Effect of the 10 Hz ILCx stimulation onto BNST neurons at different stages of nicotine acquisition and maintenance. A, Stimulation and recording protocol. B, Histological control of stimulation (ILCx, *) and recording (BNST, arrow) sites. Scale bar, 1 mm. C, LTP seen in NIC-60 d rats but not in NIC-1 d, NIC-8 d, SAL-60 d, or yoked rats. D, Baseline and post-tetanic stimulation responses of ILCx–BNST projection neurons in NIC-60 d rats. Stimulus delivered at time = 0 (arrow). Each histogram consists of 100 trials individually illustrated in the associated raster. Bin width, 5 ms. E, The 10 Hz ILCx stimulation induces NMDA-dependent LTP within the BNST. Microinjection of the NMDA antagonist AP5 (400 μm, 60 nl) blocks the induction of LTP. Data are mean ± SEM.