Previously unknown sensory organ identified.

Pain is the most common reason for physician consultation in most developed countries with almost one in five people experiencing constant pain in their lifetime. However, sensitivity to pain is also required for survival proffering a protective function. It prompts reflex which prevents damage to tissue, such as a person pulling their hand away when they feel a jab from a sharp object or when they burn themselves. To date, the exact circuitry behind this reaction is still not fully understood. Now, a study from researchers at Karolinska Institutet identifies a new sensory pain organ in mice which detects painful mechanical damage, such as pricks and impacts. The team state their discovery changes the understanding of the cellular mechanisms of physical sensation and may be of significance in the understanding of chronic pain. The study is published in the journal Science.

Previous studies show that pain can be classified as neuropathic pain which is initiated by a disease in the somatosensory nervous system, or nociceptive pain which represents the normal response to noxious injury of tissues such as skin or bone, or inflammatory pain involving the activation of the nociceptive pain pathway at a site of tissue inflammation. All of the aforementioned type of pain is thought to be initiated by activation of free nerve endings without end organs in the skin. The current study identifies a previously unknown mesh like organ covering the skin in rodents which senses dangerous environmental stimuli.

The current study shows the organ, dubbed the nociceptive glio-neural complex, is made up of a network of cells called glial cells, which surround and support the body’s nerve cells. Results show the glial cells form a mesh-like structure between the skin’s outer and inner layers, with filament-like protrusions which extend into the skin’s outer layer. The lab tested the functionality of the sensory organ by measuring the rodents’ responses to different types of pain. Data findings show when the cells in the organ were turned off via gene editing, the animals exhibited a reduced response to mechanical pain, discomfort caused by pressure, pricking, or other impacts to the skin.

The team state that these glial cells are a type of octopus shaped Schwann cell, which wrap around and engulf nerve cells. They go on to explain that the body of the Schwann cells sit below the outer layer of the skin with long extensions which wrap around the ends of pain-sensing nerve cells that extend up into the epidermis, the outer layer of the skin. The group conclude the Schwann cells, which wrap around unmyelinated nociceptive nerves, are mechanosensitive and transmit nociceptive information to the nerve.

The team surmise they have identified a previous unknown organ involved in the sensation of pain. For the future, the researchers state they now plan to investigate whether this sensory organ also exists in humans.

Source: Karolinska Institutet

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