Effects of serotonin antagonists on m-chlorophenylpiperazine-mediated responses in normal subjects

Meta-Chlorophenylpiperazine-Induced Behavioral Changes in Obsessive-Compulsive Disorder Research: A Systematic Review of Rodent Studies

Meta-chlorophenylpiperazine (mCPP) was one of the first compounds used in clinical and preclinical studies that demonstrated the role of serotonin in Obsessive-Compulsive Disorder (OCD). This systematic review aimed to (a) identify publications that report in rodents the effects of mCPP relevant to OCD, (b) explore the methodological characteristics of these studies, and (c) summarize the profile of mCPP effects. A comprehensive literature search was performed using PubMed, Scopus, and Web of Science. Search terms were a combination of obsessive-compulsive disorder or OCD and meta-chlorophenylpiperazine or mCPP. Twenty-nine articles were included in the review. The years of publication ranged from 1993 to 2021. Most studies used adult male Wistar or Sprague-Dawley rats. The most frequent dose of mCPP was 1.0 mg/kg administered acutely, intraperitoneally. In general, available preclinical evidence suggests increased defensive and compulsive behaviors associated with a decreased locomotor activity. But other results besides these and the absence of significant mCPP effects were also observed. Among the factors that may contribute to the variability of mCPP effects, differences in methods are highlighted, such as characteristics of the species/strains studied, mCPP doses and treatment regimens used. The heterogeneity of the OCD-like behaviors evaluated and the interaction of mCPP with different receptors may also be critical variables for discrepancies in the findings with mCPP. The information described in this review may contribute to a better understanding of how mCPP-induced behavioral changes in rodents have been used to study OCD, highlighting the main challenges for future investigations in this field.

Nonsynonymous HTR2C polymorphism predicts cortisol response to psychosocial stress II: Evidence from two samples

The 5-HT2C receptor is the primary serotonin receptor located in the corticotrophin releasing hormone (CRH) neurons of the hypothalamus. These neurons initiate the signaling cascade that culminates in cortisol release. Therefore, genetic variation in the 5-HT2C receptor gene (HTR2C) is a prime candidate for affecting cortisol reactivity to stress. Accordingly, we examined the association of a nonsynonymous polymorphism (Cys23Ser; rs6318) in HTR2C with stress reactivity in two Trier Social Stress Tests conducted at separate sites. In both Study 1 (N=128) and Study 2 (N=185), Cys23 homozygous females and hemizygous males had greater cortisol reactivity. There was no relation between this polymorphism and self-reported affective response (Studies 1 and 2) or cardiovascular reactivity (Study 2). Additionally, the short/short genotype of a polymorphism (5-HTTLPR) in the serotonin transporter gene was associated with greater cortisol reactivity in Study 1 as well as in Study 2 (previously reported). The Cys23Ser polymorphism and the 5-HTTLPR were independently associated with cortisol reactivity in both studies. These findings emphasize the important role of genetic variation in the serotonin system on regulating cortisol reactivity to social evaluative stress. Comparison of the present associations with those of prior studies underscores the likely importance of situational and psychological factors in determining the direction and magnitude of the association between genotype and phenotype.

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.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

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.

Serotonin and the neuroendocrine regulation of the hypothalamic--pituitary-adrenal axis in health and disease

Serotonin (5-hydroxytryptamine, 5-HT)-containing neurons in the midbrain directly innervate corticotropin-releasing hormone (CRH)-containing cells located in paraventricular nucleus of the hypothalamus. Serotonergic inputs into the paraventricular nucleus mediate the release of CRH, leading to the release of adrenocorticotropin, which triggers glucocorticoid secretion from the adrenal cortex. 5-HT1A and 5-HT2A receptors are the main receptors mediating the serotonergic stimulation of the hypothalamic-pituitary-adrenal axis. In turn, both CRH and glucocorticoids have multiple and complex effects on the serotonergic neurons. Therefore, these two systems are interwoven and communicate closely. The intimate relationship between serotonin and the hypothalamic-pituitary-adrenal axis is of great importance in normal physiology such as circadian rhythm and stress, as well as pathophysiological disorders such as depression, anxiety, eating disorders, and chronic fatigue.

