What is pain?

On the other hand, it is the most common symptom of various diseases and one of the most serious problems that plague human health today. With the advancement of medicine and the improvement of human living standards, severe infectious diseases are gradually being controlled, and the relative position of pain in human physical and mental pain and medical expenses will become more and more important. Because it is difficult to conduct in-depth mechanism research on pain in the human body, it is necessary to establish an animal model of pain. But pain is a combination of multiple sensations that vary in nature, strength, and extent, and is often intertwined with autonomic nervous system, motor response, mental and emotional responses, and it is neither simply related to a part of the body. Changes are not transmitted by a single conduction beam, nucleus and neurotransmitter in the nervous system, so it is difficult to directly relate an objective indicator to pain. Therefore, we can only speculate on the degree of pain based on the protective response and protective behavior of the model animals on noxious stimuli. Today, we will introduce some pain models.

Acute pathological pain model

When the pain is not caused by external environmental causes, the pain sensation will continue and cannot escape. The pain at this time belongs to the pathological pain range. Pathological pain can be divided into acute and chronic according to its course of disease. The former is mostly caused by a certain injury or inflammatory reaction, and when the injury is healed or the inflammation disappears, the pain can be eliminated. The latter is caused by chronic inflammation or neuropathy that is difficult to eliminate, and the course of disease often lasts for a long time.

1. Formalin tumorigenic model

The purpose of this model is to simulate persistent pain caused by acute tissue damage. Rats were generally used as experimental subjects. Intravenous injection of a diluted formalin solution into the animal's foot, resulting in changes in animal behavior such as flexing legs during exercise, lameness during exercise, and lameness. The extent of these behaviors (such as lameness time) is directly proportional to the concentration of formalin and is generally considered a symbol of pain. In addition, other behaviors such as grooming, exploration and exercise activities are also affected by formalin injections.

2. White pottery - colander gum inflammation model

The purpose of this model is to simulate the pain caused by subacute inflammation. Kaolin is a fine-grained substance with a composition of alumina, which acts as a mechanical stimulus. Carrageenan is a colloidal substance extracted from the aquatic plant Carrageenan and has an over-stimulation effect. Inhibition of carrageenan alone can induce inflammation, and if combined with white clay, the inflammation is more intense. Rabbits or rats can be used as experimental subjects. This model is suitable for acute pharmacological experiments and electrophysiological experiments comparing changes before and after the onset of inflammation.

Chronic pathological pain model

Pain that lasts more than 6 months clinically is considered chronic pain. Chronic pathological pain is characterized by long-lasting pain, which generally involves systemic diseases of the body (such as abnormal immune response or abnormalities in the nervous system). The pain has no obvious external stimuli as an inducement or the degree of pain is not proportional to the severity of the local lesion. In this sense, cancer pain is not a chronic pain because it has a clear local persistent stimulus and should be a persistent state of acute pain. Chronic pathological pain models are mainly divided into two types: inflammatory and neurogenic.

1. Inflammatory pain model

Inflammation is the most common cause of pain. Many unexplained pain conditions are actually caused by aseptic inflammation of soft tissues. Therefore, studying the characteristics and mechanisms of inflammatory pain in animal models may help to understand pain and find effective analgesic methods.

2. Neuralgia model

Neuropathic pain refers to pain caused by a lesion in the peripheral nerve, spinal dorsal root, spinal cord, or certain areas of the brain caused by trauma or disease. It has several different types of characteristic abnormal pain sensations. Spontaneous pain is most common, and may be persistent surface burning or deep soreness; it can also be manifested as electro-surgical paroxysmal pain. Patients often exhibit pain and analgesia with heat, cold and mechanical stimuli. The mechanism of neuropathic pain is unknown, and clinical treatment effects are often unsatisfactory. Due to the ever-changing clinical symptoms, clinical research on neurogenic pain is difficult. Therefore, recreating this condition in experimental animals is of great significance for relevant research.

The meaning of the pain model

There is no doubt that the establishment of animal models will assist in the diagnosis and treatment of corresponding painful conditions. The existing research results show that different types of pain models have great differences in the central process. This suggests that pain may not be determined by a simple central mechanism; pain tempering and pain itself may involve a complex combination of several central mechanisms. Comparing the central mechanisms of different pain models may help to reveal the true central nature of pain, which has led to a dramatic leap in our understanding of pain phenomena and clinical outcomes. Such comparative studies may also help us understand some of the pain conditions that do not currently know the cause and therefore fail to prepare the relevant models, and help to treat these conditions.

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