Administration Of mCPP Research Articles

Effects of ghrelin on nocturnal melatonin secretion in sheep: An in vitro and in vivo approach1

Recent studies confirmed that pineal melatonin (MEL) secretion is regulated by ghrelin (GHRL) in seasonally reproductive sheep. The first in vivo experiment investigated whether the effect of GHRL on nocturnal secretion of MEL in sheep is mediated by type 2 serotonin receptors. Sheep (n = 16) were intravenously injected with GHRL (2.5 μg/kg of BW) and meta-Chlorophenylpiperazine (mCPP; a mixed agonist of 5-HT2B/5-HT2C receptors; 1 mg/kg BW), either combined or individually, during the short-day (SDS) and long-day (LDS) seasons. Blood samples were collected at 15-min intervals for 4 h. The second in vitro experiment examined the effect of GHRL (10 ng/mL) on MEL secretion by pineal gland (PG) explants incubated for 5 h. The expression levels and/or concentrations of tryptophan 5-hydroxylase 1 (TPH1), aralkylamine N-acetyltransferase (AA-NAT), and the phosphorylated form of AA-NAT (p31T-AA-NAT) were determined at selected time points during the SDS and LDS seasons. The experiments demonstrated that GHRL reduced MEL secretion (P < 0.01) during the SDS season. Administration of mCPP or a combination of GHRL + mCPP stimulated MEL secretion (P < 0.01) regardless of the season. Furthermore, GHRL regulated nightly MEL secretion in a TPH1-independent manner. However, during the SDS season, GHRL reduced p31T-AA-NAT expression and the AA-NAT concentration (P < 0.01) and inhibited MEL secretion (P < 0.001), whereas during the LDS season, GHRL had no effect on MEL secretion or on the expression of the examined enzymes. These findings indicate that GHRL directly and indirectly affects PG activity in sheep and that the photoperiod modulates the effects of GHRL.

Effects of ghrelin on nocturnal melatonin secretion in sheep: An in vitro and in vivo approach.

Recent studies confirmed that pineal melatonin (MEL) secretion is regulated by ghrelin (GHRL) in seasonally reproductive sheep. The first in vivo experiment investigated whether the effect of GHRL on nocturnal secretion of MEL in sheep is mediated by type 2 serotonin receptors. Sheep ( = 16) were intravenously injected with GHRL (2.5 μg/kg of BW) and meta-Chlorophenylpiperazine (mCPP; a mixed agonist of 5-HT2B/5-HT2C receptors; 1 mg/kg BW), either combined or individually, during the short-day (SDS) and long-day (LDS) seasons. Blood samples were collected at 15-min intervals for 4 h. The second in vitro experiment examined the effect of GHRL (10 ng/mL) on MEL secretion by pineal gland (PG) explants incubated for 5 h. The expression levels and/or concentrations of tryptophan 5-hydroxylase 1 (TPH1), aralkylamine N-acetyltransferase (AA-NAT), and the phosphorylated form of AA-NAT (p31T-AA-NAT) were determined at selected time points during the SDS and LDS seasons. The experiments demonstrated that GHRL reduced MEL secretion ( < 0.01) during the SDS season. Administration of mCPP or a combination of GHRL + mCPP stimulated MEL secretion ( < 0.01) regardless of the season. Furthermore, GHRL regulated nightly MEL secretion in a TPH1-independent manner. However, during the SDS season, GHRL reduced p31T-AA-NAT expression and the AA-NAT concentration ( < 0.01) and inhibited MEL secretion ( < 0.001), whereas during the LDS season, GHRL had no effect on MEL secretion or on the expression of the examined enzymes. These findings indicate that GHRL directly and indirectly affects PG activity in sheep and that the photoperiod modulates the effects of GHRL.

