Inhibition of visceral sensation by cannabinoids in the gastrointestinal tract

来自胃肠道的内脏感觉始于肠壁内的神经末梢，其细胞体位于背根神经节（DRG）。虽然大麻素已经使用了几个世纪来调节感觉，但尚不清楚它们是否调节胃肠道传入神经，或者它们对内脏感觉的影响是否在中枢神经系统中介导。这是高度相关的，因为内源性大麻素是在胃肠道中合成的，这些大麻素可能在平衡这些神经的兴奋方面发挥重要作用。我们的长期目标是确定大麻素受体单独或与其他受体信号联合抑制胃肠道传入神经的机制。我们的初步数据表明，大麻素1受体（CB1R）减少胃肠道传入神经的感觉信号。由于阿片样物质是胃肠道传入神经的最佳表征抑制剂，我们还研究了大麻素和阿片样物质受体在这些神经上是否存在相互作用。有趣的是，CB1R激动剂和mu阿片受体激动剂的亚阈浓度组合抑制了这些神经。基于这些发现，我们的假设是大麻素受体的细胞内信号机制与阿片受体的细胞内信号机制汇合，协同抑制结肠传入神经。为了验证这一假设，我们有两个目标：1)表征大麻素受体对外源性结肠传入神经的抑制信号机制。在这里，我们将利用结肠传入神经的离体细胞外记录和结肠投射DRG神经元的膜片钳记录来进一步探讨CB1R和CB2R在这些神经中的作用。我们将使用药理学和分子方法来研究哪些细胞内信号通路参与了它们的抑制作用。2)确定大麻素和阿片受体同时激活后结肠传入神经协同抑制所需的信号机制。在这里，我们将使用电生理和免疫组织化学技术来检查受体在结肠传入神经上的共表达。我们将使用药理学和分子方法来阐明在受体同时激活后协同作用所必需的细胞内途径。这些研究将表征大麻素受体在胃肠道传入神经上的信号传导，并推进我们对大麻素和阿片受体如何相互作用以调节内脏感觉的理解。此外，我们的发现可能会激发商业机会，开发专门针对胃肠道传入神经的治疗方法。此外，该研究项目将培养多名本科生和研究生，以及一名博士后。他们在培训期间获得的技能将转移到他们从事的任何职业中，使他们能够为加拿大的经济发展做出贡献。

Visceral sensation from the gastrointestinal (GI) tract begins with nerve terminals within the wall of the gut whose cell bodies reside in the dorsal root ganglion (DRG). While cannabinoids have been used for centuries to modulate sensation, it is unknown whether they modulate GI afferent nerves or if their effects on visceral sensation are mediated in the CNS. This is highly relevant as endogenous cannabinoids are synthesized in the GI tract and these may play an important a role in counterbalancing excitation of these nerves. Our long-term goal is to identify mechanisms how cannabinoid receptors, alone or in combination with signaling of other receptors, inhibit GI afferent nerves. Our preliminary data demonstrates that a cannabinoid 1 receptor (CB1R) reduces the sensory signaling of GI afferent nerves. Since opioids are the best characterized inhibitors of GI afferent nerves, we also investigated whether there was an interaction of cannabinoid and opioid receptors on these nerves. Interestingly, a combination of subthreshold concentrations of a CB1R agonist and a mu opioid receptor agonist inhibited these nerves. Based on these findings, our hypothesis is that intracellular signaling mechanisms of cannabinoid receptors converge with intracellular signaling mechanisms of opioid receptors to synergistically inhibit colonic afferent nerves. To test this hypothesis, we have two objectives: 1)Characterize the inhibitory signaling mechanisms of cannabinoid receptors on extrinsic colonic afferent nerves. Here we will employ ex vivo extracellular recordings of colon afferent nerves and patch clamp recordings of colon projecting DRG neurons to further explore the role of CB1R and CB2R on these nerves. We will use pharmacological and molecular approaches to investigate which intracellular signaling pathway(s) is involved in their inhibitory effect. 2)Determine signaling mechanisms necessary for synergistic inhibition of colonic afferent nerves following simultaneous activation of cannabinoid and opioid receptors. Here we will use electrophysiological and immunohistochemical techniques to examine the co-expression of the receptors on colon afferent nerves. We will use pharmacological and molecular approaches to elucidate intracellular pathway(s) necessary for synergism following simultaneous activation of the receptors. These studies will characterize cannabinoid receptor signaling on GI afferent nerves as well as advance our understanding of how cannabinoid and opioid receptors interact to modulate visceral sensation. Furthermore, our findings may spark commercial opportunities to develop therapeutics that specifically target GI afferent nerves. In addition, this research program will train multiple undergraduate students and graduate students, and a post-doctoral fellow. The skills obtained during their training will be transferable to employment to any career they pursue enabling them to contribute to Canadian economic development.