Effects of citalopram treatment on hypothermic and hormonal responses to the 5-HT1A receptor agonist buspirone in patients with major depression and therapeutic response

Rapid reorganization of serotonin projections and antidepressant response to 5-HT1A-biased agonist NLX-101 in fluoxetine-resistant cF1ko mice

Selective serotonin (5-HT) reuptake inhibitors (SSRIs) like fluoxetine remain a first-line treatment for major depression, but are effective in less than half of patients and can take 4-8 weeks to show results. In this study, we examined cF1ko mice with genetically induced upregulation of 5-HT1A autoreceptors that reduces 5-HT neuronal activity. These mice display anxiety- and depression-related behaviors that did not respond to chronic fluoxetine treatment. We examined treatment with NLX-101, a biased agonist that preferentially targets 5-HT1A heteroreceptors. By testing different doses of NLX-101, we found that a dose of 0.2 mg/kg was effective in reducing depression-related behavior in cF1ko mice without causing hypothermia, a 5-HT1A autoreceptor-mediated response. After 1 h, this dose activated dorsal raphe 5-HT neurons and cells in the medial prefrontal cortex (mPFC), increasing nuclear c-fos labelling in cF1ko mice. In cF1ko mice but not wild-type littermates, 0.2 mg/kg NLX-101 administered 1 h prior to each behavioral test for two weeks reduced depressive behavior in the forced swim test, but increased anxiety-related behaviors in the open field, elevated plus maze, and novelty suppressed feeding tests. During this treatment, NLX-101 induced widespread increases in the density of 5-HT axons, varicosities, and especially synaptic and triadic structures, particularly in depression-related brain regions including mPFC, hippocampal CA1 and CA2/3, amygdala and nucleus accumbens of cF1ko mice. Overall, NLX-101 was rapid and effective in reducing depressive behavior in SSRI-resistant mice, but also induced anxiety-related behaviors. The increase in serotonin innervation induced by intermittent NLX-101 may contribute to its behavioral actions.

The Serotonin 1A (5-HT1A) Receptor as a Pharmacological Target in Depression

Clinical depression is a common, debilitating and heterogenous disorder. Existing treatments for depression are inadequate for a significant minority of patients and new approaches are urgently needed. A wealth of evidence implicates the serotonin 1A (5-HT1A) receptor in the pathophysiology of depression. Stimulation of the 5-HT1A receptor is an existing therapeutic target for treating depression and anxiety, using drugs such as buspirone and tandospirone. However, activation of 5-HT1A raphe autoreceptors has also been suggested to be responsible for the delay in the therapeutic action of conventional antidepressants such as selective serotonin reuptake inhibitors (SSRIs). This narrative review provides a brief overview of the 5-HT1A receptor, the evidence implicating it in depression and in the effects of conventional antidepressant treatment. We highlight that pre- and post-synaptic 5-HT1A receptors may have divergent roles in the pathophysiology and treatment of depression. To date, developing this understanding to progress therapeutic discovery has been limited, partly due to a paucity of specific pharmacological probes suitable for use in humans. The development of 5-HT1A 'biased agonism', using compounds such as NLX-101, offers the opportunity to further elucidate the roles of pre- and post-synaptic 5-HT1A receptors. We describe how experimental medicine approaches can be helpful in profiling the effects of 5-HT1A receptor modulation on the different clinical domains of depression, and outline some potential neurocognitive models that could be used to test the effects of 5-HT1A biased agonists.

Cortisol as a Biomarker of Mental Disorder Severity

Cortisol—the most important steroid hormone with a significant effect on body metabolism—strongly affects peripheral tissues and the central nervous system. Fluctuations in cortisol secretion often accompany psychiatric disorders, and normalization of its levels correlates with improvement in the patient’s health. This indicates that cortisol may be useful as a biological marker that can help determine the likelihood of mental illness, its impending onset, and the severity of symptoms, which is especially important in the face of the increasing prevalence of mental disorders, including those associated with social isolation and anxiety during the COVID-19 pandemic. This publication reviews recent reports on cortisol levels in healthy participants and shows the current state of knowledge on changes in the levels of this hormone in people at risk for depression, bipolar disorder, and psychosis. It shows how people with psychiatric disorders react to stressful situations and how the applied therapies affect cortisol secretion. The influence of antidepressants and antipsychotics on cortisol levels in healthy people and those with mental disorders is also described. Finally, it reviews publications on the patterns of cortisol secretion in patients in remission.

