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Age-dependent attenuation of the decrease of C fibers by capsaicin and its effects on responses to nociceptive
A Hiura1, E López Villalobos, H Ishizuka
1Department of Oral Anatomy, School of Dentistry, Tokushima University, Japan.
Somatosensory & Motor Research
|January 1, 1992
Summary
Capsaicin treatment in mice, particularly during early development, significantly reduces unmyelinated (C) fibers, impacting thermal pain responses. This effect on C fibers and pain sensitivity is age-dependent, though plasma extravasation reduction is not.
Area of Science:
- Neuroscience
- Developmental Biology
- Pain Research
Background:
- Capsaicin is a neurotoxin known to affect sensory neurons.
- The development of unmyelinated (C) fibers plays a crucial role in pain perception.
- Understanding the age-dependent effects of capsaicin is important for pain management strategies.
Purpose of the Study:
- To investigate the impact of early-life capsaicin exposure on the development of unmyelinated (C) fibers in mice.
- To evaluate the age-dependent effects of capsaicin on thermal nociception and neurogenic plasma extravasation.
- To correlate the reduction in C fibers with changes in pain responses.
Main Methods:
- Subcutaneous administration of capsaicin to mice at various ages (10, 15, 20, 30, 60 days).
- Histological examination of L4 dorsal roots to quantify C fiber density.
- Assessment of thermal nociception using the hot plate test (55°C).
- Measurement of neurogenic plasma extravasation as an indicator of chemogenic nociception.
Main Results:
- Capsaicin treatment, especially in young mice, significantly reduced the number of unmyelinated (C) fibers.
- The reduction in C fibers was dose- and age-dependent, with greater effects observed in younger animals.
- Thermal nociception (hot plate latency) was significantly increased in capsaicin-treated young mice, correlating with C fiber reduction.
- Neurogenic plasma extravasation was reduced by capsaicin regardless of treatment age, indicating a persistent effect on sensory neuron function.
Conclusions:
- Capsaicin's impact on thermal nociception is age-dependent and linked to the reduction of C fibers.
- While C fiber reduction correlates with altered thermal pain, the relationship is not always linear.
- Capsaicin effectively reduces neurogenic plasma extravasation irrespective of developmental stage, suggesting a robust effect on primary sensory neurons.