Abstract
Skeletal metastases are frequently accompanied by chronic pain that is mechanoceptive in nature and not easily managed by available therapies. The peripheral sensory profile of primary afferents responsible for transmitting the pain-related messages from cancerous bone to central sites is investigated here. We imaged thousands of primary sensory dorsal root ganglion neurons in vivo in healthy (sham-operated) and cancer-induced bone pain (CIBP) rats in order to analyse and compare their function. Utilising Markov Cluster Analysis we identified distinct clusters of primary afferent responses to limb compression and position. In CIBP rats, three times as many sensory afferents responded to knee compression in the leg ipsilateral to the tumour compared to sham-operated rats. We present evidence that the observed increase in sensory afferent response was not due to increased individual afferent activity but rather represents activation of ‘silent’ nociceptors, whose origin we propose is largely from outside of the bone.
Footnotes
We have updated the analysis of neuronal responses applying Markov Cluster Analysis. This largely unsupervised method of clustering large longitudinal data was adopted here, for the first time, in order to cluster neuronal responses to defined stimuli. It revealed several primary afferent types responding differently to mechanical forces applied to the peripheral receptive field. Therefore, the emphasis of the manuscript in now on the impact of bone cancer on the peripheral encoding of mechanical pressure stimuli, rather than the mechanisms underlying 'unsilencing' of silent nociceptors. We believe, that a more thorough analysis of the involvement of Piezo2 mechanosensor needs to be performed (i.e. using murine KO for the channel, rather than presented in the earlier version of the manuscript block with the spider toxin) and it can be a direction for future studies. Advillin data has been removed and will constitute a separate article focusing on the role of Advillin negative afferents. The ATF3 studies will be included in the Advillin paper. Manuscript was modified accordingly given the changes made.