Anxiety-like effects of meta-chlorophenylpiperazine in paradoxically sleep-deprived mice

Chlorophenylpiperazines (CPP) are psychotropic drugs used in nightclub parties and are frequently used in a state of sleep deprivation, a condition which can potentiate the effects of psychoactive drugs. This study aimed to investigate the effects of sleep deprivation and sleep rebound (RB) on anxiety-like measures in mCPP-treated mice using the open field test. We first optimized our procedure by performing dose-effect curves and examining different pretreatment times in naïve male Swiss mice. Subsequently, a separate cohort of mice underwent paradoxical sleep deprivation (PSD) for 24 or 48h. In the last experiment, immediately after the 24h-PSD period, mice received an injection of saline or mCPP, but their general activity was quantified in the open field only after the RB period (24 or 48h). The dose of 5mgmL(-1) of mCPP was the most effective at decreasing rearing behavior, with peak effects 15min after injection. PSD decreased locomotion and rearing behaviors, thereby inhibiting a further impairment induced by mCPP. Plasma concentrations of mCPP were significantly higher in PSD 48h animals compared to the non-PSD control group. Twenty-four hours of RB combined with mCPP administration produced a slight reduction in locomotion. Our results show that mCPP was able to significantly change the behavior of naïve, PSD, and RB mice. When combined with sleep deprivation, there was a higher availability of drug in plasma levels. Taken together, our results suggest that sleep loss can enhance the behavioral effects of the potent psychoactive drug, mCPP, even after a period of rebound sleep.

Cannabidiol reverses the mCPP‐induced increase in marble‐burying behavior

Cannabidiol (CBD), one of the main components of Cannabis sp., presents clinical and preclinical anxiolytic properties. Recent results using the marble-burying test (MBT) suggest that CBD can also induce anticompulsive-like effects. Meta-chloro-phenyl-piperazine (mCPP) is a nonspecific serotonergic agonist (acting mainly at 5HT1A, 5HT2C and 5HT1D receptors) reported to increase symptoms in OCD patients and block the anticompulsive-like effect of serotonin reuptake inhibitors (SRIs) in animal models. The aim of this study was to investigate the interference of CBD on mCPP effects in repetitive burying. Administration of mCPP showed dual effects in the MBT, increasing the number of buried marbles at lower (0.1 mg/kg) while decreasing it at higher doses (1 mg/kg), an effect not related to a general increase in anxiety-like behavior. As found previously, CBD (30 mg/kg) and the positive control fluoxetine (FLX; 10 mg/kg) decreased burying behavior without changing general exploratory activity. A similar effect was found when subeffective doses of CBD (15 mg/kg) and FLX (3 mg/kg) were administered together. These subeffective doses alone were also able to block mCPP-induced repetitive burying. The results, in addition to reinforcing a possible anticompulsive effect of CBD, also suggest that mCPP-induced repetitive burying could be a useful test for the screening of compounds with presumed anticompulsive properties.

Mo1996 Cancer-Related Gastrointestinal Dysmotility Is Mediated by the Suppression of Ghrelin-Neuropeptide Y Signaling via Serotonin 2C Receptor in the Hypothalamus

