An apomorphine-induced vomiting model for antiemetic studies in man

Dopamine D2 receptors in the nucleus accumbens modulate erectile function in a rat model of nonorganic erectile dysfunction

Background

The central molecular mechanisms of nonorganic erectile dysfunction remains unknown.

Objective

This study aimed to investigate the association of dopaminergic neurons projecting to the nucleus accumbens of male rats with nonorganic erectile dysfunction.

Materials/methods

Nonorganic erectile dysfunction was induced by chronic mild stress. The sucrose consumption test, sexual behavior test, and apomorphine test were carried out to select depression‐like rats with erectile dysfunction. These rats were considered as nonorganic erectile dysfunction model rats. Dopamine D1/D2 receptor agonist/antagonist was infused into the nucleus accumbens to observe the effect on sexual behavior. Dopaminergic projections to the nucleus accumbens were labeled with both the retrograde tracer FluoroGold injected into the nucleus accumbens and tyrosine hydroxylase. The expression level of tyrosine hydroxylase in dopaminergic neurons projecting to the nucleus accumbens in the ventral tegmental area was measured. The expression levels of dopamine D1/D2 receptors and tyrosine hydroxylase in the nucleus accumbens were also measured.

Results

Nonorganic erectile dysfunction was proved by the sucrose consumption test, sexual behavior test, and apomorphine test in model rats. After central infusion of the dopamine D2 receptor agonist into the nucleus accumbens, the recovery of erectile function, sexual arousal, and motivation were indicated by increased intromission ratio and decreased mount latency. Decreased expression levels of dopamine D2 receptors and tyrosine hydroxylase in the nucleus accumbens and decreased expression level of tyrosine hydroxylase in the dopaminergic neurons projecting to the nucleus accumbens were observed in model rats.

Discussion

These results suggest the impairment of dopaminergic neurons projecting to the nucleus accumbens and dopamine D2 signaling in the nucleus accumbens, causing the suppression of erectile function, sexual arousal, and motivation.

Conclusion

These results suggest that the impaired dopamine D2 receptor pathway in the nucleus accumbens may be one of the main pathway involved in the development of nonorganic erectile dysfunction in the present model.

An assay of drug-induced emesis in the squirrel monkey (Saimiri sciureus)

BACKGROUND

Emesis has significant evolutionary value as a defense mechanism against ingested toxins; however, it is also one of the most common adverse symptoms associated with both disease and medical treatments of disease. The development of improved antiemetic pharmacotherapies has been impeded by a shortage of animal models.

METHODS

The present studies characterized the responses of the squirrel monkey to pharmacologically diverse emetic drugs. Subjects were administered nicotine (0.032-0.56 mg/kg), lithium chloride (150-250 mg/kg), arecoline (0.01-0.32 mg/kg), or apomorphine (0.032-0.32 mg/kg) and observed for emesis and prodromal hypersalivation.

RESULTS

Nicotine rapidly produced emesis and hypersalivation. Lithium chloride produced emesis with a longer time course without dose-dependent hypersalivation. Arecoline produced hypersalivation but not emesis. Apomorphine failed to produce emesis or hypersalivation.

CONCLUSIONS

The squirrel monkey is sensitive to drug-induced emesis by a variety of pharmacological mechanisms and is well-positioned to examine antiemetic efficacy and clinically important side effects of candidate antiemetic pharmacotherapies.

The Many Faces of Apomorphine: Lessons from the Past and Challenges for the Future

Apomorphine is now recognized as the oldest antiparkinsonian drug on the market. Though still underused, it is increasingly prescribed in Europe for patients with advanced Parkinson's disease (PD) with motor fluctuations. However, its history is far from being limited to movement disorders. This paper traces the history of apomorphine, from its earliest empirical use, to its synthesis, pharmacological development, and numerous indications in human and veterinary medicine, in light of its most recent uses and newest challenges. From shamanic rituals in ancient Egypt and Mesoamerica, to the treatment of erectile dysfunction, from being discarded as a pharmacological tool to becoming an essential antiparkinsonian drug, the path of apomorphine in the therapeutic armamentarium has been tortuous and punctuated by setbacks and groundbreaking discoveries. Throughout history, three main clinical indications stood out: emetic (gastric emptying, respiratory disorders, aversive conditioning), sedative (mental disorders, clinical anesthesia, alcoholism), and antiparkinsonian (fluctuations). New indications may arise in the future, both in PD (palliative care, nonmotor symptoms, withdrawal of oral dopaminergic medication), and outside PD, with promising work in neuroprotection or addiction.

