College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia.
Am J Physiol Gastrointest Liver Physiol. 2022 Aug 1;323(2):G71-G87. doi: 10.1152/ajpgi.00055.2022. Epub 2022 May 3.
Colonic motor complexes (CMCs) are a major neurogenic activity in guineapig distal colon. The identity of the enteric neurons that initiate this activity is not established. Specialized intrinsic primary afferent neurons (IPANs) are a major candidate. We aimed to test this hypothesis. To do this, segments of guineapig distal colon were suspended vertically in heated organ baths and propulsive forces acting on a pellet inside the lumen were recorded by isometric force transducer while pharmacological agents were applied to affect IPAN function. In the absence of drugs, CMCs acted periodically on the pellet, generating peak propulsive forces of 12.7 ± 5 g at 0.56 ± 0.22 cpm, lasting 49 ± 17 s (215 preparations; = 60). Most but not all CMCs were abolished by nicotinic receptor blockade to inhibit fast excitatory synaptic transmission (50/62 preparations; = 25). Remarkably, CMCs inhibited by hexamethonium were restored by a pharmacological strategy that aimed to enhance IPAN excitability. Thus, CMCs were restored by increased smooth muscle tension (using BAY K8644, bethanechol or carbachol) and by IPAN excitation using phorbol dibutyrate; NK3 receptor agonist, senktide; and partially by αCGRP. The IPAN inhibitor, 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazole-2-one (DCEBIO), decreased CMC frequency. CGRP, but not NK3-receptor antagonists, decreased CMC frequency in naive preparations. Finally, CMCs were blocked by tetrodotoxin, and this was not reversed by any drugs listed above. These results support a major role for IPANs that does not require fast synaptic transmission, in the periodic initiation of neurogenic propulsive contractions. Endogenous CGRP plays a role in determining CMC frequency, whereas further unidentified signaling pathways may determine their amplitude and duration. The colonic motor complex (CMC) initiates propulsion in guinea pig colon. Here, CMCs evoked by an intraluminal pellet were restored during nicotinic receptor blockade by pharmacological agents that directly or indirectly enhance intrinsic primary afferent neuron (IPAN) excitability. IPANs are the only enteric neuron in colon that contain CGRP. Blocking CGRP receptors decreased CMC frequency, implicating their role in CMC initiation. The results support a role for IPANs in the initiation of CMCs.
结肠运动复合波（CMCs）是豚鼠远端结肠的主要神经源性活动。启动这种活动的肠神经元的身份尚未确定。专门的内在初级传入神经元（IPANs）是主要的候选者。我们旨在验证这一假设。为此，将豚鼠远端结肠的节段垂直悬挂在加热的器官浴中，并通过等力换能器记录腔内颗粒上的推进力，同时应用药物来影响 IPAN 功能。在没有药物的情况下，CMC 周期性地作用于颗粒，产生 12.7±5g 的峰值推进力，频率为 0.56±0.22cpm，持续 49±17s（215 个标本； =60）。大多数 CMC 被烟碱受体阻断剂阻断，但不是全部（50/62 个标本； =25）。值得注意的是，被六烃季铵抑制的 CMC 通过旨在增强 IPAN 兴奋性的药理学策略得以恢复。因此，通过增加平滑肌张力（使用 BAY K8644、bethanechol 或 carbachol）和使用佛波酯、NK3 受体激动剂 senktide 以及部分使用 αCGRP 来恢复被六烃季铵抑制的 CMC。IPAN 抑制剂 5,6-二氯-1-乙基-1,3-二氢-2H-苯并咪唑-2-酮（DCEBIO）降低了 CMC 的频率。在未处理的标本中，CGRP 而非 NK3 受体拮抗剂降低了 CMC 的频率。最后，CMC 被河豚毒素阻断，上述任何药物均不能逆转。这些结果支持 IPAN 在周期性启动神经源性推进收缩中起主要作用，而不需要快速突触传递。内源性 CGRP 在确定 CMC 频率中起作用，而进一步未确定的信号通路可能决定其幅度和持续时间。结肠运动复合波（CMC）启动豚鼠结肠的推进。在这里，通过腔内颗粒诱发的 CMC 在烟碱受体阻断后，通过直接或间接增强内在初级传入神经元（IPAN）兴奋性的药物得以恢复。IPAN 是结肠中唯一含有 CGRP 的肠神经元。阻断 CGRP 受体降低了 CMC 的频率，提示其在 CMC 启动中的作用。结果支持 IPAN 在 CMC 启动中的作用。
