Blockade of nicotinic acetylcholine receptor enhances the responsiveness to bupropion in the mouse forced swim test

The objective of the present study is to investigate the role of α4, α5, α6 or β2 nAChR subunits in the antidepressant-like effect of bupropion. Adult male mice were treated with subcutaneous acute doses of bupropion (3 and 10 mg/kg) 30 min before the forced swim test (FST) in α4, α5, α6, or β2 nAChR subunit knockout (KO) and wild-type (WT) mice. In addition, the effects of β2* antagonist dihydro-β-erythroidine (DHβE, 3 mg/kg) on antidepressant-like effects of bupropion in C57BL/6 J mice were assessed. Our results showed that baseline immobility and climbing time did not differ between KO and corresponding WT mice except for β2 KO. Bupropion significantly decreased immobility time and increased climbing time in the α4, α6 and β2 nAChR KO mice in comparison to WT littermates, indicating that lack of these nAChR subunits enhanced antidepressant effects of bupropion. On the contrary, the α5 nAChR subunit deletion did not alter the FST behavior in the bupropion-treated mice. Not only in the transgenic mice, bupropion also showed antidepressant-like effects in the WT mice. In addition, DHβE pretreatment before bupropion administration resulted in decreased immobility time and increased climbing time. Taken together, the present study provides evidence on the involvement of α4*, α6*, and β2* (* indicates possible presence of other subunits) nAChRs in the antidepressant-like effects of bupropion in the FST.

The α7 nicotinic receptor dual allosteric agonist and positive allosteric modulator GAT107 reverses nociception in mouse models of inflammatory and neuropathic pain

BACKGROUND AND PURPOSE

Orthosteric agonists and positive allosteric modulators (PAMs) of the α7 nicotinic ACh receptor (nAChR) represent novel therapeutic approaches for pain modulation. Moreover, compounds with dual function as allosteric agonists and PAMs, known as ago-PAMs, add further regulation of receptor function.

EXPERIMENTAL APPROACH

Initial studies examined the α7 ago-PAM, GAT107, in the formalin, complete Freund's adjuvant (CFA), LPS inflammatory pain models, the chronic constriction injury neuropathic pain model and the tail flick and hot plate acute thermal nociceptive assays. Additional studies examined the locus of action of GAT107 and immunohistochemical markers in the dorsal horn of the spinal cord in the CFA model.

KEY RESULTS

Complementary pharmacological and genetic approaches confirmed that the dose-dependent antinociceptive effects of GAT107 were mediated through α7 nAChR. However, GAT107 was inactive in the tail flick and hot plate assays. In addition, GAT107 blocked conditioned place aversion elicited by acetic acid injection. Furthermore, intrathecal, but not intraplantar, injections of GAT107 reversed nociception in the CFA model, suggesting a spinal component of action. Immunohistochemical evaluation revealed an increase in the expression of astrocyte-specific glial fibrillary acidic protein and phosphorylated p38MAPK within the spinal cords of mice treated with CFA, which was attenuated by intrathecal GAT107 treatment. Importantly, GAT107 did not elicit motor impairment and continued to produce antinociceptive effects after subchronic administration in both phases of the formalin test.

CONCLUSIONS AND IMPLICATIONS

Collectively, these results provide the first proof of principle that α7 ago-PAMs represent an effective pharmacological strategy for treating inflammatory and neuropathic pain.

Oleo-gum-resin suppresses indomethacin-induced elevation of proinflammatory biomarker and gastric injury in rats

AIM

To investigate the mucosal protective effect and the mechanisms of action of the anti-ulcer drug oleo-gum-resin in gastric injury induced by indomethacin in rats.

METHODS

Gastric mucosal injury was induced in male Wistar rats by oral administration of indomethacin at a dose of 60 mg/kg. One hour before indomethacin treatment, animals were orally pretreated with oleo-gum-resin at doses of 125 mg/kg, 250 mg/kg or 500 mg/kg. Four hours after indomethacin administration, the animals were sacrificed and their stomachs were rapidly removed and processed for the evaluation of gastric mucosal damage and the determination of the concentrations of TNF-α, IL-1β, IL-6, NO, PGE2 and myeloperoxidase (MPO) in mucosal tissues.

RESULTS

Linear hemorrhagic mucosal lesions were observed primarily in the glandular stomach 4 h after oral administration of indomethacin. Pretreatment with oleo-gum-resin markedly reduced the number and severity of gastric lesions in a dose dependent manner. The mucosal concentrations of TNF-α, IL-1β, IL-8, NO, and MPO, which indicates the degree of mucosal infiltration by neutrophils, increased concomitantly with the occurrence of gastric injury in the indomethacin administered rats while PGE2 levels inhibited in this group. Pretreatment with oleo-gum-resin significantly decreased the levels of these inflammatory factors in gastric tissue elicited by indomethacin and enhanced the PGE2 levels.

