m-Chlorophenylpiperazine as a probe of serotonin function

Effects of meta-chlorophenylpiperazine on neuroendocrine and behavioral responses in male schizophrenic patients and normal volunteers

Functional alterations in the central serotonergic system, including presynaptic and postsynaptic function, have been reported in schizophrenia. Recently, there have been conflicting reports that the increase in plasma cortisol or prolactin concentrations induced by meta-chlorophenylpiperazine (mCPP) was significantly blunted in schizophrenic patients compared with normal volunteers. Studies of the behavioral effects of mCPP, a serotonin (5-HT) receptor partial agonist with high affinity for 5-HT1C binding sites, have also yielded conflicting results in schizophrenic patients. The purpose of this study was to examine plasma levels of prolactin and cortisol, body temperature, and behavioral responses to mCPP and placebo in a single-blind study in 25 schizophrenic and 15 normal men. No differences either between schizophrenic patients and normal volunteers or between paranoid and undifferentiated/residual subtypes of schizophrenia were found in mCPP-induced prolactin, cortisol, or temperature responses. Schizophrenic patients and normal volunteers reported significant increases in feeling calm and feeling strange of comparable magnitude following mCPP. No significant differences between normal volunteers and schizophrenic patients were found in post-mCPP behavioral ratings, such as anxiety, irritability, depression, restlessness, or arousal.

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.

Hostility is associated with a low prolactin response to meta-chlorophenylpiperazine in abstinent alcoholics

The prolactin response to the administration of serotonin agonists is an index of central nervous system serotonin (5HT) activity. This index is blunted in association with hostile aggression in personality-disordered individuals without substance abuse. We tested whether prolactin response to the partial 5HT agonist meta-chlorophenylpiperazine (MCPP) (0.35 mg/kg po) was associated with measures of trait hostility in alcoholics who were completing a 3-week rehabilitation program after medical detoxification. We also tested whether the same 5HT index differed in the group of alcoholics compared with the healthy volunteers. The prolactin response to MCPP was inversely associated with the main index of trait hostility and was similarly inversely associated with an index of depression. There was, however, no difference in neuroendocrine or temperature responses to MCPP between the alcohol-dependent group and the healthy volunteers.

Cerebral metabolic effects of serotonin drugs and neurotoxins

The functional effects of serotonin (5-HT) drugs and toxins on regional cerebral metabolic rates for glucose (rCMRglc) have been determined in rats with the in vivo, quantitative, autoradiographic [14C]2-deoxyglucose technique. Serotonin agents produced rCMRglc patterns different and more specific that one would predict from binding studies. At low doses 5-HT1 agonists reduced rCMRglc in limbic areas and at high doses increased rCMRglc in brain motor regions. The 5-HT2 agonists dose-dependently decreased rCMRglc in proencephalic areas and increased it in thalamic nuclei. 5-HT3 receptor antagonism resulted in rCMRglc decreases in limbic, auditory and visual areas and agents with 5-HT3 receptor activity increased rCMRglc in brain regions with high 5-HT3 receptor densities. Serotonin anxiolytics (e.g. azapirones) and antidepressants (e.g. tryciclic and non-tryciclic 5-HT reuptake inhibitors) reduced rCMRglc selectively in limbic areas and in brainstem monoaminergic nuclei. Dose, time from administration, receptor affinity, behavioral and neurochemical correlates, 5-HT system lesion and circulating glucocorticoid were all relevant factors in determining the rCMRglc effects of 5-HT drugs. Acutely neurotoxic amphetamines markedly increased rCMRglc in brain regions such as the nucleus accumbens that are thought to mediate amphetamine reinforcing properties; on the long term, toxic or electrolytic lesions or chronic treatment with 5-HT agonists produced minimal rCMRglc alterations in spite of marked and persistent changes in 5-HT function. In lesioned or chronically treated rats, acute challanges with 5-HT and non 5-HT agonists demonstrated specific deficits that were not detected in a resting state. Serotonin neuromodulation has been studied in humans by using positron emission tomography with 15O-water. Sequential measurements of regional cerebral blood flow (rCBF) were obtained during combined pharmacological challange with the 5-HT1A agonist buspirone and cognitive activation. Buspirone increased a memory related rCBF activation in task specific regions. This technique can provide a strong theoretical basis for the understanding of 5-HT drug mode of action in normal human brain and in neuropsychiatric diseases. Brain metabolism studies in animals will still be needed to elucidate the factors (e.g. pharmacokinetic and pharmacodynamic) relevant to the cerebral response to 5-HT drugs in humans.

