Muscle sympathetic single units can respond differentially to stress but whether these responses are linked to the degree of sympathoexcitation is unclear. Fifty-three muscle sympathetic single units (microneurography) were recorded in 17 participants (8 women; 24±3 yr). Five 40-second bouts of 10% static handgrip were performed during a 10 min forearm ischemia to progressively increase metabolite accumulation. Each static handgrip was separated by a 75 sec ischemic rest (post-exercise circulatory occlusion [PECO]) to assess the isolated action of the muscle metaboreflex. During each set of PECO, individual single units were classified as activated, non-responsive, or inhibited if the spike frequency was above, within, or below the baseline variability, respectively. From sets 1-5 of PECO, the proportion of single units with activated (34, 45, 68, 87, 89%), non-responsive (43, 44, 23, 7, 9%), or inhibited (23, 11, 9, 6, 2%) responses changed (P<0.001) as total muscle sympathoexcitation increased. 51/53 (96%) single units were activated in at least one set of PECO, 16 (31%) initially inhibited prior to activation. This response pattern delayed the activation onset compared to non-inhibited units (set 3±1 vs. 2±1, P<0.001). Once activated, the spike frequency rate-of-rise was similar (8.5±6.5 vs. 7.1±6.0 spikes/min/set, P=0.48). Muscle sympathetic single-unit firing demonstrated differential control during muscle metaboreflex activation. Single units that were initially inhibited during progressive metaboreflex activation were capable of being activated in later sets. These findings reveal that single-unit activity is influenced by convergent neural inputs (i.e. both inhibitory and excitatory), which yield heterogenous single-unit activation thresholds.

中文翻译：

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年轻健康成人渐进性肌肉代谢反射激活期间的肌肉交感神经单单位反应模式。

肌肉交感神经单个单位对压力的反应不同，但这些反应是否与交感神经兴奋程度有关尚不清楚。在 17 名参与者（8 名女性；24±3 岁）中记录了 53 个肌肉交感神经单单元（显微神经成像）。在 10 分钟的前臂缺血期间进行了 5 次 40 秒的 10% 静态手柄，以逐渐增加代谢物的积累。每个静态手柄被 75 秒的缺血性休息（运动后循环闭塞 [PECO]）隔开，以评估肌肉代谢反射的孤立作用。在每组 PECO 期间，如果尖峰频率高于、在或低于基线变异性，则单独的单个单元被分类为激活、无响应或抑制。从 PECO 的 1-5 组中，单个单元被激活的比例（34、45、68、87, 89%)、无反应 (43, 44, 23, 7, 9%) 或抑制 (23, 11, 9, 6, 2%) 反应随着总肌肉交感神经兴奋的增加而改变 (P<0.001)。51/53 (96%) 单个单位在至少一组 PECO 中被激活，16 个 (31%) 在激活前最初被抑制。与非抑制单位相比，这种响应模式延迟了激活开始（设置为 3±1 对 2±1，P<0.001）。一旦激活，尖峰频率上升率相似（8.5±6.5 vs. 7.1±6.0 尖峰/分钟/组，P=0.48）。肌肉交感神经单单元射击在肌肉代谢反射激活过程中表现出不同的控制。在渐进性代谢反射激活过程中最初被抑制的单个单元能够在以后的组中被激活。这些发现表明，单一单位的活动受到会聚神经输入的影响（即