Lack of evidence for ectopic sprouting of genetically labeled A beta touch afferents in inflammatory and neuropathic trigeminal pain

作者：Zhang Yi; Chen Yong; Liedtke Wolfgang; Wang Fan^*

来源：Molecular Pain, 2015, 11: 18.

DOI：10.1186/s12990-015-0017-2

• Mechanical allodynia
• A beta fibers
• Sprouting
• Inflammatory pain
• Neuropathic pain

Background: Mechanical and in particular tactile allodynia is a hallmark of chronic pain in which innocuous touch becomes painful. Previous cholera toxin B (CTB)-based neural tracing experiments and electrophysiology studies had suggested that aberrant axon sprouting from touch sensory afferents into pain-processing laminae after injury is a possible anatomical substrate underlying mechanical allodynia. This hypothesis was later challenged by experiments using intra-axonal labeling of A-fiber neurons, as well as single-neuron labeling of electrophysiologically identified sensory neurons. However, no studies have used genetically labeled neurons to examine this issue, and most studies were performed on spinal but not trigeminal sensory neurons which are the relevant neurons for orofacial pain, where allodynia oftentimes plays a dominant clinical role.
Findings: We recently discovered that parvalbumin::Cre (Pv::Cre) labels two types of A beta touch neurons in trigeminal ganglion. Using a Pv::CreER driver and a Cre-dependent reporter mouse, we specifically labeled these A beta trigeminal touch afferents by timed taxomifen injection prior to inflammation or infraorbital nerve injury (ION transection). We then examined the peripheral and central projections of labeled axons into the brainstem caudalis nucleus after injuries vs controls. We found no evidence for ectopic sprouting of Pv::CreER labeled trigeminal A beta axons into the superficial trigeminal noci-receptive laminae. Furthermore, there was also no evidence for peripheral sprouting.
Conclusions: CreER-based labeling prior to injury precluded the issue of phenotypic changes of neurons after injury. Our results suggest that touch allodynia in chronic orofacial pain is unlikely caused by ectopic sprouting of A beta trigeminal afferents.

• 出版日期2015-4-10