What is nausea? A historical analysis of changing views

The connotation of "nausea" has changed across several millennia. The medical term 'nausea' is derived from the classical Greek terms ναυτια and ναυσια, which designated the signs and symptoms of seasickness. In classical texts, nausea referred to a wide range of perceptions and actions, including lethargy and disengagement, headache (migraine), and anorexia, with an awareness that vomiting was imminent only when the condition was severe. However, some recent articles have limited the definition to the sensations that immediately precede emesis. Defining nausea is complicated by the fact that it has many triggers, and can build-up slowly or rapidly, such that the prodromal signs and symptoms can vary. In particular, disengagement responses referred to as the "sopite syndrome" are typically present only when emetic stimuli are moderately provocative, and do not quickly culminate in vomiting or withdrawing from the triggering event. This review considers how the definition of "nausea" has evolved over time, and summarizes the physiological changes that occur prior to vomiting that may be indicative of nausea. Also described are differences in the perception of nausea, as well as the accompanying physiological responses, that occur with varying stimuli. This information is synthesized to provide an operational definition of nausea.

Future sexual medicine physiological treatment targets

INTRODUCTION

Sexual function in men and women incorporates physiologic processes and regulation of the central and peripheral nervous systems, the vascular system, and the endocrine system. There is need for state-of-the-art information as there is an evolving research understanding of the underlying molecular biological factors and mechanisms governing sexual physiologic functions.

AIM

To develop an evidence-based, state-of-the-art consensus report on the current knowledge of the major cellular and molecular targets of biologic systems responsible for sexual physiologic function.

METHODS

State-of-the-art knowledge representing the opinions of seven experts from four countries was developed in a consensus process over a 2-year period.

MAIN OUTCOME MEASURES

Expert opinion was based on the grading of evidence-based medical literature, widespread internal committee discussion, public presentation, and debate.

RESULTS

Scientific investigation in this field is needed to increase knowledge and foster development of the future line of treatments for all forms of biological-based sexual dysfunction. This article addresses the current knowledge of the major cellular and molecular targets of biological systems responsible for sexual physiologic function. Future treatment targets include growth factor therapy, gene therapy, stem and cell-based therapies, and regenerative medicine.

CONCLUSIONS

Scientific discovery is critically important for developing new and increasingly effective treatments in sexual medicine. Broad physiologic directions should be vigorously explored and considered for future management of sexual disorders.

Use of antipsychotic medication in chemotherapy-induced nausea and vomiting

Nausea and vomiting continue to present significant problems for cancer patients undergoing chemotherapy. Initial work suggested an important role for central dopamine transmission in the underlying pathophysiology. However, recent evidence has implicated central and peripheral serotonin release. Although the implementation of 5-HT(3) receptor antagonists has resulted in significant improvement in acute symptoms of nausea and vomiting, they have not demonstrated optimal efficacy in anticipatory and delayed emetic syndromes and are significantly more expensive than other antiemetic therapies. The use of typical antipsychotic medication to reduce nausea and vomiting in cancer patients is discussed, as is the potential efficacy of newer atypical antipsychotics, which have activity at receptors implicated in the control of chemotherapy-induced nausea and vomiting and demonstrate an improved side-effect profile.

Opportunities for the replacement of animals in the study of nausea and vomiting

Nausea and vomiting are among the most common symptoms encountered in medicine as either symptoms of disease or side effects of treatments. Developing novel anti-emetics and identifying emetic liability in novel chemical entities rely on models that can recreate the complexity of these multi-system reflexes. Animal models (especially the ferret and dog) are the current gold standard; however, the selection of appropriate models is still a matter of debate, especially when studying the subjective human sensation of nausea. Furthermore, these studies are associated with animal suffering. Here, following a recent workshop held to review the utility of animal models in nausea and vomiting research, we discuss the limitations of some of the current models in the context of basic research, anti-emetic development and emetic liability detection. We provide suggestions for how these limitations may be overcome using non-animal alternatives, including greater use of human volunteers, in silico and in vitro techniques and lower organisms.

