Systemic naloxone increases the incidence of motion sickness in the cat

Effects of naloxone on motion sickness in cats alone and with broad spectrum antiemetics

Doses of naloxone far below those which elicit emesis increase the sensitivity to motion sickness. In order to evaluate the possible interaction with broad spectrum antiemetics, low doses of naloxone were tested alone and in combination with 8-hydroxy-2-(di-n-propylamine)tetralin (DPAT), fentanyl and the NK1 antagonist CP-99994. A modified autonomic symptom rating scale was unaffected by any drug and thus considered of little value. Fentanyl and NK1 antagonists decreased the duration of the retch/vomit sequence. Naloxone alone and in combination with each of the drugs increased the duration of retching/vomiting. Naloxone also increased the number of vomiting sequences. The results are interpreted in terms of possible site(s) of action of the antiemetic drugs.

Intensification and Habituation of Experimental Motion Sickness in Squirrel Monkeys by Repeated Horizontal Rotation

The aim of this research was to quantify the development of habituation or intensification of experimental motion sickness induced in Bolivian squirrel monkeys by repeated exposures to horizontal rotation. Incidence, frequency, and latency of vomiting responses were recorded from monkeys rotated daily in a transparent testing chamber at 30 rpm for periods of 1 or 2 hours. Data showed that more than half of the subjects revealed habituation in terms of increased latencies for vomiting. Some showed a tendency to vomit increasingly earlier with multiple daily exposures to rotation. The development of habituation and intensification was evident as early as the second day of rotation. The number of emetic episodes per day decreased as a consequence of repeated rotation, but intensification of vomiting frequency did not occur beyond the fifth day.

Naloxone-induced taste aversions in opiate-naïve Lewis and Fischer 344 rat strains

BACKGROUND

The Lewis (LEW) and Fischer (F344) rat strains appear differentially sensitive to the aversive effects of several used and abused drugs. Naloxone, a mu opioid receptor antagonist that induces aversions in outbred rats but has no abuse potential, was assessed to determine the characteristics of compounds for which the strains differ.

METHODS

Opioid-naïve male LEW and F344 rats were given access to saccharin followed by low (Experiment 1) and high (Experiment 2) doses of naloxone every 4th day for five pairings. Aversions were assessed in both one-bottle and two-bottle tests.

RESULTS

In Experiment 1, aversions were evident at 10mg/kg (one-bottle) and at 5.6 and 10mg/kg (two-bottle) with no apparent strain difference for either assessment. In Experiment 2, aversions were evident for LEW animals (but not F344) at 18 and 32 mg/kg (one-bottle). LEW animals injected with 32 mg/kg displayed greater aversions than F344 animals receiving the same dose. Both strains displayed aversions at all doses in the two-bottle test with no strain difference.

CONCLUSIONS

Naloxone induced aversions that were strain dependent only at specific doses and under the one-bottle testing condition. These results parallel those of several other used and abused drugs but differ dramatically from those seen with morphine in the two strains (F344>LEW). Further assessments utilizing the LEW-F344 model should investigate other drugs to establish the set of compounds for which the strains differ and to characterize the mechanism underlying the observed differences.

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.

Opioid receptor involvement in the adaptation to motion sickness in Suncus murinus