Serotonin: a never-ending story

The neurotransmitter serotonin is an evolutionary ancient molecule that has remarkable modulatory effects in almost all central nervous system integrative functions, such as mood, anxiety, stress, aggression, feeding, cognition and sexual behavior. After giving a short outline of the serotonergic system (anatomy, receptors, transporter) the author's contributions over the last 40 years in the role of serotonin in depression, aggression, anxiety, stress and sexual behavior is outlined. Each area delineates the work performed on animal model development, drug discovery and development. Most of the research work described has started from an industrial perspective, aimed at developing animals models for psychiatric diseases and leading to putative new innovative psychotropic drugs, like in the cases of the SSRI fluvoxamine, the serenic eltoprazine and the anxiolytic flesinoxan. Later this research work mainly focused on developing translational animal models for psychiatric diseases and implicating them in the search for mechanisms involved in normal and diseased brains and finding new concepts for appropriate drugs.

GPER1 stimulation alters posttranslational modification of RGSz1 and induces desensitization of 5-HT1A receptor signaling in the rat hypothalamus

Hyperactivity of the hypothalamic-pituitary-adrenal axis is a consistent biological characteristic of depression, and response normalization coincides with clinical responsiveness to antidepressant medications. Desensitization of serotonin 1A receptor (5-HT1AR) signaling in the hypothalamic paraventricular nucleus of the hypothalamus (PVN) follows selective serotonin reuptake inhibitor (SSRI) antidepressant treatment and contributes to the antidepressant response. Estradiol alone produces a partial desensitization of 5-HT1AR signaling and synergizes with SSRIs to result in a complete and more rapid desensitization than with SSRIs alone as measured by a decrease in the oxytocin and adrenocorticotrophic hormone (ACTH) responses to 5-HT1AR stimulation. G protein-coupled estrogen receptor 1 (GPER1) is necessary for estradiol-induced desensitization of 5-HT1AR signaling, although the underlying mechanisms are still unclear. We now find that stimulation of GPER1 with the selective agonist G-1 and nonselective stimulation of estrogen receptors dramatically alter isoform expression of a key component of the 5-HT1AR signaling pathway, RGSz1, a GTPase-activating protein selective for Gαz, the Gα subunit necessary for 5-HT1AR-mediated hormone release. RGSz1 isoforms are differentially glycosylated, SUMOylated, and phosphorylated, and differentially distributed in subcellular organelles. High-molecular-weight RGSz1 is SUMOylated and glycosylated, localized to the detergent-resistant microdomain (DRM) of the cell membrane, and increased by estradiol and G-1 treatment. Because activated Gαz also localizes to the DRM, increased DRM-localized RGSz1 by estradiol and G-1 could reduce Gαz activity, functionally uncoupling 5-HT1AR signaling. Peripheral G-1 treatment produced a partial reduction in oxytocin and ACTH responses to 5-HT1AR stimulation similar to direct injections into the PVN. Together, these results identify GPER1 and RGSz1 as novel targets for the treatment of depression.

Antidepressant treatment reduces serotonin-1A autoreceptor binding in major depressive disorder

BACKGROUND

Chronic selective serotonin reuptake inhibitor (SSRI) administration to rodents desensitizes or downregulates raphe 5-hydroxytryptamine 1A (5-HT1A) autoreceptors. We previously found elevated 5-HT1A binding in antidepressant-naive and not recently medicated major depressive disorder (MDD) and now report the effect of SSRI treatment on 5-HT1A autoreceptors in depressed patients.

