Fig. 1. Confocal photomicrographs showing Neurobiotin transfer from cell Tr2, in the subesophageal ganglion (SEG), to neurons identified as synthesizing DA. (A) Shown are Tr2 and Neurobiotin-containing neuronal populations visualized with Cy3-streptavidin. The soma of only one Tr2 neuron was iontophoretically injected with Neurobiotin using 500 ms pulses of positive current (1.5 nA) at a rate of 1 Hz for about 30 min. Cell Tr2 is shown crossing the midline and descending out of the SEG. (B) Same sample as in (A) showing Cy5 fluorescence from the network of dopaminergic neurons stained with an antibody against tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of dopamine (DA). (C) Merged two-color fluorescence showing neurons (yellow) that contain both Neurobiotin (green) and TH (red). In this sample, arrows indicate the presence of four TH-immunoreactive (TH-ir) cells that are dye coupled to Tr2. (D) In another sample, the processes and projection patterns of the TH-ir neurons are displayed. Scale bars, 100 µm.