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Researchers might be able to treat an annoying cough in disease without disrupting the protective cough we need for optimal lung health by targeting the various brain circuits involved. That emerges from new research published this week in the Journal of Physiology.
More people seek medical advice for an unwanted, excruciating cough than for any other illness. In some people, the cough can last for years without relief because effective treatments are not readily available.
These findings from Australian researchers have very important implications for the understanding and potential treatment of cough disorders, as it appears that different types of coughs may use different brain circuits.
The coughing process typically begins with an irritant stimulus in the larynx, airways, or lungs that activates the cough-inducing sensory nerves. These sensory nerves transmit this information to the brain, where the information modifies the actions of the respiratory muscles to produce a cough response. These signals are also sometimes combined with "higher order" signals that can tickle your throat, make you feel annoyed or anxious about a cough, and allow you to voluntarily suppress or intensify your cough.
Previous research in animals and humans suggested that the brain processes all input from sensory coughing nerves in a single area. However, in an earlier study of guinea pigs published this year in the Journal of Physiology, the same research team from Monash University and the University of Melbourne showed that this is likely not the case.
Instead, they discovered that separate pathways in the brain are involved in responding to a good (to clear the airways to ensure optimal lung health) and a bad cough (a sign of illness).
In this new study, human participants were subjected to behavioral tests to assess the sensitivity of the cough reflex, followed by functional imaging of the brain in an MRI scanner while inhaling various chemical substances.
One chemical stimulus was capsaicin, the active ingredient in hot chili peppers that is known to activate two subsets of sensory airway nerves that are involved in coughing.
Another chemical stimulus was adenosine triphosphate (ATP), best known as an energy molecule in cells, but also selectively activating one of the two subsets of sensory nerves involved in coughing.
The final chemical stimulus was saline, which was used as a control stimulus as it does not activate sensory nerves.
High resolution brainstem scans were collected during repeated randomized presentations of these stimuli, and the scans were analyzed to determine where in the brainstem the neuronal responses to capsaicin and ATP reside.
The result showed that capsaicin inhalation activated both the core of the solitary tract and the area of the brainstem that contained the paratrigeminal nucleus, while ATP inhalation activated only the core of the solitary tract.
The data confirms the team's previous studies in guinea pigs, in which one cough pathway (sensitive to capsaicin and ATP) is integrated into the core of the solitary tract, while the other cough pathway (sensitive to capsaicin only) involves integration into the paratrigeminal core.
Commenting on the study, senior author Professor Stuart Mazzone said, "Chronic cough is a terribly uncomfortable disease. People can cough hundreds of times per hour of their waking life for years, and current medications are simply not effective." to alleviate this condition. "
"We are now conducting a similar study comparing how these two distinct brain networks respond in patients with chronically troublesome coughs compared to healthy subjects. This new study is also motivated by the recent results of clinical studies showing promising cough suppressant effects of Medicines That Inhibit ATP Receptors How ATP is implicated in coughing is not fully understood, we suspect that the response to ATP may change in patients with chronic cough and that the newly identified cough circuit in the brain may be involved in this change . "
Research has shown that the sound of coughing does not tell you whether a person is sick
Michael J. Farrell et al., Evidence of Multiple Bulbar and Higher Brain Circuitry Processing Sensory Input from the Human Respiratory System, The Journal of Physiology (2020). DOI: 10.1113 / JP280220
The physiological society
The good and the bad cough (2020, October 8)
accessed on October 8, 2020
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