Dynamic memory in rodent C-fibres and its impact on spinal nociceptive processing

Area of Science:

• Neuroscience
• Pain Research
• Sensory Physiology

Background:

• C-fibre nociceptors, crucial for detecting tissue injury, exhibit low-level spontaneous firing.
• This spontaneous firing dynamically regulates activity-dependent slowing (ADS), creating a memory of prior activity levels.
• Previous human studies indicated peripheral nerve C-fibres retain activity memory influencing signal relay.

Purpose of the Study:

• To investigate if low-frequency C-fibre stimulation ('manipulation') alters subsequent C-fibre activity-dependent slowing (ADS).
• To determine if this 'dynamic memory' effect is sex-dependent in rodents.
• To explore the impact of this C-fibre dynamic memory on spinal cord pain processing.

Main Methods:

• Compound action potential (CAP) recordings from isolated rat and mouse dorsal roots.
• Stimulation protocols involved low-frequency manipulation followed by higher frequency trains.
• Patch-clamp and current-clamp recordings in spinal slices to assess effects on noxious heat-responsive neurons.

Main Results:

• Low-frequency manipulation altered C-fibre ADS in response to subsequent stimuli in both rats and mice.
• This dynamic memory effect was not sex-dependent, despite differences in baseline ADS.
• C-fibre dynamic memory influenced synaptic transmission and altered action potential firing in spinal neurons.

Conclusions:

• Rodent C-fibres possess a sex-independent dynamic memory mechanism affecting signal relay.
• This peripheral C-fibre memory is communicated to and modulates activity in spinal pain circuits.
• Ongoing C-fibre firing during injury dynamically regulates spinal cord pain processing.