The 5-HT3 antagonist, BRL 46470 does not attenuate m-chlorophenylpiperazine (mCPP)-induced changes in human volunteers

Effects of the 5-HT2C receptor agonist meta-chlorophenylpiperazine on appetite, food intake and emotional processing in healthy volunteers

RATIONALE

The treatment of obesity is an increasing global health priority, yet few effective drug treatments are currently available. The discovery of novel anti-obesity therapies could be assisted by the validation of experimental (translational) medicine models in healthy volunteers that assess efficacy and safety at an early stage of drug development.

OBJECTIVES

The aim of this study was to examine the effects of the 5-HT2C receptor agonist meta-chlorophenylpiperazine (mCPP) in an experimental medicine model assessing both appetite and mood.

METHODS

Using a between-subjects, double-blind, placebo-controlled design, 24 male and 24 female participants were randomly assigned to either placebo, 15- or 30-mg mCPP treatment groups. Lunch was eaten from a Universal Eating Monitor (UEM) that measured eating rate, and the participants completed the P1vital® Oxford Emotional Test Battery (ETB) and a series of appetite and mood ratings.

RESULTS

mCPP reduced appetite and, in women, enhanced measures of satiation. The drug also enhanced memory for emotional material in the word recall and recognition memory tasks of the ETB.

CONCLUSIONS

The results provide new insight into the effects of mCPP on appetite, satiety and memory in humans. In addition, our data provide an illustration of the value of measuring changes in appetite and mood in healthy volunteers to determine the potential efficacy and safety of novel anti-obesity drugs.

Hypersensitivity of 5-HT2 receptors in OCD patients. An increased prolactin response after a challenge with meta-chlorophenylpiperazine and pre-treatment with ritanserin and placebo

INTRODUCTION

Several studies in obsessive compulsive disorder (OCD) have provided circumstantial evidence that the 5-HT-system is involved in the pathophysiology of OCD. To further examine the role of 5-HT receptors we studied the behavioural and neuroendocrine effects of different doses of meta-chlorophenylpiperazine (mCPP) in OCD patients and healthy controls, after pre-treatment with ritanserin, a 5-HT2 receptor antagonist, and placebo.

DESIGN

Twenty patients and 20 healthy controls received 0.1, 0.3 or 0.5 mg/kg mCPP or placebo orally. Each subject was tested two times, receiving both times the same dosage of mCPP or placebo with ritanserin or placebo pre-treatment. All was done under double-blind conditions. OC-symptoms and hormone levels were measured.

RESULTS

The increase in prolactin level after mCPP administration was more robust in patients than in controls. The prolactin response following 0.5 mg/kg of mCPP was partially blocked by ritanserin in patients, but totally blocked in healthy controls. The cortisol responses in both groups did not differ statistically significant from each other and were entirely blocked by ritanserin. None of the subjects experienced an exacerbation of obsessive compulsive symptoms.

CONCLUSION

The neuroendocrine results show an enhanced susceptibility of OCD patients for the mCPP-induced prolactin response, which effect seems to be due to an increased sensitivity of 5-HT2 receptors.

gamma-Aminobutyric acid-serotonin interactions in healthy men: implications for network models of psychosis and dissociation

BACKGROUND

This study tested the hypothesis that deficits in gamma-aminobutyric acid type A (GABA(A)) receptor function might create a vulnerability to the psychotogenic and perceptual altering effects of serotonergic (5-HT(2A/2C)) receptor stimulation. The interactive effects of iomazenil, an antagonist and partial inverse agonist of the benzodiazepine site of the GABA(A) receptor complex, and m-chlorophenylpiperazine (m-CPP), a partial agonist of 5-HT(2A/2C) receptors, were studied in 23 healthy male subjects.

METHODS

Subjects underwent 4 days of testing, during which they received intravenous infusions of iomazenil/placebo followed by m-CPP/placebo in a double-blind, randomized crossover design. Behavioral, cognitive, and hormonal data were collected before drug infusions and periodically for 200 min after.

