College of Medicine and Public Health, Flinders University, Adelaide, South Australia, Australia.
Department of Surgery, Flinders Medical Centre, Bedford Park, South Australia, Australia.
Physiol Rep. 2023 Jan;11(1):e15567. doi: 10.14814/phy2.15567.
The speed of pellet propulsion through the isolated guinea pig distal colon in vitro significantly exceeds in vivo measurements, suggesting a role for inhibitory mechanisms from sources outside the gut. The aim of this study was to investigate the effects of sympathetic nerve stimulation on three different neurogenic motor behaviors of the distal colon: transient neural events (TNEs), colonic motor complexes (CMCs), and pellet propulsion. To do this, segments of guinea pig distal colon with intact connections to the inferior mesenteric ganglion (IMG) were set up in organ baths allowing for simultaneous extracellular suction electrode recordings from smooth muscle, video recordings for diameter mapping, and intraluminal manometry. Electrical stimulation (1-20 Hz) of colonic nerves surrounding the inferior mesenteric artery caused a statistically significant, frequency-dependent inhibition of TNEs, as well as single pellet propulsion, from frequencies of 5 Hz and greater. Significant inhibition of CMCs required stimulation frequencies of 10 Hz and greater. Phentolamine (3.6 μM) abolished effects of colonic nerve stimulation, consistent with a sympathetic noradrenergic mechanism. Sympathetic inhibition was constrained to regions with intact extrinsic nerve pathways, allowing normal motor behaviors to continue without modulation in adjacent extrinsically denervated regions of the same colonic segments. The results demonstrate differential sensitivities to sympathetic input among distinct neurogenic motor behaviors of the colon. Together with findings indicating CMCs activate colo-colonic sympathetic reflexes through the IMG, these results raise the possibility that CMCs may paradoxically facilitate suppression of pellet movement in vivo, through peripheral sympathetic reflex circuits.
颗粒推进通过离体豚鼠远端结肠的速度明显超过体内测量值，这表明肠道外来源的抑制机制起作用。本研究的目的是研究交感神经刺激对远端结肠三种不同神经源性运动行为的影响：瞬态神经事件（TNEs）、结肠运动复合波（CMCs）和颗粒推进。为此，建立了具有完整肠系膜下神经节（IMG）连接的豚鼠远端结肠段，允许同时进行平滑肌的细胞外抽吸电极记录、视频记录以进行直径映射和腔内测压。围绕肠系膜下动脉的结肠神经的电刺激（1-20 Hz）引起 TNEs 和单个颗粒推进的统计学上显著的、频率依赖性抑制，从 5 Hz 及更高频率开始。CMC 的显著抑制需要 10 Hz 及更高的刺激频率。酚妥拉明（3.6 μM）消除了结肠神经刺激的作用，这与交感去甲肾上腺素能机制一致。交感抑制仅限于具有完整外生神经通路的区域，允许相同结肠段的相邻外生去神经区域不受调制而继续正常运动行为。结果表明，不同的神经源性运动行为对交感输入的敏感性不同。与 CMCs 通过 IMG 激活结肠-结肠交感反射的发现一起，这些结果提出了 CMCs 可能通过周围交感反射回路在体内促进颗粒运动抑制的可能性。