Background & aim: Elderly people often exhibit a lack of appetite, which is known to cause increased morbidity and the progression of physical disorders. Although various factors contribute to decreased appetite, anxiety is the main cause of restricted dietary intake. Activation of the serotonin 2C receptor (5-HT2CR) induces an anxiety-like response in young animals, causing a restriction of dietary intake. However, the contribution of 5-HT2CR toward stress-induced anorexia in aged animals remains unclear. In this study, aged mice were exposed to a novel hypophagia paradigm to investigate the effects of a selective 5-HT2CR antagonist and a traditional Japanese medication, rikkunshito (RKT). Methods: After having group-housed C57BL/6 male mice (young mice, 6 weeks old; aged mice, 79-80 weeks old), the mice were transferred to individual cages to induce novel environmental stress. Changes in the amount of food intake after 6 and 24 h were measured, and blood samples were collected to measure stress hormones using the ELISA method. 5-HT2CR mRNA expression in the hypothalamus was evaluated by real time RT-PCR and in situ hybridization. The 5HT2CR antagonist SB242084, RKT or the 5-HT2CR agonist mCPP were administered to both the mice under stress and the non-stressed mice and the amount of food intake was measured to clarify the role of the 5-HT2CR on feeding behavior. Results: In the aged mice, exposure to a novel environment reduced the amount of food intake and increased corticosterone secretion. These responses were significant compared with those in the young mice. The administration of SB242084 to control mice increased the amount of food intake of aged mice only over 24 h. In addition, the administration of low-dose mCPP to the control mice induced a greater decrease in appetite in the aged mice than in the young mice. This suggests that there may be a constant hyperfunction or increased 5-HT2CR sensitivity in aged mice. 5-HT2CR mRNA expression in the hypothalamus (e.g. paraventricular nucleus) was increased in the aged mice following novel environmental stress. In the aged mice placed under novel environment stress, the SB242084 and RKT suppress the increase in stress hormone level as well as the decrease in food intake. Conclusion: These results suggest that the excessive enhancement of 5-HT2CR function causes an anxiety-like reaction in an aged mouse and greatly contributes to a decrease in food intake. Similar to SB242084, RKT is thought to suppress the decrease in food intake in aged mice under novel environment stress by controlling 5-HT2CR activity.

5-HT2C receptor involvement in the control of persistence in the Reinforced Spatial Alternation animal model of obsessive–compulsive disorder

ObjectiveThe serotonergic system is implicated in the pathophysiology of obsessive–compulsive disorder (OCD). However, the distinct role of serotonin (5-HT) receptor subtypes remains unclear. This study investigates the contribution of 5-HT2A and 5-HT2C receptors in the modulation of persistence in the reinforced spatial alternation model of OCD. MethodsMale Wistar rats were assessed for spontaneous and pharmacologically induced (by m-chlorophenylpiperazine: mCPP) directional persistence in the reinforced alternation OCD model. Systemic administration of mCPP (non-specific 5-HT agonist, 2.5mg/kg), M100907 (selective 5-HT2A receptor antagonist, 0.08mg/kg), SB242084 (selective 5-HT2C receptor antagonist, 0.5mg/kg) and vehicle was used. Experiment 1 investigated M100907 and SB242084 effects in animals spontaneously exhibiting high and low persistence during the early stages of alternation training. Experiment 2 investigated M100900 and SB242084 effects on mCPP-induced persistence. ResultsUnder the regime used in Experiment 1, 5-HT2A or 5-HT2C receptor antagonism did not affect spontaneous directional persistence in either high or low persistence groups. In Experiment 2, 5-HT2C but not 5-HT2A receptor antagonism significantly reduced, but did not abolish, mCPP-induced directional persistence. ConclusionsThese findings suggest that 5-HT2C but not 5-HT2A receptors contribute to the modulation of mCPP-induced persistent behaviour, raising the possibility that the use of 5-HT2C antagonists may have a therapeutic value in OCD.

Залучення деяких підтипів 5-ht2-рецепторів до афективної поведінки самиць щурів

The present work was devoted to the comparative analysis of influence of chronic administration of 5-HT(2B/2C) receptors agonist - m-CPP (0,5 mg/kg, i.p.) and 5-HT(2A/2C) receptors antagonist - ketanserine (0,1 mg/kg, i.p.) for 14 days on the anxiety and depressive-like behavior in adult female rats. It was established that chronic ketanserine administration rendered antidepressive and anxiolytic effects in females during estrous and proestrous. M-CPP administration also resulted in antidepressive effect in estrous and proestrous. Also, it was noted definite modulation of anxiety behavior in connection of ovary cycle phases in rats treated with m-CPP: at increased level of estrogens was anxiolytic effect while at reduced level of estrogen - anxiogenic effect. It is suggested the involvement of different subtypes of 5-HT receptors in the mechanisms of anxiety-depressive-like behavior at alterations of hormonal balance during ovary cycle. The data obtained indicate a close interaction between the ovary hormonal and serotonergic systems of the brain in the mechanisms of anxiety and depression.