The effects of paroxetine and nefazodone on sleep: a placebo controlled trial

We studied the effect of acute (1 day) and subacute (16 days) administration of the new antidepressant, nefazodone (400 mg daily), and the selective serotonin re-uptake inhibitor (SSRI), paroxetine (30 mg daily), on the sleep polysomnogram of 37 healthy volunteers using a random allocation, double-blind, placebo-controlled design. Compared to placebo, paroxetine lowered rapid eye movement (REM) sleep and increased REM latency. In addition, paroxetine increased awakenings and reduced Actual Sleep Time and Sleep Efficiency. In contrast, nefazodone did not alter REM sleep and had little effect on measures of sleep continuity. We conclude that in contrast to typical SSRIs, nefazodone administration has little effect on sleep architecture in healthy volunteers.

Hormonal responses to meta-chlorophenylpiperazine (m-CPP) are undiminished by acute m-CPP pretreatment

Two challenges with meta-chlorophenylpiperazine (m-CPP, 0.5 mg/kg, p.o.) were performed in healthy volunteers to test the short-term stability of hormonal responses. Challenges were performed in an identical fashion and were conducted on sequential days. Circulating m-CPP plasma levels, as well as prolactin and cortisol responses to m-CPP, were correspondingly similar in magnitude on the 2 days. These data suggest that both prolactin and cortisol responses to single oral administrations of m-CPP are stable over at least a 24-h period.

The interaction of clozapine with the meta-chlorophenylpiperazine (mCPP) discriminative stimulus

The psychotropic effects of the 5-HT2C agonist mCPP in human subjects are blocked by the atypical antipsychotic clozapine, but not by typical antipsychotics. An understanding of the mechanistic basis for the interaction of clozapine and mCPP would provide further insight into the basis for its unique therapeutic effects in humans. Drug-induced stimulus control provides an animal model for the subjective effects of psychotropic agents in humans. In the present study, the interaction of the atypical antipsychotic clozapine and the typical antipsychotic fluphenazine with the mCPP-stimulus were defined. Neither drug antagonized the stimulus effects of mCPP in vivo. In contrast, clozapine fully antagonized the mCPP-stimulated phosphoinositide turnover at the 5-HT2C receptor in vitro. The present data indicate that the paradigm of mCPP-induced stimulus control does not facilitate the differentiation of atypical and typical antipsychotic activities.

Effects of carbamazepine coadministration on plasma concentrations of trazodone and its active metabolite, m-chlorophenylpiperazine

Effects of carbamazepine coadministration on plasma concentrations of trazodone and its active metabolite, m-chlorophenylpiperazine (m-CPP) were studied in six depressed patients treated with trazodone. The daily dose of trazodone was 150 mg in three cases and 300 mg in three cases. Carbamazepine, 400 mg/day, was coadministered for 4 weeks, and blood samples were taken before carbamazepine addition and at weekly intervals after the addition. Carbamazepine significantly (p < 0.01) decreased plasma concentrations of not only trazodone but also m-CPP at each week. On the average, plasma concentrations of trazodone and m-CPP at 4 weeks were 24 and 40% of the corresponding precarbamazepine values. This study thus suggests that carbamazepine coadministration decreases plasma concentrations of trazodone and m-CPP by inducing the metabolism of these compounds.

5-HT2C receptor-mediated phosphoinositide turnover and the stimulus effects of m-chlorophenylpiperazine

The present study was designed to investigate the hypothesis that agonist interactions at 5-HT2C receptors mediate the discriminative stimulus properties of m-chlorophenylpiperazine (mCPP). Three structural classes of compounds have been described to stimulate increases in phosphoinositide (PI) hydrolysis at the 5-HT2C receptor site: phenylpiperazines, phenylalkylamines, and indolamines. Four representative phenylpiperazines, mCPP, TFMPP, MK-212 and quipazine, one phenylalkylamine, (-)DOM, and one indolamine, LSD, were employed in the present study. The efficacies of these compounds were defined (1) in vitro, with respect to their abilities to stimulate increases in PI hydrolysis in the choroid plexus, and (2) in vivo with respect to their abilities to substitute for the mCPP discriminative stimulus. In vitro intrinsic activity at the 5-HT2C site was expressed as a fraction of the maximal PI hydrolysis response elicited by serotonin (5-HT). MK-212 (fractional efficacy = 1.1) and (-)DOM (0.77) were full agonists, while mCPP (0.72), LSD (0.27), quipazine (0.24), and TFMPP (0.22) were partial agonists with respect to the stimulation of PI hydrolysis at the 5-HT2C receptor. In vivo, each of the phenylpiperazines fully substituted for the mCPP stimulus, while (-)DOM (75%), and LSD (67%) elicited only partial substitution. While compounds with agonist activity at the 5-HT2C receptor in vitro substitute for the mCPP stimulus in vivo, no clear relationship exists between in vitro intrinsic activity at the 5-HT2C receptor with respect to the stimulation of PI turnover and maximal substitution for the mCPP stimulus in vivo. The present data suggest that mCPP elicits a compound stimulus which is mediated by agonist interactions at the 5-HT2C receptor and possibly additional interactions with 5-HT2A, 5-HT3, and/or 5-HT1B receptors.

