Projection from the BNST to the VTA revealed by antidromic stimulation from the VTA and retrograde labeling in the BNST after injection of CTb into the VTA. A, Diagram of the stimulation protocol used in this experiment. Here, the IL was stimulated with a 100-pulse train, and BNST neurons projecting to the VTA were identified by antidromic activation from the VTA. B, Left, Recording location for a BNST neuron projecting to the VTA (dark spot, black arrow). Right, Electrical stimulation site in the VTA (lesioned area, black arrow). Scale bars, 0.5 mm. C, D, Five superimposed traces illustrating high-frequency activation and collision test for a BNST cell driven from the VTA. C, Driven spikes (black circles) elicited by each paired stimuli (vertical lines, 2 ms interpulse interval), indicating frequency following for this cell at 500 Hz. D, Left, Stimulation of the VTA 12 ms after spontaneous spikes (left side of traces) elicit driven spikes (black circle) at 9.5 ms latency. Right, Driven spikes are occluded for similar stimuli delivered 10 ms after spontaneous impulses indicating collision between spontaneous and driven spikes. The asterisk indicates when driven spikes would have occurred had there been no collision. E, Schematic presentation of neuronal recording sites in the BNST of neurons projecting to the VTA. Black circles, Locations of synaptically driven BNST neurons by single-pulse ILCx electrical stimulation. Numbers refer to stereotaxic coordinates. Note that all of the BNST neurons projecting to the VTA tested were driven by ILCx stimulation. F–H, Projection from the BNST to the VTA revealed by retrograde labeling in the BNST after injection of CTb into the VTA. F, Epifluorescence photomicrographs illustrating retrograde labeling in the dorsal and ventral parts of the BNST after CTb injection into the VTA. G, Photomicrograph illustrating a representative CTb injection site in the VTA. The sections have been processed dually for CTb (red) and TH (green). Scale bars: F, 100 μm; G, 200 μm. H, Bar histograms comparing the density of CTb-immunoreactive neurons in the dorsal and ventral BNST after an injection of CTb in the VTA (n = 15 rats perfused 7 d after receiving CTb into the VTA). t test was used to establish statistical differences between the dorsal and the ventral part of the BNST. *p < 0.05, Student's t test. REC, Recording electrode; STIM, stimulation.