Sexual Dimorphism in Nociceptor Sensitization UPSC

NOCICEPTOR CELLS

Source: Hindu

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Context

A study led by University of Arizona Health Sciences researchers demonstrated for the first time functional sexual dimorphism in nociceptors, the nerve cells responsible for perceiving pain.

Details

Nociceptor Cells

Pain is a crucial sensory experience that warns us of potential harm.
Nociceptors are specialized nerve cells that detect harmful stimuli and transmit pain signals to the brain.
These receptors are found throughout the body, including the skin, bones, joints, and muscles.

Types of Nociceptors

Mechanical Nociceptors: Respond to physical damage like cutting or pressure. They often exhibit polymodal characteristics, meaning they can also respond to thermal and chemical stimuli.
Thermal Nociceptors: Activated by extreme temperatures. They use ion channels such as TRPV1 for heat and TRPA1 for cold to detect temperature changes.
Chemical Nociceptors: React to chemical stimuli including irritants like capsaicin or acrolein. They can detect both external chemicals and internal changes in tissue chemistry.
Sleeping/Silent Nociceptors: Remain inactive until tissue damage or inflammation occurs. These nociceptors are crucial for detecting injury-induced pain.
Polymodal Nociceptors: Capable of responding to a combination of mechanical, thermal, and chemical stimuli. They are the most common type of C-fiber nociceptors.

SEXUAL DIMORPHISM

Sexual dimorphism refers to the differences in size, shape, color, and structure between males and females of the same species. These differences often arise due to the different roles each sex plays in reproduction and survival.

Examples of Sexual Dimorphism

Size Differences: In many mammal species, males are larger than females (e.g., lions, gorillas). However, in some species, females are larger (e.g., certain species of spiders and anglerfish).
Coloration: In many bird species, males are more brightly colored than females (e.g., peacocks, where males have extravagant plumage, while females are more subdued in color).

Morphological Structures:

Insects: Male stag beetles have large mandibles used for fighting, while females have much smaller mandibles.
Fish: Male anglerfish are much smaller than females and often attach to them for survival.
Behavioral Differences: Males and females in human exhibit different behaviors due to hormonal differences and social roles.

Causes of Sexual Dimorphism

Sexual Selection:
- Mate Choice: Traits that are attractive to the opposite sex (e.g., bright plumage in birds) can become more pronounced.
- Male-Male Competition: Traits that help males compete with each other for access to females (e.g., large size, antlers in deer) can become exaggerated.
Natural Selection: Traits that help one sex survive better in its particular role (e.g., females having better camouflage to protect offspring) can lead to dimorphism.
Genetic and Hormonal Factors: Differences in sex chromosomes and hormones (e.g., testosterone and estrogen) contribute to the development of distinct male and female traits.

Key Findings

Prolactin and Orexin-B: The study found that prolactin increased nociceptor sensitivity in females, whereas orexin-B had a similar effect in males. This was consistent across mice, monkeys, and human samples.
Threshold Differences: The nociceptor response threshold was lower in females than in males. This means that females' nociceptors are more easily activated by stimuli that might not affect males as strongly.
Potential Mechanisms: The differences in nociceptor sensitivity could be attributed to peripheral nociceptor sensitization, where the threshold for pain is lowered by external factors, causing receptors to respond to normally non-painful stimuli.

Implications

Sex-specific Therapies: The findings suggest that medical practitioners should consider the patient's sex when prescribing pain management therapies. This is because the biological mechanisms driving pain perception differ between males and females.
Clinical Trials: It is crucial for clinical trials to include a balanced number of male and female participants to identify any sex-specific effects of new pain treatments. Some previously 'failed' trials might need reevaluation to check for sex-specific responses.

Summary

Aspect	Description
Types of Nociceptors	- Mechanical - Thermal - Chemical - Polymodal - Silent/Sleeping
Activation Mechanisms	- TRP Channels (e.g., TRPV1, TRPA1) - ASIC (Acid-Sensing Ion Channels) - Purinergic Receptors
Pathways	- Ascending Pathway - Descending Pathway
Sexual Dimorphism	- Prolactin sensitizes female nociceptors - Orexin-B sensitizes male nociceptors
Response Threshold	- Lower in females compared to males
Conditions Involving Nociceptors	- Chronic pain - Inflammatory pain - Neuropathic pain
Potential Therapies	- Targeted based on sex-specific nociceptor sensitization
Role in Pain Perception	- Detect extreme pressure, temperature, and chemicals - Relay signals to the brain
Research Findings	- Nociceptor activation differs between males and females

Sources:

Hindu

PRACTICE QUESTION

Q: Discuss the concept of sexual dimorphism. Explain its causes and significance in the animal kingdom, providing specific examples. How does sexual dimorphism manifest in humans, and what are its implications for human society? (250 Words)