Prior stress interferes with the anxiolytic effect of exercise in c57bl/6j mice.

Recent reports demonstrate that the beneficial effects of voluntary exercise may be sensitive to stress prior to and during the wheel access period. Here, a variate stress procedure is used with socially isolated mice for 7 days prior to the introduction of running wheels to assess the impact of prior and concurrent stress on the anxiolytic effect of exercise. Following stress exposure, functioning or nonfunctioning running wheels were introduced into stressed and unstressed group-housed control cages. Following 3 weeks of wheel access, the anxiolytic effect of exercise was assessed using acoustic startle, stress-induced hyperthermia, and a challenge with the anxiogenic drug metachlorophenylpiperazine (mCPP). Variate stress was demonstrated to interfere with normal weight gain. Further, exercise was not anxiolytic in stressed mice. Consistent with previous reports unstressed exercising mice demonstrated reduced acoustic startle, attenuated stress induced hyperthermia, and a blunted increase in startle following mCPP administration when compared with unstressed sedentary controls. Stressed exercising mice were indistinguishable from stressed sedentary and unstressed sedentary controls on each anxiety measure. Although running distance varied between individual mice, the distance run did not predict the level of anxiety on any measure. These findings suggest that prior and ongoing stress delays or prevents the anxiolytic effect of exercise without affecting exercise itself.

Estradiol increases the anorexia associated with increased 5-HT2C receptor activation in ovariectomized rats

Estradiol's inhibitory effect on food intake is mediated, in part, by its ability to increase the activity of meal-related signals, including serotonin (5-HT), which hastens satiation. The important role that postsynaptic 5-HT2C receptors play in mediating 5-HT's anorexigenic effect prompted us to investigate whether a regimen of acute estradiol treatment increases the anorexia associated with increased 5-HT2C receptor activation in ovariectomized (OVX) rats. We demonstrated that intraperitoneal and intracerebroventricular (i.c.v.) administration of low doses of the 5-HT2C receptor agonist meta-chlorophenylpiperazine (mCPP) decreased 1-h dark-phase food intake in estradiol-treated, but not oil-treated, OVX rats. During a longer feeding test, we demonstrated that i.c.v. administration of mCPP decreased 22-h food intake in oil-treated and, to a greater extent, estradiol-treated OVX rats. In a second study, we demonstrated that estradiol increased 5-HT2C receptor protein content in the caudal brainstem, but not hypothalamus, of OVX rats. We conclude that a physiologically-relevant regimen of acute estradiol treatment increases sensitivity to mCPP's anorexigenic effect. Our demonstration that this same regimen of estradiol treatment increases 5-HT2C receptor protein content in the caudal hindbrain of OVX rats provides a possible mechanism to explain our behavioral findings.

Neurohormonal mechanisms of the antidepressant effect of ketanserin in ovariectomized rats

In the present study we investigated the effects of chronic administration of m-CPP (0.5 mg/kg, i.p.), a 5-HT2B/2C receptor agonist, and ketanserin (0.1 mg/kg, i.p.), a 5-HT2A/2C receptor antagonist, alone or in a combination with 17β-estradiol (0.5 μg per animal, i.m.) over 14 days on depressive behavior and the concentration of different monoamines in the hippocampus in adult ovariectomized (OVX) female rats. Depression-like behavior was assessed using the Porsolt’s test. The concentrations of monoamines and their metabolites were determined using HPLC. We found that chronic ketanserin administration has an antide-pressant effect in OVX rats. Chronic ketanserin administration in combination with 17β-estradiol in OVX females potentiated antidepressant action. The antidepressant effect of ketanserin in OVX rats correlated with the restoration of noradrenergic, serotonergic, and dopaminergic neurotransmission in the hippocampus. Our data indicate a close interaction between the ovary hormonal and serotonergic systems of the brain in mechanisms of depression.

