Emetic effects of centrally administered angiotensin II, arginine vasopressin and neurotensin in the dog

Mechanisms of Nausea and Vomiting: Current Knowledge and Recent Advances in Intracellular Emetic Signaling Systems

Nausea and vomiting are common gastrointestinal complaints that can be triggered by diverse emetic stimuli through central and/or peripheral nervous systems. Both nausea and vomiting are considered as defense mechanisms when threatening toxins/drugs/bacteria/viruses/fungi enter the body either via the enteral (e.g., the gastrointestinal tract) or parenteral routes, including the blood, skin, and respiratory systems. While vomiting is the act of forceful removal of gastrointestinal contents, nausea is believed to be a subjective sensation that is more difficult to study in nonhuman species. In this review, the authors discuss the anatomical structures, neurotransmitters/mediators, and corresponding receptors, as well as intracellular emetic signaling pathways involved in the processes of nausea and vomiting in diverse animal models as well as humans. While blockade of emetic receptors in the prevention of vomiting is fairly well understood, the potential of new classes of antiemetics altering postreceptor signal transduction mechanisms is currently evolving, which is also reviewed. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide potential answers.

COVID-19, nausea, and vomiting

Exclusion of nausea (N) and vomiting (V) from detailed consideration as symptoms of COVID-19 is surprising as N can be an early presenting symptom. We examined the incidence of NV during infection before defining potential mechanisms. We estimate that the overall incidence of nausea (median 10.5%), although variable, is comparable with diarrhea. Poor definition of N, confusion with appetite loss, and reporting of N and/or V as a single entity may contribute to reporting variability and likely underestimation. We propose that emetic mechanisms are activated by mediators released from the intestinal epithelium by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) modulate vagal afferents projecting to the brainstem and after entry into the blood, activate the area postrema (AP) also implicated in anorexia. The receptor for spike protein of SARS-CoV-2, angiotensin 2 converting enzyme (ACE2), and transmembrane protease serine (for viral entry) is expressed in upper gastrointestinal (GI) enterocytes, ACE2 is expressed on enteroendocrine cells (EECs), and SARS-CoV-2 infects enterocytes but not EECs (studies needed with native EECs). The resultant virus-induced release of epithelial mediators due to exocytosis, inflammation, and apoptosis provides the peripheral and central emetic drives. Additionally, data from SARS-CoV-2 show an increase in plasma angiotensin II (consequent on SARS-CoV-2/ACE2 interaction), a centrally (AP) acting emetic, providing a further potential mechanism in COVID-19. Viral invasion of the dorsal brainstem is also a possibility but more likely in delayed onset symptoms. Overall, greater attention must be given to nausea as an early symptom of COVID-19 and for the insights provided into the GI effects of SARS-CoV-2.

Utilization of the least shrew as a rapid and selective screening model for the antiemetic potential and brain penetration of substance P and NK1 receptor antagonists

Substance P (SP) is thought to play a cardinal role in emesis via the activation of central tachykinin NK1 receptors during the delayed phase of vomiting produced by chemotherapeutics. Although the existing supportive evidence is significant, due to lack of an appropriate animal model, the evidence is indirect. As yet, no study has confirmed that emesis produced by SP or a selective NK1 receptor agonist is sensitive to brain penetrating antagonists of either NK1, NK2, or NK3 receptors. The goals of this investigation were to demonstrate: 1) whether intraperitoneal (i.p.) administration of either SP, a brain penetrating (GR73632) or non-penetrating (e.g. SarMet-SP) NK1 receptor agonist, an NK2 receptor agonist (GR64349), or an NK3 receptor agonist (Pro7-NKB), would induce vomiting and/or scratching in the least shrew (Cryptotis parva) in a dose-dependent manner; and whether these effects are sensitive to the above selective receptor antagonists; 2) whether an exogenous emetic dose of SP (50 mg/kg, i.p.) can penetrate into the shrew brain stem and frontal cortex; 3) whether GR73632 (2.5 mg/kg, i.p.)-induced activation of NK1 receptors increases Fos-measured neuronal activity in the neurons of both brain stem emetic nuclei and the enteric nervous system of the gut; and 4) whether selective ablation of peripheral NK1 receptors can affect emesis produced by GR73632. The results clearly demonstrated that while SP produced vomiting only, GR73632 caused both emesis and scratching behavior dose-dependently in shrews, and these effects were sensitive to NK1-, but not NK2- or NK3-receptor antagonists. Neither the selective, non-penetrating NK1 receptor agonists, nor the selective NK2- or NK3-receptor agonists, caused a significant dose-dependent behavioral effect. An emetic dose of SP selectively and rapidly penetrated the brain stem but not the frontal cortex. Systemic GR73632 increased Fos expression in the enteric nerve plexi, the medial subnucleus of nucleus tractus solitarius, and the dorsal motor nucleus of the vagus, but not the area postrema. Ablation of peripheral NK1 receptors attenuated the ability of GR73632 to induce a maximal frequency of emesis and shifted its percent animals vomiting dose-response curve to the right. The NK1-ablated shrews exhibited scratching behavior after systemic GR73632-injection. These results, for the first time, affirm a cardinal role for central NK1 receptors in SP-induced vomiting, and a facilitatory role for gastrointestinal NK1 receptors. In addition, these data support the validation of the least shrew as a specific and rapid behavioral animal model to screen concomitantly both the CNS penetration and the antiemetic potential of tachykinin NK1 receptor antagonists.