METHODS

5-HT1A binding (BPF) was quantified in medication-free subjects using positron emission tomography (PET) with [11C]-WAY-100635 before and after treatment of MDD with an SSRI for 5 to 9 weeks (mean 47 ± 8 days). Nineteen subjects without recent history of antidepressant pharmacotherapy completed both [11C]WAY-100635 PET scans with a metabolite-corrected arterial input function and depression severity was rated before and after the treatment course.

RESULTS

5-HT1A autoreceptor BPF in the raphe was reduced 18% on SSRI treatment (df = 1,18; F = 5.12; p = .036). However, the degree of reduction in 5-HT1A autoreceptor BPF was unrelated to improvement in depression (df = 1,16; F = 1.27; p = .276).

CONCLUSIONS

Downregulation of 5-HT1A autoreceptor binding by SSRI treatment of major depression is consistent with animal studies. This may be a necessary but insufficient requirement for clinical response to SSRIs. A PET agonist ligand that binds selectively to the high-affinity conformation of this receptor can determine whether SSRIs also cause desensitization of the autoreceptor as reported by some rodent studies and whether that effect may be related to clinical response.

Salivary cortisol in women with major depressive disorder under selective serotonin reuptake inhibitors therapy

Depression is one of the widespread diseases whose etiology is still unclear. Dysregulation of the hypothalamic-pituitary-adrenal axis can be the cause of this illness which is concomitant with a high level of cortisol. For this reason, the purpose of the study was to estimate the influence of the selective serotonin reuptake inhibitors (SSRIs) therapy used in monotherapy and polypragmasy on cortisol level in saliva of depressed women. Cortisol was determined in saliva collected from 40 depressed patients treated with SSRIs. HPLC with UV detection was used for quantification of cortisol after its extraction with dichloromethane. For statistical evaluation of the data, the cluster analysis and principal components analysis were used. Results of the study have shown that the SSRIs treatment reduces the cortisol level in saliva. The therapy with sertraline and polypragmasy had a strong influence on suppressing the cortisol secretion. Besides, the amplitude of changes of the cortisol level during the treatment had an impact on the duration of hospitalization. In conclusion, it can be stet that the process of reduction of the cortisol level is multiphasic and that the combination treatment had a stronger influence on suppressing the cortisol secretion than did antidepressants used in monotherapy.

The relation of developmental changes in brain serotonin transporter (5HTT) and 5HT1A receptor binding to emotional behavior in female rhesus monkeys: effects of social status and 5HTT genotype

The goal of the present study was to examine how social subordination stress and 5HTT polymorphisms affect the development of brain serotonin (5HT) systems during the pubertal transition in female rhesus monkeys. We also examined associations with developmental changes in emotional reactivity in response to a standardized behavioral test, the Human Intruder (HI). Our findings provide the first longitudinal evidence of developmental increases in 5HT1A receptor and 5HTT binding in the brain of female primates from pre- to peripuberty. The increase in 5HT1A BP(ND) in these socially housed female rhesus monkeys is a robust finding, occurring across all groups, regardless of social status or 5HTT genotype, and occurring in the left and right hemispheres of all prefrontal regions studied, as well as the amygdala, hippocampus, hypothalamus, and raphe nuclei. 5HTT BP(ND) also showed an increase with age in raphe, anterior cingulate cortex, and dorsolateral prefrontal cortex. These changes in brain 5HT systems take place as females establish more adult-like patterns of social behavior, as well as during the HI paradigm. Indeed, the main developmental changes in behavior during the HI (increase in freezing and decrease in submission/appeasement) were related to neurodevelopmental increases in 5HT1A receptors and 5HTT, because the associations between these behaviors and 5HT endpoints emerge at peripuberty. We detected an effect of social status on 5HT1A BP(ND) in the hypothalamus and on 5HTT BP(ND) in the orbitofrontal cortex, with subordinates showing higher BP(ND) than dominants in both cases during the pubertal transition. No main effects of 5HTT genotype were observed for 5HT1A or 5HTT BP(ND). Our findings indicate that adolescence in female rhesus monkeys is a period of central 5HT reorganization, partly influenced by exposure to the social stress of subordination, that likely functions to integrate adrenal and gonadal systems and shape the behavioral response to emotionally challenging social situations.