CONCLUSION

The mucosal protective effects afforded by oleo-gum-resin on gastric injury induced by indomethacin are mediated by inhibition of mucosal proinflammatory cytokine production and neutrophil infiltration, leading to suppression of mucosal inflammation and subsequent tissue destruction.

Expression and pharmacological modulation of visceral pain-induced conditioned place aversion in mice

Pain encompasses both a sensory as well as an affective dimension and these are differentially processed in the brain and periphery. It is therefore important to develop animal models to reflect the non-reflexive assays in pain. In this study, we compared effects of the mu opioid receptor agonist morphine, the nonsteroidal anti-inflammatory drug ketoprofen and the kappa receptor opioid agonist U50,488H and antagonist JDTic on acetic acid-induced stretching and acetic acid-induced aversion in the condition place aversion (CPA) test in male ICR mice. Intraperitoneal administration of acetic acid (0.32-1%) was equipotent in stimulating stretching and CPA. Ketoprofen, morphine and U50,488H all inhibited the acid-induced stretching. Ketoprofen and morphine also blocked the acid-induced CPA but U50,488H failed to do so. The reversal ability of ketoprofen and morphine on acid-induced CPA is unique to pain-stimulated place aversion since these drugs failed to reduce non-noxious LiCl-induced CPA. Overall, this study characterized and validated a preclinical mouse model of pain-related aversive behavior that can be used to assess genetic and biological mechanisms of pain as well as improving the predictive validity of preclinical studies on candidate analgesics.

The flavonoid, rutin, ameliorates neurodegeneration in the retina of diabetic rats (CAM1P.164)

Diabetic retinopathy remains the leading cause of blindness worldwide. Dietary flavonoid, rutin may protect the diabetes induced retinal damage. The purpose of this study was to examine the ameliorative effect of rutin on diabetic rat retina through neurotrophic, inflammatory and immunological parameters. Diabetes was induced in male Wistar rats by streptozotocin (65mg/kg). Rutin (100mg/kg) was orally administered to normal and diabetic rats after two weeks of diabetes induction and continued for five weeks. After treatments, retinas were isolated and analyzed for potential neuroinflammatory and immunological markers. Our results indicate that the reduced level of brain derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in the diabetic retina were significantly improved by rutin. Increased levels of soluble intracellular adhesion molecule (sICAM-1) and monocyte chemotactic protein (MCP-1) in the diabetic retinas were significantly attenuated to normal level by rutin. Reduced level of GSH in diabetic retina was increased and the increased level of TBARS in the diabetic retina was significantly decreased by rutin administration. The increased level of caspase-3, and decreased level of Bcl-2 in diabetic retina were significantly ameliorated to normal levels by rutin. These results suggest the effectiveness of rutin in protection of diabetic induced damage to the retina by maintaining neurotrophic support, and antioxidants levels.

{alpha}7-nAChR-mediated suppression of hyperexcitability of colonic dorsal root ganglia neurons in experimental colitis

Controlled clinical trials of nicotine transdermal patch for treatment of ulcerative colitis have been shown to improve histological and global clinical scores of colitis. Here we report that nicotine (1 microM) suppresses in vitro hyperexcitability of colonic dorsal root ganglia (DRG) (L(1)-L(2)) neurons in the dextran sodium sulfate (DSS)-induced mouse model of acute colonic inflammation. Nicotine gradually reduced regenerative multiple-spike action potentials in colitis mice to a single action potential. Nicotine's effect on hyperexcitability of inflamed neurons was blocked in the presence of an alpha(7)-nicotinic acetylcholine receptor (nAChR) antagonist, methyllicaconitine, while choline, the alpha(7)-nAChR agonist, induced a similar effect to that of nicotine. Consistent with these findings, nicotine failed to suppress hyperexcitability in colonic DRG neurons from DSS-treated alpha(7) knockout mice. Furthermore, colonic DRG neurons from DSS-treated alpha(7) knockout mice were characterized by lower rheobase (10 +/- 5 vs. 77 +/- 13 pA, respectively) and current threshold (28 +/- 4 vs. 103 +/- 8 pA, respectively) levels than DSS-treated C57BL/J6 mice. An interesting observation of this study is that 8 of 12 colonic DRG (L(1)-L(2)) neurons from control alpha(7) knockout mice exhibited multiple-spike action potential firing while no wild-type neurons did. Overall, our findings suggest that nicotine at low 1 microM concentration suppresses in vitro hyperexcitability of inflamed colonic DRG neurons in a mouse model of acute colonic inflammation via activation of alpha(7)-nAChRs.