A Hard-wired Glutamatergic Circuit Pools Dim UV Signals to Mediate Spectral Preference in Drosophila Visual System

Wednesday, November 06, 2013 — Poster Session I
4:00 p.m. – 6:00 p.m.	FAES Academic Center (Upper-Level Terrace)	NICHD	NEURO-17

Authors

T. Karuppudurai
T.Y. Lin
C.Y. Ting
C.H. Lee

Abstract

Drosophila prefer ultraviolet (UV) to visible light, a behavior that depends on UV-sensing R7 photoreceptors and their synaptic targets, the Dm8 amacrine neurons. Using a combinatorial expression system we identify three classes neurons, Tm5a/b/c, which arborize dendrites in the M3 and M6 layers and receive Dm8 and R7/R8 inputs. By manipulating activity in these neurons, we determined that Tm5c, but not Tm5a/b neurons are required for UV preference. Using a single-cell GRASP (GFP reconstitution across synaptic partners) method we identified synaptic contacts between Dm8 and Tm5c. Single-cell transcript profiling suggests that Dm8 and Tm5c neurons express vesicular glutamate transporters (vGlut) and therefore are likely glutamatergic. RNAi-mediated knockdown of vGlut in Dm8 or Tm5c significantly reduced animals’ innate UV preference. We further determined that Tm5c expresses four kainate-type glutamate receptors and at least one of them, Clumsy, is required for optimal UV preference. We propose that Dm8 enhances UV sensitivity by pooling about 16-R7 histaminergic inputs and providing excitatory glutamatergic input to Tm5c. Although Tm5c receives excitatory glutamatergic and inhibitory histaminergic inputs from Dm8 and R7&R8 neurons, respectively, the indirect pathway R7->Dm8->Tm5c is both required and sufficient for UV preference.