Dimethylphenylpiperazinium-induced vomiting: nicotinic mediation in area postrema

Looking beyond 5-HT(3) receptors: a review of the wider role of serotonin in the pharmacology of nausea and vomiting

The concept that 5-hydroxytryptamine (5-HT; serotonin) is involved in the emetic reflex was revealed using drugs that interfere with its synthesis, storage, release and metabolism ahead of the discovery of selective tools to modulate specific subtypes of receptors. This review comprehensively examines the fundamental role of serotonin in emesis control and highlights data indicating association of 5-HT1-4 receptors in the emetic reflex, whilst leaving open the possibility that 5-HT5-7 receptors may also be involved. The fact that each receptor subtype may mediate both emetic and anti-emetic effects is discussed in detail for the first time. These discussions are made in light of known species differences in emesis control, which has sometimes affected the perception of the translational value of data in regard to the development of novel anti-emetic for use in man.

Pathology of emesis: its autonomic basis

Vagal and non-vagal pathways as well as several brainstem nuclei participate in vomiting in response to different emetic stimuli. Autonomic pathways involved in nausea are less well understood. Numerous gastrointestinal disorders with prominent nausea and vomiting including gastroparesis, cyclic vomiting syndrome, and motion sickness have associated autonomic nervous system dysfunction. Autonomic disturbances are also seen with non-gastrointestinal diseases with gut manifestations such as migraine headaches, orthostatic intolerance, and familial dysautonomia. Stimulation of emetic pathways involves activation of a range of receptor subtypes. Agents acting on these receptors form the basis for antiemetic therapies. Chemotherapy-induced nausea and vomiting, a prevalent and severe consequence of anticancer treatment, is preventable in many instances by agents acting on the autonomic nervous system. Likewise, non-medication therapies may act in part via modulation of some of these same autonomic pathways.

Nicotinic ACh receptors in area postrema neurons of immature rat brain

The electrophysiological properties of nicotinic ACh receptors (nAChR) were investigated in acutely dissociated area postrema (AP) neurons of the immature rat brain using the whole-cell patch-clamp recording method. ACh induced a transient inward current exhibiting a strong inward rectification. The ACh response was mimicked by nicotine and cytisine, and was inhibited by nAChR antagonists, but not by 10(-7) M atropine. Muscarinic AChR agonists did not induce any current. We confirmed the Ca2+ permeability of nAChR. These results indicate the presence of nAChR on AP neurons, and suggest that the activation of nAChR play important roles in cardiovascular functions in rats.

Neuronal activation in the medulla oblongata during selective elicitation of the laryngeal adductor response

Swallow and cough are complex motor patterns elicited by rapid and intense electrical stimulation of the internal branch of the superior laryngeal nerve (ISLN). The laryngeal adductor response (LAR) includes only a laryngeal response, is elicited by single stimuli to the ISLN, and is thought to represent the brain stem pathway involved in laryngospasm. To identify which regions in the medulla are activated during elicitation of the LAR alone, single electrical stimuli were presented once every 2 s to the ISLN. Two groups of five cats each were studied; an experimental group with unilateral ISLN stimulation at 0.5 Hz and a surgical control group. Three additional cats were studied to evaluate whether other oral, pharyngeal, or respiratory muscles were activated during ISLN stimulation eliciting LAR. We quantified < or = 22 sections for each of 14 structures in the medulla to determine if regions had increased Fos-like immunoreactive neurons in the experimental group. Significant increases (P < 0.0033) occurred with unilateral ISLN stimulation in the interstitial subnucleus, the ventrolateral subnucleus, the commissural subnucleus of the nucleus tractus solitarius, the lateral tegmental field of the reticular formation, the area postrema, and the nucleus ambiguus. Neither the dorsal motor nucleus of the vagus, usually active for swallow, nor the nucleus retroambiguus, retrofacial nucleus, and the lateral reticular nucleus, usually active for cough, were active with elicitation of the laryngeal adductor response alone. The results demonstrate that the laryngeal adductor pathway is contained within the broader pathways for cough and swallow in the medulla.