GPR30 is necessary for estradiol-induced desensitization of 5-HT1A receptor signaling in the paraventricular nucleus of the rat hypothalamus

Estrogen therapy used in combination with selective serotonin reuptake inhibitor (SSRI) treatment improves SSRI efficacy for the treatment of mood disorders. Desensitization of serotonin 1A (5-HT(1A)) receptors, which takes one to two weeks to develop in animals, is necessary for SSRI therapeutic efficacy. Estradiol modifies 5-HT(1A) receptor signaling and induces a partial desensitization in the paraventricular nucleus (PVN) of the rat within two days, but the mechanisms underlying this effect are currently unknown. The purpose of this study was to identify the estrogen receptor necessary for estradiol-induced 5-HT(1A) receptor desensitization. We previously showed that estrogen receptor β is not necessary for 5-HT(1A) receptor desensitization and that selective activation of estrogen receptor GPR30 mimics the effects of estradiol in rat PVN. Here, we used a recombinant adenovirus containing GPR30 siRNAs to decrease GPR30 expression in the PVN. Reduction of GPR30 prevented estradiol-induced desensitization of 5-HT(1A) receptor as measured by hormonal responses to the selective 5-HT(1A) receptor agonist, (+)8-OH-DPAT. To determine the possible mechanisms underlying these effects, we investigated protein and mRNA levels of 5-HT(1A) receptor signaling components including 5-HT(1A) receptor, Gαz, and RGSz1. We found that two days of estradiol increased protein and mRNA expression of RGSz1, and decreased 5-HT(1A) receptor protein but increased 5-HT(1A) mRNA; GPR30 knockdown prevented the estradiol-induced changes in 5-HT(1A) receptor protein in the PVN. Taken together, these data demonstrate that GPR30 is necessary for estradiol-induced changes in the 5-HT(1A) receptor signaling pathway and desensitization of 5-HT(1A) receptor signaling.

Estradiol induces partial desensitization of serotonin 1A receptor signaling in the paraventricular nucleus of the hypothalamus and alters expression and interaction of RGSZ1 and Gαz

Hyperactivity of hypothalamic-pituitary mediated hormone responses, such as to stimulation with a serotonin 1A (5-HT(1A)) receptor agonist, are a feature of depression which are normalized with clinical improvement during drug therapy. We previously reported that SSRIs induce desensitization of 5-HT(1A) receptor signaling in the paraventricular nucleus of the hypothalamus (PVN) while estradiol benzoate (EB) produces a more rapid, partial desensitization. In the current study, time course and dose-response experiments demonstrated that two once daily doses of EB is the minimum needed to induce the desensitization response as indicated by 5-HT(1A) receptor-stimulated release of oxytocin and that 10 μg/kg/day EB produces the maximal response, a partial desensitization of approximately 40%. The effects of two once daily injections of 10 μg/kg/day EB on Gαz and RGSZ1 proteins were examined as components of the 5-HT(1A) receptor signaling system, which mediates the release of oxytocin and adrenocorticotropic hormone. RGSZ1 appears to be a major target for EB-mediated responses in the 5-HT(1A) receptor signaling system. A 55 kD membrane-associate RGSZ1 protein was greatly increased in the PVN and rest of the hypothalamus and moderately increased in the dorsal hippocampus and amygdala after EB treatment as well as after an acute dose of a 5-HT(1A) receptor agonist. These results suggest that EB is a candidate for adjuvant therapy with SSRIs to hasten the therapeutic response and that RGSZ1 is a major target of EB therapy which could be explored as a target for novel therapeutic approaches for the treatment of depression.

Hormonal responses to the 5-HT1A agonist buspirone in remitted endogenous depressive patients after long-term imipramine treatment

INTRODUCTION

The serotonin-1A (5-HT1A) receptor subtypes are considered as targets of a variety of antidepressant drugs. Previous studies have suggested different adaptive changes in pre- and post-synaptic 5-HT receptors in the brain after treatment with non-selective tricyclic antidepressants (TCA) and selective 5-HT re-uptake inhibitors (SSRIs). The present study aimed to investigate the adaptive effect of the TCA imipramine on the post-synaptic 5-HT1A receptor function in the hypothalamus.

