RESUMO
Objective To study the effect of dexmedetomidine (DEX), an α2- adrenoceptor agonist, on the pain-related anxiety-like and depression-like behaviour induced by complete Freund' s adjuvant (CFA) injection and its possible regulatory mechanism. Methods Thirty-six ICR female mice were randomly divided into normal saline (NS) group, CFA group and DEX + CFA group, n = 12 for each group. Chronic inflammatory pain model was established by subcutaneous injection of 10 μl CFA into the right hind limb of mice. DEX + CFA group mice were injected intraperitoneally with 0.025 mg/kg DEX 30 minutes before nociceptive behavior test, and once a day for 7 days. Von-frey fiber was used to evaluate the threshold of mechanical pain in mice, n = 12 for each group. The anxiety-like behavior of mice were detected by open field test, n = 12 for each group. Sucrose preference, tail suspension test and forced swimming test were used to detected the depression-like behavior of mice, n = 12 for each group. The expression of adrenergic receptor β2 (ADRB2), Brain-derived neurotrophic factor (BDNF), tyrosine kinase B receptor (TrkB), and glutamate receptors 1 (GluR1) and GluR2 were detected by Western blotting, n = 8 for each group. Immunohistochemical staining was used to detect the expression of recombinant doublecortin(DCX), which is a marker of newborn neurons in the hippocampus, n = 4 for each group. Results Compared with the NS group, the mechanical threshold of mice on the 1st, 3rd and 7th day after CFA injection decreased significantly (P 0.05). Compared with the NS group, the time spent in the inner ares (P<0.01), number of entering the central grid area (P<0.01) and distance travelled in the inner area (P<0.01) of CFA group mice reduced significantly, while the time (P<0.01), numbers (P < 0.05) and distance (P < 0.05) of DEX + CFA group mice entering the central grid area enhanced significantly. The result of depression-like behavior tests showed that the sucrose preference percentage (P < 0.05) reduced significantly in CFA group when compared with NS group, and the immobility time increased significantly in tail suspension test (P<0.01) and forced swimming test (P< 0.001) in CFA mice when compared with NS group, while DEX intervention could significantly increase the sucrose preference scores (P<0.05) and decreased the immobility time in tail suspension test (P<0.05) and forced swimming test (P<0.05). The result of Western blotting showed that compared with the NS group, the levels of ADRB2 (P<0.0010), BDNF (P < 0.001), TrkB (P < 0.01), GluR1 (P < 0.001) and GluR2 (P < 0.001) in the hippocampus of CFA group were significantly decreased, while DEX intervention could significantly increase the expression of ADRB2 (P<0.05), BDNF (P < 0.001), TrkB (P < 0.001), GluR1 (P < 0.001) and GluR2 (P < 0.001). Immunohistochemical result showed that compared with the NS group, the average absorbance (AA) of DCX decreased significantly in hippocampus of CFA group (P<0.05), but increased significantly in DEX+CFA group (P < 0.05). Conclusion Dexmedetomidine may promote hippocampal neurogenesis through upregulated the expression of BDNF-TrkB, thus improving CFA-induced anxiety-like and depression-like behaviors in mice.
RESUMO
Objective To investigate the alteration of mood and hippocampal microglia morphology in a mouse model of chronic inflammatory pain induced by complete Freund' s adjuvant (CFA). Methods Thirty-two male ICR mice were randomly divided into two groups, including normal saline control group (NS) and CFA model group (CFA). The pain model was established by right hindpaw intraplantar CFA injection. The change of mechanical pain threshold after CFA injection was measured by von Frey fiber needle, the locomotor activity and anxiety-like behavior were determined by open field test (OFT), the depression-like behavior was determined by sucrose preference test (SPT) and forced swimming test (FST). The expression of microglia marker ionized calcium binding adaptor molecule-1 (IBA-1) in the hippocampus was determined by immunohistochemistry and its morphological change was analyzed by Sholl analysis. Results Compared with the NS group, the mechanical pain threshold of CFA group decreased significantly (P<0.01). The behavior result showed that the CFA group showed remarkably reduced time in the inner area (P<0.01) compared with the NS group in the open field test; In the sucrose preference test, the percentage of sucrose preference (P<0.01) of CFA mice decreased significantly compared with the NS mice, while the immobility time of CFA mice (P<0.01) increased significantly in the forced swimming test compared with the NS mice. The immunohistochemistry showed that the number of microglia in the dentate gyrus (DG) of CFA mice increased significantly compared with the NS mice. The Sholl analysis result showed that compared with the NS mice, the number of intersections of microglia in hippocampal DG decreased significantly in CFA mice. Conclusion Our finding indicates that the negative emotions in CFA-induced chronic inflammatory pain may be related to the morphological changes of hippocampal microglia in the mice.