Role of the hypothalamic paraventricular nucleus in 5-HT1A, 5-HT2A and 5-HT2C receptor-mediated oxytocin, prolactin and ACTH/corticosterone responses

To test the hypothesis that the mechanisms of 5-HT1 and 5-HT2 receptor-mediated hormonal responses are different, we compared the effects of hypothalamic paraventricular nucleus (PVN) lesions on the ACTH/corticosterone, prolactin and oxytocin responses to the 5-HT1A agonist ipsapirone (1 and 2 mg/kg), the 5-HT2C agonist m-chlorophenylpiperazine (m-CPP, 0.6 mg/kg), which also binds to other 5-HT receptors with lower affinity, and the 5-HT2A/2C agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI, 1 mg/kg) in chronically cannulated, freely moving male rats. Pharmacological characterization using antagonists with different affinity for 5-HT2A and 5-HT2C receptors revealed that DOI's responses were mediated mainly by 5-HT2A receptors and m-CPP's responses were almost exclusively mediated by 5-HT2C receptors. ACTH/corticosterone responses to ipsapirone, DOI and m-CPP were almost completely blocked after PVN lesions. Prolactin responses were significantly different in lesioned rats only after DOI and m-CPP challenges. Oxytocin responses to ipsapirone and DOI, but not m-CPP were markedly attenuated after PVN lesions. The present findings suggest that the PVN, or neural pathways close to it, mediate corticosterone and in some cases prolactin and oxytocin responses to selective stimulation of 5-HT1A, 5-HT2A, or 5-HT2C receptors.

Neuroendocrine responses to serotonergic agonists as indices of the functional status of central serotonin neurotransmission in humans: a preliminary comparative analysis of neuroendocrine endpoints versus other endpoint measures

The status of central serotonergic neurotransmission and of specific serotonin (5-HT) receptor subtype sensitivity has been inferred from neuroendocrine and other endpoint responses to serotonergic agents given to humans. The question of whether changes in neuroendocrine responsivity to the 5-HT2C partial agonist, meta-chlorophenylpiperazine (m-CPP), are accompanied by similar changes in other endpoints (temperature, behavior) is addressed in this brief review of published studies. These studies were selected based on the following criteria: (1) neuroendocrine (cortisol, prolactin increases) and at least one other endpoint (behavior and/or temperature increases) were measured in the same populations, and (2) statistically significant changes were observed after m-CPP in the healthy volunteer control or pre-long-term-treatment subjects. Parenthetically, in the 13 of 14 studies that reported both prolactin and cortisol responses, the results were congruent for the two neuroendocrine measures in 12 of the 13 (92%). However, neuroendocrine versus behavioral results were in agreement in fewer (7 of the 13) studies (54%). Neuroendocrine vs. temperature results were non-concordant in all 4 of the studies which included temperature measurements. These generally disparate findings suggest that these different endpoints may reflect brain serotonin neuroanatomic and receptor subsystem complexity and/or m-CPP's complex pharmacological properties. Thus, these neuroendocrine response measures cannot at this time be considered a general index of the other response measures, nor necessarily an index of the functional status of central serotonergic neurotransmission until this is established by more direct experimental investigations.

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.

Serotonergic modulation of anticholinergic effects on cognition and behavior in elderly humans

Cholinergic neurotransmission is thought to be modulated by serotonin as documented in animal and human studies. We examined the effects of the muscarinic antagonist scopolamine (0.4 mg IV) given alone or together with the serotonin mixed agonist/antagonist m-chlorophenylpiperazine (m-CPP, 0.08 mg/kg IV), and the selective 5-HT3 receptor antagonist ondansetron (0.15 mg/kg IV). Ten normal elderly volunteers each received five separate pharmacologic challenges (placebo, ondansetron, scopolamine, scopolamine+ondansetron, and scopolamine+m-CPP). Cognitive, behavioral, and physiologic variables were analyzed using repeated measures analysis of variance. The acute effects of scopolamine in certain cognitive, behavioral, and physiological measures were significantly exaggerated by the addition of m-CPP. Scopolamine's cognitive effects were unaffected by ondansetron at the dose tested, nor did ondansetron given alone affect basal cognitive performance. This pilot study suggests that the serotonin mixed agonist/antagonist m-CPP may influence cholinergic neurotransmission. The changes associated with the combination of scopolamine and m-CPP do not appear to be secondary to simple pharmacokinetic alterations and suggest a complex interaction between the cholinergic and serotonergic systems centrally.

