L4 [FBbt_00003722]

L4

ID: FBbt_00003722

A lamina monopolar neuron that arborizes in the proximal lamina, forms a spreading arbor in medulla layer M2 and a small terminal arbor in M4-M5 that penetrates adjacent columns (Fischbach and Dittrich, 1989; Takemura et al., 2008; Takemura et al., 2011). In the medulla it forms presynaptic terminals in both M2 and M4-M5 with transmedullary neuron Tm2; three L4 neurons, one from the parent column and two from the posterior ones contact the same Tm2 neuron (Takemura et al., 2008; Takemura et al., 2011). It seems to be capable of both cholinergic and GABAergic neurotransmission.

Note, Fischbach and Dittrich (1989) have this as arborizing in M4, but we follow the more detailed analysis of Takemura and colleagues (2008) who place the terminal arbor in M5. This difference may have to do with the different ways the two papers define L4. Note also that L4x and L4y are simply a way of referring to L4 collaterals from an adjacent cartridge in descriptions of synaptic connectivity (see Meinertzhagen and O'Neil, 1991) and are not separate neurons. Connectivity in the medulla was extrapolated from serial EM of 3 columns from a single sample (Takemura et al., 2008; Takemura et al., 2011). Takemura et al. (2011) and Davis et al. (2020) report the neurotransmitter to be acetylcholine as assessed by single cell RT-PCR measurement of choline acetyltransferase (FBgn0000303) expression and scRNAseq detection of both choline acetyltransferase and vesicular acetylcholine transporter (FBgn0270928). However, Raghu et al. (2013) report this neuron to be GABAergic as assessed by the intersection of the expression of the VGAT-GAL4 driver (FBtp0069181) and an antibody against GABA.