A Complex Impact of Systemically Administered 5-HT2A Receptor Ligands on Conditioned Fear.

BACKGROUND: Though drugs binding to serotonergic 5-HT2A receptors have long been claimed to influence human anxiety, it remains unclear if this receptor subtype is best described as anxiety promoting or anxiety dampening. Whereas conditioned fear expressed as freezing in rats is modified by application of 5-HT2A-acting drugs locally into different brain regions, reports on the effect of systemic administration of 5-HT2A receptor agonists and 5-HT2A antagonists or inverse agonists on this behavior remain sparse. METHODS: We assessed the possible impact of systemic administration of 5-HT2A receptor agonists, 5-HT2A receptor inverse agonists, and a selective serotonin reuptake inhibitor (SSRI)-per se or in combination-on the freezing displayed by male rats when re-exposed to a conditioning chamber in which they received foot shocks 7 days earlier. RESULTS: The 5-HT2A receptor agonists psilocybin and 25CN-NBOH induced a reduction in conditioned fear that was countered by pretreatment with 5-HT2A receptor inverse agonist MDL 100907. While both MDL 100907 and another 5-HT2A receptor inverse agonist, pimavanserin, failed to impact freezing per se, both compounds unmasked a robust fear-reducing effect of an SSRI, escitalopram, which by itself exerted no such effect. CONCLUSIONS: The results indicate that 5-HT2A receptor activation is not a prerequisite for normal conditioned freezing in rats but that this receptor subtype, when selectively over-activated prior to expression, exerts a marked fear-reducing influence. However, in the presence of an SSRI, the 5-HT2A receptor, on the contrary, appears to counter an anti-freezing effect of the enhanced extracellular serotonin levels following reuptake inhibition.

Determining maximal achievable effect sizes of antidepressant therapies in placebo-controlled trials.

OBJECTIVE: Antidepressants outperform placebo with an effect size of around 0.30. It has been suggested that effect sizes as high as 0.875 are necessary for a minimal clinically important difference. Whether such effect sizes are achievable in placebo-controlled trials is unknown. Therefore, we aimed to assess what effect sizes are theoretically achievable in placebo-controlled trials of antidepressants. METHODS: Patient-level analyses comparing Hamilton Depression Rating Scale (HDRS-17) outcomes for simulated antidepressant therapies to placebo-treated participants (n = 2201) from clinical trials of selective serotonin reuptake inhibitors. RESULTS: An optimally effective antidepressant, where all treated participants achieve HDRS-17 scores comparable to those displayed by healthy volunteers (remission-type model), had a maximum effect size of 1.75, with a mean difference of 11.6 points on the HDRS-17. In simulations where patients received an additional 50% symptom reduction over that obtained with placebo (improvement-type model), the maximum effect size was 1.08 with a mean HDRS-17 difference of 7.2. When adjusting for normal rates of treatment discontinuation, maximum effect sizes were 1.10 (remission-type model) and 0.76 (improvement-type model) with HDRS-17 mean differences of 8.8 and 5.6, respectively. CONCLUSIONS: Three methodological issues (i) a large and variable placebo response, (ii) a high rate of dropout and (iii) HDRS-17-ratings significantly larger than zero in healthy volunteers, reduce the degree of treatment-placebo separation achievable in depression trials. Assuming that those who discontinue treatment have only partial response, even a highly effective antidepressant would have difficulties surpassing such effect size cut-offs as have been suggested to signify a minimal clinically important difference.

Expression of 22 serotonin-related genes in rat brain after sub-acute serotonin depletion or reuptake inhibition.