Evidence for 5-hydroxytryptamine1A receptor involvement in the control of prolactin secretion in man

The effects of pindolol pretreatment (2 days) on prolactin and cortisol responses to a single dose of (+)-fenfluramine (30 mg po) were examined in nine healthy male volunteers. Pindolol pretreatment attenuated the (+)-fenfluramine-induced increase in prolactin concentrations but failed to affect the (+)-fenfluramine-induced cortisol increase. These data provide evidence in support of 5-HT1A receptor involvement in the regulation of prolactin secretion but question its importance in the regulation of cortisol secretion in man.

Hormonal responses to the administration of m-chlorophenylpiperazine in patients with seasonal affective disorder and controls

We report on the plasma cortisol and prolactin responses to the serotonergic agonist m-CPP (0.1 mg/kg) in 10 patients with winter seasonal affective disorder (SAD) and 10 controls during the winter, in both untreated and bright light-treated conditions; and on 8 other SAD patients and 8 other controls during the summer. Following m-CPP infusion, untreated patients had exaggerated prolactin (p < .05) and cortisol (p < .05) responses compared to controls. Light treatment significantly reduced responses of both hormones to m-CPP (prolactin: p < .01; cortisol: p < .01). When untreated winter subjects and summer subjects were compared, cortisol, but not prolactin responses to m-CPP were found to be higher in patients than in controls during the winter, and lower in patients than in controls during the summer (diagnosis by season: p < .05). These results are consistent with those of our previous report on the behavioral responses to m-CPP in the same patients and suggest an abnormality in serotonergic function in untreated SAD patients in winter, which is normalized following treatment with light therapy and naturally during the summer.

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.

Behavioral and neuroendocrine responses to metaCPP in anorexia nervosa

In response to the partial serotonin agonist meta-chlorophenylpiperazine (metaCPP), patients with obsessive-compulsive disorder have been reported to exhibit an increase in obsessive symptoms and a diminished release of prolactin and/or cortisol compared to controls. We examined the response to metaCPP of 10 patients with anorexia nervosa, before and after weight gain, and of eight healthy controls. Prior to weight gain, the patients exhibited a greater behavioral response to metaCPP than the controls and diminished prolactin and cortisol responses. Only the prolactin abnormality persisted after weight gain. These observations suggest that, in patients with anorexia nervosa, weight loss is associated with the development of neurobiological disturbances which are in some ways similar to those of obsessive-compulsive disorder.

Paraventricular nucleus controls 5-HT2C receptor-mediated corticosterone and prolactin but not oxytocin and penile erection responses

There is evidence that administration of the 5-HT2C receptor agonist, m-chlorophenylpiperazine (m-CPP), increases plasma concentrations of oxytocin, prolactin, corticosterone, induces penile erections and excessive grooming in male rats. To test the hypothesis that the hypothalamic paraventricular nucleus mediates these neuroendocrine and behavioural responses, we measured the effects of m-CPP (0.6 mg/kg i.v.) on these parameters in chronically cannulated, freely moving male rats after surgical lesion of the paraventricular nucleus or sham operation. Paraventricular nucleus lesion markedly attenuated prolactin, corticosterone and excessive grooming, but not oxytocin and penile erection responses to m-CPP. In contrast, both oxytocin and corticosterone responses to the dopamine receptor agonist, apomorphine (0.05 mg/kg i.v.), were attenuated in lesioned rats. The present studies suggest that the paraventricular nucleus mediates m-CPP-induced prolactin, corticosterone and probably also excessive grooming responses, and the mechanisms of apomorphine and m-CPP action on oxytocin secretion and penile erection responses differ.

Behavioural profile of two potential antidepressant pyridazine derivatives including arylpiperazinyl moieties in their structure, in mice

The potential antidepressant effects of two pyridazine derivatives, 5-benzyl 6-methyl 2-[4-(3-trifluoro-methyl phenyl) piperazin-1-yl] methylpyridazin-3-one (PC4) and 5-benzyl 6-methyl 2-[4-(3-chlorophenyl) piperazin-1-yl] methylpyridazin-3-one (PC13), were evaluated using classical psychopharmacological tests in mice. The intraperitoneal LD50 values of PC4 and PC13 were respectively 1125.8 and 429.6 mg kg-1. Only at intraperitoneal doses of 100 mg kg-1 did PC4 or PC13 significantly decrease locomotor activity. Both compounds (5-20 mg kg-1, i.p.) reduced the duration of immobility of mice in the forces swimming test, antagonized reserpine (2.5 mg kg-1, i.p.)-induced ptosis, and potentiated reserpine (2.5 mg kg-1, i.p.)-induced hypothermia. PC4 and PC13 (20 mg kg-1, i.p.) partly reversed hypothermia induced by low dose apomorphine (5 mg kg-1, s.c.) but were less effective for higher doses of apomorphine (16 mg kg-1, s.c.). At 200 mg kg-1, intraperitoneal PC13 enhanced the toxic effects of yohimbine (30 mg kg-1, s.c.), while PC4 was inactive. Head twitches produced either by L-5-hydroxytryptophan (4 mg kg-1, i.p.) in mice pretreated with pargyline (100 mg kg-1, i.p.) or by 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (3 mg kg-1, i.p.) were antagonized by both pyridazine derivatives (20 mg kg-1, i.p.). PC4 and PC13 showed analgesic properties in the phenylbenzoquinone-induced abdominal constriction test (5.0 < ED50 < 5.5 mg kg-1, i.p.) and in the hot-plate test (10 to 37% of analgesia at 10 mg kg-1, i.p.).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of pharmacologic treatments on the sleep of depressed patients