Blockade of 5-HT2A/2C-Type Receptors Impairs Learning in Female Rats in the Course of Estrous Cycle

We studied the effects of chronic administration (14 days) of agonist of 5-HT2B/2C serotonin receptors m-CPP (0.5 mg/kg subcutaneously) and agonist of 5-HT2A/2C serotonin receptors ketanserin (0.1 mg/kg intraperitoneally) on conditioned reactions in female rats in different phases of the estrous cycle. Passive avoidance (PA) paradigm and Morris water maze were used as behavioral tests. Chronic administration of m-CPP did not affect PA retrieval during the proestrus and estrus phases, but improved the dynamics of spatial learning in Morris water maze in comparison with control rats. Chronic administration of ketanserin uniformly impaired processes of spatial and nonspatial learning in female rats irrespective to the phase of the estrous cycle. A modulating role of 5-HT2A/2C and 5-HT2B/2C serotonin receptors in process of learning in female rats during the key phases of the estrous cycle was demonstrated.

Thermogenic effect of YM348, a novel 5-HT2C-receptor agonist, in rats

We have investigated the effect of S-2-(7-ethyl-1H-furo[2,3-g]indazol-1-yl)-1-methylethylamine (YM348), a novel 5-HT(2C)-receptor agonist, on body temperature and energy expenditure in Wistar rats. m-Chlorophenylpiperazine (mCPP) and S-2-(6-chloro-5-fluoroindol-1-yl)-1-methylethylamine (RO 60-0175) were used as reference 5-HT(2C)-receptor agonists. Administration of YM348, mCPP and RO 60-0175 dose-dependently and significantly increased body temperature in rats. YM348- or RO 60-0175-induced hyperthermia was significantly attenuated by the non-selective 5-HT(2)-receptor antagonist methysergide and the selective 5-HT(2C)-receptor antagonist SB242084, but not by the selective 5-HT(2A)-receptor antagonist MDL100907. mCPP-induced hyperthermia was significantly attenuated by methysergide, SB242084 and MDL100907. In addition to the increase in body temperature, YM348, mCPP and RO 60-0175 produced dose-related and significant increases in energy expenditure. YM348-, mCPP- and RO 60-0175-induced increases in energy expenditure were significantly attenuated by methysergide and SB242084 but not by MDL100907. These results suggested that 5-HT(2C)-receptor stimulation increased body temperature and energy expenditure and that the 5-HT(2C)-receptor was the target receptor in the thermogenic effect of YM348 in Wistar rats.

Synergistic actions of apomorphine and m-chlorophenylpiperazine on ejaculation, but not penile erection in rats

It has been suggested that dopamine (DA) and serotonin (5-HT) and their receptors, particularly D(2)-like and 5-HT(2C) receptors, may play a significant role in the control of male sexual function. The purpose of this study was to investigate whether the combination of a dopamine receptor agonist apomorphine and a 5-HT(2) receptor agonist m-CPP would potentiate penile erection and ejaculation in male rats. Systemic administration of either apomorphine (0.01-0.1 mg/kg, s.c.) or m-CPP (0.01-0.3 mg/kg, i.p.) dose-dependently elicited penile erections, but did not induce ejaculation. When combined, there was a drastic increase in both the incidence of ejaculation and the amount of ejaculated seminal materials, while the proerectile effect induced by each drug was not potentiated. The proejaculatory effect induced by the combination of apomorphine (0.1 mg/kg, s.c.) and m-CPP (0.3 mg/kg, i.p.) was completely blocked by pretreatment with the D(2)-like receptor antagonists haloperidol and sulpiride, but not by the D(1)-like receptor antagonist SCH-23390. The synergistic action for ejaculation was also blocked by domperidone, the D(2)-like receptor antagonist that dose not cross the blood-brain barrier. The rats pretreated with the 5-HT(2C) receptor antagonist SB242084 did not show the synergistic action by the combination of apomorphine and m-CPP, whereas the rats pretreated with the 5-HT(2A) receptor antagonist ketanserin and the 5-HT(2B) receptor antagonist SB204741 showed the combination-induced synergistic action. These results suggest that the combination of a small dose of apomorphine and m-CPP potently and selectively facilitates the ejaculatory response through the activation of D(2)-like and 5-HT(2C) receptors, respectively. The D(2)-like receptors involved in the synergistic action may be, at least in part, located in the peripheral sites.

