Kelly Meyers

Behavioral Patterns Associated with Chemotherapy-Induced Emesis: A Potential Signature for Nausea in Musk Shrews

Nausea and vomiting are common symptoms in patients with many diseases, including cancer and its treatments. Although the neurological basis of vomiting is reasonably well known, an understanding of the physiology of nausea is lacking. The primary barrier to mechanistic research on the nausea system is the lack of an animal model. Indeed investigating the effects of anti-nausea drugs in pre-clinical models is difficult because the primary readout is often emesis. It is known that animals show a behavioral profile of sickness, associated with reduced feeding and movement, and possibly these general measures are signs of nausea. Studies attempting to relate the occurrence of additional behaviors to emesis have produced mixed results. Here we applied a statistical method, temporal pattern (t-pattern) analysis, to determine patterns of behavior associated with emesis. Musk shrews were injected with the chemotherapy agent cisplatin (a gold standard in emesis research) to induce acute (<24 h) and delayed (>24 h) emesis. Emesis and other behaviors were coded and tracked from video files. T-pattern analysis revealed hundreds of non-random patterns of behavior associated with emesis, including sniffing, changes in body contraction, and locomotion. There was little evidence that locomotion was inhibited by the occurrence of emesis. Eating, drinking, and other larger body movements including rearing, grooming, and body rotation, were significantly less common in emesis-related behavioral patterns in real versus randomized data. These results lend preliminary evidence for the expression of emesis-related behavioral patterns, including reduced ingestive behavior, grooming, and exploratory behaviors. In summary, this statistical approach to behavioral analysis in a pre-clinical emesis research model could be used to assess the more global effects and limitations of drugs used to control nausea and its potential correlates, including reduced feeding and activity levels.

Post-anesthesia vomiting: Impact of isoflurane and morphine on ferrets and musk shrews

Although partially controlled with antiemetic drugs, postoperative nausea and vomiting (PONV) continues to be a problem for many patients. Clinical research suggests that opioid analgesics and volatile anesthetics are the main triggers of PONV. The aim of this study was to develop an animal model for post-anesthesia vomiting for future studies to further determine mechanisms and preclinical drug efficacy. Ferrets (N=34) were initially used because they have served as a gold standard for emesis research. Ferrets were tested with several doses of morphine, inhaled isoflurane, and a positive control injection of cisplatin (a chemotherapy agent) to induce emesis. Musk shrews (a small animal model; N=36) were also tested for emesis with isoflurane exposure. A control injection of cisplatin produced emesis in ferrets (ip, 129.8±22.0 retches; 13.7±2.3 vomits; mean±SEM). Morphine also produced a dose-response on emesis in ferrets, with maximal responses at 0.9 mg/kg (sc, 29.6±12.6 retches; 1.8±0.9, vomits). Isoflurane exposure (2-4% for 10 min to 6h exposure) failed to induce vomiting, was not associated with an increased frequency in emesis when combined with a low dose of morphine (0.1 mg/kg, sc), and failed to produce consistent effects on food and water intake. In contrast to ferrets, musk shrews were very sensitive to isoflurane-induced emesis (0.5 to 3%, 10 min exposure; up to 11.8±2.4 emetic episodes). Overall, these results indicate that ferrets will not be useful for delineating mechanisms responsible for isoflurane-induced emesis; however, musk shrews may prove to be a model for vomiting after inhalation of volatile agents.

Computerized detection and analysis of cancer chemotherapy-induced emesis in a small animal model, musk shrew.

