Neuropathic pain is a chronic condition caused by damage or dysfunction in the nervous system. While the spleen may influence neuropathic pain, its role has been poorly understood. This study demonstrates that the spleen plays a crucial role in regulating neuropathic pain through the bed nucleus of the stria terminalis (BNST) - paraventricular nucleus of the hypothalamus (PVN) neural circuit in a chronic constriction injury (CCI) mouse model. Splenectomy, splenic denervation, or splenic sympathectomy significantly increased the mechanical withdrawal threshold (MWT) and reduced macrophage infiltration in the dorsal root ganglia (DRG) of CCI mice. Pseudorabies virus injections into the spleen revealed connections to the BNST and PVN in the brain. Chemogenetic inhibition of the BNST-PVN circuit increased macrophage infiltration in the DRG and decreased the MWT; these effects were reversed by splenectomy, splenic denervation, or sympathectomy. These findings underscore the critical role of the spleen, regulated by the BNST-PVN circuit, in neuropathic pain.
Animals ; Neuralgia/pathology* ; Septal Nuclei/physiopathology* ; Male ; Spleen/physiopathology* ; Paraventricular Hypothalamic Nucleus/physiopathology* ; Mice, Inbred C57BL ; Splenectomy ; Mice ; Neural Pathways/physiopathology* ; Disease Models, Animal ; Ganglia, Spinal/physiopathology* ; Sympathectomy ; Macrophages

The nucleus accumbens (NAc) plays an important role in various emotional and motivational behaviors that rely on heightened wakefulness. However, the neural mechanisms underlying the relationship between arousal and emotion regulation in NAc remain unclear. Here, we investigated the roles of a specific subset of inhibitory corticotropin-releasing hormone neurons in the NAc (NAc^CRH) in regulating arousal and emotional behaviors in mice. We found an increased activity of NAc^CRH neurons during wakefulness and rewarding stimulation. Activation of NAc^CRH neurons converts NREM or REM sleep to wakefulness, while inhibition of these neurons attenuates wakefulness. Remarkably, activation of NAc^CRH neurons induces a place preference response (PPR) and decreased basal anxiety level, whereas their inactivation induces a place aversion response and anxious state. NAc^CRH neurons are identified as the major NAc projection neurons to the bed nucleus of the stria terminalis (BNST). Furthermore, activation of the NAc^CRH-BNST pathway similarly induced wakefulness and positive emotional behaviors. Taken together, we identified a basal forebrain CRH pathway that promotes the arousal associated with positive affective states.
Animals ; Septal Nuclei/metabolism* ; Nucleus Accumbens/physiology* ; Corticotropin-Releasing Hormone/metabolism* ; Wakefulness/physiology* ; Neurons/metabolism* ; Male ; Mice ; Mice, Inbred C57BL ; Neural Pathways/physiology* ; Anxiety/physiopathology* ; Reward