Antidepressant drugs produce striking effects on sleep architecture that are best understood in terms of their interactions with the monoamine pathways controlling sleep and wakefulness. Many different antidepressant drugs, including tricyclic antidepressants (TCAs), monoamine oxidase inhibitors (MAOIs), and selective 5-hydroxytryptamine (5-HT; serotonin) reuptake inhibitors (SSRIs), decrease rapid eye movement (REM) sleep. The reduction in REM sleep produced by antidepressants may be an important part of their mechanism of action; however, the ability of new antidepressant compounds, such as nefazodone and moclobemide, to increase REM sleep throws doubt on this suggestion. The effects of antidepressants on slow-wave sleep (SWS) are quite diverse; in general, antidepressants having significant 5-HT2A/2C receptor antagonist properties increase SWS, whereas other drugs, such as SSRIs or MAOIs, either lower SWS or produce no change. Sleep continuity is improved acutely following administration of antidepressants with sedating properties such as certain TCAs, trazodone, and mianserin. Some nonsedating drugs (ritanserin and nefazodone) also improve sleep continuity measures, possibly through 5-HT2A/2C receptor blockade.

A comparison of augmenting central serotonin and noradrenaline function in healthy subjects: implications for studies on the neurochemistry of anxiety

Biochemical and psychophysiological effects of augmenting serotonergic and noradrenergic function were compared in 12 normal volunteers. Fluvoxamine (100 mg), a serotonin (5-HT) re-uptake inhibitor, maprotiline (75 mg), a noradrenaline re-uptake inhibitor, and placebo were given for 7 days each to each subject. Subjects were tested pre-drug on days 1, 4 and 8 of each treatment. Catecholamines in 24 h urine, 'platelet-rich' plasma 5-HT and hormones, EEG, auditory evoked response, skin conductance, and bodily and psychological responses were monitored. Augmentation of central 5-HT by fluvoxamine was demonstrated by the decrease of 5-HT plasma levels. Fluvoxamine also reduced urinary dopamine, indicating a decrease in dopamine metabolism in response to augmentation of 5-HT function. Decrease in pulse rate, loss of appetite and a mild arousing effect were also detected with administration of fluvoxamine. Thus, further investigations on the neuro chemistry of anxiety disorders should include the study of mechanisms of interaction of neurotransmitters.

The role of serotonin in schizophrenia

The hypothesis that the LSD psychosis and by inference schizophrenic psychoses are related to dysfunctions in central serotonergic systems, formulated by Woolley and Shaw in the early 1950s was the first testable theory of modern biological psychiatry. Initially, it did not get the scientific attention it deserved. First, because LSD fell into disrepute and was to all intents and purposes banned from human experimentation. Secondly, the antipsychotics were discovered in the same period, and it became clear that these compounds block dopaminergic transmission and hence for many years thereafter the dopaminergic system occupied center stage in biological schizophrenia research. Presently, interest in the relation between serotonin and schizophrenia has been revived, due to the development of serotonin-blocking agents that appear to exert therapeutic effects in schizophrenia. In this paper the evidence for and against a link between serotonergic defects and schizophrenia psychopathology is critically discussed. The conclusion to be reached is threefold. (1) Interruption of certain serotonergic circuits represents an antipsychotic principle. (2) Tentative evidence suggests the involvement of serotonergic dysfunctions in the pathogenesis of schizophrenic psychoses. (3) It is not yet known whether serotonergic lesions contribute directly to the occurrence of schizophrenic psychopathology or via alterations in the dopaminergic system.

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.

