Chemical anatomy of pain pathways 1.2 Flashcards
Q: What are the two main subgroups of nociceptors?
A: Aδ-fibres (thinly myelinated, respond to noxious mechanical or thermal stimuli) and C-fibres (unmyelinated, respond to chemical, thermal, or polymodal stimuli).
Q: What is the main question regarding nociceptor subpopulations?
A: Whether different subpopulations of C-fibres are modality-specific or if most nociceptors are polymodal.
Q: What are the two possibilities for nociceptor modality specificity?
1) Different subpopulations are modality-specific.
2) Their central connections confer modality specificity.
Q: What does polymodal mean in the context of nociceptors?
A: A nociceptor that responds to more than one type of stimulus, such as mechanical, thermal, or chemical.
Q: What do electrophysiological studies suggest about C-fibre nociceptors?
A: The incidence of polymodality in nociceptors varies widely (11-100%), and some C-fibres respond to multiple stimuli, though not necessarily all types.
Q: What was the result of selectively eliminating TRPV1+ neurons in Cavanaugh et al.’s study?
A: Complete loss of heat pain sensitivity, but responses to noxious mechanical and cold stimuli were unaffected.
Q: What was the result of selectively eliminating Mrgprd+ neurons?
A: Deficits in response to noxious mechanical stimuli, but no deficits in response to heat or cold stimuli.
Q: What is conditional genetic ablation of neurons?
A: A method where neurons that express a specific gene are selectively ablated in adults, under controlled conditions.
Q: What evidence supports modality specificity in nociceptors?
A: Studies using genetic ablation, such as eliminating TRPV1+ or Mrgprd+ neurons, show that specific subpopulations mediate distinct nociceptive behaviors.
Q: What do optogenetic studies suggest about nociceptor function?
A: Optogenetic activation of TRPV1+ neurons causes aversion in mice, while activating MrgD+ neurons does not, indicating functional differences.
Q: What did Sally Lawson’s 2019 analysis conclude about polymodal nociceptors?
A: Polymodal nociceptors (PMNs) represent only 10.9% of total nociceptors, challenging the idea that most nociceptors are polymodal.
Q: What is the controversy regarding nociceptor polymodality?
A: Some studies suggest polymodality is rare, while others report a high incidence of polymodal responses, with varying results depending on the method used.
Q: What is the significance of labelled line theory in nociception?
A: It proposes that different sensory modalities are transmitted by distinct, specialized nociceptors, contrasting with the idea of polymodal activation.