Vomiting is a common side effect of cancer chemotherapy and many drug treatments and diseases. In animal studies, the measurement of vomiting usually requires direct observation, which is time consuming and often lacks temporal precision. Musk shrews have been used to study the neurobiology of emesis and have a rapid emetic episode (∼1 s for a sequence of retching and expulsion). The aim of the current study was to develop a method to automatically detect and characterize emetic episodes induced by the cancer chemotherapy agent cisplatin. The body contour in each video frame was tracked and normalized to a parameterized shape basis. The tracked shape was projected to a feature space that maximized the shape variations in the consecutive frames during retching. The resulting one dimensional projection was sufficient to detect most emetic episodes in the acute (peak at 2h) and delayed (peak at 54 h) phases after cisplatin treatment. Emetic episodes were relatively invariant in the number of retches (∼6.2), duration (∼1.2s), inter-retch interval (∼198 ms), and amplitude during the 72 h after cisplatin treatment. This approach should open a new vista into emesis research to permit tracking and analysis of emesis in a small animal model and facilitate the development of new antiemetic therapies. These results also yield a better understanding of the brains central pattern generator for emesis and indicate that the retching response in the musk shrew (at ∼5.4 Hz) is the fastest ever recorded in a free-moving animal.

Delineation of vagal emetic pathways: intragastric copper sulfate-induced emesis and viral tract tracing in musk shrews

Signals from the vestibular system, area postrema, and forebrain elicit nausea and vomiting, but gastrointestinal (GI) vagal afferent input arguably plays the most prominent role in defense against food poisoning. It is difficult to determine the contribution of GI vagal afferent input on emesis because various agents (e.g., chemotherapy) often act on multiple sensory pathways. Intragastric copper sulfate (CuSO4) potentially provides a specific vagal emetic stimulus, but its actions are not well defined in musk shrews (Suncus murinus), a primary small animal model used to study emesis. The aims of the current study were 1) to investigate the effects of subdiaphragmatic vagotomy on CuSO4-induced emesis and 2) to conduct preliminary transneuronal tracing of the GI-brain pathways in musk shrews. Vagotomy failed to inhibit the number of emetic episodes produced by optimal emetic doses of CuSO4 (60 and 120 mg/kg ig), but the effects of lower doses were dependent on an intact vagus (20 and 40 mg/kg). Vagotomy also failed to affect emesis produced by motion (1 Hz, 10 min) or nicotine administration (5 mg/kg sc). Anterograde transport of the H129 strain of herpes simplex virus-1 from the ventral stomach wall identified the following brain regions as receiving inputs from vagal afferents: the nucleus of the solitary tract, area postrema, and lateral parabrachial nucleus. These data indicate that the contribution of vagal pathways to intragastric CuSO4-induced emesis is dose dependent in musk shrews. Furthermore, the current neural tracing data suggest brain stem anatomical circuits that are activated by GI signaling in the musk shrew.

Novel dynamic measures of emetic behavior in musk shrews.

The emetic reflex occurs as a pattern of motor responses produced by a network of neurons in the hindbrain. Despite an understanding of the sequence of motor outputs that form an emetic episode (EE), the variability in the dynamics of multiple EEs across time remains a mystery. Many clinical investigations rely on once a day patient recall of total amount of vomiting, and preclinical studies frequently report only the total number of EE per unit time. The aim of the current study was to develop novel temporal measures of emetic activation in a preclinical model. Male and female musk shrews were tested with prototypical emetic stimuli: motion exposure (1 Hz), nicotine (5 mg/kg, sc), and copper sulfate (120 mg/kg, ig). New emetic measures included duration (time from first to last episode), rate, standard deviation of the inter-episode interval (SD-I), and a survival analysis of emetic latency (analyzed with Cox regression). Behavioral patterns associated with emesis were also assessed using statistical temporal pattern (T-pattern) analysis to measure nausea-like behaviors (e.g., immobility). The emetic stimuli produced different levels of total EE number, duration, rate, and SD-I. A typical antiemetic, the neurokinin 1 receptor antagonist CP-99,994, suppressed the number of EEs but was less effective for reducing the duration or prolonging the emetic latency. Overall, the current study shows the use of novel dynamic behavioral measures to more comprehensively assess emesis and the impact of therapies.