Subthalamic neurons show increased firing to 5-HT 2C receptor activation in 6-hydroxydopamine-lesioned rats

The subthalamic nucleus is innervated by 5-HT afferents from the dorsal raphe nucleus and expresses high density of 5-HT 2C receptors. However, the role of these receptors in neuronal firing of subthalamic neurons in vivo is unknown. In the present study, we examined the changes in the firing rate and firing pattern of subthalamic neurons, and the effect of the nonselective 5-HT 2C receptor agonist m-CPP and selective antagonist SB242084 on the neuronal firing of subthalamic neurons in normal rats, sham rats, and rats with 6-hydroxydopamine lesions of the substantia nigra pars compacta by using extracellular recording. Results showed an increase in the percentage of subthalamic neurons exhibiting burst-firing pattern with no change in firing rate during the third week after the lesion compared to normal rats. The systemic administration of m-CPP (20–320 μg/kg, i.v.) dose-dependently increased the firing rate of subthalamic neurons, and the local application of m-CPP, 4 μg, in the subthalamic nucleus also increased the firing rate of subthalamic neurons in the lesioned rats. Similarly, at the same doses, the systemic and local administration of m-CPP induced the excitatory effects on subthalamic neurons in normal and sham rats. The excitatory effect of m-CPP was reversed by the subsequent administration of SB242084 (200 μg/kg, i.v.). These results suggest that the response of subthalamic neurons to 5-HT 2C receptor stimulation is not altered after 6-hydroxydopamine lesions of the substantia nigra pars compacta.

Hypersensitivity of 5-HT 2 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-HT 2 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-HT 2 receptors.

Serotonin systems upregulate the expression of hypothalamic NUCB2 via 5-HT2C receptors and induce anorexia via a leptin-independent pathway in mice

NEFA/nucleobindin2 (NUCB2), a novel satiety molecule, is associated with leptin-independent melanocortin signaling in the central nervous system. Here, we show that systemic administration of m-chlorophenylpiperazine ( mCPP), a serotonin 5-HT1B/2C receptor agonist, significantly increased the expression of hypothalamic NUCB2 in wild-type mice. The increases in hypothalamic NUCB2 expression induced by mCPP were attenuated in 5-HT2C receptor mutant mice. Systemic administration of mCPP suppressed food intake in db/db mice with leptin receptor mutation as well as lean control mice. On the other hand, the expression of hypothalamic NUCB2 and proopiomelanocortin (POMC) was significantly decreased in hyperphagic and non-obese 5-HT2C receptor mutants compared with age-matched wild-type mice. Interestingly, despite increased expression of hypothalamic POMC, hypothalamic NUCB2 expression was decreased in 5-HT2C receptor mutant mice with heterozygous mutation of β-endorphin gene. These findings suggest that 5-HT systems upregulate the expression of hypothalamic NUCB2 via 5-HT2C receptors, and induce anorexia via a leptin-independent pathway in mice.

