Antidromic activation of one parabrachiothalamic neuron recorded in the PBil. A, Superimposition of five antidromic spikes; note the perfect stability of the latency.B, High-frequency stimulation (5 pulses, 600 Hz); note the capacity of the antidromic response to follow high-frequency stimulation. C, Collision test. Filled circle shows the expected location of the antidromic spike, andblack triangle indicates the antidromic shock.C1, The orthodromic spike fired before the 2t + r collision period, and the antidromic spike occurred with 11 msec latency. C2–C4, The orthodromic spike fired within the 2t +r collision period, and the antidromic spike did not occur. D, Microphotograph of the corresponding Prussian blue point in the paracentral nucleus. E1,E2, Antidromic activation sites with thresholds <200 μA (asterisks) and >200 μA (black dots). F, Distribution histogram of the antidromic latencies. Scale bar (in D), 1 mm.CM, Central medial thalamic nucleus; fr, fasciculus retroflexus; ml, medial lemniscus;OPC, oval paracentral thalamic nucleus;Pf, parafascicula thalamic nucleus; Po, posterior thalamic nuclear group; VPM, ventral posteromedial thalamic nucleus; VPPC, ventral posterior parvicellular thalamic nucleus.