Translating the promise of 5HT4 receptor agonists for the treatment of depression.

Animal experimental studies suggest that 5-HT4 receptor activation holds promise as a novel target for the treatment of depression and cognitive impairment. 5-HT4 receptors are post-synaptic receptors that are located in striatal and limbic areas known to be involved in cognition and mood. Consistent with this, 5-HT4 receptor agonists produce rapid antidepressant effects in a number of animal models of depression, and pro-cognitive effects in tasks of learning and memory. These effects are accompanied by molecular changes, such as the increased expression of neuroplasticity-related proteins that are typical of clinically useful antidepressant drugs. Intriguingly, these antidepressant-like effects have a fast onset of their action, raising the possibility that 5-HT4 receptor agonists may be a particularly useful augmentation strategy in the early stages of SSRI treatment. Until recently, the translation of these effects to humans has been challenging. Here, we review the evidence from animal studies that the 5-HT4 receptor is a promising target for the treatment of depression and cognitive disorders, and outline a potential pathway for the efficient and cost-effective translation of these effects into humans and, ultimately, to the clinic.

A role for 5-HT4 receptors in human learning and memory.

BACKGROUND: 5-HT4 receptor stimulation has pro-cognitive and antidepressant-like effects in animal experimental studies; however, this pharmacological approach has not yet been tested in humans. Here we used the 5-HT4 receptor partial agonist prucalopride to assess the translatability of these effects and characterise, for the first time, the consequences of 5-HT4 receptor activation on human cognition and emotion. METHODS: Forty one healthy volunteers were randomised, double-blind, to a single dose of prucalopride (1 mg) or placebo in a parallel group design. They completed a battery of cognitive tests measuring learning and memory, emotional processing and reward sensitivity. RESULTS: Prucalopride increased recall of words in a verbal learning task, increased the accuracy of recall and recognition of words in an incidental emotional memory task and increased the probability of choosing a symbol associated with a high likelihood of reward or absence of loss in a probabilistic instrumental learning task. Thus acute prucalopride produced pro-cognitive effects in healthy volunteers across three separate tasks. CONCLUSIONS: These findings are a translation of the memory enhancing effects of 5-HT4 receptor agonism seen in animal studies, and lend weight to the idea that the 5-HT4 receptor could be an innovative target for the treatment of cognitive deficits associated with depression and other neuropsychiatric disorders. Contrary to the effects reported in animal models, prucalopride did not reveal an antidepressant profile in human measures of emotional processing.

Lived experience codesign of self-harm interventions: a scoping review.

OBJECTIVES: This study aims to map existing literature describing how people with lived experience of self-harm have engaged in codesigning self-harm interventions, understand barriers and facilitators to this engagement, and how the meaningfulness of codesign has been evaluated. DESIGN: Scoping review by Joanna Briggs Institute methodology. A protocol was published online (http://dx.doi.org/10.17605/OSF.IO/P52UD). DATA SOURCES: PubMed, Embase, PsycINFO, Web of Science, Cochrane Library, PROSPERO, ClinicalTrials.gov and relevant websites were searched on 24 December 2022 (repeated 4 November 2023). ELIGIBILITY CRITERIA: We included studies where individuals with lived experience of self-harm (first-hand or caregiver) have codesigned self-harm interventions. DATA EXTRACTION AND SYNTHESIS: Results were screened at title and abstract level, then full-text level by two researchers independently. Prespecified data were extracted, charted and sorted into themes. RESULTS: We included 22 codesigned interventions across mobile health, educational settings, prisons and emergency departments. Involvement varied from designing content to multistage involvement in planning, delivery and dissemination. Included papers described the contribution of 159 female, 39 male and 21 transgender or gender diverse codesigners. Few studies included contributors from a minoritised ethnic or LGBTQIA+ group. Six studies evaluated how meaningfully people with lived experience were engaged in codesign: by documenting the impact of contributions on intervention design or through postdesign reflections. Barriers included difficulties recruiting inclusively, making time for meaningful engagement in stretched services and safeguarding concerns for codesigners. Explicit processes for ensuring safety and well-being, flexible schedules, and adequate funding facilitated codesign. CONCLUSIONS: To realise the potential of codesign to improve self-harm interventions, people with lived experience must be representative of those who use services. This requires processes that reassure potential contributors and referrers that codesigners will be safeguarded, remunerated, and their contributions used and valued.

The association between childhood bullying victimisation and childhood maltreatment with the clinical expression of bipolar disorder.

