Pain is a complex physiological phenomenon triggered by the activation of sensory neurons called nociceptors, serving as a vital protective mechanism for organisms. Damage or diseases of the sensory nervous system can lead to neuropathic pain. A deep understanding of the sensory nervous system's mechanisms and the pathophysiological changes in neuropathic pain is crucial for identifying novel therapeutic targets and developing innovative analgesic drugs.
Pain mechanisms are generally categorized into peripheral and central mechanisms. Peripheral mechanisms primarily involve primary afferent fibers, nociceptors, and peripheral sensitization. Central mechanisms encompass central sensitization, disinhibition and enhanced facilitation, structural remodeling, and ectopic excitability. Peripheral and central sensitization are key factors contributing to post-injury hyperalgesia. Peripheral sensitization is a major mechanism in inflammatory pain and certain neuropathic pain conditions (such as postherpetic neuralgia). Central sensitization can be involved in inflammatory pain, neuropathic pain, and functional pain. Disinhibition and enhanced facilitation, structural remodeling, and ectopic excitability are unique mechanisms in neuropathic pain.
In experimental animals, pain assessment largely relies on observing spontaneous behaviors, such as paw withdrawal reflex, frequent licking or scratching, excessive grooming, vocalization, reduced exploratory behavior, increased stereotypic behaviors, and changes in facial expressions. When animals are in a pathological pain state, pain sensitization leads to an enhanced response to stimuli and a decreased pain threshold. Even mild stimuli can elicit significant behavioral changes, such as paw withdrawal, licking, or abdominal contraction. Therefore, during experiments, researchers can apply specific stimuli using experimental equipment or reagents to induce behavioral changes in animals, thereby converting pain intensity into quantifiable values for objective pain assessment. Currently, common methods for evaluating pain sensitization in animals include mechanical, thermal, and cold pain sensitivity tests.
Applications of Pain Models:
Pain models are essential tools for studying pain mechanisms, drug mechanisms of action, and evaluating drug efficacy and safety, providing critical evidence for drug development.
Common Animal Species:
Mice, rats, non-human primates (monkeys), rabbits, pigs, etc.
Common Pain Models and Model Establishment Methods:
- Inflammatory Pain Model: CFA Model: Chronic inflammatory pain induced by subcutaneous injection of Complete Freund's Adjuvant, commonly used in mice and rats.
- Formalin Model: Short-term and long-term pain responses induced by subcutaneous or intradermal injection of formalin, commonly used in mice and rats.
- Neuropathic Pain Models:
- Nerve Injury Model: Neuropathic pain induced by surgically created nerve injuries, such as partial sciatic nerve transection or compression, commonly used in mice and rats.
- Chronic Constriction Injury (CCI) Model: Chronic neuropathic pain induced by ligating the sciatic nerve or other peripheral nerves, commonly used in rats.
- Capsaicin Model: Nociceptive pain induced by local or systemic injection of capsaicin to activate nociceptors.
- Chemical Pain Model: Acetic Acid Model: Local pain induced by subcutaneous or intraperitoneal injection of acetic acid, commonly used in mice and rats.
- Cancer Pain Model: Tumor pain induced by transplanting tumor cells into animals, commonly used in mice and rats. Model establishment methods include invasive surgery and injections.
Challenges in Utilizing Pain Model Data for Drug Evaluation and Development:
- Individual Variability: Significant inter-animal variability in sensitivity to pain stimuli can challenge the interpretation and reproducibility of experimental results.
- Model Selection: Choosing an appropriate pain model requires careful consideration of experimental objectives, research questions, animal strains, and other factors. Different models may mimic different types of pain.
- Clinical Translation: Animal models cannot fully replicate the complexity of human pain, posing challenges in translating findings from animal models to clinical applications.
- Ethical Considerations: Experiments using animal pain models must strictly adhere to ethical guidelines, including minimizing the number of animals used and maximizing animal welfare and protection throughout the experimental process.
Prisys Biotech's Strengths in Pain Models
Prisys Biotech has established and validated a variety of non-human primate pain models. We are capable of customizing optimal model solutions based on clients' research needs and drug mechanisms of action. Our services cover model and animal strain selection, control design, data collection and analysis, Institutional Animal Care and Use Committee (IACUC) review, biomarker detection, and more.
Prisys Biotech's professional research team, through comprehensive optimization methods and strategies, is dedicated to enhancing model reliability and predictability, and improving data reproducibility and comparability, effectively addressing the challenges in pain model development and application. We aim to provide clients with more realistic and accurate drug evaluation reports, facilitating the success of preclinical and clinical drug research.
