ABSTRACT
Itch is an unpleasant sensation that urges people and animals to scratch. Neuroimaging studies on itch have yielded extensive correlations with diverse cortical and subcortical regions, including the insular lobe. However, the role and functional specificity of the insular cortex (IC) and its subdivisions in itch mediation remains unclear. Here, we demonstrated by immunohistochemistry and fiber photometry tests, that neurons in both the anterior insular cortex (AIC) and the posterior insular cortex (PIC) are activated during acute itch processes. Pharmacogenetic experiments revealed that nonselective inhibition of global AIC neurons, or selective inhibition of the activity of glutaminergic neurons in the AIC, reduced the scratching behaviors induced by intradermal injection of 5-hydroxytryptamine (5-HT), but not those induced by compound 48/80. However, both nonselective inhibition of global PIC neurons and selective inhibition of glutaminergic neurons in the PIC failed to affect the itching-scratching behaviors induced by either 5-HT or compound 48/80. In addition, pharmacogenetic inhibition of AIC glutaminergic neurons effectively blocked itch-associated conditioned place aversion behavior, and inhibition of AIC glutaminergic neurons projecting to the prelimbic cortex significantly suppressed 5-HT-evoked scratching. These findings provide preliminary evidence that the AIC is involved, at least partially via aversive emotion mediation, in the regulation of 5-HT-, but not compound 48/80-induced itch.
Subject(s)
Humans , Animals , Serotonin , Insular Cortex , Pruritus/chemically induced , Cerebral Cortex/physiology , NeuronsABSTRACT
Pain consists of sensory-discriminative and emotional-affective components. The anterior cingulate cortex (ACC) is a critical brain area in mediating the affective pain. However, the molecular mechanisms involved remain largely unknown. Our recent study indicated that C-X-C motif chemokine 13 (CXCL13) and its sole receptor CXCR5 are involved in sensory sensitization in the spinal cord after spinal nerve ligation (SNL). Whether CXCL13/CXCR5 signaling in the ACC contributes to the pathogenesis of pain-related aversion remains unknown. Here, we showed that SNL increased the CXCL13 level and CXCR5 expression in the ACC after SNL. Knockdown of CXCR5 by microinjection of Cxcr5 shRNA into the ACC did not affect SNL-induced mechanical allodynia but effectively alleviated neuropathic pain-related place avoidance behavior. Furthermore, electrophysiological recording from layer II-III neurons in the ACC showed that SNL increased the frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), decreased the EPSC paired-pulse ratio, and increased the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor/N-methyl-D-aspartate receptor ratio, indicating enhanced glutamatergic synaptic transmission. Finally, superfusion of CXCL13 onto ACC slices increased the frequency and amplitude of spontaneous EPSCs. Pre-injection of Cxcr5 shRNA into the ACC reduced the increase in glutamatergic synaptic transmission induced by SNL. Collectively, these results suggest that CXCL13/CXCR5 signaling in the ACC is involved in neuropathic pain-related aversion via synaptic potentiation.
ABSTRACT
Objective To explore neurobiological mechanisms of the withdrawal-induced aversion,the changes of protein kinase A(PKA) were measured in shell of accumbens nucleus (AcbSH) of CPA model rats.Methods 1.All 36 male SD rats were divided into three groups,model group ( MN group),and control group (MS group and SN group).MN group was injected with morphine,6.5 days,10mg/kg,intraperitoneally (IP),twice per day,naloxone injection,0.3 mg/kg,ip,along with conditioned place aversion training,to develop the CPA model.The MS group was administrated equivalent volume of morphine and saline.Also the SN group was injected with equivalent volume of saline and naloxone.2.During the development of CPA,the expression of protein kinase A was assayed with immunohistochemistry in the AcbSH.Results Before the development of CPA,PKA expressions were no significant differences among the three groups in the AcbSH (F=2.306,P=0.130).However,after development of CPA,PKA expressions showed significant differences among the three groups(F =36.516,P =0.000).The average gray intensity of MN group (109.50 ± 4.661 ) was apparently higher than the MS group (126.50 ±3.697,P＜0.01),than the SN group (133.50 ±6.364,P＜0.01).Conclusions 1.Protein kinase A expression,leading to the aversion in the AcbSH probably is a key pathway contributing to the development of CPA.2.The neuroadaptation mediated by PKA may be one of important molecular underpinnings of CPA.