Reduction in calcium responses to whisker stimulation in the primary somatosensory and motor cortices of the model mouse with trigeminal neuropathic pain

Objective: Chronic constriction injury (CCI) of the infraorbital nerve induces neuropathic pain, such as allodynia and hyperalgesia, in the orofacial area. However, the changes in the local circuits of the central nervous system following CCI remain unclear. This study aimed to identify the changes following CCI in Thy1-GCaMP6s transgenic mice.

Methods: Neural activity in the primary somatosensory cortex (S1) and motor cortex (M1) following whisker stimulation was assessed using in vivo Ca²⁺ imaging. CCI-induced changes in responses were analyzed.

Results: Before CCI, whisker stimulation induced a greater Ca²⁺ response in the contralateral S1 than in the ipsilateral S1 and contralateral M1. The peak Ca²⁺ response amplitude in the bilateral S1 and contralateral M1 decreased two days after CCI compared to before CCI. Decreased Ca²⁺ response amplitude in these regions was observed until four days after CCI. Seven days after CCI, the Ca²⁺ response amplitude in the contralateral S1 decreased, whereas that in the ipsilateral S1 and contralateral M1 recovered to control levels.

Conclusion: These results suggest that neural activity in regions receiving excitatory inputs via corticocortical pathways recovers earlier than in regions receiving thalamocortical inputs. (185/250 words).