Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Ontario M5G 0A4, Canada.
Institute of Biomedical Engineering, University of Toronto, Toronto, Ontario M5S 3G9, Canada.
J Neurosci. 2024 Nov 13;44(46):e1252242024. doi: 10.1523/JNEUROSCI.1252-24.2024.
Somatosensory coding in rodents has been mostly studied in the whisker system and hairy skin, whereas the function of low-threshold mechanoreceptors (LTMRs) in the rodent glabrous skin has received scant attention, unlike in primates where the glabrous skin has been the focus. The relative activation of different LTMR subtypes carries information about vibrotactile stimuli, as does the rate and temporal patterning of LTMR spikes. Rate coding depends on the probability of a spike occurring on each stimulus cycle (reliability), whereas temporal coding depends on the timing of spikes relative to the stimulus cycle (precision). Using in vivo extracellular recordings in male rats and mice of either sex, we measured the reliability and precision of LTMR responses to tactile stimuli including sustained pressure and vibration. Similar to other species, rodent LTMRs were separated into rapid-adapting (RA) or slow-adapting based on their response to sustained pressure. However, unlike the dichotomous frequency preference characteristic of RA1 and RA2/Pacinian afferents in other species, rodent RAs fell along a continuum. Fitting generalized linear models to experimental data reproduced the reliability and precision of rodent RAs. The resulting model parameters highlight key mechanistic differences across the RA spectrum; specifically, the integration window of different RAs transitions from wide to narrow as tuning preferences across the population move from low to high frequencies. Our results show that rodent RAs can support both rate and temporal coding, but their heterogeneity suggests that coactivation patterns play a greater role in population coding than for dichotomously tuned primate RAs.
在啮齿动物中，躯体感觉编码主要在胡须系统和有毛皮肤中进行研究，而低阈值机械感受器（LTMR）在啮齿动物无毛皮肤中的功能则很少受到关注，与灵长类动物形成鲜明对比，灵长类动物的无毛皮肤一直是研究的重点。不同 LTMR 亚型的相对激活携带有关振动触觉刺激的信息，就像 LTMR 尖峰的频率和时间模式一样。速率编码取决于每个刺激周期发生尖峰的概率（可靠性），而时间编码取决于相对于刺激周期的尖峰时间（精度）。我们使用雄性大鼠和小鼠的体内细胞外记录，测量了 LTMR 对触觉刺激（包括持续压力和振动）的反应的可靠性和精度。与其他物种类似，根据对持续压力的反应，啮齿动物的 LTMR 被分为快速适应（RA）或缓慢适应。然而，与其他物种中 RA1 和 RA2/帕西尼传入纤维的二元频率偏好特征不同，啮齿动物的 RAs 沿着一个连续体分布。将广义线性模型拟合到实验数据中，再现了啮齿动物 RAs 的可靠性和精度。由此产生的模型参数突出了 RA 谱中关键的机制差异；具体来说，不同 RAs 的整合窗口从宽变窄，而群体的调谐偏好从低频向高频移动。我们的研究结果表明，啮齿动物的 RAs 可以支持速率和时间编码，但它们的异质性表明，与二元调谐的灵长类动物 RAs 相比，共同激活模式在群体编码中起着更大的作用。