Central serotonergic effects of m-chlorophenylpiperazine (mCPP) among normal control adolescents

Central serotonin function was studied among 21 adolescents (12 males, 9 females), mean age 14.4+/-1.5 years. A placebo-controlled design was used to measure three neuroendocrine hormones (prolactin, cortisol and growth hormone) following a challenge with the central serotonergic agonist m-chlorophenylpiperazine (mCPP). Infusion of mCPP resulted in augmented prolactin, cortisol and growth hormone release. Gender effects were significant for prolactin, cortisol and growth hormone. Females had higher baseline prolactin without significant interactions with infusion or time, cortisol levels were higher in males than in females at all time points without significant interactions with infusion or time, and the augmented growth hormone response to mCPP was limited to males. Systolic and diastolic blood pressure, heart rate and temperature were all mildly elevated following mCPP infusion. Side effects to mCPP infusion were mild and lasted approximately 20 min. We conclude that mCPP is useful in the study of serotonergic neuroendocrine hormones in adolescents, is well tolerated, and the levels of prolactin, cortisol and growth hormone are influenced by gender.

Psychomotor slowing, neuroendocrine responses, and behavioral changes after oral administration of meta-chlorophenylpiperazine in normal volunteers

The mixed 5-HT receptor agonist/antagonist meta-chlorophenylpiperazine (mCPP) is known to suppress locomotor activity in mice and rats. This study aimed: (1) to determine whether mCPP induces cognitive and motor changes in normal human volunteers and how these changes relate to the neuroendocrine effects of mCPP; and (2) to compare these cognitive and motor changes to the known cognitive and motor slowing patterns in depression and schizophrenia. A computerized method (used in previous research) analyzed fine motor behavior during figure-copying tasks. In 14 normal male volunteers behavioral responses, body temperature, plasma levels of prolactin and cortisol, and cognitive and motor performance during figure-copying tasks were measured after a single oral dose of mCPP (0.5 mg/kg). mCPP-induced prolongation of the reaction times in all copying tasks, parallel to increases in cortisol and prolactin and some self-reported behavioral effects. There were no changes in the movement times or the velocities of the writing movements. In conclusion, mCPP induced cognitive, but not motor slowing, in normal male volunteers. This indicates that the human serotonin system is also implicated in psychomotor behavior. This pattern of slowing was different from that in depressed and schizophrenic patients.

Serotonin dysregulation in adolescents with major depression: hormone response to meta-chlorophenylpiperazine (mCPP) infusion

This study examined central serotonin disturbance, as reflected by neuroendocrine hormones, among adolescents with major depression. Prolactin, cortisol, and growth hormone were measured following the infusion of a serotonin agonist, meta-chlorophenylpiperazine (mCPP). Twelve (M=6, F=6) medication-free adolescents with major depression (MDD) were compared with 12 (M=6, F=6) matched normal control subjects, ranging in age from 13 to 17 years. Baseline evaluations and a battery of laboratory tests were completed. mCPP, 0.1 mg/kg i. v., was administered in a placebo-controlled design. Analyses of the neuroendocrine hormones revealed that the depressed group had a higher baseline prolactin level and an augmented prolactin response to mCPP challenge than did the control group. The depressed group experienced a sharper baseline-cortisol decline between 08.00 and 11.00 h, and compared to control subjects they displayed an augmented response to the challenge. The depressed group reported more side effects than the control group during saline infusion, but not during mCPP infusion. Findings suggest that depressed adolescents have an elevated baseline prolactin level, and also experience enhanced prolactin and cortisol responses to the serotonergic challenge. These preliminary findings will be confirmed during our ongoing study.

Gonadal steroids in the treatment of mood disorders

Increased interest in the complex interplay between gonadal steroids and neurotransmitter systems involved in mood has led investigators to question the role of gonadal steroids in the treatment of affective disorders, especially in women.

OBJECTIVES

The purpose of this article is to provide a rationale for using gonadal hormones in the treatment of depression in women.

METHODS

The literature is reviewed regarding 1) sex-specific phenomenologic and epidemiologic differences in the manifestation of psychiatric illness, 2) sex-specific differences in the therapeutic and adverse effects of psychotropic medications, 3) the complex interplay between gonadal steroids and neurotransmitter systems implicated in psychiatric disorders, and 4) the growing literature regarding the use of estrogen and progesterone in the treatment of mood disorders in women and androgens in the treatment of depression and sexual dysfunction in both men and women.

RESULTS

Findings from pharmacologic trials of estrogen and androgens are encouraging, albeit mixed, in the treatment of mood disorders and decreased libido in women, respectively. Controlled studies have failed to confirm early open-label reports of the effectiveness of progesterone in the treatment of premenstrual syndrome.

CONCLUSIONS

Pending replication, estrogen may become an important pharmacologic agent in the treatment of postnatal and perimenopausal depression, whereas androgens have been shown to improve libido in postmenopausal women and hypogonadal men. Progesterone cannot be recommended as a treatment for premenstrual syndrome or postnatal depression.

