Fig. 1.

(a) Coincidence of primary afferents from the GON (left) and the TG (right) in the TCC region. CTB-immunolabeled fibers are shown in two horizontal sections through dorsal levels of spinal and medullary regions that extend from mid-medullary levels (top) to cervical segment C₃ (bottom). The vertical line marks the approximate rostrocaudal extent of the TCC. In these sections it is clearly seen that afferents from the GON concentrate in TCC at the level of segment C2, while TG afferents extend continuously further caudally. The seeming interruption in TG labeling corresponds to the entry of the dorsal root of spinal nerve C₂ entering the cord, selected for topographic reference. DC, dorsal column; TCC, trigeminocervical complex. Scale bar = 500 μm. (b) Two representative examples of small electrolytic lesions (asterisks) through the recording electrode at the end of the recording session. These cases show recording sites in laminae II inner (left) and IV (right) in the ventrolateral one-half of the dorsal horn. Most recordings were placed within the area demarcated by these lesions. (c) The recording sites fell within a territory with substantial innervation of CTB-labeled fibers from the GON (shown in magenta). I-IV laminar boundaries are outlined, and blue stippling indicate IB4-labeled, presumably unmyelinated, afferents in laminae I and II, which were virtually restricted to segments C₂ and C₃ (diagram reproduced from Garcia-Magro et al., 2018). Scale bar = 500 μm