METHODS

A longitudinal design was used in 14 patients with major depressive disorder (DSM-IV) with endogenous features (Newcastle Scale) in order to assess the functional status of post-synaptic 5-HT1A receptors before and after successful antidepressant treatment with imipramine. The effect of the 5-HT1A receptor agonist, buspirone, on ACTH, cortisol, and prolactine (PRL) plasma levels was used to assess the functional status of hypothalamic 5-HT1A receptors. A group of 15 concurrent normal subjects were used as control.

RESULTS

Endogenous depressed patients in remission and currently receiving treatment with imipramine (mean length of treatment 145 days, SD=27) presented significantly lower buspirone responses to ACTH and cortisol than in the pre-treatment condition (Deltamax p< or =.05; AUC p<.001) and to ACTH in comparison with healthy controls (Deltamax p<.01; AUC p<.05). No significant differences were found between the post-treatment and pre-treatment PRL responses, or between patients in both conditions and controls; nevertheless, the PRL response in patients in remission and receiving treatment almost reached the values seen in controls.

CONCLUSIONS

This study extends previous findings from our group using the SSRI citalopram as an antidepressant. Imipramine and citalopram induce similar changes in the endocrine response to buspirone in depressed patients. As the direction of change in ACTH-cortisol and PRL responses after treatment is the opposite, we cannot substantiate increases or decreases in the sensitivity of post-synaptic 5-HT1A receptors in the hypothalamus by long-term imipramine treatment and/or resolution of illness. Therefore, the hormonal changes may result from different or multiples unknown mechanisms.

5HT1A-mediated stimulation of cortisol release in major depression: use of non-invasive cortisol measurements to predict clinical response

The purpose of the present study was to explore 5HT1A-mediated cortisol release in major depressive disorder (MDD) patients in order to determine whether the degree of 5HT1A-receptor sensitivity can predict response to treatment with selective serotonin reuptake inhibitors (SSRIs). We examined whether the sensitivity of the 5HT1A receptor, as measured by the difference in salivary cortisol levels immediately before and 90 min following the administration of a single dose of the 5HT1A-selective agonist buspirone, predicted treatment outcome following an 8-week, fixed-dose, open trial of the SSRI escitalopram in 17 outpatients with MDD. Change in cortisol levels before and 90 min after the administration of buspirone were not found to predict treatment outcome, whether defined as clinical response (50% or greater reduction in symptom severity), or remission of symptoms. In conclusion, in the present study, we did not find that the change in salivary cortisol levels following the administration of a 5HT1A-selective agonist predicted treatment outcome following an 8-week, fixed-dose, open-label trial of the SSRI escitalopram among outpatients with MDD. Although the 5HT1A-desensitization hypothesis is still a valid one, the results of the present study could not provide any evidence in support.

Vilazodone, a novel dual-acting serotonergic antidepressant for managing major depression

Major depressive disorder (MDD) affects <or= 15% of the general population and imparts a significant economic and psychosocial burden. Despite the availability of a wide range of drugs for treating MDD, the majority of patients fail to achieve complete and sustained remission of symptoms. Vilazodone is a novel dual-acting serotonergic antidepressant currently in clinical development for the treatment of MDD. Vilazodone combines the effects of a selective serotonin reuptake inhibitor with 5-HT(1A) receptor partial agonist activity. In a recent Phase III clinical trial, vilazodone showed significant antidepressant efficacy compared to placebo with a statistically significant onset of effect at 1 week. Overall dropout rates were low. Diarrhea, nausea and headache were the most common adverse events reported. In addition, there was no significant difference between placebo and vilazodone in terms of sexual dysfunction as measured by the Arizona Sexual Experiences Scale. A unique feature of the vilazodone clinical program is the concurrent development of biomarkers that may predict treatment response and common side effects. Vilazodone offers a dual mechanism of action, good general tolerability with the potential for less impairment of sexual function than selective serotonin reuptake inhibitors and the possibility of personalized treatment for MDD.