Signals for nausea and emesis: Implications for models of upper gastrointestinal diseases

Nausea and vomiting are amongst the most common symptoms encountered in medicine as either symptoms of diseases or side effects of treatments. In a more biological setting they are also important components of an organism's defences against ingested toxins. Identification of treatments for nausea and vomiting and reduction of emetic liability of new therapies has largely relied on the use of animal models, and although such models have proven invaluable in identification of the anti-emetic effects of both 5-hydroxytryptamine(3) and neurokinin(1) receptor antagonists selection of appropriate models is still a matter of debate. The present paper focuses on a number of controversial issues and gaps in our knowledge in the study of the physiology of nausea and vomiting including: The choice of species for the study of emesis and the underlying behavioural (e.g. neophobia), anatomical (e.g. elongated, narrow abdominal oesophagus with reduced ability to shorten) and physiological (e.g. brainstem circuitry) mechanisms that explain the lack of a vomiting reflex in certain species (e.g. rats); The choice of response to measure (emesis[retching and vomiting], conditioned flavour avoidance or aversion, ingestion of clay[pica], plasma hormone levels[e.g. vasopressin], gastric dysrhythmias) and the relationship of these responses to those observed in humans and especially to the sensation of nausea; The stimulus coding of nausea and emesis by abdominal visceral afferents and especially the vagus-how do the afferents encode information for normal postprandial sensations, nausea and finally vomiting?; Understanding the central processing of signals for nausea and vomiting is particularly problematic in the light of observations that vomiting is more readily amenable to pharmacological treatment than is nausea, despite the assumption that nausea represents "low" intensity activation of pathways that can evoke vomiting when stimulated more intensely.

Zingiber officinale Rosc. modulates gamma radiation-induced conditioned taste aversion

The aim of the present study was to investigate the neurobehavioral protective efficacy of a hydroalcoholic extract of ginger (Zingiber officinale Rosc.) in mitigating gamma radiation-induced conditioned taste aversion in Sprague-Dawley rats. Administration of Zingiber extract 1 h before 2-Gy gamma irradiation was effective in blocking the saccharin avoidance response for 5 post-treatment observational days, both in a dose- and time-dependent manner, with 200 mg/kg b.w. i.p. being the most effective dose. Highest saccharin intake in all the groups was observed on the fifth post-treatment day. The potential of ginger extract to inhibit lipid peroxidation induced by radiation (2 Gy) and ascorbate-ion stress in brain homogenate and its ability to scavenge highly reactive superoxide anions were evaluated. The 1000-microg/ml and 2000-microg/ml concentration of ginger extract showed the highest efficiency in scavenging free radicals and in inhibiting lipid peroxidation. The lipid peroxidation and superoxide-anion scavenging ability of the extract further supports its radioprotective properties. The results clearly establish the neurobehavioral efficacy of ginger extract and the antioxidant properties appear to be a contributing factor in its overall ability to modulate radiation-induced conditioned taste aversion. Ginger extract has tremendous potential for clinical applications in mitigation of radiation-induced emesis in humans.

