A class of Group III muscle afferent neurons has branching sensory terminals in the connective tissue between layers of mouse abdominal muscles (“CT3 muscle afferents”). These sensory endings are both mechanosensitive and metabosensitive. In the present study, responses of CT3 afferents to lactate ions and changes in temperature were recorded. Raising muscle temperature from 32.7°C to 37°C had no consistent effects on CT3 afferent basal firing rate or responses to either von Frey hair stimulation or to an applied load. Superfusion with lactate ions (15 mM, pH 7.4) was associated with an increase in firing from 6 ± 0.7 Hz to 11.7 ± 6.7 Hz (14 units, n = 13, P < 0.05, P = 0.0484) but with considerable variability in the nature and latency of response. Reducing the concentration of extracellular divalent cations, which mimicked the chelating effects of lactate, did not increase firing. Raised concentrations of divalent cations (to compensate for chelation) did not block excitatory effects of lactate on CT3 afferents, suggesting that effects via ASIC3 were not involved. Messenger RNA for the G-protein coupled receptor, hydroxyl carboxylic acid receptor 1 (HCAR1) was detected in dorsal root ganglia and HCAR1-like immunoreactivity was present in spinal afferent nerve cell bodies retrogradely labeled from mouse abdominal muscles. HCAR1-like immunoreactivity was also present in axons in mouse abdominal muscles. This raises the possibility that some effects of lactate on group III muscle afferents may be mediated by HCAR1.

一类III类肌肉传入神经元在小鼠腹部肌肉（“ CT3肌肉传入”）之间的结缔组织中具有分支的感觉末端。这些感觉的结局是机械敏感的和代谢敏感的。在本研究中，记录了CT3传入对乳酸离子的反应和温度的变化。将肌肉温度从32.7°C升高到37°C不会对CT3传入的基础射击频率或对von Frey毛发刺激或施加的负荷产生反应。乳酸离子（15 mM，pH 7.4）的超融合与击发从6±0.7 Hz增加到11.7±6.7 Hz（14个单位，ñ = 13 P <0.05， P= 0.0484），但响应的性质和潜伏期存在很大差异。降低模仿乳酸盐的螯合作用的细胞外二价阳离子的浓度并没有增加放电。提高二价阳离子的浓度（以补偿螯合）并没有阻止乳酸对CT3传入分子的兴奋作用，这表明这种作用通过没有涉及ASIC3。在背根神经节中检测到G蛋白偶联受体，羟基羧酸受体1（HCAR1）的Messenger RNA，并且从小鼠腹部肌肉逆行标记的脊髓传入神经细胞体中存在HCAR1样的免疫反应性。小鼠腹部肌肉的轴突中也存在类似HCAR1的免疫反应性。这增加了乳酸对III组肌肉传入神经的某些作用可能由HCAR1介导的可能性。