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.

Central α-adrenoceptor subtypes involved in the emetic pathway in cats

The intracerebroventricular (i.c.v.) injection of clonidine, xylazine, adrenaline and methoxamine elicited dose-dependent vomiting in cats in that order of potency. The vomiting induced by clonidine, xylazine and adrenaline was antagonized by i.c.v. yohimbine and phentolamine possessing alpha 2-adrenoceptor-blocking activity, but not by prazosin showing alpha 1-adrenoceptor-blocking activity. In contrast, methoxamine-induced vomiting was antagonized by prazosin, but not by yohimbine. The vomiting induced by xylazine and adrenaline was not prevented by i.c.v. 6-hydroxydopamine treatment, but was prevented by i.c.v. reserpine treatment. Ablation of the area postrema with some damage to extremely adjacent areas abolished the vomiting induced by each alpha-adrenoceptor agonist. These results indicate that both central alpha 1- and alpha 2-adrenoceptors are involved in the emetic pathway in cats, although alpha 2-adrenoceptors seem to have the main role. It is also suggested that monoamines, and in particular 5-hydroxytryptamine in the brain, are involved in the regulation of alpha-adrenoceptor-mediated vomiting.

Differential inhibition by ethanol of norepinephrine- and clonidine-induced emesis in cats

The effect of acute ethanol administration into the cerebral ventricles on the unanesthetized cat upon emesis produced by norepinephrine and clonidine injected similarly as well as upon emesis evoked by copper sulfate given orally was compared and investigated. Ethanol inhibited the norepinephrine- and clonidine-induced emesis. The inhibitory effect of ethanol occurred after a transient and inconsistent emetic action of the drug. Norepinephrine-induced emesis was about 12 times more sensitive than clonidine-induced emesis to the inhibitory effect of ethanol. In addition, norepinephrine-, but not clonidine-induced emesis was abolished after ablation of the area postrema. On the contrary, intracerebroventricular ethanol had virtually no effect on emesis caused by intragastric copper sulfate. The inhibitory effect of ethanol is ascribed to an action on alpha-2 adrenoceptors within the area postrema and on imidazoline-preferring sites and/or muscarinic cholinoceptors outside the area postrema, but not on the emetic region of the brainstem reticular formation. It follows then that ethanol can differentiate alpha-2 adrenoceptors from imidazoline-preferring sites and/or muscarinic cholinoceptors in the brain of the cat.

Selective effect of ethanol on norepinephrine- and nicotine-induced emesis in cats

The effect of acute ethanol administration into the cerebral ventricles of the unanesthetized cat upon emesis produced by norepinephrine and nicotine injected similarly was investigated. Ethanol inhibited the norepinephrine- and nicotine-induced emesis. The inhibitory effect of ethanol occurred after a transient and inconsistent emetic action of the drug. Ethanol was about 10 times more potent inhibiting the emesis caused by nicotine. On the other hand, intracerebroventricular ethanol had virtually no effect on emesis produced by intragastric copper sulfate. The inhibitory effect of ethanol is ascribed to an action on alpha-noradrenergic and nicotinic receptors in the area postrema. Differential responses to ethanol most probably reflect the microenvironment of alpha-noradrenergic and nicotinic synapses in the area postrema of the cat.

Direct vagal input to neurons in the area postrema which project to the parabrachial nucleus: an electron microscopic-HRP study in the cat

This study in cat examines the synaptic relationship of vagal afferents to parabrachial projecting neurons in the area postrema (AP) using anterograde and retrograde transport of horseradish peroxidase (HRP). Wheat germ agglutinin-HRP injected into the parabrachial nucleus (PBN) produced retrograde neuronal labeling in the AP and in the nucleus of the tractus solitarius bilaterally, but with an ipsilateral predominance. Labeled neurons were confined mainly to the caudal 2/3's of the AP. Following injection of WGA-HRP into the PBN and HRP into the nodose ganglion in the same animal, examination of sections of the AP with the electron microscope revealed anterogradely labeled axon terminals in apposition to retrogradely labeled somata and dendrites. In some instances, labeled terminals were observed to form synaptic contacts with retrogradely labeled neurons. We conclude that in the cat a vagal input to neurons in the AP is monosynaptically relayed to the PBN.