Serotonin syndrome after challenge with the 5-HT agonist meta-chlorophenylpiperazine

meta-Chlorophenylpiperazine (mCPP) is a non-selective 5-HT-receptor agonist/antagonist that is used extensively in psychiatry to assess central serotonergic function. We report on three patients who developed symptoms of the serotonin syndrome when they participated in an mCPP (0.5 mg/kg body weight p.o.) challenge test as part of a research protocol. They had relatively high plasma mCPP concentrations. The syndrome did not occur in normal volunteers who had comparable plasma concentrations of mCPP. Investigators should be aware of the possible occurrence of the serotonin syndrome after a single oral dose of mCPP.

Effects of methysergide and loratadine on food intake, mood, and performance of humans living in a residential laboratory

The effects of loratadine, a peripherally acting histamine (H1) antagonist, and methysergide, a serotonin (5-HT) antagonist, were evaluated in seven normal-weight, male research volunteers, participating in a placebo-controlled, double-blind, 17-day residential study. Participants received oral loratadine (10 or 20 mg), methysergide (4 or 8 mg), or placebo at 1000 and 1700 hours daily. Active drug was administered on Days 4, 5, 7, 8, 11, 12, 15, and 16; placebo was administered on all other days. Drug and dose order were counterbalanced across participants. Food intake, performance, and subjective ratings were measured repeatedly throughout the day. Loratadine had no effect on food intake, performance, or subjective ratings. In contrast, total caloric intake significantly decreased from approximately 3500 kcal during placebo administration to 3065 kcal on the first but not the second day of methysergide administration. Consumption of carbohydrate (p < 0.055), protein, and fat decreased on the first day of methysergide administration. This decrease in food intake was due to a decrease in meal size; the number of meals consumed was not affected. The proportion of calories derived from carbohydrates significantly increased on the first day of methysergide administration. Methysergide also significantly impaired performance of a psychomotor task on the first day of high-dose administration and increased ratings of several subjective measures, including "Vomiting," "Stomach Pain," and "Miserable." These results suggest that the anorectic effect occurred as a result of the somatic and mood changes produced by methysergide. In addition, the inability of loratadine to affect food intake indicates that antagonism of central histamine receptors may be responsible for the increases in food intake produced by other antihistamines (e.g., diphenhydramine).

The influence of ondansetron and m-chlorophenylpiperazine on scopolamine-induced cognitive, behavioral, and physiological responses in young healthy controls

BACKGROUND

There is evidence from animal and human experiments that learning and memory come under the separate influence of both cholinergic and serotonergic pathways. We were interested in learning whether serotonergic drugs could attenuate or exacerbate the memory-impairing effects of anticholinergic blockade in humans.

METHODS

The selective serotonin 5-HT3 receptor antagonist ondansetron (0.15 mg/kg i.v.) and the serotonergic agent m-chlorophenylpiperazine (m-CPP; 0.08 mg/kg i.v.) were administered in combination with the anticholinergic agent scopolamine (0.4 mg PO) and compared to scopolamine alone in 10 young, healthy volunteers. Testing occurred on three separate days.

RESULTS

As expected, i.v. administration of scopolamine induced significant impairments in episodic memory and processing speed; however, these scopolamine-induced cognitive deficits were not attenuated by pretreatment with i.v. ondansetron (0.15 mg/kg), nor were they exacerbated by administration of i.v. m-CPP (0.8 mg/kg) in addition to scopolamine; however, administration of i.v. m-CPP was followed by a significant increase of self-rated functional impairment, altered self-reality, and dysphoria ratings, and scopolamine's effect on pupil size was potentiated.

CONCLUSIONS

Together, these results suggest that in young, healthy volunteers scopolamine-induced changes of cognitive performance are only minimally modulated by the serotonergic effects on ondansetron and m-CPP. Further studies with older controls are needed to test whether these findings may be influenced by age.

Serotonin function in panic disorder: intravenous administration of meta-chlorophenylpiperazine

A placebo-controlled study of the direct serotonin receptor agonist meta-chlorophenylpiperazine (MCPP), intravenously infused over 90 s in a 0.06 mg/kg dose, was conducted in 10 patients with panic disorder and 9 normal control subjects. Cortisol, MCPP serum levels, and behavioral responses in both groups. Differences between intravenous and oral administration of MCPP are discussed, and the present findings are related to the serotonergic hypothesis of panic disorder.

