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24 March 2023
Published online 29 July 2022
Alterations to the spinal networks that carry sensory messages to the brain may explain heightened pain sensitivity in people with attention-deficit/hyperactivity disorder.
Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental condition, symptoms of which include inattention, hyperactivity and impulsivity. People with ADHD often describe a heightened sensitivity to pain, suggesting that pain hypersensitivity and ADHD may be comorbidities, with one condition influencing the other and vice versa.
Now, Marc Landry, Mohamed Bennis, Otmane Bouchatta, and co-workers at the University of Bordeaux, France, and Cadi Ayyad University in Marrakesh, Morocco, have shown that an ADHD mouse model exhibits significant sensitivity to pain compared with control mice.
Pain sensations occur when pain receptors are triggered to send electrical signals to the spinal cord, which then relays the message to the brain.
“Pain processing in the brain is often modified by other neurological situations, including neurodegenerative or neuropsychiatric disorders,” says Landry. “We’re interested in the links between alterations of pain sensitivity and anxiety, depression and ADHD. The Moroccan laboratory is a leading animal facility, with experts in rodent behaviour and neuroanatomy. We worked closely with them to develop a reliable mouse model of ADHD.”
This mouse model enabled the team to systematically study pain sensitivity in detail under ADHD-like conditions. They used mechanical, heat and cold stimuli to measure pain sensitivity in the ADHD mice, and compared their responses and behaviours with those of control mice.
The team found that the hyperexcitability of neurons in the anterior cingulate cortex – a region of the brain that is altered in ADHD – directly results in changes to spinal networks carrying pain messages.
“It is not only how the pain feels, but also how the actual sensory information is transmitted in the spinal cord that is altered under ADHD conditions,” says Landry. “Importantly, we also demonstrated that this sensitization to pain is further amplified by pathological conditions, like chronic inflammation, and this may worsen the conditions of ADHD patients facing painful disorders.”
The researchers have started to elucidate the pathways involved in pain hypersensitivity and will continue their investigations into ADHD and other neurological conditions.
“Our results suggest that we should specifically search for sensory alterations in patients with ADHD and pay attention to those people with associated pathologies that could trigger pain hypersensitization,” says Landry. “We must bear in mind that people with ADHD have very different perceptions and responses to the environment and external stimuli. It may be that treating pain could also reduce the burden of ADHD symptoms, but this remains to be investigated.”
Bouchatta, O. et al. Pain hypersensitivity in a pharmacological mouse model of attention-deficit/hyperactivity disorder. PNAS http://dx.doi.org/10.1073/pnas.2114094119 (2022).