Ablation of the area postrema and emesis

The emetic action of dopamine, norepinephrine, epinephrine, nicotine, dimethylphenyl-piperazinium (DMPP), and 4-m-chlorophenylcarbamoyloxy-2-butynyltrimethylammonium (McN-A-343) injected intracerebroventricularly (i.c.v.) to the unanesthetized cat was investigated and compared. ED50 values (mg) were as follows: nicotine, 0.011; epinephrine, 0.047; norepinephrine, 0.57; DMPP, 0.9; dopamine, 1.66; and McN-A-343, 4.42. The most potent was nicotine, whereas the least active McN-A-343. On the other hand, DMPP produced the longest emetic response, about 30 min, while McN-A-343-induced emesis lasted up to 1 min. The ablation of the area postrema abolished the emetic response to i.c.v. dopamine, norepinephrine, epinephrine, nicotine, and DMPP. However, the emetic response to i.c.v. McN-A-343 was significantly reduced in cats with an ablated area postrema. Taken together, the results obtained show that the area postrema is almost always involved in the central regulation of emesis and that the area postrema represents, in most cats, a common site of confluence of different inputs subserving the emesis.

Area postrema: cholinergic and noradrenergic regulation of emesis. A new concept

In unanaesthetized cats the biochemical mechanisms and the functional characteristics of the emetic action of injection of noradrenaline and McN-A-343, a ganglionic muscarinic stimulant into the cerebral ventricle (i.c.v.) through chronically implanted cannulae were investigated. Both produced dose-dependent and shortlasting emetic response. The emesis evoked by noradrenaline was abolished, whereas the emesis induced by McN-A-343 was not completely blocked after ablation of the area postrema. Further, the emetic response to noradrenaline as well as to McN-A-343 was attenuated or blocked in cats pretreated with 6-hydroxydopamine (i.c.v.) and hemicholinium (i.c.v.); it was abolished in cats pretreated with reserpine (i.c.v.). On the other hand, the emetic response to i.c.v. noradrenaline and to i.c.v. McN-A-343 was not virtually altered in cats pretreated with bretylium (i.c.v.), alpha-methyl-p-tyrosine (i.c.v.) and 5,6-dihydroxytryptamine (i.c.v.). It is postulated that noradrenergic neurones as well as cholinergic axon terminals within the area postrema are necessary for the emetic action of noradrenaline, whereas cholinergic axon terminals within the area postrema subserve the emetic response to McN-A-343. A functional link between cholinergic terminals and noradrenergic neurones as well as a modulatory role of noradrenergic afferents on cholinergic afferents mediating emesis within the area postrema is further proposed. Thus, noradrenergic neurones might represent a common site of confluence of different inputs subserving the emesis in the area postrema. Finally, cholinergic terminals sometimes bypass this area and synapse in the emetic regions of the brainstem regulating emesis.

Emesis induced by 4-(m-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium chloride (McN-A-343): evidence for a predominant central muscarinic M1 mediation