RESULTS

Iomazenil and m-CPP interacted in a synergistic manner to produce mild psychotic symptoms and perceptual disturbances without impairing cognition. Iomazenil and m-CPP increased anxiety in an additive fashion. Iomazenil and m-CPP interacted in a synergistic manner to increase serum cortisol.

CONCLUSIONS

Gamma-aminobutyric acid-ergic deficits might increase the vulnerability to the psychotomimetic and perceptual altering effects of serotonergic agents. These data suggest that interactions between GABA(A) and 5-HT systems might contribute to the pathophysiology of psychosis and dissociative-like perceptual states.

A preliminary open study of the tolerability and effectiveness of nefazodone in major depressive disorder: comparing patients who recently discontinued an SSRI with those on no recent antidepressant treatment

Anecdotal evidence suggests that the recent discontinuation of an SSRI may confound the tolerability of the initiation of nefazodone treatment. We sought to determine whether recent discontinuation of an SSRI interferes with effectiveness and/or tolerability of nefazodone. Twenty-six depressed subjects, 21-63 years old, were recruited at the Massachusetts General Hospital. Thirteen subjects (50%) had discontinued an SSRI within 1-4 weeks due to ineffectiveness and/or side effects. Thirteen subjects (50%) had not taken antidepressants for the previous 6 months. Subjects were administered open nefazodone 50 mg p.o. b.i.d., and doses were increased as tolerated to a maximum of 600 mg/day. Subjects were followed for 12 weeks and were assessed for response and side effects using HAM-D-6 and clinical interviews. Both groups improved significantly on nefazodone; however, there was no statistically significant difference in response (>or=50% decrease in HAM-D-6) rates between completers with prior SSRI treatment (80%) and completers without recent exposure to antidepressants (67%). Response rates based on intent-to-treat (ITT) analysis were 31% for both groups. Association between prior SSRI treatment and discontinuation of nefazodone due to side effects or non-response was not statistically significant. Our study suggests that the rate of negative outcomes with nefazodone is no different whether patients have recently failed an SSRI.

A 5-HT2C agonist elicits hyperactivity and oral dyskinesia with hypophagia in rabbits

Serotonergic 5-HT2C and 5-HT1B receptors mediate inhibitory controls of eating. Questions have arisen about potential behavioral and neurological toxicity of drugs that stimulate the 2C site. We evaluated eating and other motor responses in male Dutch-belted rabbits after administration of m-chlorophenylpiperazine (mCPP). Studies conducted in vitro and in vivo assessed the pharmacological specificity of the ingestive actions of this agent. mCPP (0.15-10 micromol/kg sc) reduced consumption of chow and 20% sucrose solution with equal potencies (ED50 approximately equal 0.6 micromol/kg). In radioligand binding to rabbit cortex, mCPP displayed 15-fold higher affinity for 5-HT2C than for 5-HT1B receptors. The serotonin antagonist mesulergine (7000-fold selective for 5-HT2C) reversed the hypophagic action of mCPP, but the 5-HT1B/1D antagonist GR127,935 did not. GR127,935 (0.5 micromol/kg) did prevent hypophagia produced by the highly selective 5-HT1B/1D agonist GR46,611. Observational methods demonstrated that mCPP decreased the frequency of eating chow but increased other motor activities. When rabbits consumed sucrose, videoanalysis revealed that mCPP reduced total time licking and the duration of individual bouts, but not bout frequency or the actual rate of consumption. mCPP increased locomotor and other activities, and greatly increased vacuous oromotor stereotypies and tongue protrusions. Nonetheless, rabbits licked accurately at the spout for sucrose. When sucrose was infused intraorally through a cheek catheter, mCPP actually increased the peak amplitude and overall magnitude of jaw movements. We conclude that mCPP stimulates 5-HT2C receptors to reduce food intake in rabbits. This hypophagia involves disruption of appetitive components of eating and is accompanied by adverse motor actions. This profile raises questions about the use of the 5-HT2C receptor as a target for novel therapeutic agents for obesity.

