. Therefore, the directionality of Tm2 observed in its wiring is likely to serve other functions than in directional motion detection. We propose that Tm2, instead of being itself directionally selective for front-to-back motion, rather represents an important and indispensable input element to the T5 dendrite within the OFF-pathway.

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References

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Keywords: OFF Pathway, Drosophila melanogaster, Reichardt-Detector, motion vision, LPTC

Conference: International Conference on Invertebrate Vision, Fjälkinge, Sweden, 1 Aug - 8 Aug, 2013.

Presentation Type: Poster presentation preferred

Topic: Motion vision

Citation: Meier M, Serbe E and Borst A (2019). Tm2 & L4: Major ‘OFF-Pathway’ Elements in the Drosophila Motion Circuit. Front. Physiol. Conference Abstract: International Conference on Invertebrate Vision. doi: 10.3389/conf.fphys.2013.25.00088

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Received: 26 Feb 2013; Published Online: 09 Dec 2019.

* Correspondence:
Mr. Matthias Meier, Max Planck Institute for Neurobiology, Circuits Computations Models, Martinsried, 82152, Germany, mmeier@neuro.mpg.de
Mr. Etienne Serbe, Max Planck Institute for Neurobiology, Circuits Computations Models, Martinsried, 82152, Germany, serbe@neuro.mpg.de