The emetic action of 4-(m-chlorophenylcarbamoyloxy)-2- butynyltrimethylammonium chloride (McN-A-343) was investigated in the unanaesthetized cat, after it was injected into the cerebral ventricles, through chronically-implanted cannulae. Intracerebroventricular injection of McN-A-343 produced dose-dependent and shortlasting emesis, which was not completely abolished after ablation of the area postrema. The predominantly selective muscarinic M1 antagonist, pirenzepine as well as the mixed muscarinic M1 and M2 antagonist, atropine, injected into the cerebral ventricles, attenuated or abolished the emesis evoked by intracerebroventricular McN-A-343. Both atropine and pirenzepine produced dose-dependent inhibition of the emesis evoked by McN-A-343. However, the ID50 value for atropine was approximately five times greater than that for pirenzepine. Abolition of McN-A-343-induced emesis only occurred with the largest dose of atropine (1 mg). On the other hand, selected ganglionic blocking agents, an alpha- and beta-adrenoceptor blocking agent, a dopamine antagonist, a 5-hydroxytryptamine antagonist and an antihistamine, all injected into the cerebral ventricles, had no significant effect on emesis evoked by McN-A-343, similarly injected. The emetic response to intracerebroventricular injection of McN-A-343 was attenuated or abolished in cats pretreated with hemicholinium-3, triethylcholine, reserpine and 6-hydroxydopamine, intracerebroventricularly. On the contrary, the emetic response to intracerebroventricular injection of McN-A-343 was not altered in cats pretreated with intracerebroventricular injections of bretylium, alpha-methyl-p-tyrosine and 5,6-dihydroxytryptamine. It is postulated that the emesis produced by McN-A-343, injected into the cerebral ventricles, is mediated through muscarinic M1 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Noradrenaline-induced emesis. Alpha-2 adrenoceptor mediation in the area postrema

The emetic action of noradrenaline was investigated in unanesthetized cats, after it was injected into the cerebral ventricles through chronically implanted cannulae. Intracerebroventricular injection of noradrenaline produced dose-dependent and shortlasting emesis, which was abolished after ablation of the area postrema. However, copper sulphate, given orally, evoked emesis in cats with an ablated area postrema. The selective alpha-2 adrenoceptor antagonist, yohimbine, as well as the mixed alpha-1 and alpha-2 adrenoceptor blocking drugs, phentolamine, tolazoline, phenoxybenzamine and dihydroergotamine, but not the selective alpha-1 adrenoceptor antagonist, prazosin, all injected into the cerebral ventricles, attenuated or blocked the emesis evoked by intracerebroventricular injection of noradrenaline. Of the alpha-adrenoceptor antagonist, only yohimbine produced dose-dependent inhibition of the emesis induced by noradrenaline. On the contrary, selected beta-adrenoceptor blocking agents, an antimuscarinic drug, a ganglionic blocking agent, an antihistamine, dopamine antagonists and a 5-hydroxytryptamine antagonist, all injected into the cerebral ventricles, had no significant effect on the emesis induced by noradrenaline, similarly injected. The emetic response to intracerebroventricular injection of noradrenaline, as well as to intragastric administration of copper sulphate was not altered in cats pretreated with intracerebroventricular injections of alpha-methyl-p-tyrosine and bretylium. On the other hand, the emetic response to intracerebroventricular injection of noradrenaline and to intragastric administration of copper sulphate was attentuated or blocked in cats pretreated with reserpine intracerebroventricularly. Moreover, in cats pretreated with intracerebroventricular injection of 6-hydroxydopamine and hemicholinium, the emesis induced by intracerebroventricular administration of noradrenaline but not that produced by intragastric injection of copper sulphate, was depressed.(ABSTRACT TRUNCATED AT 250 WORDS)

Rostral hypothalamus: a new neuroanatomical site of neurochemically-induced emesis in the cat

The localized effect of noradrenergic agonists administered directly in the anterior hypothalamic preoptic area (AH/POA) in inducing emesis in the cat was investigated. Of the noradrenergic agonists tested, which included norepinephrine, clonidine, phenylephrine and methoxamine, only clonidine in doses of 5.0-50.0 micrograms was found to evoke emesis consistently when micro-injected in a volume of 1.0 microliter into AH/POA of the unrestrained cat. The emetic response to clonidine was short-lasting, generally dose-dependent in terms of latency and frequency, and occurred in bouts of one to three episodes. The sequence of the vomiting response, beginning with licking and retching, functionally resembled a normal pattern of an emetic response. The clonidine-induced emesis was not antagonized by the following antagonists micro-injected in AH/POA just prior to clonidine: alpha-adrenergic blocking agents, yohimbine, RX 781094 and phentolamine; the antimuscarinic drug, atropine; the serotonin antagonist, methysergide; the opioid antagonist, naloxone; and the dopamine antagonist, chlorpromazine. Therefore, it would appear that clonidine-induced emesis is not mediated by alpha noradrenergic, serotonergic, dopaminergic, muscarinic and opiate receptor systems within the AH/POA of the cat. Finally, the obtained results show that apart from the area postrema and a circumscribed zone of the brain-stem reticular formation, the hypothalamus is now implicated as a neuroanatomical site in the central nervous system mechanism underlying neurochemically-induced emesis.