The application of the principles of clinical drug development to pharmacological challenge tests of the serotonergic system

Pharmacological challenge tests of the serotonergic system have extensively been used during the past 20 years and new tests are in development. It is of crucial importance to standardize challenge tests to ascertain that observed variability is due to the state of the challenged system and not caused by variability of the test itself. This is even more important now that challenge tests increasingly are used in complex studies (e.g. in combination with neuroimaging and in large population studies with repeated tests over time). The Guideline for Good Clinical Practice may be of great help in the standardization of these tests. This is a recently developed guideline for pharmaceutical drug-development, which increasingly is used as a reference for all research in humans. To exemplify the possible usefulness of this approach, we apply it to meta-chlorophenylpiperazine, one of the most commonly used drugs in serotonergic challenge tests. We conclude that much can be learned from the development of this particular challenge. In the discussion, we address general issues that emerged from this review and their relevance to the development of future challenge tests.

Discriminative stimulus effects of m-chlorophenylpiperazine as a model of the role of serotonin receptors in anxiety

Serotonin is known to play a role in anxiety. The roles of serotonin reuptake and 5-HT1A receptors have been well characterized, but the contribution of other serotonin receptor subtypes is not as clear. 1-(3-Chlorophenyl)-piperazine (mCPP), which binds non-selectively to a wide range of serotonin receptors, has often been used to produce anxiety in humans and in animal models. Because functional assays indicate that mCPP is significantly more potent at 5-HT2C receptors, it may serve as a tool to investigate the contribution of 5-HT2C receptors to anxiety. This paper reviews the results of behavioral tests using mCPP, including the drug discrimination assay, to model anxiety. Although the discriminative stimulus effects of mCPP do not seem to be a useful screen for general anxiolytics, they do seem to be useful for characterization of the contribution of 5-HT1B and 5-HT2C receptors to the mediation of anxiety-like behaviors.

Synthesis and structure-activity relationship of 2-(aminoalkyl)-2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine derivatives: a novel series of 5-HT(2A/2C) receptor antagonists. Part 1

The synthesis of a series of novel 2-(aminoalkyl)-2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine derivatives as well as their 5-HT(2A/2C) and H(1) receptor binding affinities are described. The in vivo activity as potential anxiolytics of the synthesised compounds was measured in a mCPP challenge test. One of the compounds, 2a, proved to be a potent 5-HT(2A/2C) receptor antagonist showing as well oral activity and therefore could be considered as a potential anxiolytic/antidepressant agent.

Effects of the CCK(B) antagonist CI-988 on responses to mCPP in generalized anxiety disorder

In order to evaluate the effect of the CCK(B) antagonist CI-988 on behavioral, neuroendocrine, and physiologic responses to the mixed, post-synaptic serotonin (5-HT) agonist/antagonist mCPP, 16 patients with a principal DSM-III-R diagnosis of generalized anxiety disorder (GAD) were enrolled in a study that involved two challenge tests. On one day, patients received a single oral dose of CI-988 followed 30 min later by an i.v. infusion of 0.1 mg/kg mCPP. On a second test day patients received placebo CI-988 followed 30 min later by active i.v. mCPP. The sequence of CI-988 was randomly assigned and the testing was conducted in double-blind fashion. In an initial dose-finding phase (N = 6) with a dose of CI-988 of 25 mg, there were no significant between-test differences in behavioral response to mCPP. Accordingly, the second phase of the study was conducted with a CI-988 dose of 100 mg in another of patients (N = 10). CI-988 (100 mg) was well tolerated and had no significant effects on pretest anticipatory anxiety. There was no significant blunting of the anxiety response to mCPP as a result of CI-988 administration, nor did CI-988 affect physiologic or neuroendocrine measures. Correlations between peak changes in plasma levels of CI-988 and mCPP-induced anxiety in the high-dose patient group were not significant. Overall, these findings did not provide evidence of anxiolytic effects of CI-988 in patients with GAD. The lack of effect of CI-988 on neuroendocrine and physiological measures further suggests that CI-988's pharmacological effects could be independent of 5-HT function. However, follow-up studies using higher doses of CI-988 are indicated to confirm this preliminary finding as are studies more closely evaluating the interrelationship between CCK and 5-HT function in GAD.

