Whisker sensory information is conveyed to the somatosensory cortex through two main pathways from the brain stem. One is the lemniscal pathway, which conveys tactile information of whiskers, and the other is the paralemniscal pathway, which conveys nociceptive information and/or whisker-position information. In the present study, to reveal how these two inputs change in the somatosensory cortex following whisker nerve injury, we compared cortical activity between these two pathways after ligation of whisker sensory nerve with absorbable surgical thread. First, we found that, in the ligation group on post-operative day 7, number of c-Fos positive neurons significantly increased in the dysgranular area, which surrounds the barrel cortex and receives paralemniscal input, in freely moving mice with tactile exploration under enriched environment. However, in the sham group, c-Fos positive neurons were mainly observed in the layer 4 of the primary somatosensory cortex (SI), which receives lemniscal inputs. Second, we applied tactile stimulation on whisker and/or the mandibular part, and simultaneously recorded intrinsic optical signal from the SI and dysgranular area following the ligation for several weeks. In the sham group, significant signals, evoked by either whisker or mandibular stimulation, were detected in the barrel cortex or the mandibular area of SI, while no significant signal was observed in the dysgranular area with either stimulation. Even simultaneous stimulation of whisker and mandibular parts could not evoke significant signal in the dysgranular area. In the ligation group, we could not detect any significant signal evoked by whisker stimulation in the barrel and dysgranular area on post-operative day 7, and the signal did not change when only the mandibular part was stimulated. Notably, though, simultaneous stimulation of whiskers and the mandibular parts evoked strong signal in the dysgranular area. After losing retention strength of the thread, the signal in the barrel cortex reappeared, while the strong signal in the dysgranular area evoked by simultaneous stimulation decreased and returned to the normal level. These results indicate that injury of whisker sensory nerves can induce hyperactivity of the paralemniscal pathway when whiskers and the mandibular part are simultaneously stimulated.

研究助成：Research funds : KAKENHI（15H01667, 15K21387）