Suncus murinus: a new experimental model in emesis research

Effects of various emetic and antiemetic drugs were studied using Suncus murinus for its potential use as an experimental model in emetic research. Subcutaneous injection of nicotine bitartrate (10-15 mg/kg), veratrine sulfate (0.5-1.0 mg/kg), emetine dihydrochloride (40-80 mg/kg) and oral administration of copper sulfate (20-100 mg/kg) caused dose-dependent emesis in suncus. The ED50 of nicotine, veratrine, emetine and copper sulfate were 7.9, 0.4, 47.6 and 21.4 mg/kg, respectively. However, subcutaneously injected apomorphine hydrochloride (0.1-100 mg/kg), digitoxin (0.5-1.0 mg/kg) and orally administered emetine dihydrochloride (10-80 mg/kg) did not induce the vomiting. Chlorpromazine and promethazine decreased the emetic effect of nicotine, veratrine and copper sulfate, but scopolamine hydrobromide was not effective. These results indicate that the Suncus murinus is sensitive to various emetic and antiemetic drugs and can be used as a new experimental animal model for the emesis. Emetic behavior of suncus was discussed in comparison with other animals.

Central neurotoxic effects of guanethidine: altered serotonin and enkephalin neurons within the area postrema

This study reveals that the 5-HT and enkephalin cell body population of the area postrema (AP) is dramatically reduced via exposure to the peripherally circulating neurotoxin guanethidine. Efforts to restore cell body numbers to control levels, with colchicine and monoamine oxidase inhibitors, subsequent to guanethidine treatment are ineffective. However, 5-HT and enkephalin immunostaining of surrounding bulbar nuclei appears normal, implying that the neurotoxic effect of guanethidine is restricted to the AP. In addition, gamma-aminobutyric acid and neurotensin immunostaining within the AP appears normal, subsequent to guanethidine treatment, suggesting that the neurotoxic effect is restricted to specific AP cell populations.

Further studies on nicotine-induced emesis: nicotinic mediation in area postrema

In unanesthetized cats the emetic action of an injection of nicotine into the cerebral ventricle through chronically implanted cannulae was investigated. Nicotine injected in doses of 0.02-1.0 mg produced dose-dependent vomiting, which was abolished after ablation of the area postrema. However, copper sulfate given intragastrically evoked vomiting in cats with an ablated area postrema. The emetic response to intracerebroventricular (ICV) nicotine as well as the vomiting produced by intragastric copper sulfate was depressed or abolished in cats pretreated with ICV reserpine. On the other hand, the emetic response to ICV nicotine and to intragastric copper sulfate was virtually unchanged in cats pretreated with ICV 6-hydroxydopamine and 5,6-dihydroxytryptamine. The duration of vomiting produced by intragastric copper sulfate, but not that of ICV nicotine, was potentiated in cats pretreated with hemicholinium-3. Ganglionic blocking agents, mecamylamine and hexamethonium, injected ICV prevented the vomiting elicited by ICV nicotine. On the other hand, selected anti-muscarinic drugs, alpha and beta adrenergic receptor antagonists, dopamine antagonists, antihistamines and a 5-hydroxytryptamine antagonist all injected into the cerebral ventricle had virtually no effect on the vomiting induced by ICV nicotine. It is postulated that nicotine evokes vomiting by its action on nicotinic receptors within the area postrema but not on catecholaminergic or serotonergic neurones. Finally, acetylcholine could also be involved in the inhibition of the complex mechanisms underlying the central regulation of vomiting.