Daily administration of m-chlorophenylpiperazine to healthy human volunteers rapidly attenuates many of its behavioral, hormonal, cardiovascular and temperature effects

The serotonergic agent meta-chlorophenylpiperazine (m-CPP) increases temperature and plasma ACTH and other hormones and decreases social interaction, locomotor activity and food intake in rats, most likely via stimulation of 5-HT2C receptors. Repeated daily administration of m-CPP to rats induces rapid tolerance to these effects of m-CPP. As m-CPP has been used in challenge tests and in preliminary treatment trials in humans, we evaluated the possible development of tolerance to m-CPP in ten healthy human volunteers using a double-blind, random assignment crossover study of placebo versus daily m-CPP infusions. Psychological and physical symptoms of anxiety, temperature, pupil size, diastolic blood pressure, and plasma ACTH, cortisol, and prolactin concentrations were increased by the first administration of m-CPP (0.08 mg/kg) compared to placebo. All of these responses were attenuated on m-CPP days 2 and 3. Plasma m-CPP levels did not differ across the 3 m-CPP days. Repeated m-CPP administration thus appears to induce rapid tolerance to its behavioral and physiological effects in humans. Further investigations of the mechanisms involved in the development of subsensitivity to m-CPP may contribute to increased understanding of the regulation of serotonin-mediated functions and of anxiety disorders.

5-HT2a/2c receptor blockade by amesergide fully attenuates prolactin response to d-fenfluramine challenge in physically healthy human subjects

Prolactin responses to d-fenfluramine (d-FEN) challenge (0.5 mg/kg PO) were examined after pre-treatment with and without the 5-HT2a/2c receptor antagonist amesergide in eight physically healthy male volunteers. Compared to pretreatment with placebo, pre-treatment with amesergide completely blocked the prolactin (PRL) response to d-FEN challenge in all subjects. These data are consistent with data demonstrating a complete blockade of the PRL response to d-FEN with the 5-HT2a/2c receptor antagonist ritanserin, and suggest that the PRL response to d-FEN challenge in humans may largely be due to activation of the 5-HT2a/2c receptor.

Pindolol pretreatment blocks stimulation by meta-chlorophenylpiperazine of prolactin but not cortisol secretion in normal men

Previous reports from this laboratory have shown that pindolol, a partial serotonin1A receptor agonist, inhibited prolactin, but not cortisol secretion induced by administration of the serotonin (5-HT) precursor L-5-hydroxytryptophan or the direct-acting 5-HT2A/5HT2C receptor agonist MK-212. The findings suggest additive or interactive effects of 5-HT1A and 5-HT2A/5-HT2C receptors in modulating 5-HT-related prolactin, but not cortisol, responsivity. To examine further the role of 5-HT1A and 5-HT2A/5-HT2C receptors in prolactin and cortisol secretion in healthy men, the effects of meta-chlorophenylpiperazine (mCPP), a potent 5-HT receptor agonist, on the above hormones were studied in eight healthy men with and without pindolol pretreatment. It has previously been demonstrated that ketanserin, a 5-HT2A antagonist, and ritanserin, a 5-HT2A/5-HT2C antagonist, block the prolactin and attenuate the hypothalamic-pituitary-adrenal axis responses to mCPP in man or rodents. Administration of mCPP induced a significant increase in plasma concentrations of prolactin and cortisol. The mCPP-induced prolactin concentrations were significantly blocked by pretreatment with pindolol, whereas mCPP-stimulated cortisol levels were not diminished by pindolol pretreatment. Thus, mCPP-induced prolactin secretion appears to require the availability of both 5-HT2C and 5-HT1A receptor activation, since blockade of either of these receptors may diminish the mCPP-induced prolactin response. Cortisol secretion stimulated by mCPP may occur following 5-HT2C receptor stimulation in the presence of 5-HT1A receptor blockade.

m-Chlorophenylpiperazine in patients with obsessive-compulsive disorder: absence of symptom exacerbation

Oral administration of the serotonin mixed agonist-antagonist meta-chlorophenylpiperazine (mCPP) at 0.5 mg/kg has been reported to exacerbate symptoms of obsessive-compulsive disorder (OCD). In an attempt to replicate these findings, double-blind behavioral and biochemical measures were obtained in 12 drug-free patients (9 men, 3 women) with OCD who received either oral mCPP (0.5 mg/kg), intravenous (IV) mCPP (0.1 mg/kg over 20 min), or placebo in random order on 3 separate test days. Neither oral nor IV mCPP had significant effects on the severity of OCD symptoms. The magnitude of the mCPP-induced plasma prolactin response and plasma mCPP levels were similar to those values obtained in other published studies in which mCPP exacerbated OCD symptoms. In contrast, both oral and IV mCPP were associated with significant increases in ratings of anxiety. These findings suggest that mCPP, whether administered by an oral or intravenous route (as a slow infusion), may not be a reliable probe for investigating obsessive-compulsive symptoms. It is possible, however, that more reproducible behavioral findings might be obtained by identifying susceptible subgroups of OCD or by including a behavioral exposure condition.