Behavioural and pharmacological characterisation of the elevated "zero-maze" as an animal model of anxiety

The elevated "zero-maze" is a modification of the elevated plus-maze model of anxiety in rats which incorporates both traditional and novel ethological measures in the analysis of drug effects. The novel design comprises an elevated annular platform with two opposite enclosed quadrants and two open, removing any ambiguity in interpretation of time spent on the central square of the traditional design and allowing uninterrupted exploration. Using this model, the reference benzodiazepine anxiolytics, diazepam (0.125-0.5 mg/kg) and chlordiazepoxide (0.5-2.0 mg/kg) significantly increased the percentage of time spent in the open quadrants (% TO) and the frequency of head dips over the edge of the platform (HDIPS), and reduced the frequency of stretched attend postures (SAP) from the closed to open quadrants. In contrast, the anxiogenic drug m-chlorophenyl-piperazine (mCPP; 0.25-1.0 mg/kg) induced the opposite effects, decreasing %TO and HDIPS, and increasing SAP. The 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.001-0.1 mg/kg) had no effects on either %TO or HDIPS, but did decrease SAP at 0.01 mg/kg although not at higher or lower doses. Similarly, the 5-HT3 receptor antagonist, ondansetron (0.0001-1.0 mg/kg) decreased SAP and increased %TO at 0.01 mg/kg, but not at other doses. The present data suggest that a combination of the novel "zero-maze" design and a detailed ethological analysis provides a sensitive model for the detection of anxiolytic/anxiogenic drug action.

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.

Clozapine treatment and its effect on neuroendocrine responses induced by the serotonin agonist, m-chlorophenylpiperazine

The effects of clozapine treatment on neuroendocrine responses induced by the serotonin agonist, m-chlorophenylpiperazine (mCPP) were examined. mCPP and placebo were administered after a 2-week drug-free period and again after 5 weeks of clozapine treatment in nine schizophrenic inpatients. Adrenocorticotropic hormone (ACTH), prolactin, and mCPP levels were measured. Clozapine treatment completely blocked mCPP-induced ACTH and prolactin release suggesting that clozapine blocks serotonin receptors that mediate these hormone responses.

Behavioral responses to intravenous meta-chlorophenylpiperazine in patients with seasonal affective disorder and control subjects before and after phototherapy

A comparison of the baseline and post-infusion effects of the serotonin agonist meta-chlorophenylpiperazine (m-CPP) in 10 patients with seasonal affective disorder (SAD) and 11 healthy control subjects revealed significantly different subjective response profiles between the groups. Several baseline and m-CPP-stimulated responses in symptoms putatively related to serotonergic function changed significantly after a week's exposure to phototherapy in the SAD patients but not the control subjects. Before phototherapy, depressed patients with SAD reported activation-euphoria responses to m-CPP and significant decreases in carbohydrate hunger, but insignificant changes in feeling slowed or sleepy, while control subjects reported no mood or appetite changes but significant increases in feeling slowed down following m-CPP. After phototherapy, which led to a significant reduction in baseline depressive symptom rating to near-euthymic levels in the SAD patients, almost all of the patients' responses to m-CPP were normalized and no longer differed from the control subjects' responses. These results provide evidence of a possible dysregulation in serotonergic neurotransmission in depressed SAD patients that normalizes following treatment with phototherapy.

Brain 5-HT1C receptors and antidepressants

A variety of antidepressants of different chemical classes were tested for their in vivo and in vitro activity at 5-HT1C receptors in the brain. Conventional tricyclic antidepressants (imipramine, desipramine, maprotiline, clomipramine, trimipramine, amitriptyline, nortriptyline, doxepin, amoxapine, oxaprotiline) and two atypical antidepressants (mianserin and trazodone) were found to display affinity for 5-HT1C receptors in the nanomolar range. Antidepressants of other chemical classes and mechanisms of action (serotonin uptake inhibitors: fluoxetine, citalopram, sertraline, fluvoxamine; noradrenaline-dopamine uptake inhibitors: nomifensine, bupropion, amineptine; or monoamine oxidase inhibitors: moclobemide, iproniazid) had affinities in the micromolar range for 5-HT1C receptors, except fluoxetine. When tested in an in vivo functional model revealing agonistic or antagonistic properties at 5-HT1C receptors, all antidepressants displaying high affinity for this receptor type (except fluoxetine, clomipramine, trimipramine and oxaprotiline) were antagonists at 5-HT1C receptors. Antidepressants with lower 5-HT1C receptor affinity (except nomifensine) were inactive in this functional in vivo model. Antagonism at brain 5-HT1C receptors is a component of the antiserotonergic properties of a number of established antidepressants, especially of the tricyclic class.

Effects of ipsapirone in healthy subjects: a dose-response study

A dose-response study of ipsapirone (IPS), a 5HT1a partial agonist, was conducted in healthy male subjects. IPS was administered in doses of 5, 10 and 20 mg PO in a placebo-controlled, double-blind design to 15 subjects on 4 test days separated by at least 3 days. Oral temperature, ACTH, cortisol, prolactin, blood pressure, pulse rate and behavioral variables were assessed every 30 min for 3 h after administration of tablets (at 10:00 A.M.). IPS at 20 mg significantly decreased temperature and increased cortisol levels. Although IPS increased ACTH levels at 20 mg, this effect was variable and not significant. IPS did not affect prolactin levels nor did it have any behavioral effects. Although 20 mg IPS decreased blood pressure and pulse rate in one subject, overall it had no significant effect on these parameters. IPS at 20 mg PO appears a useful probe to test 5HT1a function when temperature and cortisol are used as response variables. These results replicate earlier studies on the effect of IPS in healthy human subjects.