Effects of peptides on animal and human behavior: a review of studies published in the first twenty years of the journal Peptides

This review catalogs effects of peptides on various aspects of animal and human behavior as published in the journal Peptides in its first twenty years. Topics covered include: activity levels, addiction behavior, ingestive behaviors, learning and memory-based behaviors, nociceptive behaviors, social and sexual behavior, and stereotyped and other behaviors. There are separate tables for these behaviors and a short introduction for each section.

The connectivity of the area postrema in the ferret

The area postrema (AP) is the chemosensitive trigger zone for the emetic reflex. We have investigated the connectivity of the AP and adjacent solitary complex (SC) to identify possible sites of the motor emetic center. The AP and SC were infused with HRP or WGA-HRP in 30 ferrets that were perfused transcardially after 24-72 h. A block from the pons to upper cervical spinal cord, and one with hypothalamus and basal forebrain, was cut at 50 microns, reacted, and mounted. Data support the conclusion, at variance with those from other preparations, that in ferrets the AP has reciprocal connections only with the SC, which serves as a relay in both ascending and descending pathways between AP and higher levels of the neuraxis. Connectivity of the SC with brain stem and forebrain structures including the rostral ventrolateral medulla, parabrachial nuclei, paraventricular nucleus, and amygdala was demonstrated. At least in ferrets, our results suggest that the motor emetic center must be located within the SC. While this may not apply to all species, it is also possible that some reports of AP projections elsewhere were results of label within the SC. Alternatively, the somewhat different pattern of emesis in the ferret as compared to the dog (greater role for vagal inputs in response to radiation and cytotoxic drugs, lesser role for humoral inputs) may reflect differences in AP connectivity.

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.

Vasopressin and oxytocin express excitatory effects on respiratory and respiration-related neurones in the nuclei of the tractus solitarius in the cat

The effects of the iontophoretic application of vasopressin and oxytocin were examined on the activity of single neurones recorded in the region of the nuclei of the tractus solitarius (NTS) of the cat that were functionally classified as respiratory neurones or presumed reflex interneurones. The excitatory effects observed in half to two-thirds of these neurones tested (n = 37) suggest a role of these peptides in respiratory control and further support recent evidence that their involvement in autonomic control may include an action in NTS.

Neural mechanisms of swallowing: neurophysiological and neurochemical studies on brain stem neurons in the solitary tract region

Neurophysiological studies of the nuclei of the tractus solitarius (NTS) and adjacent regions have provided a partial understanding of the integrative brainstem network underlying swallowing and related functions such as respiration. The NTS is also richly endowed with an abundance of neuropeptides and other neuroactive substances, but only limited information is available on their influences on neurons involved specifically in swallowing. Since dysfunction of these neurophysiological and neurochemical regulatory mechanisms in the NTS region may be important in pathophysiological conditions such as dysphagia, increased awareness of and focus on these mechanisms are warranted. This paper outlines recent neurophysiological and neurochemical data that provide information on the afferent inputs and neurophysiological properties of neurons in NTS and adjacent caudal brainstem regions implicated in swallowing, respiration, and respiratory-related reflexes.

Identification and characterization of the emetic effects of peptide YY

Emesis was noted following intravenous bolus injections into dogs of a chromatographic subfraction derived from porcine small intestinal tissue extracts. The active agent was isolated from this subfraction using sequential ion-exchange and reverse-phase HPLC and demonstrated to be the recently identified regulatory peptide PYY. The threshold dose for PYY-induced emesis in the dog is less than 120 pmol/kg. Emesis was sometimes seen following large IV bolus doses of neuropeptide Y (NPY), but none was seen following IV injection of pancreatic polypeptide (PP). Dogs prepared with discrete, bilateral lesions of the area postrema were refractory to a suprathreshold emetic dose of PYY. PYY is the most potent, circulating emetic peptide identified to date.