The role of the 5-HT2A and 5-HT2C receptors in the stimulus effects of m-chlorophenylpiperazine

m-Chlorophenylpiperazine (mCPP), a major metabolite of the atypical antidepressant trazadone, has been observed to produce marked physiological and behavioral effects in both humans and animals. These effects have been attributed to the interaction of mCPP with serotonergic receptors. The present study was designed to characterize those interactions of mCPP with central serotonergic receptors which mediate mCPP-induced stimulus control. A series of serotonergic antagonists (mesulergine, pizotyline, ketanserin, spiperone, risperidone, ritanserin, metergoline, pirenpirone, and LY53857) was tested for the ability to block the mCPP stimulus. The affinity of these antagonists for 5-HT2A and 5-HT2C receptors was then correlated with maximal percent inhibition of the mCPP stimulus. Kd at the 5-HT2C receptor was inversely proportional (r = -0.75, P < 0.05), and Kd at the 5-HT2A receptor directly proportional (r = +0.67, P < 0.05) to the maximal percent inhibition of the mCPP stimulus. The 5-HT2C selectivity ratio [Kd(5-HT2A)/Kd(5-HT2C)] of the antagonists was directly proportional (r = +0.86, P < 0.01) to maximal percent inhibition of the mCPP stimulus. A multiple regressions analysis indicated that 81% of the variance in the ability of a given antagonist to block the mCPP stimulus could be predicted on the basis of its affinity for 5-HT2A and 5-HT2C receptors. It is concluded that the stimulus effects of mCPP are mediated predominantly by a combination of agonist activity at 5-HT2C receptors and antagonist activity at 5-HT2A receptors.

Estrogen augments serotonergic activity in postmenopausal women

To investigate the influence of estrogen replacement on serotonergic activity in postmenopausal women, the serotonin agonist meta-chlorophenylpiperazine (m-CPP) (0.5 mg/kg) was given orally to 18 normal postmenopausal women, 11 of whom were also tested following 30 days' treatment with estrogen transdermal patches (estraderm 0.1 mg). Fifteen normal, healthy women of reproductive status served as a control group. Cortisol and prolactin responses to m-CPP were measured. Without estrogen, the prolactin and cortisol responses of postmenopausal women to m-CPP were blunted compared to those of reproductive women. Estrogen replacement increased the hormonal responses. It is suggested that decreased serotonergic activity in postmenopausal women might contribute to their vulnerability to affective disorders. Estrogen replacement therapy might decrease this vulnerability and might add to the efficacy of serotonergic antidepressants when warranted.

Effects of alprazolam on increases in hormonal and anxiety levels induced by meta-chlorophenylpiperazine

The effects of alprazolam, a triazolobenzodiazepine, on hormonal and behavioral responses induced by meta-chlorophenylpiperazine (MCPP), a serotonin receptor agonist, were investigated in 10 healthy men. Alprazolam (0.5 mg) or placebo was given 1 hour before MCPP (0.5 mg/kg) or placebo. Cortisol, prolactin, and growth hormone (GH) release, MCPP and alprazolam plasma levels, anxiety level, and panic symptoms were measured over 210 minutes. MCPP was found to increase cortisol, prolactin, GH, and anxiety levels. Alprazolam decreased cortisol and GH levels but had no effect on prolactin. When used in combination with MCPP, alprazolam blunted MCPP-induced cortisol and GH release, and it blocked the anxiogenic effects of MCPP.

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

Results from animal studies have suggested that serotonin (5-HT) antagonists acting on the 5-HT3 receptor may have anxiolytic properties. We have assessed whether pretreatment with the 5-HT3 receptor antagonist BRL 46470 (1 mg orally) attenuates the increase in anxiety induced in healthy volunteers by intravenous infusion of m-chlorophenylpiperazine (mCPP: 0.08 mg/kg over 2 min). In this double-blind placebo-controlled crossover study in 12 healthy men who were volunteers, infusion of mCPP caused significant increases in self-ratings for the psychological and physical symptoms of anxiety, for the symptoms of panic attack, and in the plasma levels of cortisol and prolactin, with four subjects (33%) experiencing an mCPP-induced "panic attack." Pretreatment with BRL 46470 did not attenuate any of these mCPP-induced changes. These results do not support suggestions from animal studies that 5-HT3 receptor antagonists can attenuate mCPP-induced anxiety, although it is conceivable that a different dose of BRL 46470 may have been effective.