Rikkunshito, an Herbal Medicine, Suppresses Cisplatin-Induced Anorexia in Rats Via 5-HT2 Receptor Antagonism

Chemotherapy with an anticancer agent generally causes gastrointestinal tract disorders such as vomiting and anorexia, but the mechanism remains unclear. Rikkunshito, a kampo preparation, is known to alleviate such adverse reactions. In this study, we attempted to clarify the mechanism. We investigated the decreases of plasma acylated-ghrelin level and food intake caused by cisplatin, serotonin (5-HT), 5-HT agonists, and vagotomy as well as the decrease-suppressing effects of rikkunshito and 5-HT antagonists. In addition, binding affinities of rikkunshito components were determined in receptor-binding assays using 5-HT2B and 5-HT2C receptors. Cisplatin, 5-HT, BW723C86 (5-HT2B-receptor agonist), and m-chlorophenylpiperazine HCl (5-HT2C agonist) markedly decreased plasma acylated-ghrelin levels, although 5-HT3 and 5-HT4 agonists had no effect. In contrast, 5-HT2B and 5-HT2C antagonists suppressed the cisplatin-induced decrease of plasma acylated-ghrelin level and food intake. Administration of rat ghrelin improved the cisplatin-induced decrease in food intake. Vagotomy decreased the plasma acylated-ghrelin level, which was decreased further by cisplatin. Rikkunshito suppressed such cisplatin-induced decreases of plasma acylated-ghrelin level and food intake. The suppressive effect of rikkunshito was blocked by a ghrelin antagonist. Components of rikkunshito, 3,3',4',5,6,7,8-heptamethoxyflavone, hesperidin, and iso-liquiritigenin showed a 5-HT2B-antagonistic effect in vitro, and oral administration of rikkunshito suppressed the cisplatin-induced decrease in the plasma acylated-ghrelin level. The cisplatin-induced decreases of the plasma acylated-ghrelin level and food intake are mediated by 5-HT2B/2C receptors and suppressed by flavonoids in rikkunshito.

Ejaculatory response induced by a 5-HT 2 receptor agonist m-CPP in rats: Differential roles of 5-HT 2 receptor subtypes

It has been reported that systemic administration of m-CPP (1-[3-chlorophenyl] piperazine hydrochloride), a 5-HT 2 receptor agonist, produces a 5-HT 2C receptor-mediated penile erections and self-grooming in rats. In the present study, we examined the ability of m-CPP to induce ejaculation in rats and determined which 5-HT 2 receptor subtypes may be involved in the m-CPP-induced ejaculation. The ejaculatory response was assessed by weighing the seminal materials accumulated over 30 min. In Experiment 1, systemic administration of m-CPP (0.1–3.0 mg/kg, i.p.) produced a dose-dependent increase in both the incidence of ejaculation and the weight of the seminal materials. The inverted U-shaped dose-response effects of m-CPP on penile erection and genital grooming were also observed, with maximum effects at 0.6 mg/kg. Pretreatment with SB242084 (0.1 and 0.3 mg/kg, i.p.), a selective 5-HT 2C receptor antagonist, dose-dependently attenuated the ejaculatory response induced by m-CPP (3.0 mg/kg). The proejaculatory effect of m-CPP was also attenuated by ketanserin (0.3 and 1.0 mg/kg, i.p.), a 5-HT 2A receptor antagonist, whereas SB204741 (0.1 and 0.3 mg/kg, i.p.), a selective 5-HT 2B receptor antagonist, significantly potentiated the m-CPP-induced ejaculatory response. Penile erection and genital grooming induced by m-CPP (0.3 mg/kg, i.p.) was only blocked by SB242084. In Experiment 2 (termed as corset test), in rats fitted with a corset at the thoracic level to prevent the loss of seminal materials by genital grooming, the proejaculatory effect of m-CPP was more efficiently detected than in the non-fitted animals: the ED 50 value for inducing ejaculation was reduced to less than 50% of the ED 50 in non-fitted animals. In this test, the proejaculatory effect of m-CPP (0.6 mg/kg, i.p.) was completely blocked by SB242084 (0.3 mg/kg, i.p.), whereas ketanserin (0.3 mg/kg, i.p.) or SB204741 (0.3 mg/kg, i.p.) did not affect the m-CPP -induced ejaculation. From these observations, it is suggested that the 5-HT 2 receptor agonist m-CPP at low doses (0.3–1.0 mg/kg) possesses the proejaculatory as well as proerectile effects in rats that are primarily associated with the activation of 5-HT 2C receptors, and that the activation of 5-HT2B receptors may produce an inhibitory effect on ejaculation induced by a high dose (3.0 mg/kg) of m-CPP . Furthermore, the results of the present study also indicate that the corset test employed in this study may be useful for detecting the proejaculatory effect of the compounds.