OBJECTIVE: Although the assessment of expression of serotonin-related genes in experimental animals has become a common strategy to shed light on variations in brain serotonergic function, it remains largely unknown to what extent the manipulation of serotonin levels causes detectable changes in gene expression. We therefore chose to investigate how sub-acute depletion or elevation of brain serotonin influences the expression of a number of serotonin-related genes in six brain areas. METHODS: Male Wistar rats were administered a serotonin synthesis inhibitor, para-chlorophenylalanine (p-CPA), or a serotonin reuptake inhibitor, paroxetine, for 3 days and then sacrificed. The expression of a number of serotonin-related genes in the raphe nuclei, hypothalamus, amygdala, striatum, hippocampus and prefrontal cortex was investigated using real-time quantitative PCR (rt-qPCR). RESULTS: While most of the studied genes were uninfluenced by paroxetine treatment, we could observe a robust downregulation of tryptophan hydroxylase-2 in the brain region where the serotonergic cell bodies reside, that is, the raphe nuclei. p-CPA induced a significant increase in the expression of Htr1b and Htr2a in amygdala and of Htr2c in the striatum and a marked reduction in the expression of Htr6 in prefrontal cortex; it also enhanced the expression of the brain-derived neurotrophic factor (Bdnf) in raphe and hippocampus. CONCLUSION: With some notable exceptions, the expression of most of the studied genes is left unchanged by short-term modulation of extracellular levels of serotonin.

Good news regarding SSRI safety in Danish meta-analysis.

In two previous letters on an selective serotonin reuptake inhibitor (SSRI) meta-analysis conducted by the Copenhagen Trial Unit at Copenhagen University Hospital, we have commented on a large number of errors, almost all of which have tilted the results in an anti-drug direction, that unfortunately mar this publication. While the authors have acknowledged many of these mishaps, and may now be expected to submit an extensive errata list to the journal where their paper was once published, we regretfully note that also their latest contribution to this exchange is surprisingly inaccurate. However, its many shortcomings notwithstanding, their meta-analysis does add to the current literature by confirming that SSRIs do not seem to enhance the risk for suicide or death, and also that these drugs seem to enhance the risk of side effects categorised as serious only in the elderly.

Effects of selective serotonin reuptake inhibitors on rating-scale-assessed suicidality in adults with depression.

BACKGROUND: Selective serotonin reuptake inhibitors (SSRIs) have been claimed to elicit or aggravate suicidal ideation. Aims To explore the effect of SSRIs on the suicidality item of the Hamilton Rating Scale for Depression (HRSD). METHOD: We undertook a patient-level mega-analysis of adults with depression participating in industry-sponsored studies of sertraline, paroxetine or citalopram, comparing patients on an SSRI (n = 5681) with those on placebo (n = 2581) with respect to HRSD-rated suicidality. Separate analyses were conducted for young adults (age 18-24; n = 537) and adults (age ≥25; n = 7725). RESULTS: Among adults, the reduction in mean rating of suicidality was larger and the risk for aggravation of suicidality lower in patients receiving an SSRI from week 1 and onwards. In young adults, SSRI treatment neither reduced nor increased suicidality ratings relative to placebo at the end-point. CONCLUSIONS: The net effect of SSRIs on suicidality appears beneficial in people above the age of 24 and neutral in those aged 18-24. Declaration of interest F.H. has received speaker's fees from Servier. E.E. has previously been on the advisory boards and/or received speaker's honoraria and/or research grants from Eli Lilly, GlaxoSmithKline, Servier and Lundbeck.

Katakam and co-workers have not shown SSRIs to be harmful and ineffective and should stop claiming that they have.

Funded by the Danish state to provide guidance in health-related matters, the Copenhagen Trial Unit (CTU) at Rigshospitalet may cause considerable societal harm if allowing their analyses to be influenced by bias and prejudice rather than rigor and impartiality. This is why we found it worthwhile to comment on a report from the CTU in which the authors invoked analyses marred by numerous errors and methodological mistakes to claim that selective serotonin reuptake inhibitors (SSRIs) are harmful and ineffective. The CTU group has now produced a response to our comment which is on par with their original contribution in terms of bias, misconceptions and mistakes. Our conclusion is that the reputation of the CTU would be best served by the authors asking for retraction of their SSRI paper.

Multiple possible inaccuracies cast doubt on a recent report suggesting selective serotonin reuptake inhibitors to be toxic and ineffective.

