Compound 48/80 blocks transmission and increases the excitability of ganglion neurons

Curcumin inhibits the pruritus in mice through mast cell MrgprB2 receptor

BACKGROUND

Curcumin is a diketone compound extracted from the rhizomes of some plants in the Zingiberaceae and Araceae family. It possesses a variety of biological activities, including antioxidant, anti-inflammatory and anti-cancer properties. However, the cellular and molecular antipruritic mechanisms of curcumin remain to be explored.

OBJECTIVE

Our objective was to study the role of curcumin in pruritus and determine whether its antipruritic effect is related to MrgprB2 receptor.

METHODS

The effect of curcumin on pruritus in mice was examined by scratching behavior test. The antipruritic mechanism of curcumin was explored by using transgenic mice (MrgprB2^-/- mice, MrgprB2Cre^Td/tomato mice), histological analysis, western blot and immunofluorescence. In addition, the relationship between curcumin and MrgprB2/X2 receptor was studied in vitro by using calcium imaging, plasmid transfection and molecular docking RESULTS: In the current study, we found that curcumin had obvious antipruritic effect. Its antipruritic effect was related to the regulation of MrgprB2 receptor activation and mast cells tryptase release. In vitro, mouse peritoneal mast cells activated by compound 48/80 could be inhibited by curcumin. In addition, curcumin was also found to suppress the calcium flux in MrgprX2 or MrgprB2-overexpression HEK cells induced by compound 48/80, substance P, and PAMP 9-20, displaying the specific relation with the MrgprB2/X2 receptor. Moreover, molecular docking results showed that curcumin had affinity to MrgprX2 protein.

CONCLUSIONS

Overall, these results indicated that curcumin has the potential to treat pruritus induced by mast cell MrgprB2 receptor.

The mast cell degranulator compound 48/80 directly activates neurons

Background

Compound 48/80 is widely used in animal and tissue models as a “selective” mast cell activator. With this study we demonstrate that compound 48/80 also directly activates enteric neurons and visceral afferents.

Methodology/Principal Findings

We used in vivo recordings from extrinsic intestinal afferents together with Ca⁺⁺ imaging from primary cultures of DRG and nodose neurons. Enteric neuronal activation was examined by Ca⁺⁺ and voltage sensitive dye imaging in isolated gut preparations and primary cultures of enteric neurons. Intraluminal application of compound 48/80 evoked marked afferent firing which desensitized on subsequent administration. In egg albumen-sensitized animals, intraluminal antigen evoked a similar pattern of afferent activation which also desensitized on subsequent exposure to antigen. In cross-desensitization experiments prior administration of compound 48/80 failed to influence the mast cell mediated response. Application of 1 and 10 µg/ml compound 48/80 evoked spike discharge and Ca⁺⁺ transients in enteric neurons. The same nerve activating effect was observed in primary cultures of DRG and nodose ganglion cells. Enteric neuron cultures were devoid of mast cells confirmed by negative staining for c-kit or toluidine blue. In addition, in cultured enteric neurons the excitatory action of compound 48/80 was preserved in the presence of histamine H₁ and H₂ antagonists. The mast cell stabilizer cromolyn attenuated compound 48/80 and nicotine evoked Ca⁺⁺ transients in mast cell-free enteric neuron cultures.

Conclusions/Significance

The results showed direct excitatory action of compound 48/80 on enteric neurons and visceral afferents. Therefore, functional changes measured in tissue or animal models may involve a mast cell independent effect of compound 48/80 and cromolyn.

Muscarinic transmission decreases the number of SIF cells demonstrating catecholamine histofluorescence in rat superior cervical ganglia

Preganglionic electrical stimulation of the cervical sympathetic trunk to the rat superior cervical ganglia produced a mean reduction in the number of visible small intensely fluorescent (SIF) cells demonstrating catecholamine histofluorescence to 32% of the unstimulated contralateral control. The reduction in the number of catecholamine-positive SIF cells required the presence of specific blockers of catecholamine uptake and synthesis and was dependent on normal synaptic transmission. No change in the number of catecholamine-positive SIF cells was observed when ganglionic transmission occurred in solutions containing both hexamethonium and atropine or with atropine alone (97% of the unstimulated control). Furthermore, preganglionic stimulation in the presence of high magnesium/low calcium solutions, which effectively blocked synaptic transmission, prevented the stimulation-induced decrease in the number of catecholamine-positive SIF cells. Prolonged antidromic stimulation of the internal carotid nerve only reduced the number of catecholamine-positive SIF cells to 75% of the unstimulated contralateral control. These results suggest that preganglionic synaptic impulses can induce the release of catecholamines from SIF cells via muscarinic receptor activation. Furthermore, the necessity for pharmacological intervention of uptake and synthesis blockers of catecholamines in order to detect the synaptically-induced reduction in the number of catecholamine-positive SIF cells, suggests that synaptic transmission also modulates the synthesis of catecholamines in SIF cells within the rat superior cervical ganglia.