Adverse childhood experiences are significantly associated with a worse clinical expression of bipolar disorder, however, the literature has mainly focused on childhood maltreatment (abuse and neglect) with little attention paid to other forms of adversity, such as childhood bullying victimisation (referred to here as bullying), although this is known to have a negative impact on different psychiatric illnesses. The current study aimed to investigate the association between bullying victimisation and the clinical expression of bipolar disorder individually and in combination with childhood maltreatment. This investigation consisted of 63 individuals with a diagnosis of bipolar disorder (mean age 61.4 years) who completed the Retrospective Bullying Questionnaire and the Childhood Trauma Questionnaire to measure exposure to bullying and childhood maltreatment, respectively. The clinical expression variables were assessed using self-report instruments, these were: the Cardiff Anomalous Perceptions Scale (psychotic symptoms), Suicide Behaviours Questionnaire, Self-Report Manic Inventory, Beck Anxiety and Depression Inventories. The results showed that exposure to bullying was significantly associated with more suicidal behaviours (F(1,61) = 11.02, p < .01, η2 = 0.15) and psychotic symptoms (F(1,61) = 4.21, p < .05, η2 = .06). When bullying and childhood maltreatment histories were combined, the results showed that individuals with a history of both adversity types reported significantly more suicidal behaviours (F(2,60) = 6.59, p < .01, R2=.18) compared to those with a history of one or neither form of adversity. The sample size, age and gender distribution, limit the generalisability of the findings. However, the current results underscore the need to account for bullying victimisation when considering the adverse childhood experiences-bipolar disorder relationship, especially its clinical expression.

5-HT4 Receptor Agonist Effects on Functional Connectivity in the Human Brain: Implications for Procognitive Action.

BACKGROUND: 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 procognitive 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 (rsFC) in the brain in humans is unknown. METHODS: We collected resting-state functional magnetic resonance imaging scans from 50 healthy volunteers, of whom 25 received 6 days × 1 mg prucalopride (a highly selective 5-HT4 receptor agonist) and 25 received placebo in a randomized double-blind design. RESULTS: Network analyses identified that participants in the prucalopride group had enhanced rsFC between the central executive network and the posterior/anterior cingulate cortex. Seed analyses also showed greater rsFC between the left and right rostral anterior cingulate cortex and the left lateral occipital cortex, and reduced rsFC between the hippocampus and other default mode network regions. CONCLUSIONS: Similar to other potentially procognitive medications, low-dose prucalopride in healthy volunteers appeared to enhance rsFC between regions involved in cognitive networks and reduce rsFC within the default mode network. This suggests a mechanism for the behavioral 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.

The Effect of the 5-HT4 Agonist, Prucalopride, on a Functional Magnetic Resonance Imaging Faces Task in the Healthy Human Brain.

Depression is a common and often recurrent illness with significant negative impact on a global scale. Current antidepressants are ineffective for up to one third of people with depression, many of whom experience persistent symptomatology. 5-HT4 receptor agonists show promise in both animal models of depression and cognitive deficit. We therefore studied the effect of the 5-HT4 partial agonist prucalopride (1 mg daily for 6 days) on the neural processing of emotional faces in 43 healthy participants using a randomised placebo-controlled design. Participants receiving prucalopride were more accurate at identifying the gender of emotional faces. In whole brain analyses, prucalopride was also associated with reduced activation in a network of regions corresponding to the default mode network. However, there was no evidence that prucalopride treatment produced a positive bias in the neural processing of emotional faces. Our study provides further support for a pro-cognitive effect of 5-HT4 receptor agonism in humans. While our current behavioural and neural investigations do not suggest an antidepressant-like profile of prucalopride in humans, it will be important to study a wider dose range in future studies.

Déjà-vu? Neural and behavioural effects of the 5-HT4 receptor agonist, prucalopride, in a hippocampal-dependent memory task.

Cognitive deficits commonly accompany psychiatric disorders but are often underrecognised, and difficult to treat. The 5-HT4 receptor is a promising potential treatment target for cognitive impairment because in animal studies 5-HT4 receptor agonists enhance hippocampal-dependent memory processes. To date, there has been little work translating these effects to humans. We tested whether short-term administration of the 5-HT4 partial agonist, prucalopride, modified behavioural and neural (fMRI) memory processing in 44 healthy human volunteers using an experimental medicine model. We found that participants who had received six days of prucalopride treatment were significantly better at recalling previously seen neutral images and distinguishing them from new images. At a neural level, prucalopride bilaterally increased hippocampal activity and activity in the right angular gyrus compared with placebo. Taken together, these findings demonstrate the potential of 5-HT4-receptor activation for cognitive enhancement in humans, and support the potential of this receptor as a treatment target for cognitive impairment.