The impact of treatment on HPA axis activity in unipolar major depression

Dysregulation of hypothalamic-pituitary-adrenal axis activity in major depressive disorder has been found to normalize with successful treatment, though inconsistencies exist. To determine the magnitude of change in cortisol levels from pre to post-treatment in individuals with unipolar depression quantitative methods of meta-analysis were applied. Thirty-four studies met inclusion criteria and consisted of a total of 1049 depressed patients across study samples. The overall mean effect size of pre-post-treatment cortisol measures indicated that approximately 56% of depressed participants had similar cortisol levels before and after treatment regardless of symptom improvement. The mean effect size of pre-post cortisol measures for those who responded to treatment was larger than the mean effect size of non-responders; however, this difference did not reach statistical significance. As well, no significant differences in mean effect size of pre-post cortisol measures based on type of treatment (e.g. antidepressant vs. ECT) were found. Subtype of depressive illness and length of treatment may contribute to the magnitude of change in cortisol measure before and after treatment. Inconsistent findings within the reviewed literature may confound the overall results. The type of treatment and response to treatment do not appear to impact the magnitude of change in cortisol level pre to post-treatment. Our findings suggest that the utility of cortisol as an outcome measure may be limited to specific subsets of the depressed population, and that given the variability in HPA results between studies, it is premature to state that cortisol is not a good outcome measure.

Interaction between serotonin 5-HT1A receptors and beta-endorphins modulates antidepressant response

Interactions between serotonergic and the endogenous opioid systems have been suggested to be involved in the etiopathogenesis of depression and in the mechanism of action of antidepressants. Activation of serotonin 5-HT1A receptors has been shown to increase plasma beta-endorphin (beta-END) levels in animal studies and in healthy humans.

OBJECTIVES

To assess interaction abnormalities between 5-HT1A receptors and the endogenous opioid system in patients with major depression and the possible modulating effect of citalopram.

METHODS

The beta-END response to the 5-HT1A receptor agonist, buspirone (30 mg), was measured in 30 patients with major depression and in 30 age- and sex-matched healthy controls before and after an 8-week treatment with citalopram. Pre-treatment score of the Hamilton Rating Scale for Depression (HRSD) was >or=17. Antidepressant response was defined by a 50% decrease in the HRSD. Pre- and post-treatment maximum peak response (Deltamax) and the area under the curve (AUC) of beta-END response were compared. Three time points were measured (60, 90 and 120 min). We also examined the correlations between the beta-END response and the antidepressant response. Buspirone plasma levels were not measured.

RESULTS

At baseline, beta-END response was similar in patients and controls. After 8 weeks of citalopram treatment depressed patients showed a significant decrease in the beta-END response (Deltamax: p<.001; AUC: p<.001). A significant correlation between the beta-END reduction in the response and the reduction in the HRSD score (r=.656; p<.001) was observed.

CONCLUSIONS

Changes in interaction between 5-HT1A receptor system and the endogenous opioid system may play a role both in the mechanism of action and response to antidepressant drugs.

Translational aspects of pharmacological research into anxiety disorders: the stress-induced hyperthermia (SIH) paradigm

In anxiety research, the search for models with sufficient clinical predictive validity to support the translation of animal studies on anxiolytic drugs to clinical research is often challenging. This review describes the stress-induced hyperthermia (SIH) paradigm, a model that studies the activation of the autonomic nervous system in response to stress by measuring body temperature. The reproducible and robust SIH response, combined with ease of testing, make the SIH paradigm very suitable for drug screening. We will review the current knowledge on the neurobiology of the SIH response, discuss the role of GABA(A) and serotonin (5-HT) pharmacology, as well as how the SIH response relates to infectious fever. Furthermore, we will present novel data on the SIH response variance across different mice and their sensitivity to anxiolytic drugs. The SIH response is an autonomic stress response that can be successfully studied at the level of its physiology, pharmacology, neurobiology and genetics and possesses excellent animal-to-human translational properties.