Interleukin‐1beta released by microglia initiates the enhanced glutamatergic activity in the spinal dorsal horn during paclitaxel‐associated acute pain syndrome

Patients receiving paclitaxel for cancer treatment often develop an acute pain syndrome (paclitaxel‐associated acute pain syndrome, P‐APS), which occurs immediately after paclitaxel treatment. Mechanisms underlying P‐APS remain largely unknown. We recently reported that rodents receiving paclitaxel develop acute pain and activation of spinal microglial toll like receptor 4 (TLR4) by paclitaxel penetrating into the spinal cord is a critical event in the genesis of P‐APS. Our current study dissected cellular and molecular mechanisms underlying the P‐APS. We demonstrated that bath‐perfusion of paclitaxel, at a concentration similar to that found in the cerebral spinal fluid in animals receiving i.v. paclitaxel (2 mg/kg), resulted in increased calcium activity in microglia instantly, and in astrocytes with 6 min delay. TLR4 activation in microglia by paclitaxel caused microglia to rapidly release interleukin‐1β (IL‐1β) but not tumor necrosis factor α, IL‐6, or interferon‐γ. IL‐1β release from microglia depended on capthepsin B. IL‐1β acted on astrocytes, leading to elevated calcium activity and suppressed glutamate uptake. IL‐1β also acted on neurons to increase presynaptic glutamate release and postsynaptic AMPA receptor activity in the spinal dorsal horn. Knockout of IL‐1 receptors prevented the development of acute pain induced by paclitaxel in mice. Our study indicates that IL‐1β is a crucial molecule used by microglia to alter functions in astrocytes and neurons upon activation of TLR4 in the genesis of P‐APS, and targeting the signaling pathways regulating the production and function of IL‐1β from microglia is a potential avenue for the development of analgesics for the treatment of P‐APS. Main Points Systemic administration of taxol causes rapid release of IL‐1β from spinal microglia via activating TLR4. IL‐1β enhances glutamatergic synaptic activity pre‐ and postsynaptically, and by reducing astrocytic glutamate uptake, leading to acute pain.