Effect of angiotensin II and peptide YY on cerebral and circumventricular blood flow

Angiotensin II and peptide YY (PYY) are putative neuro/humoral agents acting at several circumventricular regions. These peptides also constrict cerebral vessels. We examined the effect of acute intravenous infusion of saline, angiotensin II and peptide YY on local cerebral blood flow (14C-iodoantipyrine autoradiography) in the circumventricular and non-circumventricular brain regions of 17 conscious rats. No reductions in brain blood flow (28 regions) were observed although angiotensin II and PYY infusion elevated arterial blood pressure 15-25% without influencing heart rate, suggesting an increase in peripheral resistance. However, local blood flow was dependent on the peptide infused. During PYY infusion, blood flow was rather constant in the 20 non-circumventricular regions examined whereas an increase in blood flow and a slight decrease in cerebrovascular resistance occurred in the circumventricular regions. The area postrema exhibited the most pronounced changes--an elevation in blood flow of 44 +/- 11% and a reduction in resistance of 20 +/- 5% in comparison to that in control animals. During angiotensin II infusion, local cerebral blood flow was similar to that in controls and local cerebrovascular resistance was elevated. Thus, the local cerebral circulatory response to peptide administration was dependent on the location of the region examined (circumventricular or non-circumventricular) and on the vasoactive peptide infused.

Central mechanisms for apomorphine-induced emesis in the dog

In order to investigate whether different receptor populations mediate emesis induced by intracerebroventricular (i.c.v.) and intravenous (i.v.) apomorphine, adult beagle dogs were tested with various doses of the drug with and without central and peripheral pretreatment with the dopamine antagonist sulpiride. The threshold dose of apomorphine to induce emesis by i.c.v. injections was 30-50 times lower than via the i.v. route, while the response latencies after i.c.v. administration were typically longer and the number of bouts of vomiting greater. I.v. pretreatment with sulpiride was more effective than i.c.v. pretreatment in blocking emesis induced by i.v. apomorphine, whereas both i.v. and i.c.v. sulpiride effectively blocked vomiting after i.c.v. apomorphine. Finally, in separate experiments, surgical interruption of blood flow in the region of the area postrema permanently abolished the emetic response to i.c.v. apomorphine, but only transiently disrupted emesis induced by i.v. apomorphine. These data suggest the possibility that i.v. and i.c.v. apomorphine-induced emesis may be mediated by separate dopamine receptors on the cerebrospinal fluid-side and blood-side of the area postrema.

Angiotensin II excites neurones in cat solitary tract nuclei which are involved in respiration and related reflex activities

In anaesthetized cats, effects of iontophoretic application of angiotensin II were studied in the nuclei of the tractus solitarius. Specifically, its effects were tested on single respiratory neurones, having rhythmic activity related temporally with the phrenic nerve discharge, and on presumed reflex interneurones, which lacked rhythmic activity but responded to stimulation of vagus nerve or superior laryngeal nerve. Angiotensin II (30-100 nA positive current for 30-60 s) excited 8/27 respiratory neurones; 19 were unaffected. Five of 8 reflex interneurones were excited; 3 were unaffected. Excitation consisted of a delayed, slow increase in the rate of firing which continued for about 60-120 s following the end of ejection. These results provide physiological evidence to support the possibility that angiotensin II may be a chemical mediator of synaptic transmission in the nuclei of the tractus solitarii, in pathways related to respiratory control.

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.

Central nervous system effects of peptides, 1980-1985: a cross-listing of peptides and their central actions from the first six years of the journal Peptides

A tabular synopsis is presented for articles concerned with the effects of peptides on the central nervous system that appeared in the journal Peptides from 1980-1985. A table arranged alphabetically by peptide and one arranged by effects, both listing routes of injection, species, direction of change, and qualifying notes, provides easy cross-referencing of peptides and their effects. Over 80 peptides and over 135 effects are listed. The list of peptides includes, but is not limited to: ACTH, angiotensin, bombesin, bradykinin, calcitonin, casomorphin, CCK, ceruletide, CGRP, CRF, dermorphin, DSIP, dynorphin, endorphins, enkephalins, GRF, gastrin, LHRH, litorin, metkephamid, MIF-l, motilin, MSH, NPY, NT, oxytocin, ranatensin, sauvagine, substances P and K, somatostatin, TRH, VIP, vasopressin, and vasotocin. The list of effects includes, but is not limited to: aggression, alcohol, analgesia, attention, avoidance, behavior, cardiovascular regulation, catalepsy, conditioned behavior, convulsions, dopamine binding and metabolism, discrimination, drinking, EEG, exploration, feeding, fever, gastric secretion, GI motility, grooming, learning, locomotor behavior, mating, memory, neuronal activity, open field, operant behavior, rearing, respiration, satiety, scratching, seizure, sleep, stereotypy, temperature, thermoregulation and tolerance.