Intravenous administration of the serotonin agonist m-chlorophenylpiperazine (mCPP) increases extracellular serotonin in the diencephalon of awake rats

The serotonin (5-HT) agonist 1-(m-chlorophenyl)piperazine (mCPP) has been widely used as a pharmacological probe to assess 5-HT function. Although mCPP is known to interact with 5-HT receptors, this drug is also reported to exhibit presynaptic actions that increase extraneuronal 5-HT in vitro. In the present study, we used in vivo microdialysis to examine the effects of mCPP on extracellular 5-HT in the ventromedial diencephalon of awake rats. Intravenous mCPP (1.0 and 2.0 mg/kg) increased dialysate 5-HT in a dose-related manner, with extracellular 5-HT levels rising 8-fold above baseline after the high dose of drug. The stimulatory effect of mCPP on dialysate 5-HT was abolished by pretreatment with the 5-HT uptake blocker fluoxetine (10 mg/kg, i.p.). In complementary experiments, mCPP elevated plasma prolactin at doses equivalent to those that increased dialysate 5-HT, and fluoxetine pretreatment caused a partial, though significant, attenuation of mCPP-induced prolactin release. These results indicate that mCPP increases extracellular 5-HT in rat brain by a presynaptic mechanism involving 5-HT transporters. Moreover, the plasma prolactin response to mCPP is at least partially mediated by the presynaptic actions of the drug. Our data further suggest the possibility that mCPP exhibits indirect agonist properties in human brain. Therefore, clinical studies designed to evaluate postsynaptic 5-HT receptor sensitivity based on responsiveness to mCPP should be interpreted with caution.

Mono N-aryl ethylenediamine and piperazine derivatives are GABAA receptor blockers: implications for psychiatry

Ethylenediamine (EDA) and piperazine are known GABA-A receptor agonists and this activity appears to reside in their carbamate adducts. In CO2-free incubation medium EDA and piperazine weakly reverse the inhibitory action of 1 microM GABA on specific [35S]t-butylbicyclophosphorothionate (35S-TBPS) binding to rat brain membranes in vitro. In 25 mM sodium bicarbonate buffer, EDA and piperazine much more potently inhibit 35S-TBPS binding in a way reversible by the GABA-A receptor blocker R5135. Thus, native EDA and piperazine are weak GABA-A receptor blockers, while their presumed carbamate adducts, formed by reaction with bicarbonate, are more potent GABA-A receptor agonists. Virtually all structural modifications of EDA or piperazine result in GABA-A receptor blockers, even in the presence of bicarbonate, judging from their abilities to fully or partially reverse the inhibitory effect of GABA on 35S-TBPS binding. Of 12 non-aromatic piperazine or EDA derivatives, the piperazine derivatives are the more potent GABA antagonists, although all are weak compared to the mono N-aryl derivatives. Nineteen mono N-aryl EDA derivatives are moderately potent GABA antagonists, including 10 with demonstrated or potential antidepressant activity. Most of the N-aryl piperazines are moderately to highly potent GABA antagonists, one (pitrazepin) being 4 to 5 times more potent than bicuculline. There are several clinically effective antidepressants (e.g. Amoxapine, Mianserine) and antipsychotics (Clothiapine, Loxapine, Metiapine, Clozapine and Fluperlapine) among the more potent N-aryl piperazine GABA antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Seasonal variation in behavioral responses to m-CPP in patients with seasonal affective disorder and controls

This paper reports the behavioral responses to m-chlorophenylpiperazine (m-CPP), a serotonin agonist, in patients with seasonal affective disorder (SAD) and controls during the summer. Results are compared with the responses of SAD patients and controls given m-CPP in the winter. Results of the winter study were reported earlier by our group. Baseline Hamilton depression ratings in SAD patients were significantly lower in the summer than in winter (p < 0.05). Additionally, in both SAD patients and controls, there were seasonal differences on the National Institute of Mental Health (NIMH) self-rating scale items: "depressed affect," "dysphoria," and "functional deficit" at baseline. The behavioral responses to m-CPP across seasons differentiated patients from normals only in the "activation/euphoria" item, on which a far greater response was seen in patients than in controls during the winter. This behavioral response may be a state marker for winter depression, as it was significantly reduced after light treatment of these patients in the winter, and in the summer. SAD patients responded differently from controls on "altered self-awareness" and "dysphoria" independently of seasons, and these responses may be considered as possible trait markers for this condition. These results provide further evidence of a possible deficiency in serotonergic transmission in seasonal affective disorder.