Serotonergic function in panic disorder: endocrine responses to D-fenfluramine

1. Prolactin and cortisol responses to d-fenfluramine were measured in 16 patients with DSM-III-R panic disorder and 14 normal controls. 2. Patients showed a greater mean prolactin response than controls but the difference between groups was not statistically significant (P > 0.05, MANOVA). 3. No consistent differences were observed between patients and controls with respect to cortisol responses (P > 0.05, MANOVA). 4. The results do not support the hypothesis of hypersensitive post-synaptic serotonin receptors in patients with panic disorder. 5. Studies in larger groups are necessary to confirm the trend and to explore receptor subtype sensitivity.

Neuroendocrine and temperature effects of nefazodone in healthy volunteers

The effects of a novel antidepressant, nefazodone (50 mg, 100 mg, and 200 mg orally) on neuroendocrine function and temperature were assessed using a single-blind, crossover design in eight healthy male volunteers. Nefazodone significantly increased plasma levels of prolactin (PRL) and raised oral temperature. There was also a trend towards an increase in plasma cortisol. These results are consistent with an acute facilitatory effect of some aspects of 5-HT neurotransmission, perhaps mediated through nefazodone's metabolism to its major metabolite, m-chlorophenylpiperazine (mCPP).

Haloperidol and clozapine treatment and their effect on M-chlorophenylpiperazine-mediated responses in schizophrenia: implications for the mechanism of action of clozapine

Since clozapine is, in contrast to conventional neuroleptics, effective in treatment refractory schizophrenic patients its mechanism of action may be different from that of typical neuroleptics. Clozapine has been shown to display the highest binding affinity of all neuroleptics to one of the serotonin (5-hydroxytryptamine, 5HT) receptor subtypes, i.e., the 5HT1c receptor. Furthermore, clozapine, in contrast to conventional neuroleptics, blocks the effect of 5HT agonists on ACTH and corticosterone release in animals. This study hypothesized that clozapine, but not haloperidol would block ACTH and prolactin release induced by the 5HT agonist, m-chlorophenylpiperazine (MCPP). MCPP (0.35 mg/kg PO) was administered after a 3-week drug-free period, after 5 weeks of haloperidol treatment (20 mg/day) and finally after 5 weeks of clozapine treatment (> 400 mg/day) in ten male schizophrenic patients. Clozapine, but not haloperidol, blocked the effect of MCPP on ACTH and prolactin release. These results suggest that clozapine, in contrast to haloperidol, is a functional 5HT antagonist. Since MCPP-induced ACTH and prolactin release may be (partially) 5HT1c mediated, these results suggest that clozapine is a potent antagonist at the 5HT1c receptor.

Neuroendocrine probes of serotonergic function: a critical review

Neuroendocrine probes of serotonergic function are based on the premise that serotonin (5-HT) exhibits an excitory influence on the release of certain anterior pituitary hormones and that the extent of release of these hormones following a challenge with a 5-HT agonist would provide an index of central 5-HT activity. This paper critically reviews studies published to date on healthy volunteers to assess the validity of tests of serotonergic function. Using standardized criteria, it is concluded that although extensive data is available on 5-HT-neuroendocrine probes, there is no test that is currently available that would fulfil all the proposed requirements for a test to be acceptable, although ipsapirone, m-chlorophenylpiperazine (m-CPP), and possibly fenfluramine challenge tests come very close. The rapid development and availability of more specific and stereo-selective 5-HT agonists/antagonists seem to indicate that it will not be too long before a valid neuroendocrine test for the assessment of serotonergic function emerges.

Altered serotonergic activity in women with dysphoric premenstrual syndromes

OBJECTIVE

Dysphoric Premenstrual Syndromes (PMS) are quite prevalent and in some women they are severe enough to warrant treatment. Their pathophysiology is still unknown, despite increased interest and research. Here we review the possible role of serotonin in the multidimensional interactive pathophysiology of PMS.

METHOD

Over 170 articles are reviewed. An extensive library search has been conducted and articles are included because of their relevance to: 1) the phenomenology of PMS; 2) the putative association of serotonergic (5-HT) activity with syndromes that occur premenstrually; 3) changes in 5-HT activity along the menstrual cycle, especially the late luteal phase; 4) influence of gonadal hormones on serotonergic functions; 5) endocrine strategies for assessment of 5-HT abnormalities; and 6) treatment studies of PMS with serotonergic agonists.

