Voluntary nicotine consumption potentiates cortical excitatory drives to the VTA: analysis of input/output tests on BNST neurons projecting to the VTA after stimulation of ILCx in SAL, YOKED, and NIC rats. A, Diagram of the stimulation protocol used in this experiment. Here, the ILCx was stimulated with a 100-pulse train and BNST neurons projecting to the VTA were identified by antidromic activation from the VTA. B, Ten consecutive sweeps showing antidromic response of a BNST neuron from VTA stimulation. Stimulation of the VTA 30 ms after spontaneous spikes elicit driven spikes (black traces). Driven spikes are occluded for similar stimuli delivered 5 ms after spontaneous impulses indicating collision between spontaneous and driven spikes (red traces). C, Increasing intensity of stimulation current in ILCx evoked higher response magnitude of BNST neurons projecting to the VTA. Cortical excitatory strength onto BNST neurons projecting to the VTA was enhanced only in NIC rats. The slope of the relationship between injected current and evoked firing rate is similar in SAL and YOKED animals. Numbers of neurons recorded in each group are mentioned in brackets. ***p < 0.001 versus excitatory responses in SAL rats. D, E, Graphs illustrating the effects of treatment (SAL, YOKED, and NIC rats) on inhibitory response duration (D) and on basal activity frequency (E). Treatment had no effect on inhibition or on basal activity in SAL, YOKED, or NIC rats. F, Typical PSTHs illustrate responses of BNST neurons projecting to the VTA on ILCx stimulation (1000 μA). In this PSTHs, the stimulus is delivered at time 0 (gray vertical line). Each PSTH consists of 100 trials individually illustrated in the associated raster. Bin width, 5 ms. Numbers in brackets refers to numbers of BNST neurons recorded.