Summary: A new study has investigated how the laxative prucalopride, known to activate serotonin receptors, affects resting brain activity in healthy adults.
The study discovered that those who took prucalopride demonstrated increased functional connectivity between major cognitive networks in their resting-state. This change provides a potential neurological mechanism by which prucalopride may enhance cognition and memory.
The results strengthen the case for prucalopride and drugs impacting the 5-HT4 serotonin receptor as potential treatments for depression and cognitive impairment.
- Prucalopride, mainly a laxative, also improves cognition and memory at low doses.
- The drug enhanced brain connectivity, aiding in attention and information processing.
- Contrarily, it reduced connectivity in the brain’s default mode network, adjusting cognitive function as needed.
Cognitive deficits accompany mood disorders and other psychiatric conditions, often with debilitating effects.
Limited treatments currently exist, but studies in animals and humans have pointed to drugs such as the laxative prucalopride that activate serotonin receptors as a potential therapeutic for the symptoms. It has remained unclear, however, how the medication affects resting brain activity.
Now, a new study in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, examines the drug’s effects in healthy human adults.
Serotonin receptors and the 5-HT4-type receptors in particular are found in areas throughout the brain, including the frontal cortex, basal ganglia, and hippocampus, that are known to mediate cognitive function and regulate mood.
Serotonin receptors are the primary targets of antidepressant medications, but resolving mood disturbances often does not resolve cognitive symptoms.
The researchers enlisted 50 healthy volunteers, half of whom received a six-day course of prucalopride, a highly selective agonist of the 5-HT4 type serotonin receptor, whereas the other half of the participants received a placebo.
Participants underwent scanning with functional magnetic resonance imaging, including a “resting scan,” in which they relaxed in the scanner.
Lead author Angharad de Cates, PhD, MRCPsych, at the University of Oxford, said of the work, “Our previous studies on prucalopride demonstrated that even at low clinical doses it can improve cognition and memory in healthy volunteers. This latest research provides a neurological mechanism by which this might occur.”
Participants who received the medication displayed more functional connectivity in their resting-state (rsFC) between major cognitive networks.
This included more rsFC between the central executive network, a brain network used for processing thoughts, and the posterior and anterior cingulate cortex (ACC), brain areas that regulate information processing and attention in the brain.
There was also more rsFC between regions of the ACC and the lateral occipital cortex, a region that helps us pay attention to objects that matter.
In addition, medicated participants compared to placebo controls showed decreased rsFC in the default mode network, a brain network that is activated during mind wandering.
Dr. de Cates added, “This provides further evidence that prucalopride is having an effect in areas of the brain that improve cognitive function – both by increasing and reducing connectivity between specific brain regions as required.”
Susannah Murphy, PhD, Associate Professor and joint senior author of the study, said, “Appropriate connectivity between and within these brain networks is needed to think properly, and this connectivity has been shown to be abnormal in depression.
“Here, the participants taking prucalopride had better scores on cognitive tests the day of the scan compared to the placebo participants. That suggests that the changes in rsFC that we saw with prucalopride may serve as a ‘signature’ of a drug that improves cognition.”
Dr. Murphy continued, “Untreated cognitive problems have a significant impact on the quality of life of people with depression.
“This study adds to the growing evidence base that drugs affecting the 5-HT4 serotonin receptor hold promise as a novel way to treat depression and cognitive impairment.”
Catherine Harmer, PhD, Professor of Cognitive Neuroscience and joint senior author of the study, said, “This study adds to the evidence base that the common laxative treatment prucalopride can have important effects in the brain, particularly affecting circuits which are important for learning and memory.
“Together with previous data, this suggests that this drug might be useful as a pro-cognitive treatment in disorders such as depression.”
Cameron Carter, MD, Editor of Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, said of the work, “These data, showing modulation of resting state connectivity in the brain by the 5HT4 receptor agonist and putative cognitive enhancer prucalopride, add to previous evidence that the agent modulates brain systems that are engaged during focused, higher cognitive activity and might have therapeutic potential.”
About this neuropharmacology, serotonin, and cognition research news
Original Research: Open access.
“5-HT4 receptor agonist effects on functional connectivity in the human brain; Implications for pro-cognitive action” by Angharad de Cates et al. Biological Psychiatry: Cognitive Neuroscience and Neuroimaging
5-HT4 receptor agonist effects on functional connectivity in the human brain; Implications for pro-cognitive action
Cognitive deficits are often comorbid with mood disorders, and can cause significant functional impairment even after resolution of the primary mood symptoms. We do not currently have pharmacological treatments that adequately address these deficits. 5-HT4 receptor agonists show promise as potential pro-cognitive agents in animal and early human translational studies. Optimal cognitive performance in humans is directly associated with appropriate functional connectivity between specific resting state neural networks. However, so far the effect of 5-HT4 receptor agonism on resting-state functional connectivity in the brain in humans is unknown.
We collected resting state fMRI scans from 50 healthy volunteers; 25 of whom had received six days x 1mg prucalopride (a highly-selective 5-HT4 receptor agonist) and 25 who had received placebo in a randomised double-blind design.
Network analyses identified that participants in the prucalopride group had enhanced resting-state functional connectivity (rsFC) between the central executive network (cEN) and the posterior / anterior cingulate cortex (PCC / ACC). Seed analyses also showed greater rsFC between the left and right rostral ACC and the left lateral occipital cortex ACC, and reduced rsFC between the hippocampus and other default mode network regions.
Similar to other potentially pro-cognitive medications, low-dose prucalopride in healthy volunteers appears to enhance rsFC between regions involved in cognitive networks and reduce rsFC within the DMN. This suggests a mechanism for the behavioural cognitive enhancement previously seen with 5-HT4 receptor agonists in humans and supports the potential for 5-HT4 receptor agonists to be used in clinical psychiatric populations.