The aim of the present study was to investigate an opioid receptor involvement in the adaptation response to motion sickness in Suncus murinus. Different groups of animals were treated intraperitoneally with either saline, morphine (0.1 and 1.0 mg/kg), naloxone (1.0, 10.0 and 5.0 mg/kg) or a combination of naloxone plus morphine in the absence or 30 min prior to a horizontal motion stimulus of 1 Hz and 40 mm amplitude. For the study of adaptation, different groups received saline on the first trial, and in subsequent trials (every 2 days) they received either saline, naloxone (1.0 and 10.0 mg/kg, i.p.) or morphine (0.1 mg/kg, i.p.) 30 min prior to the motion stimulus. Pretreatment with morphine caused a dose-related reduction in emesis induced by a single challenge to a motion stimulus. Pretreatment with naloxone alone did not induce emesis in its own right nor did it modify emesis induced by a single challenge to a motion stimulus. However, pretreatment with naloxone (5.0 mg/kg, i.p.) revealed an emetic response to morphine (P<.001) (1.0 mg/kg, i.p.) and antagonised the reduction of motion sickness induced by morphine. In animals that received saline or naloxone (1.0 mg/kg), a motion stimulus inducing emesis decreased the responsiveness of animals to a second and subsequent motion stimulus challenge when applied every 2 days for 11 trials. However, the animals receiving naloxone 10.0 mg/kg prior to the second and subsequent challenges showed no significant reduction in the intensity of emesis compared to the first trial. The data are revealing of an emetic potential of morphine when administered in the presence of a naloxone pretreatment. The administration of naloxone is also revealing of an additional inhibitory opioid system whose activation by endogenous opioid(s) may play a role in the adaptation to motion sickness on repeated challenge in S. murinus.

Variables of movement amplitude and frequency in the development of motion sickness in Suncus murinus

The aim of the present study was to investigate the effect of different frequency and amplitude of horizontal movements to induce motion sickness and to identify gender differences and adaptation to motion stimulus in adult Suncus murinus. Each animal was subjected to a horizontal motion stimulus of 3, 7, 13, or 40 mm amplitude at a frequency of 0.5, 1, 2, or 3 Hz. The number of vomiting episodes and the latency of onset were recorded over a 10-min period. For the study of adaptation, different groups of males were exposed to repeated motion sickness (using 0.5 or 1 Hz frequency and the amplitude of 40 mm) either every 2 days for a period of 30 days, or once every week for a period of 28 days. In all animals the number of emetic episodes obtained at 1 and 2 Hz were significantly higher by 40-80% than those at 0.5 and 3 Hz using either 13 or 40 mm amplitude of movements; this was followed by shorter latency of emesis. Age-matched females were shown to be more responsive to the emetic stimuli than males as the number of emetic episodes at 1, 2, and 3 Hz (amplitude of 40 mm) were significantly higher by 33%, 42%, and 75%, respectively, than in males; this also was followed by a shorter latency of emetic response. In the study of adaptation, when used once every 2 days, by the second challenge (at 0.5 Hz) the number of emetic episodes was reduced by 62%, and to subsequent challenges emesis was absent or greatly reduced. Also, a reduction in responsiveness was observed at 1 Hz, which attained a maximum effect by the third challenge. The present results indicated that Suncus murinus is sensitive to horizontal motion stimulus, the emetic episodes were significantly greater at 1 and 2 Hz than at either a lower or higher frequency, a repeated challenge once every 2 days but not weekly reduced the number of emetic episodes, and in all experiments, age-matched female animals were more responsive than males to motion stimulus and in some experiments this achieved significance.

Physiological basis and pharmacology of motion sickness: an update

Motion sickness can occur when sensory inputs regarding body position in space are contradictory or are different from those predicted from experience. Signals from the vestibular system are essential for triggering motion sickness. The evolutionary significance of this malady is unclear, although it may simply represent the aberrant activation of vestibuloautonomic pathways that typically subserve homeostasis. The neural pathways that produce nausea and vomiting during motion sickness are presumed to be similar to those that generate illness after ingestion of toxins. The neural substrate of nausea is unknown but may include neurons in the hypothalamus and inferior frontal gyrus of the cerebral cortex. The principal motor act of vomiting is accomplished through the simultaneous contractions of inspiratory and expiratory respiratory muscles and is mediated by neurons in the lateral medullary reticular formation and perhaps by cells near the medullary midline. Cocontraction of the diaphragm and abdominal muscles increases pressure on the stomach, which causes gastric contents to be ejected through the mouth. Effective drugs for combating motion sickness include antihistamines, antimuscarinics, 5-HT1A (serotonergic) receptor agonists and neurokinin type 1 receptor antagonists. However, considerable information concerning the physiological basis and pharmacology of motion sickness is unknown; future research using animal models will be required to understand this condition.