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.

Prolactin response to dl-fenfluramine in panic disorder

The objective of this study was to test the hypothesis that serotonin receptors are hypersensitive in patients with panic disorder. Eleven patients and 12 controls received a single PO dose of 60 mg of dl-fenfluramine at 0900h on a single occasion. Blood samples were collected with an indwelling intravenous catheter at 30-min intervals from 0930h to 1530h and prolactin determined by radioimmunoassay. In both groups, fenfluramine induced a rise in the plasma prolactin concentration from baseline. The patients showed a greater increase in prolactin response than the normal controls. This result is consistent with the hypothesis of increased serotonin receptor function in patients with panic disorder.

Effect of m-chlorophenylpiperazine on plasma homovanillic acid concentrations in healthy subjects

In view of the abundant anatomical and functional interactions between serotonin and dopamine systems, this study examined the effect of the serotonin agonist, m-chlorophenylpiperazine (mCPP) on plasma concentrations of the dopamine metabolite, homovanillic acid. Plasma prolactin levels, body temperature, and mCPP blood level were also measured. mCPP (0.35 mg/kg) and placebo were administered orally to 10 healthy men in a randomized double-blind design. Variables were measured for 210 min after administration of capsules. mCPP raised prolactin and temperature as compared to placebo, but did not affect plasma homovanillic acid concentrations. Results suggest that mCPP does not alter dopamine function.

Serotonin function in schizophrenia: effects of meta-chlorophenylpiperazine in schizophrenic patients and healthy subjects

This study examined serotonin (5-hydroxytryptamine; 5HT) receptor responsivity in 22 chronic schizophrenic patients and 17 healthy control subjects. The 5HT agonist meta-chlorophenylpiperazine (MCPP) was used as a probe of serotonergic function. MCPP (0.35 mg/kg) or placebo was administered orally after a 3-week drug-free period in a randomized double-blind design. Hormonal (adrenocorticotropic hormone and prolactin), temperature, and behavioral responses and MCPP blood levels were assessed for 210 minutes after administration of the capsules. The schizophrenic patients had blunted temperature responses compared with those of the healthy control subjects: MCPP raised body temperature in the control subjects, but not in the patients. Behavioral responses also differed in the two groups: MCPP increased the total Brief Psychiatric Rating Scale (BPRS) score in the control subjects and tended to decrease it in the patients. In patients, MCPP decreased the BPRS psychosis subscore. Hormonal responses did not differ significantly in the two groups. These findings suggest that further exploration of 5HT function in schizophrenia is warranted.

Endocrine and receptor pharmacology of serotonergic anxiolytics, antipsychotics and antidepressants

Several classes of drugs that modify serotonin (5-HT) neurotransmission are either currently used, or are being evaluated for their potential use in the treatment of anxiety, schizophrenia, and depression. 5-HT1A agonists are considered potential anxiolytics, while some atypical antipsychotics are potent 5-HT2 antagonists (and also have modest dopamine D2 affinity). Furthermore, there is a diverse group of serotonergic drugs that may be effective antidepressants. Secretion of ACTH, corticosterone/cortisol, prolactin, renin, oxytocin and vasopressin are stimulated by activation of different 5-HT receptor subtypes, while other neurotransmitter receptors also influence the secretion of these hormones. We compared the receptor binding profiles of 5-HT anxiolytics, antipsychotics and antidepressants with their endocrine effects. These comparisons could aid in understanding both the therapeutic and side effects of these drugs.

Effect of m-chlorophenylpiperazine on plasma arginine-vasopressin concentrations in healthy subjects

It has been demonstrated convincingly that ACTH and prolactin release are under the stimulatory control of serotonin (5-hydroxytryptamine, 5HT). Recent animal studies suggest that stimulation of 5HT activity also induces the release of arginine-vasopressin (AVP). More specifically, m-chlorophenylpiperazine (MCPP), a 5HT agonist widely used to examine 5HT receptor responsivity in human subjects, has been found to induce AVP release in rodents. This study examined whether MCPP increased plasma AVP levels in healthy human subjects. MCPP was administered orally to 17 healthy subjects in a placebo-controlled design in doses of 0.25 and 0.5 mg/kg. AVP was measured twice hourly over a 210 min period after administration of capsules. MCPP did not significantly alter AVP levels as compared to placebo. However, female subjects had significantly lower plasma AVP levels than males. Since it has been suggested that MCPP-induced AVP release in animals is due to stimulation of 5HT1c receptors, the fact that MCPP did not induce the release of AVP in humans suggests that either MCPP is not a potent 5HT1c agonist or that AVP is not released by stimulation of 5HT(1c) receptors in human subjects. The observation of gender differences in plasma AVP levels suggests that this factor should be taken into account in future studies of AVP secretion in plasma.