Betamethasone does not prevent nausea and vomiting induced by the dopamine-agonist apomorphine

PURPOSE

The mechanism of the antiemetic actions of corticosteroids is not known. The purpose of this study was to evaluate if betamethasone can prevent nausea, vomiting or increase of vasopressin induced by apomorphine. Metoclopramide, a dopamine antagonist, was used as a control substance.

METHODS

Ten healthy volunteers were studied on three occasions. In a randomized order they were allocated to receive pretreatment with betamethasone 8 mg iv, metoclopramide 10 mg iv, and normal saline 2 mL as placebo on the three different occasions, 15 min before the administration of apomorphine 30 microg x kg(-1) s.c.. After administration of apomorphine, episodes of vomiting were recorded, and the intensity of nausea was estimated by the subject on a visual analogue scale (VAS 0-10 cm). Blood samples for analysis of plasma concentrations of vasopressin were analyzed.

RESULTS

One volunteer decided to withdraw, as he experienced akathisia after receiving metoclopramide. During the first two hours after apomorphine, eight of nine volunteers vomited both after betamethasone and placebo. One volunteer did not vomit after betamethasone and placebo but he experienced nausea. None of the volunteers vomited after metoclopramide (P < 0.01 vs betamethasone and placebo). The maximum VAS for nausea was significantly higher after betamethasone and placebo compared to metoclopramide (P < 0.01). The vasopressin levels increased after betamethasone and placebo, but there was no increase in any volunteer after pretreatment with metoclopramide.

CONCLUSION

This study demonstrates that betamethasone does not prevent nausea, vomiting and increase of vasopressin induced by apomorphine, whereas metoclopramide prevents apomorphine-induced emesis. Our work suggests that betamethasone does not have dopamine-antagonistic effects.

Role of 5-hydroxytryptamine3 (5-HT3) antagonists in the prevention of emesis caused by anticancer therapy

Most anticancer drugs are cytotoxic and produce various side-effects, among which nausea and vomiting are almost ubiquitous and usually extremely distressing to the patient. Cancer chemotherapy elicits two main phases of vomiting: an intense, acute phase of vomiting that occurs almost immediately following anti-cancer therapy and a milder, delayed phase of nausea and vomiting of longer duration. The mechanisms underlying the induction of nausea and vomiting after cancer chemotherapy are poorly understood but may be mediated by serotonin (5-hydroxytryptamine or 5-HT), particularly in the acute phase. Serotonin activates 5-HT3 receptors, which function as ligand-gated ion channels located either in the periphery and/or in the central nervous system to produce emesis, among other effects. The peripheral 5-HT3 receptors may be pharmacologically distinct from the central 5-HT3 receptors and may exhibit some association with GTP-binding proteins. In addition, different populations may exist as distinct subtypes of the same receptor. The 5-HT3 receptor antagonist ondansetron (GR 38032F) is effective in preventing the emesis induced by cytotoxic agents currently used in the treatment of many forms of cancer. Ondansetron has, comparatively, a much higher efficacy in the treatment of acute emesis following cancer chemotherapy than it does in the delayed phase, suggesting that the late phase of emesis may be mediated by other distinct mechanisms.