According to a systematic review on the use of selective serotonin reuptake inhibitors (SSRIs) in adult depression that was recently published in BMC Psychiatry, the results of which have been widely disseminated in lay media, these drugs increase the risk for serious adverse events (SAEs) while exerting poor antidepressant efficacy. A cursory analysis, however, suggests the analysis of SAEs conducted by the authors to be marred by both methodological inaccuracies and blatant errors. After having corrected for these apparent mistakes, we conducted a sensitivity analysis in which we also accounted for a possible moderating effect of age; while this suggests SSRIs to be safe drugs in the non-elderly, they do confirm what is already known, that is, that they may enhance the risk for SAEs in the old. Given the loose definition of SAE, including also innocuous phenomena, the possible clinical significance of the latter observation, however, remains unclear until the nature and actual impact of the SAEs in question have been clarified. Moreover, with respect to efficacy, we find the paper in BMC Psychiatry misleading: first, the authors seem unaware of the well-established shortcomings associated with the conventional efficacy parameter on which their analysis is based, second, they have included suboptimal SSRI doses and third, they have missed some pivotal trials. Unless there are explanations for the many peculiarities in this paper that have escaped us, and which may be satisfactorily clarified by the authors, it seems important that the conclusions presented in this paper be publicly rectified.

Differences in Anxiety-Like Behavior within a Batch of Wistar Rats Are Associated with Differences in Serotonergic Transmission, Enhanced by Acute SRI Administration, and Abolished By Serotonin Depletion.

BACKGROUND: The anxiety-reducing effect of long-term administration of serotonin reuptake inhibitors is usually seen only in subjects with anxiety disorders, and such patients are also abnormally inclined to experience a paradoxical anxiety-enhancing effect of acute serotonin reuptake inhibition. These unique responses to serotonin reuptake inhibitors in anxiety-prone subjects suggest, as do genetic association studies, that inter-individual differences in anxiety may be associated with differences in serotonergic transmission. METHODS: The one-third of the animals within a batch of Wistar rats most inclined to spend time on open arms in the elevated plus maze were compared with the one-third most inclined to avoid them with respect to indices of brain serotonergic transmission and how their behavior was influenced by serotonin-modulating drugs. RESULTS: "Anxious" rats displayed higher expression of the tryptophan hydroxylase-2 gene and higher levels of the tryptophan hydroxylase-2 protein in raphe and also higher levels of serotonin in amygdala. Supporting these differences to be important for the behavioral differences, serotonin depletion obtained by the tryptophan hydroxylase-2 inhibitor p-chlorophenylalanine eliminated them by reducing anxiety in "anxious" but not "non-anxious" rats. Acute administration of a serotonin reuptake inhibitor, paroxetine, exerted an anxiety-enhancing effect in "anxious" but not "non-anxious" rats, which was eliminated by long-term pretreatment with another serotonin reuptake inhibitor, escitalopram. CONCLUSIONS: Differences in an anxiogenic impact of serotonin, which is enhanced by acute serotonin reuptake inhibitor administration, may contribute to differences in anxiety-like behavior amongst Wistar rats.

Item-based analysis of the effects of duloxetine in depression: a patient-level post hoc study.

Oft-cited trial-level meta-analyses casting doubt on the usefulness of antidepressants have been based on re-analyses of to what extent the active drug has outperformed placebo in reducing the sum score of the Hamilton Depression Rating Scale (HDRS-17-sum) in clinical trials. Recent studies, however, suggest patient-level analyses of individual HDRS items to be more informative when assessing the efficacy of an antidepressant. To shed further light on both symptom-reducing and symptom-aggravating effects of a serotonin and noradrenaline reuptake inhibitor, duloxetine, when used for major depression in adults, we hence applied this approach to re-analyse data from 13 placebo-controlled trials. In addition, using patient-level data from 28 placebo-controlled trials of selective serotonin reuptake inhibitors (SSRIs), the response profile of duloxetine was compared to that of these drugs. Duloxetine induced a robust reduction in depressed mood that was not dependent on baseline severity and not caused by side-effects breaking the blind. A beneficial effect on depressed mood was at hand already after one week; when outcome was assessed using HDRS-17-sum as effect parameter, this early response was however masked by a concomitant deterioration with respect to adverse event-related items. No support for a suicide-provoking effect of duloxetine was obtained. The response profile of duloxetine was strikingly similar to that of the SSRIs. We conclude that the use of HDRS-17-sum as effect parameter underestimates the true efficacy and masks an early effect of duloxetine on core symptoms of depression. No support for major differences between duloxetine and SSRIs in clinical profile were obtained.