Serotonin Dysfunction in Pathological Gamblers: Increased Prolactin Response to Oral m-CPP Versus Placebo

Acute administration of the partial serotonin (5-HT) agonist meta-chlorophenylpiperazine (m-CPP), that is used also as a street drug, has been reported to induce a "high" and craving response in various impulsive and substance addiction disorders. To clarify altered 5-HT metabolism in pathological gamblers and to explore the specific role of serotonergic system in non-substance addictions, we assessed behavioral ("high" and "craving") and neuroendocrine (prolactin and cortisol) responses to an oral single dose of m-CPP and placebo in pathological gamblers and matched controls. Moreover, the relationship between neuroendocrine outcome and clinical severity has been assessed. Twenty-six pathological gamblers and 26 healthy control subjects enter a double-blind, placebo-controlled-crossed administration of orally dose m-CPP 0.5 mg/kg. Outcome measures included prolactin and cortisol levels, gambling severity, mood, craving and "high" scales. Pathological gamblers had significantly increased prolactin response compared to controls at 180 minutes and at 210 minutes post-administration. Greater pathological gamblers severity correlated with increased neuroendocrine responsiveness to m-CCP, suggesting greater 5-HT dysregulation. Pathological gambling patients had a significantly increased "high" sensation after m-CPP administration compared with control. These results provide additional evidence for 5-HT disturbance in pathological gamblers and they support the hypotheses that the role of the 5-HT dysfunction related to the experience of "high" might represent the pathway that leads to dyscontrolled behavior in pathological gamblers. Furthermore, the "high" feeling induced by m-CPP in pathological subjects may represent a marker of vulnerability to both behavioral and substance addictions.

Does meta-chlorophenylpiperazine (mCPP) activate human platelets?

mCPP (meta-chlorophenylpiperazine), an agonist at serotonin (5-hydroxytryptamine, 5-HT) 5-HT2 receptors, has been used as a probe of serotonergic function. We assessed its effect on platelet activation by measuring median platelet volume (MPV), the Sonoclot (SCT) pattern and plasma and intraplatelet serotonin. (a) In vitro study: MPV was measured (n = 7) using a high-resolution channelyzer: Saline (median and range (5.23 fl; 5.10–6.18) vs. mCPP (5.36; 5.10–6.44) P = 0.03; ADP (5.42; 5.29–6.44) vs. ADP + mCPP (5.67; 5.42–6.63) P = 0.02; mCPP (5.36; 5.10–6.44) vs. ADP + mCPP (5.67; 5.42–6.63) P = 0.02. Therefore, mCPP increases the MPV and enhances the effect of ADP. (b) In vivo study: The SCT time to inflection (TI) and time to peak (TP) were measured following the oral administration of mCPP (0.5 mg/kg) or aspirin (300 mg) (n = 10). Ingestion of mCPP significantly shortened TI and TP indicating platelet activation. TI: 0 h (mean ± SD: 10.2 ± 2.0 min) vs. 6 h (9.3 ± 1.5) P = 0.03; TP: 0 h (31.9 ± 7.6) vs. 6 h (23.1 ± 2.9) P = 0.01. Aspirin had no effect on TI or TP. There were no significant changes in plasma and intraplatelet 5-HT. It is concluded that mCPP activates human platelets via 5-HT receptors.