Involvement of dopamine D3 receptors in the area postrema in R(+)-7-OH-DPAT-induced emesis in the ferret

We investigated the possible involvement of dopamine D3 receptors in R(+)-7-hydroxy-2-(N,N-di-n-propylamino)tetraline (R(+)-7-OH-DPAT)-induced emesis in the ferret. The R(+)enantiomer of 7-OH-DPAT (0.03-1 mg/kg, s.c.) caused emesis in a dose-dependent manner, whereas the S(-)enantiomer, even at 1 mg/kg s.c. failed to induce emesis. Quinpirole (0.1-1.0 mg/kg) and apomorphine (0.3 mg/kg, s.c. only) also elicited an emetic response. S(-)-Eticlopride, which has a high affinity for the dopamine D3 receptor, antagonized R(+)-7-OH-DPAT (0.3 mg/kg, s.c.)-induced emesis (ID50 1.4 micrograms/kg, s.c.). R(+)-7-OH-DPAT (0.1-1.0 microgram) administered into the 4th cerebral ventricle dose dependently induced emesis within 1 min of dosing in ferrets. Intracerebroventricularly administered S(-)-eticlopride (0.01-1 microgram) also inhibited the emesis induced by s.c. administration of R(+)-7-OH-DPAT. The emetic effect of R(+)-7-OH-DPAT was unaffected by abdominal vagotomy but was markedly reduced by ablation of the area postrema. These results suggest that dopamine D3 receptors in the area postrema play an important role in R(+)-7-OH-DPAT-induced emesis in the ferret.

The role of alpha-adrenergic mechanisms within the area postrema in dopamine-induced emesis

Intracerebroventricular injection of dopamine (0.5-4.0 mg) produced dose-dependent and short-lasting emesis (1-8 min) in cats, which was abolished after ablation of the area postrema. Relatively selective alpha 2-adrenoceptor antagonists (yohimbine and idazoxan) and a mixed alpha 1- and alpha 2-adrenoceptor antagonist (tolazoline), but not a non-selective alpha 1-adrenoceptor antagonist (prazosin), injected intracerebroventricularly inhibited the emesis induced by intracerebroventricular dopamine. However, dopamine receptor antagonists (chlorpromazine, droperidol, spiperone, domperidone, triflupromazine, sulpiride and metoclopramide), an antimuscarinic drug (atropine), a ganglionic blocking agent (mecamylamine), an opioid receptor antagonist (naloxone) and a 5-HT receptor antagonist (methysergide), all injected intracerebroventricularly, had no significant effect on emesis evoked by intracerebroventricular dopamine. The emetic response to intracerebroventricular dopamine was attenuated in cats pretreated with intracerebroventricular reserpine, 6-hydroxydopamine, alpha-methyl-p-tyrosine and hemicholinium-3. It is postulated that dopamine-induced emesis is mediated through the release of noradrenaline acting at alpha 2-adrenoceptors and that it depends on the integrity of monoaminergic and possibly cholinergic structures within the area postrema. It appears, therefore, that the emetic effect of intracerebroventricular dopamine is mediated by adrenergic rather than dopaminergic mechanisms in the area postrema, at least in the cat.

Behavioral studies of emetic sensitivity in the ferret

The ferrets' responsiveness to several known and putative emetic agents was evaluated using a variety of agents that were injected subcutaneously and/or intravenously. Apomorphine was consistently emetic at relatively high doses (100 micrograms/kg) when injected subcutaneously in large male ferrets (> or = 1.4 kg). The responsiveness to apomorphine was anomalous in that subcutaneous injections produced a more consistent response than intravenous ones. In addition, ferrets rapidly become tolerant or tachyphylactic to subcutaneously administered apomorphine. Area postrema ablation, but not abdominal vagotomy, rendered ferrets refractory to the emetic effects of apomorphine. This species, relative to dog and humans, proved to be insensitive to a variety of pharmacologic agents including angiotensin II, gastrin, histamine, Leu-enkephalin, neurotensin, serotonin, and vasopressin. Cisplatin elicited forceful retching and emesis. Emetic responses were obtained with substance P and Met-enkephalin in individual animals but were inconsistent. Sensitivity to DAGO [D-Ala2,MePhe4,Gly-ol5 enkephalin] was variable. Results of this study indicate that the ferret is not an optimal model for all forms of emesis.