Effects of gonadectomy and serotonin depletion on inter-individual differences in anxiety-like behaviour in male Wistar rats.

Previous studies in Wistar rats suggest inter-individual differences in anxiety-like behaviour as assessed using the elevated plus maze (EPM), both between sexes and among males, to be abolished by serotonin depletion. To shed further light on the influence of sex steroids and serotonin - and on the interplay between the two - on proneness for EPM-assessed anxiety in males, outbred Wistar rats were divided into those with high and low anxiety, respectively, and exposed to gonadectomy or sham operation followed by administration of a serotonin synthesis inhibitor, para-chlorophenylalanine, or saline. Whereas gonadectomy enhanced anxiety-like behaviour in low anxiety rats so that these no longer differed in this regard from the high anxiety group, serotonin depletion reversed this effect, and also reduced anxiety in the low anxiety group regardless of gonadal state. A previously observed association between high anxiety-like behaviour and high expression of the serotonin-synthesizing enzyme tryptophan hydroxylase 2 (Tph2) in the raphe was confirmed in sham-operated animals but absent in gonadectomised rats, an ANCOVA revealing a significant interactive effect of baseline anxiety and gonadal state on Tph2 expression. It is suggested that androgens may contribute to upholding inter-individual differences in anxiety-like behaviour in male rats by interacting with serotonergic neurotransmission.

Acute escitalopram but not contextual conditioning exerts a stronger "anxiogenic" effect in rats with high baseline "anxiety" in the acoustic startle paradigm.

RATIONALE: Acute administration of selective serotonin reuptake inhibitors (SSRIs) may enhance anxiety in humans, those with anxiety disorders being more susceptible than others. Fear-conditioned or unconditioned acoustic startle and freezing are common measures of fear and/or "anxiety" in rodents that may be used to study this effect of SSRIs preclinically. OBJECTIVES: Our aim was to shed further light on the effect of acute administration of an SSRI, escitalopram (10 mg/kg), on startle and freezing in the absence or presence of prior contextual conditioning. Repeated testing also enabled us to evaluate (i) if there are stable inter-animal variations with respect to these parameters in a batch of outbred Wistar rats, (ii) the possible relationship between the two and (iii) if baseline behaviour predicts the response to escitalopram. RESULTS: Inter-animal test-retest correlations were found for both startle and freezing at baseline, and the two parameters also correlated with each other. Both escitalopram and contextual conditioning increased freezing and startle but without exerting any synergistic effect. While animals displaying high startle at baseline showed higher susceptibility to respond to escitalopram, the effect of conditioning was more pronounced in those with low baseline startle. CONCLUSIONS: The results support the usefulness of both conditioned and non-conditioned startle and freezing to capture an "anxiogenic" influence of SSRIs. Also, they suggest that baseline non-conditioned startle may predict this response in a manner reflecting the clinical situation in the sense that subjects with high baseline "anxiety" are particularly prone to respond with enhanced "anxiety" following acute SSRI administration.

Serotonin depletion-induced maladaptive aggression requires the presence of androgens.

The sex hormone testosterone and the neurotransmitter serotonin exert opposite effects on several aspects of behavior including territorial aggression. It is however not settled if testosterone exerts its pro-aggressive effects by reducing serotonin transmission and/or if the anti-aggressive effect of serotonin requires the presence of the androgen. Using the resident intruder test, we now show that administration of the serotonin synthesis inhibitor para-chlorophenylalanine (300 mg/kg x 3 days) increases the total time of attack as well as the percentage amount of social behavior spent on attack but not that spent on threat - i.e. that it induces a pattern of unrestricted, maladaptive aggression - in gonadectomized C57Bl/6 male mice receiving testosterone replacement; in contrast, it failed to reinstate aggression in those not given testosterone. Whereas these results suggest the pro-aggressive effect of testosterone to be independent of serotonin, and not caused by an inhibition of serotonergic activity, the pCPA-induced induction of maladaptive aggression appears to require the presence of the hormone. In line with these findings, pCPA enhanced the total time of attack as well the relative time spent on attacks but not threats also in wild-type gonadally intact male C57Bl/6 mice, but failed to reinstate aggression in mice rendered hypo-aggressive by early knock-out of androgen receptors in the brain (ARNesDel mice). We conclude that androgenic deficiency does not dampen aggression by unleashing an anti-aggressive serotonergic influence; instead serotonin seems to modulate aggressive behavior by exerting a parallel-coupled inhibitory role on androgen-driven aggression, which is irrelevant in the absence of the hormone, and the arresting of which leads to enhanced maladaptive aggression.