Acute intravenous administration of ondansetron and m-CPP, alone and in combination, in patients with obsessive-compulsive disorder (OCD): behavioral and biological results

Obsessive-compulsive disorder (OCD) has been linked to abnormal function of brain serotonin (5-HT) pathways. Since ondansetron is a highly selective 5-HT3 receptor antagonist, the present study was undertaken to investigate 5-HT3 function in OCD. We administered m-CPP (0.08 mg/kg i.v.) and the potent 5-HT3 antagonist, ondansetron (0.15 mg/kg i.v.), to 11 OCD patients. All of the subjects received four separate challenges (m-CPP + placebo, m-CPP + ondansetron, ondansetron + placebo and placebo + placebo). In comparison to placebo, administration of m-CPP was associated with significant behavioral effects, particularly self-rated measures of anxiety, altered self-reality, functional deficit and OCD symptoms. Pretreatment with ondansetron did not affect any of the self-rated behavioral symptoms. After administration of m-CPP relative to placebo, significant increases in plasma cortisol and prolactin were found. These changes were not affected by ondansetron. In conclusion, our results do not support the hypotheses that 5-HT3 receptor-mediated mechanisms modulate m-CPP's behavioral and neuroendocrine effects in patients with OCD.

The m-chlorophenylpiperazine test in cluster headache: a study on central serotoninergic activity

The central serotoninergic agonist m-chlorophenylpiperazine (m-CPP) stimulates several 5HT receptor subtypes. It induces the release of both cortisol and prolactin (PRL). In this study we investigated central serotoninergic responsiveness in cluster headache by monitoring cortisol and PRL responses to m-CPP administration. Twenty-three patients with episodic cluster headache and 17 sex-matched and age-matched healthy subjects were studied. The cluster headache patients were tested during a cluster period, and none were receiving prophylaxis. A single oral dose of m-CPP, 0.5 mg/kg, was given at time 0. Blood samples were drawn at -30, 0, 30, 60, 90, 120, 150 and 180 min. PRL and cortisol levels were assayed in the samples. PRL and cortisol delta maxima (delta maximum = maximum response - baseline level at time 0/baseline level at time 0) were evaluated in each patient and mean values compared. Serum levels of m-CPP were detected by HPLC and correlated to hormonal responses. Reduced cortisol (p < 0.02) and increased PRL (p < 0.05) delta maxima were observed in cluster headache patients. Increased basal cortisol plasma levels (p < 0.05) and reduced basal PRL plasma levels (p = 0.06) also characterized cluster headache patients. This is the first study evaluating central serotoninergic responsiveness to m-CPP in cluster headache and these data suggest impaired central serotoninergic function in this pathology.

Role of serotonin3 receptors in prolactin release induced by electroconvulsive therapy: a study with ondansetron

The effect of pretreatment with odansetron on prolactin (PRL) release induced by electroconvulsive therapy (ECT) was examined in 16 depressive patients in a double-blind, placebo-controlled crossover study. Ten patients were pretreated with 4 mg and the other six with 8 mg of ondansetron. The order of administration of study medication (ondansetron and placebo) was counterbalanced. The failure of ondansetron to attenuate ECT-induced PRL release suggested that serotonin3 receptors are not involved in mediating this response.