Responses of plasma oxytocin and arginine vasopressin to nausea induced by apomorphine and ipecacuanha

Apomorphine, a centrally-acting emetic, was administered subcutaneously (50 micrograms/kg) to nine normal subjects (four male, five female; aged 22-36 years) and four patients with idiopathic diabetes insipidus (DI) (one male, three female; aged 24-49 years). In the normal subjects this stimulus caused nausea (and vomiting in seven of nine) with a latency of 9.5 +/- 0.9 min which was followed by a large increase in plasma arginine vasopressin (AVP) concentration (from 0.9 +/- 0.2 pmol/l to 249 +/- 104 pmol/l at 15 min after the onset of symptoms; mean +/- SEM, P less than 0.01). There was a small but significant increase in plasma oxytocin (OXT) concentration (from 1.6 +/- 0.4 pmol/l to 6.2 +/- 3.4 pmol/l; P less than 0.05). Mean arterial pressure (MAP) fell slightly (from 87 +/- 1.9 mm Hg to 71 +/- 4.4 mm Hg; P less than 0.05) 15 min after the onset of nausea; there was no change in blood haematocrit or plasma osmolality and sodium concentration. In the DI patients apomorphine produced nausea (with vomiting in three of four) with a latency of 10.0 +/- 1.4 min but failed to cause an increase in either plasma AVP or OXT. In the DI patients the fall in MAP did not reach statistical significance (83 +/- 4 mm Hg to 71 +/- 11 mm Hg); there was also no change in haematocrit, osmolality or sodium concentration. Ipecacuanha, an emetic with both peripheral and central actions, was administered orally to seven normal subjects (three male, four female; aged 22-36 years) six of whom also underwent apomorphine tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Metoclopramide--a review

Metoclopramide has wide applications in both clinical and experimental medicine. It is useful in the management of gastro-oesophageal reflux and gastric stasis. It is being used increasingly in the management of nausea and vomiting, and at high doses will significantly relieve the emesis that is induced by cytotoxic agents. Metoclopramide also has an important place in the investigation of the role of dopamine in physiological and pathological processes.

Definition of a gastric emptying abnormality in patients with anorexia nervosa

Upper gastrointestinal symptoms may be prominent in anorexia nervosa. This study is an investigation of the gastric emptying of solid and liquid meal components in 16 female patients (mean age 20.0 years, range 14-40 years) who met accepted psychiatric diagnostic criteria for anorexia nervosa. The results were compared with those of gastric emptying studies in 10 normal females of ideal body weight (mean age 25.4 years, range 20-35), 13 normal persons (12 males), and six patients (mean age 12 years, range 9-14 years) with weight loss (less than 90 percent ideal body weight) secondary to Crohn's disease with no psychiatric symptoms. A dual-isotope technique using chicken liver intracellularly labeled with technetium-99m (99mTc) bound to sulfur colloid as the solid-phase marker, and indium-111 (111In) -labeled water as the liquid-phase marker was used. Gastric emptying was monitored for 2 hr by gamma camera. In 13 of the 16 anorexia nervosa patients (80%), gastric emptying of solids was slower than the range in the two groups of normal subjects, and mean gastric emptying was significantly slower (P less than 0.05) than in the weight-loss patients. Liquid emptying (water) in anorexia nervosa was normal and similar to the control groups studied. In 11 of the anorexia nervosa patients with delayed gastric emptying, intramuscular metoclopramide, 10 mg, significantly (P less than 0.05) accelerated the mean gastric emptying from 60 through 120 min after the meal. We conclude that in anorexia nervosa patients who are symptomatic and seeking medical care: gastric emptying of solids is significantly delayed when compared with female subjects of similar age and normal body weight and with patients of less than 90% ideal body weight but without psychiatric disorder; these data are consistent with an antral motility disturbance, either primary or secondary; and metoclopramide, a gastric prokinetic agent, accelerates (delayed) gastric emptying.

Failure of naloxone to reverse apomorphine effects in humans

Twelve male volunteers given apomorphine (20 micrograms/kg/hr) for 40 min by i.v. infusion had significant changes in growth hormone, prolactin, vasopressin, pulse rate, sedation and nausea. Naloxone, (20 mg i.v.) or placebo given in a double-blind manner 10 min before the end of the apomorphine infusion as a concealed bolus did not alter the effects of apomorphine. Vasopressin rise correlated significantly with nausea intensity. We conclude that acute opiate receptor blockade does not reverse most apomorphine effects.