Serotonin depletion counteracts sex differences in anxiety-related behaviour in rat.

BACKGROUND: Numerous studies suggest (1) that a major physiological role of brain serotonin-containing neurons is to modulate sex steroid-driven behaviour such as sex and aggression, (2) that sex steroids influence brain serotonergic neurotransmission and (3) that brain serotonergic neurotransmission displays sexual dimorphism. Such observations indicate that an important task for brain serotonin is to either enhance or counteract sex differences in behaviour. METHODS: To test this hypothesis, we explored the effect of short-term serotonin depletion on the behaviour of adult male and female rats in a behavioural paradigm in which males and females have been shown to behave differently, i.e. the elevated plus maze. RESULTS: Two rounds of testing of untreated Wistar rats confirmed the previous observation that females make more entries into open arms (round 1, p = 0.001; round 2, p = 0.008) and spend more time on these arms (round 1, p ≤ 0.001; round 2, p = 0.006) than males; in addition, males displayed fewer entries into closed arms upon habituation, i.e. at the second round (p ≤ 0.001) than did females. Administration of the tryptophan hydroxylase inhibitor para-chloro-phenylalanine, at a regimen (300 mg/kg/day for 3 days), markedly reducing brain content of serotonin, enhanced entries upon open arms (p = 0.01) and time spent on open arms (p = 0.004) in males but exerted no such effects in females (p = 0.9 and p = 0.9, respectively); moreover, it reduced entries into closed arms in females (p ≤ 0.001) but not in males (p = 0.1). CONCLUSIONS: Serotonin depletion abolishing the sex differences observed at baseline supports the theory that serotonin aids to uphold certain sex differences in behaviour.

Ghrelin influences novelty seeking behavior in rodents and men.

Recent discoveries indicate an important role for ghrelin in drug and alcohol reward and an ability of ghrelin to regulate mesolimbic dopamine activity. The role of dopamine in novelty seeking, and the association between this trait and drug and alcohol abuse, led us to hypothesize that ghrelin may influence novelty seeking behavior. To test this possibility we applied several complementary rodent models of novelty seeking behavior, i.e. inescapable novelty-induced locomotor activity (NILA), novelty-induced place preference and novel object exploration, in rats subjected to acute ghrelin receptor (growth hormone secretagogue receptor; GHSR) stimulation or blockade. Furthermore we assessed the possible association between polymorphisms in the genes encoding ghrelin and GHSR and novelty seeking behavior in humans. The rodent studies indicate an important role for ghrelin in a wide range of novelty seeking behaviors. Ghrelin-injected rats exhibited a higher preference for a novel environment and increased novel object exploration. Conversely, those with GHSR blockade drastically reduced their preference for a novel environment and displayed decreased NILA. Importantly, the mesolimbic ventral tegmental area selective GHSR blockade was sufficient to reduce the NILA response indicating that the mesolimbic GHSRs might play an important role in the observed novelty responses. Moreover, in untreated animals, a striking positive correlation between NILA and sucrose reward behavior was detected. Two GHSR single nucleotide polymorphisms (SNPs), rs2948694 and rs495225, were significantly associated with the personality trait novelty seeking, as assessed using the Temperament and Character Inventory (TCI), in human subjects. This study provides the first evidence for a role of ghrelin in novelty seeking behavior in animals and humans, and also points to an association between food reward and novelty seeking in rodents.