Inhibition of glutamatergic neurons in layer II/III of the medial prefrontal cortex alleviates paclitaxel-induced neuropathic pain and anxiety

Paclitaxel-treated patients frequently experience chemotherapy-induced peripheral neuropathy (CIPN) and mood changes, such as anxiety. Layer II/III of the medial prefrontal cortex (mPFC) is vital for generating pain and emotions. However, it is unclear whether glutamatergic neurons in layer II/III of the mPFC are involved in regulating paclitaxel-induced neuropathic pain and anxiety. Here, we determined the role of glutamatergic neurons in layer II/III of the mPFC in paclitaxel (4 mg/kg/d, consecutive 8 days, intraperitoneal injection, cumulative dose: 32 mg/kg)-induced pain and anxiety by using a combination of behavior testing's, immunostaining, chemogenetics, optogenetics, fiberphotometry, and morphological approaches. The number of c-Fos-positive neurons expressing calcium/calmodulin-dependent protein kinase II (CaMKII) (CaMKII-positive neurons) were increased in layer II/III of the mPFC in paclitaxel-treated mice. Selectively inhibiting CaMKII-positive neurons in layer II/III of the mPFC with chemogenetic or optogenetic approaches relieved paclitaxel-induced neuropathic pain and anxiety. Furthermore, paclitaxel treatment increased calcium signals in layer II/III of the mPFC CaMKII-positive neurons expressed GCaMP6m. In addition, Golgi staining was performed to analyze that basal and apical dendrites of pyramidal neurons in layer II/III of the mPFC. Compared with vehicle-treated mice, paclitaxel-treated mice displayed longer and more branches and increased spine density in layer II/III of the mPFC. Further electron microscopy analysis revealed that asymmetrical synapses and postsynaptic density 95 thickness were significantly increased in layer II/III of the mPFC in paclitaxel-treated mice. These data suggest that CaMKII neurons in the mPFC layer II/III are importantly involved in paclitaxel-induced pain and anxiety.