Changes in Fos and Jun expression in the rat brainstem in the process of vestibular compensation

By means of immunohistochemical technique, we examined the changes in Fos and Jun expression after unilateral labyrinthectomy (UL) in the rat brainstem. We observed Fos-like immunoreactivity (-LIR) in the ipsilateral medial vestibular nucleus (ipsi-MVe), the contralateral prepositus hypoglossal nucleus (contra-PrH) and the contralateral inferior olive beta subnucleus (contra-IOb) 1 h after UL. Then, Fos expression in the contra-PrH and the contra-IOb disappeared 3 days after surgery. However, we still found the residual expression in the ipsi-MVe, which disappeared within 7 days. On the other hand, no Jun-LIR was detected in the vestibular or vestibular-related nuclei before or after the operation. Fos expression in the MVe, PrH and IOb was induced immediately after UL. Then, the Fos expression disappeared in accordance with the development of the vestibular compensation. These findings suggest that the transient Fos expression in the vestibular and vestibular related nuclei is a trigger of vestibular compensation.

Changes in preproenkephalin mRNA after unilateral and bilateral labyrinthectomy in the rat medial vestibular nucleus

We examined the expression of preproenkephalin (PPE) mRNA in the vestibular nuclei in rats using in situ hybridization histochemistry. In normal rats, PPE mRNA-positive cells were observed in the medial and spinal vestibular nuclei. After unilateral labyrinthectomy, PPE mRNA was increased in the medial vestibular nucleus on the operated side from the 1st through the 3rd day after the surgery. It is suggested that the changes in PPE mRNA level after labyrinthectomy are involved in vestibular compensation.

New pharmacologic approaches to the prevention of space/motion sickness

Fundamental approaches in selection of new agents for evaluation in prevention of space/motion sickness (SMS) are reviewed. The discussion centers on drugs under investigation at the Johnson Space Center. Methodology that employs the rotating chair for measuring SMS symptomatology and susceptibility is described. The most obvious approach to the development of new agents relies on selection of agents from drug classes that possess pharmacologic properties of established anti-motion sickness agents. A second approach selects drugs that are used to prevent emesis caused by means other than exposure to motion. The third approach relies on basic research that characterizes individual differences in susceptibility. The hypothesis is: detection of individual differences leads to identification of specific drugs, which target physiologic systems that show individual differences. These physiologic systems are targets for therapy and may play a role in the etiology of SMS. Two drugs that reduce susceptibility to SMS include dexamethasone and d(CH2)5Tyr(Me)AVP, a vasopressin (AVP)V1 antagonist. The latter peptide has demonstrated complete blockade of emesis and other significant symptoms in squirrel monkeys. These studies were predicated on observations that subjects who were more resistant to SMS had higher plasma AVP after severe nausea than subjects with lower resistances. Investigations are underway to test a 0.5-mg intravenous dose in humans. Kappa opioid agonists inhibit AVP release and offer new therapeutic possibilities and advantages over AVP peptides. This review details the experimental data collected on AVP and adrenocorticotropin. The literature supports interrelated roles for AVP and opioid peptides in SMS. Experimental testing of kappa agonists is warranted because specific opioid agonists act at neuroanatomical sites causing nausea and vomiting. It is argued opioid receptors in the chemoreceptor trigger zone and vomiting center stimulate and inhibit the emetic response, respectively. The evidence suggests kappa and/or mu receptors at VC are involved in inhibition of emesis, whereas delta opioid receptors at CTZ are involved in stimulation of emesis.

The effects of naloxone on body rotation-induced analgesia and anorexia in male mice