RESULTS AND CONCLUSIONS

The data presented here suggest that post-synaptic serotonergic responsivity might be altered during the late-luteal-premenstrual phase of the menstrual cycle. Some serotonergic functions of women with PMS might be altered during the entire cycle and be associated with a vulnerability trait. It is hypothesized that gonadal hormones might cause changes in levels of activity of 5-HT systems as part of a multidimensional interactive system. Strategies to evaluate 5-HT activities in the context of the menstrual cycle are discussed--leading to the conclusion that the most promising approach is active stimulation with specific post-synaptic serotonin agonists. Treatment outcome studies of some imperfect compounds that are currently applied as a symptomatic treatment of PMS support the notion that 5-HT is involved in the pathophysiology of these syndromes.

A comparison of the behavioral effects of oral versus intravenous mCPP administration in OCD patients and the effect of metergoline prior to i.v. mCPP

In prior studies form three centers, an exacerbation of obsessive-compulsive disorder (OCD) symptoms was reported in some (55%-83%) patients with OCD receiving the serotonergic agonist m-chlorophenylpiperazine (m-CPP) orally, whereas intravenously administered mCPP produced anxiety but no OCD symptom exacerbation. In the present replication attempt, 27 OCD patients were given mCPP either orally (n = 17) or intravenously (n = 10) under double-blind conditions, using identical behavioral rating measures. OCD symptoms were significantly increased after intravenous mCPP (0.1 mg/kg), but not after oral mCPP (0.5 mg/kg). Anxiety and other ratings were markedly elevated after intravenous mCPP administration. After oral mCPP administration, anxiety and most other self-ratings were only slightly elevated in comparison to placebo administration, and behavioral rating increases were no different for the OCD patients compared to age-matched healthy controls. Pretreatment with the potent serotonin (5-HT) antagonist, metergoline, prior to intravenous mCPP was associated with essentially complete blockade of the exacerbation in OCD symptoms and the other behavioral responses in the OCD patients. These results suggest that the behavioral response of OCD patients to mCPP are variable and depend on the route and dose of mCPP. In addition, the ability of metergoline to antagonize the behavioral effects of intravenous mCPP suggests that these responses are mediated by 5-HT1/5-HT2 receptors.

About the centrality of mood lowering in mood disorders. Plenary Lecture ECNP Congress, Monte Carlo, October 1991

5-HT disturbances in depression (as exemplified by lowered CSF 5-HIAA) are not syndrome specific but related to components of the depressive syndrome, specifically to increased anxiety and aggression. These 5-HT disturbances are probably core pathogenetic processes not derivative features. I hypothesized that in this subtype of depression, i.e. in "5-HT related depression", the key psychopathological disturbances are dysregulation of anxiety and aggression, while mood lowering is a "by-product". Based on this hypothesis it was predicted that agents which ameliorate anxiety and/or aggression via harmonization of 5-HT ergic transmission will, in addition, exert overall antidepressant effect in "5-HT related depression". The study of the relative "weight" of the various psychopathological components of depression is a basic exercise in understanding the nature of that condition and could, as such, greatly facilitate the goal-directed search for new and innovative antidepressants.

Functional interrelationship of serotonin and norepinephrine: cortisol response to MCPP and DMI in patients with panic disorder, patients with depression, and normal control subjects

The relationship between norepinephrine (NE) and serotonin (5-hydroxytryptamine; 5HT) functioning was explored in a neuroendocrine challenge paradigm. Ten normal control subjects, 17 patients with major depression, and 22 patients with panic disorder volunteered to participate in this study. Each subject received a challenge with meta-chlorophenylpiperazine (MCPP; 0.25 mg/kg, p.o.), a 5HT agonist, and desmethylimipramine (DMI; 75 mg, i.m.), an indirect NE agonist, in randomized order. The peak-minus-baseline cortisol response to MCPP was used as an indicator of 5HT function, and cortisol response at 75 minutes-minus-baseline to DMI was used as an indicator of NE function. The cortisol responses to DMI and MCPP were found to be highly negatively correlated in the total sample, in particular in the patients with major depression and panic disorder. This finding suggests that the functions (or dysfunctions) of the NE and 5HT systems may not be separate as is usually believed, and that the NE and 5HT disturbances observed in major depression and panic disorder may not be independent. Rather, there may be a joint disturbance of NE-5HT in these disorders.

