title: 5-HT2CReceptor Knockdown in the Amygdala Inhibits Neuropathic-Pain-Related Plasticity and Behaviors.
abstract: Neuroplasticity in the amygdala drives pain-related behaviors. The central nucleus (CeA) serves major amygdala output functions and can generate emotional-affective behaviors and modulate nocifensive responses. The CeA receives excitatory and inhibitory inputs from the basolateral nucleus (BLA) and serotonin receptor subtype 5-HT2CR in the BLA, but not CeA, has been implicated anxiogenic behaviors and anxiety disorders. Here, we tested the hypothesis that 5-HT2CR in the BLA plays a critical role in CeA plasticity and neuropathic pain behaviors in the rat spinal nerve ligation (SNL) model. Local 5-HT2CR knockdown in the BLA with stereotaxic injection of 5-HT2CR shRNA AAV vector decreased vocalizations and anxiety- and depression-like behaviors and increased sensory thresholds of SNL rats, but had no effect in sham controls. Extracellular single-unit recordings of CeA neurons in anesthetized rats showed that 5-HT2CR knockdown blocked the increase in neuronal activity (increased responsiveness, irregular spike firing, and increased burst activity) in SNL rats. At the synaptic level, 5-HT2CR knockdown blocked the increase in excitatory transmission from BLA to CeA recorded in brain slices from SNL rats using whole-cell patch-clamp conditions. Inhibitory transmission was decreased by 5-HT2CR knockdown in control and SNL conditions to a similar degree. The findings can be explained by immunohistochemical data showing increased expression of 5-HT2CR in non-GABAergic BLA cells in SNL rats. The results suggest that increased 5-HT2CR in the BLA contributes to neuropathic-pain-related amygdala plasticity by driving synaptic excitation of CeA neurons. As a rescue strategy, 5-HT2CR knockdown in the BLA inhibits neuropathic-pain-related behaviors.SIGNIFICANCE STATEMENTNeuroplasticity in the amygdala has emerged as an important pain mechanism. This study identifies a novel target and rescue strategy to control abnormally enhanced amygdala activity in an animal model of neuropathic pain. Specifically, an integrative approach of gene transfer, systems and brain slice electrophysiology, behavior, and immunohistochemistry was used to advance the novel concept that serotonin receptor subtype 5-HT2Ccontributes critically to the imbalance between excitatory and inhibitory drive of amygdala output neurons. Local viral vector-mediated 5-HT2CR knockdown in the amygdala normalizes the imbalance, decreases neuronal activity, and inhibits neuropathic-pain-related behaviors. The study provides valuable insight into serotonin receptor (dys)function in a limbic brain area.
authors.affiliation: Department of Pharmacology and Neuroscience and.
authors.forename: Guangchen
authors.initials: G
authors.lastname: Ji
authors.affiliation: Department of Pharmacology and Neuroscience and.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Pharmacology and Neuroscience and.
authors.forename: Lenin
authors.initials: L
authors.lastname: Mahimainathan
authors.affiliation: Department of Pharmacology and Neuroscience and.
authors.forename: Madhusudhanan
authors.initials: M
authors.lastname: Narasimhan
authors.affiliation: Department of Pharmacology and Neuroscience and.
authors.forename: Takaki
authors.initials: T
authors.lastname: Kiritoshi
authors.affiliation: Department of Pharmacology and Toxicology, The University of Texas Medical Branch, Galveston, Texas 77555.
authors.forename: Xiuzhen
authors.initials: X
authors.lastname: Fan
authors.affiliation: Department of Pharmacology and Toxicology, The University of Texas Medical Branch, Galveston, Texas 77555.
authors.forename: Jigong
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Pharmacology and Toxicology, The University of Texas Medical Branch, Galveston, Texas 77555.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Green
authors.affiliation: Department of Pharmacology and Neuroscience and volker.neugebauer@ttuhsc.edu.|Center of Excellence for Translational Neuroscience and Therapeutics, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, and.
authors.forename: Volker
authors.initials: V
authors.lastname: Neugebauer
mesh_terms: D000679:Amygdala / Q000378:metabolism*; D000818:Animals; D055785:Gene Knockdown Techniques / Q000379:methods; D008297:Male; D018782:Maze Learning / Q000502:physiology; D009437:Neuralgia / Q000235:genetics / Q000378:metabolism*; D009473:Neuronal Plasticity / Q000502:physiology*; D009924:Organ Culture Techniques; D010147:Pain Measurement / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D044405:Receptor, Serotonin, 5-HT2C / Q000172:deficiency* / Q000235:genetics; D014828:Vocalization, Animal / Q000502:physiology
chemical_list: D044405:Receptor, Serotonin, 5-HT2C
keywords: amygdala; depression; pain; plasticity; serotonin