The effects of body rotation in a horizontal plane and the opiate antagonist, naloxone, on the nociceptive responses and the feeding behavior of male mice were examined. In the first experiment the mice were rotated (70 rpm, schedule of 15 sec on; 5 sec off) for 60 minutes or exposed to sham rotation for the same duration. Midway through the rotation or sham procedure the mice were either injected with naloxone (1 mg/kg) or isotonic saline. At the end of the 60-minute treatment period the animals were placed on a warm surface (47.5 degrees C) and their latency to show a foot-licking response was measured. The rotation procedure produced a significant (p less than 0.01) increase in response latency in the saline-injected mice and the naloxone injections blocked this analgesic effect. This finding provides evidence for opioid involvement in the rotation-induced analgesia. In Experiment 2 mice on a food restriction schedule were rotated (70 rpm, 15 sec on; 5 sec off) or sham exposed for 60 minutes. Midway through this treatment period the mice were either injected with naloxone (1 mg/kg) or isotonic saline. Following the treatment period the mice were given access to food for 2 hours. The rotation procedure produced a significant (p less than 0.01) reduction in feeding (anorexia) in the first 30 minutes of food access for the saline-injected mice. Injections of naloxone significantly (p less than 0.05) enhanced the rotation-induced anorexia. These experiments demonstrate that rotation-induced analgesia in mice is blocked by the opiate antagonist, naloxone, whereas rotation-induced anorexia is not.(ABSTRACT TRUNCATED AT 250 WORDS)

Intensification and habituation of experimental motion sickness in squirrel monkeys by repeated horizontal rotation

The aim of this research was to quantify the development of habituation or intensification of experimental motion sickness induced in Bolivian squirrel monkeys by repeated exposures to horizontal rotation. Incidence, frequency, and latency of vomiting responses were recorded from monkeys rotated daily in a transparent testing chamber at 30 rpm for periods of 1 or 2 hours. Data showed that more than half of the subjects revealed habituation in terms of increased latencies for vomiting. Some showed a tendency to vomit increasingly earlier with multiple daily exposures to rotation. The development of habituation and intensification was evident as early as the second day of rotation. The number of emetic episodes per day decreased as a consequence of repeated rotation, but intensification of vomiting frequency did not occur beyond the fifth day.

Behavioral conditioning and experimental motion-induced sickness

Adult male squirrel monkeys were the subjects of experiments conducted to determine whether or not repeated exposures to sickness-inducing horizontal rotation would result in behavioral conditioning of emetic responses. The development of conditioned food aversion and feeding suppression as a consequence of pre- and postrotation eating was quantified. It was concluded that neither instrumental conditioning nor classical conditioning were valid alternative hypotheses for the occurrence of repeated vomiting episodes over a period of ten daily exposures to motion. Conditioned aversion to fresh banana and feeding suppression developed gradually if rotation, which induced multiple bouts of vomiting, was sustained for 1- or 2-hour sessions. If spinning was terminated immediately after the first emetic response, no aversion or suppression emerged. The occurrence of food aversion, by itself, is questioned as a valid index of the presence of subjective concomitants of motion sickness in animals.

Experimental motion sickness induced in squirrel monkeys by continuous off-axis horizontal rotation

Under a variety of experimental conditions, nonrestrained adult male squirrel monkeys were subjected to continuous rotation in the horizontal plane at 33 rpm. Severity of motion-induced sickness was quantified by measuring latencies of three responses associated with sickness. Per- and postrotational nystagmus was recorded from a subsample of monkeys with permanent recording electrodes implanted in the bony orbits. Incidence of sickness depended on the time limits of stimulation imposed, and it occurred in a maximum of about 90 per cent of test sessions if rotation was continued for two hours. When subjected to ten once-per-day rotation sessions, only a few monkeys showed evidence of developing transient habituation of onset of motion sickness. Mean frequency of emetic episodes, however, declined over the latter half of the rotation series. Restricting visual cues by blindfolding the monkeys prevented most subjects from vomiting.

Endogenous opiates: 1983

This paper is the sixth in an annual series of reviews of research involving the endogenous opiates, each installment being restricted to work published during the previous year. Although the early articles in the series attempted to be comprehensive and cover the complete range of research with the opiate peptides, in the last two years we have limited our coverage to non-analgesic and behavioral work due to the enormous number of articles published in the field. The specific areas discussed here include stress, tolerance and dependence, consummatory responses, other gastrointestinal functions, interactions with alcohol, mental illness, learning and memory, cardiovascular responses, respiratory effects, thermoregulation, neurological disorders, activity, and miscellaneous other topics. As in previous years, we have attempted to present a relatively complete review of the subjects covered only for the previous year and generally have not tried to evaluate their contributions relative to those of past years.