A dose-response study of intravenous m-chlorophenylpiperazine in normal subjects

A placebo-controlled dose-response study of the direct serotonin receptor agonist m-chlorophenylpiperazine (MCPP), intravenously infused over 90 s in 0.06 and 0.08 mg/kg doses, was conducted in nine normal male subjects. Cortisol, prolactin, MCPP serum levels and behavioral responses were measured over a 210-min period. Both doses caused significant cortisol and prolactin release and were associated with significantly greater behavioral effects as compared to placebo. Though the two doses were associated with different MCPP serum levels, they did not significantly differ in their hormonal and behavioral effects.

m-Chlorophenylpiperazine as a probe of serotonin function

m-Chlorophenylpiperazine (mCPP) is the most extensively used probe of serotonin function in psychiatry. This article reviews its in vitro and in vivo properties in animals, normal human subjects, and psychiatric patients. mCPP is a safe, reliable, direct 5-hydroxytryptamine (5HT) agonist, which may be used to evaluate 5HT receptor sensitivity. It causes a consistent, dose-dependent elevation of ACTH, cortisol, and prolactin levels in both animals and humans, as well as increased body temperature in man. It also causes a variety of behavioral effects, depending on the population studied. These effects are probably 5HT receptor-related, although specific 5HT receptor subtype mechanisms have not yet been established. mCPP may be considered an important addition to armamentarium of 5HT receptor probes, which is especially useful until more selective 5HT receptor agonists have been tested.

Effects of ritanserin on the behavioral, neuroendocrine, and cardiovascular responses to meta-chlorophenylpiperazine in healthy human subjects

Ten healthy male subjects were administered i.v. meta-chlorophenylpiperazine (MCPP) (0.1 mg/kg) after oral ritanserin (5-10 mg), a putative 5HT1c/5HT2 (serotonin) antagonist, or placebo. Behavioral responses, cardiovascular effects, and neuroendocrine responses (cortisol, growth hormone, and prolactin) were measured serially for 4 hours after MCPP infusion. Premedication with ritanserin attenuated the MCPP-induced increases in self-rated anxiety and prolactin, and completely antagonized MCPP cortisol elevations. In contrast, ritanserin did not significantly alter growth hormone response to MCPP. These findings suggest a role for 5-HT1c/5-HT2 receptors in the endocrine and behavioral responses to the mixed serotonin agonist MCPP in humans.

Serotonin receptor sensitivity and aggression

This study investigated the relationship between increased serotonin (5-hydroxytryptamine, 5HT) receptor sensitivity and human aggression. A low oral dose of meta-chlorophenylpiperazine (MCPP), a postsynaptic 5HT receptor agonist, was administered in a placebo-controlled design to depressed (n = 22) and panic disorder (n = 20) patients classified with or without signs of outwardly directed aggression, patients with a history of suicide attempts (inwardly directed aggression) (n = 11), and normal controls (n = 19). Hormones under 5HT control were measured at 30-min intervals. Results were as follows: (1) MCPP did not induce or reduce anger, (2) patients with outwardly directed aggression did not have significantly greater MCPP-induced cortisol or prolactin release than did patients without signs of outwardly directed aggression, (3) patients with a history of suicide attempts did not have significantly greater MCPP-induced cortisol or prolactin release than did normal controls, and (4) MCPP-induced hormone release was unrelated to measures of aggression.

Pituitary hormone responses to meta-chlorophenylpiperazine in panic disorder and healthy control subjects

The present study reports adrenocorticotropic hormone (ACTH) and prolactin responses after oral administration of 0.25 mg/kg of the serotonin agonist, meta-chlorophenylpiperazine (MCPP), in patients with panic disorder (PD) and in healthy subjects. MCPP blood levels were similar for the two groups, but almost twice as high in males as in females. Female patients had augmented ACTH and prolactin release as compared to healthy females, while ACTH and prolactin release in male patients was similar to that of male controls. These results suggest that female PD patients have hypersensitive serotonin receptors. Moreover, they indicate that pharmacokinetic gender differences may affect challenge studies, and that different doses may be required to study neuroendocrine responses in males and females.

Comment on 5-HT and mechanisms of defence

The paper by Deakin and Graeff is a thought-provoking tour-de-force. They propose a comprehensive theory about serotonin (5-hydroxytryptamine; 5-HT) and anxiety, covering much of the same literature which we previously reviewed (Kahn et al., 1988a). We certainly agree that there seems to be an association between 5-HT function and anxiety, but we take issue with several important aspects of Deakin and Graeff's hypothesis. We limit our comments to their discussion of anxiety and panic.