L3 [FBbt_00003721]

L3

ID: FBbt_00003721

Lamina monopolar neuron with short spines that project to one side of the main projection as it extends through the lamina (Fischbach and Dittrich, 1989; Kind et al., 2021). It terminates with an arborization in medulla layer M3 (Fischbach and Dittrich, 1989; Kind et al., 2021). In the lamina it is postsynaptic to the outer photoreceptors (R1-R6) (Rivera-Alba et al., 2011). It also receives input from the inner photoreceptors, partly in the first optic chiasm and partly in the medulla (Kind et al., 2021). It forms presynaptic terminals in medulla layer M3 (Takemura et al., 2008), with strong outputs to Mi9 and Tm20 (Takemura et al., 2013). It is a GABAergic neuron (Raghu et al., 2013). There is usually one of these cells per optic column (Nern et al., 2025).

Cell connectivity in the lamina was determined by analysis of semi-automated EM reconstruction of 749 serial sections of 21 complete lamina cartridges. The number of synaptic connections for L3 (presynaptic/postsynaptic) in a single lamina cartridge with each cell type was the following: R1 (-/11), R2 (-/10), R3 (-/4), R4 (-/8), R5 (-/6), R6 (-/12), L4 (-/1), L5 (1/-), Lai (-/10) and Lawf (-/17) (Rivera-Alba et al., 2011). Connectivity in the medulla was extrapolated from serial EM of 3 columns from a single sample (Takemura et al., 2008) or from 7 columns (Takemura et al., 2013). The neurotransmitter was assessed by the intersection of the expression of the VGAT-GAL4 driver (FBtp0069181) and an antibody against GABA (Raghu et al., 2013).