My back hurts, my hand hurts: is pain different in different parts of the body?
or technically,
Sparse genetic tracing reveals regionally specific functional organization of mammalian nociceptors.
[See Original Abstract on Pubmed]
Authors of the study: William Olson, Ishmail Abdus-Saboor, Lian Cui, Justin Burdge, Tobias Raabe, Minghong Ma, Wenqin Luo
Have you ever wondered why you can feel the details of an object with your fingertips, but not with your elbow? Your body detects sensations including touch and pain using specialized nerves that detect information in your environment and transmit it to your brainThe brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals.. Together, these nerves are called the “sensory system.” As you may have noticed, however, this system does not treat all body regions the same. This is why your fingertips are much more sensitive to touch stimuli than other parts of your body (imagine trying to feel Braille with the back of your hand). Our fingertips are very sensitive to touch mainly because they contain more ‘touch-sensitive’ nerve endings than other body regions.
Pain perception relies on ‘pain-sensitive’ nerve endings that are distinct from our ‘touch-sensitive’ nerve endings. But just like for touch, certain regions of our body, like our fingertips, are more sensitive to pain than others. Interestingly, unlike for touch, this is not because we have more ‘pain-sensitive’ nerve endings in pain-sensitive areas. In fact, we have relatively few ‘pain-sensitive’ nerve endings in our fingertips -- even though they are extremely sensitive to pain! This observation surprised Will Olson, a neuroscience graduate student in Wenqin Luo’s lab. He wondered how certain parts of the body are more sensitive to pain than others.
To figure this out, he carefully studied the shape and size of pain nerve endings in mice. These nerves are like wires that run all the way from your skin into your spinal cord. This means there are two endings of these nerves: one in the skin and one in the spinal cord. Will took a good look at both ends. He saw that, in general, ‘pain-sensitive’ nerves come in different shapes and sizes depending on where in the body they are found. Interestingly, he found that pain nerve endings have a low density in the mouse paw, just like in the human hand! The pain nerve endings in the paw also looked very similar to pain nerve endings in other parts of the mouse. This surprised Will because he knew that mice have very high pain sensitivity in their paws. He wondered, if the density and the shape of the pain nerves in the paw skin is the same as in other parts of the body, then why are paws so sensitive to pain?! The answer became clear when Will looked at these nerves in the spinal cord -- in the spinal cord, paw pain nerves look completely different from pain nerves that come from other parts of the mouse. Will hypothesized that the special shape of these paw pain nerves could enhance pain sensation in the paw. And in fact, Will found that these paw pain nerves are better at sending information to the spinal cord than pain nerves that come from other parts of the mouse.
While these findings are interesting and could even help some of us decide on the least painful place to get a tattoo, this study might also help people with chronic pain. Chronic pain occurs when people feel pain for weeks, months or even years. Based on this study, we may be able to identify specific causes of chronic pain in different parts of the body. For example, chronic back pain might be very different from chronic joint pain. Our current pain medications are not effective as treatments for many forms of chronic pain. The lack of good treatments has contributed to the increase in opioid prescriptions that led to opioid addiction crisis. Identifying more specific causes of chronic pain could give researchers ideas for better ways to treat it.
Pain perception relies on ‘pain-sensitive’ nerve endings that are distinct from our ‘touch-sensitive’ nerve endings. But just like for touch, certain regions of our body, like our fingertips, are more sensitive to pain than others. Interestingly, unlike for touch, this is not because we have more ‘pain-sensitive’ nerve endings in pain-sensitive areas. In fact, we have relatively few ‘pain-sensitive’ nerve endings in our fingertips -- even though they are extremely sensitive to pain! This observation surprised Will Olson, a neuroscience graduate student in Wenqin Luo’s lab. He wondered how certain parts of the body are more sensitive to pain than others.
To figure this out, he carefully studied the shape and size of pain nerve endings in mice. These nerves are like wires that run all the way from your skin into your spinal cord. This means there are two endings of these nerves: one in the skin and one in the spinal cord. Will took a good look at both ends. He saw that, in general, ‘pain-sensitive’ nerves come in different shapes and sizes depending on where in the body they are found. Interestingly, he found that pain nerve endings have a low density in the mouse paw, just like in the human hand! The pain nerve endings in the paw also looked very similar to pain nerve endings in other parts of the mouse. This surprised Will because he knew that mice have very high pain sensitivity in their paws. He wondered, if the density and the shape of the pain nerves in the paw skin is the same as in other parts of the body, then why are paws so sensitive to pain?! The answer became clear when Will looked at these nerves in the spinal cord -- in the spinal cord, paw pain nerves look completely different from pain nerves that come from other parts of the mouse. Will hypothesized that the special shape of these paw pain nerves could enhance pain sensation in the paw. And in fact, Will found that these paw pain nerves are better at sending information to the spinal cord than pain nerves that come from other parts of the mouse.
While these findings are interesting and could even help some of us decide on the least painful place to get a tattoo, this study might also help people with chronic pain. Chronic pain occurs when people feel pain for weeks, months or even years. Based on this study, we may be able to identify specific causes of chronic pain in different parts of the body. For example, chronic back pain might be very different from chronic joint pain. Our current pain medications are not effective as treatments for many forms of chronic pain. The lack of good treatments has contributed to the increase in opioid prescriptions that led to opioid addiction crisis. Identifying more specific causes of chronic pain could give researchers ideas for better ways to treat it.
About the brief writer: Patti Murphy
Patti is a PhD Candidate in Michael Granato's lab. Patti is interested in understanding and developing therapeutics for functional nerve regeneration, particularly to restore voluntary motor control after spinal cord injury.