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J. Neurochem. (2011) 119, 594-603. Abstract Painful neuropathy is one of the most serious complications of diabetes and remains difficult to treat. The muscarinic acetylcholine receptor (mAChR) agonists have a profound analgesic effect on painful diabetic neuropathy. Here we determined changes in T-type and high voltage-activated Ca2+ channels (HVACCs) and their regulation by mAChRs in dorsal root ganglion (DRG) neurons in a rat model of diabetic neuropathy. The HVACC currents in large neurons, T-type currents in medium and large neurons, the percentage of small DRG neurons with T-type currents, and the Cav3.2 mRNA level were significantly increased in diabetic rats compared with those in control rats. The mAChR agonist oxotremorine-M significantly inhibited HVACCs in a greater proportion of DRG neurons with and without T-type currents in diabetic than in control rats. In contrast, oxotremorine-M had no effect on HVACCs in small and large neurons with T-type currents and in most medium neurons with T-type currents from control rats. The M2 and M4 antagonist himbacine abolished the effect of oxotremorine-M on HVACCs in both groups. The selective M4 antagonist muscarinic toxin-3 caused a greater attenuation of the effect of oxotremorine-M on HVACCs in small and medium DRG neurons in diabetic than in control rats. Additionally, the mRNA and protein levels of M4, but not M2, in the DRG were significantly greater in diabetic than in control rats. Our findings suggest that diabetic neuropathy potentiates the activity of T-type and HVACCs in primary sensory neurons. M4 mAChRs are up-regulated in DRG neurons and probably account for increased muscarinic analgesic effects in diabetic neuropathic pain. [ABSTRACT FROM AUTHOR]

Abstract: ω-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) enhances cognitive functions; however, the underlying molecular mechanism remains unclear. Compelling evidence suggests that the endocannabinoid/endovanilloid systems play a pivotal role in regulating cognitive function. Thus, to correlate the effect of DHA on cognitive performance with the expression of endocannabinoid and endovanilloid receptors, we supplemented the diet of rats with DHA and performed in vitro experiments that focused on the endocannabinoid/endovanilloid receptors. We found that in vivo supplementation with an appropriate dose of DHA (150 or 300mg/kg/d) significantly improved learning and memory but that a higher intake (600mg/kg/d) increased the risk of memory impairment. In addition, we found that some subtypes of endocannabinoid/endovanilloid receptors (cannabinoid [CB] and transient receptor potential vanilloid [TRPV] receptors) were regulated in vitro by different concentrations of DHA in primary hippocampal neuron culture medium. Real-time polymerase chain reaction and western blot analysis showed that expression of both CB1 and TRPV1 was upregulated in a dose-dependent manner and reached a maximum level at 30μmol/L (CB1) and 60μmol/L (TRPV1) DHA. However, TRPV2 expression was downregulated in a dose-dependent fashion, and the peak of TRPV2 suppression was observed at 60μmol/L. The dose-dependent effects of DHA on the expression of these receptors were well correlated with DHA''s effect on spatial memory. Meanwhile, CB2, TRPV3, and TRPV4 expressions were not altered at diverse concentrations of DHA. We concluded that some subtypes of endocannabinoid/endovanilloid receptors might be involved in enhanced spatial memory induced by DHA supplementation. [Copyright &y& Elsevier]

Aim: To investigate the effect of capsaicin on IA and IK in cultured rat trigeminal ganglion (TG) neurons., Methods: Whole-cell patch clamp technique was used to record the IA and IK before and after capsaicin perfusion at different concentrations., Results: In capsaicin-sensitive (CS) neurons, capsaicin was shown to selectively inhibit IA in dose-dependent manner, the IC50 was 0.99 micromol x L(-1). Yet capsaicin showed no inhibitory effect on IK, capsaicin (10 micromol x L(-1)) only slightly inhibited IK by 13.2%. In capsaicin-insensitive (CIS) neurons, capsaicin (1 micromol x L(-1)) showed no significant inhibitory effect on IA and IK, capsaicin (10 micromol x L(-1)) only slightly inhibited IA and IK by 16.8% and 15.3%, respectively. Neither 1 micromol x L(-1) nor 10 micromol x L(-1) capsaicin showed effect on the G-V curve of IA and IK., Conclusion: Capsaicin was found to selectively inhibit the IA current in CS neurons, and this effect may contribute to hyperalgesia when capsaicin was first used.