Conditioned disgust in rats (anticipatory nausea) to a context paired with the effects of the toxin LiCl: Influence of sex and the estrous cycle

Evaluation of Sex Differences in the Potential of Δ9-Tetrahydrocannabinol, Cannabidiol, Cannabidiolic Acid, and Oleoyl Alanine to Reduce Nausea-Induced Conditioned Gaping Reactions in Sprague-Dawley Rats

Introduction: Cancer patients report nausea as a side effect of their chemotherapy treatment. Using the pre-clinical rodent model of acute nausea-lithium chloride (LiCl)-induced conditioned gaping-our group has demonstrated that exogenous cannabinoids may have antinausea potential. Materials and Methods: With the goal of evaluating the role of sex as a factor in pre-clinical research, we first compared the conditioned gaping reactions produced by varying doses of LiCl in male and female rats using the taste reactivity test (Experiment 1). Results: LiCl produced dose-dependent conditioned gaping similarly in male and female rats with the highest dose (127.2 mg/kg) producing robust conditioned gaping, with this dose used in subsequent experiments. Next, we examined the antinausea potential of THC (Experiment 2), CBD (Experiment 3), cannabidiolic acid (CBDA; Experiment 4) and oleoyl alanine (OlAla; Experiment 5) in both male and female rats. THC, CBD, CBDA, and OlAla dose dependently reduced conditioned gaping in both male and female rats in a similar manner. Conclusions: These results suggest that cannabinoids may be equally effective in treating nausea in both males and females.

Genetic and environmental influences on one-trial conditioned context aversion in mice

Anticipatory nausea (AN) is caused by an association between contextual cues and the experience of nausea (the side effects of chemotherapy or radiation treatment) and it develops predominantly in female patients undergoing chemotherapy. Preclinical studies in rodents show that the administration of an illness-inducing agent in the presence of novel contextual cues can cause conditioned context aversion (CCA) and this has been proposed to model AN. The literature also suggests that brief pre-exposure to a novel context prior to shock delivery is critical in the development of contextual fear conditioning in rodents (a phenomenon known as Immediate Shock Deficit), but this has not been assessed in CCA. The aim of present study was to develop a CCA paradigm to assess this in outbred (CD1) and inbred (C57BL/6J) mice and evaluate potential sex differences. The results revealed that a single conditioning trial in which a distinctive context was paired with LiCl-induced illness was sufficient to elicit a conditioned response in both female and male CD1 outbred mice, but not in C57BL/6J inbred mice. In addition, CCA was facilitated when animals had prior experience with the context. Finally, outbred female mice showed longer and more robust retention of CCA than male mice, which parallels clinical findings. The results indicate the importance of using CD1 outbred mice as an animal model of AN as well as examining sex differences in the CCA paradigm. Similar findings in humans encourage the future use of this novel CCA preclinical mouse model.

Male and female rats exhibit comparable gaping behavior but activate brain regions differently during expression of conditioned nausea

Twenty-five to fifty percent of patients undergoing chemotherapy will develop anticipatory nausea and vomiting (ANV), in which symptoms occur in anticipation of treatment. ANV is triggered by environmental cues and shows little response to traditional antiemetic therapy, suggesting that unique neural pathways mediate this response. Understanding the underlying neural mechanisms of this disorder is critical to the development of novel therapeutic interventions. The purpose of the present study was to identify brain areas activated during ANV and characterize sex differences in both the behavior and the brain areas activated during ANV. We used a rat model of ANV by pairing a novel context with the emetic drug lithium chloride (LiCl) to produce conditioned nausea behaviors in the LiCl-paired environment. We quantitated gaping, an analog of human vomiting, after acute or repeated LiCl in a unique environment. To identify brain regions associated with gaping, we measured c-fos activation by immunochemical staining after these same treatments. We found that acute LiCl activated multiple brain regions including the supraoptic nucleus of the hypothalamus, central nucleus of the amygdala, nucleus of the solitary tract and area postrema, none of which were activated during ANV. ANV activated c-fos expression in the frontal cortex, insula and paraventricular nucleus of the hypothalamus of males but not females. These data suggest that therapies such as ondansetron which target the area postrema are not effective in ANV because it is not activated during the ANV response. Further studies aimed at characterizing the neural circuits and cell types that are activated in the conditioned nausea response will help identify novel therapeutic targets for the treatment of this condition, improving both quality of life and outcomes for patients undergoing chemotherapy.

Considering Organismal Physiology in Laboratory Studies of Rodent Behavior

Any experiment conducted in a rodent laboratory is done so against the backdrop of each animal's physiological state at the time of the experiment. This physiological state can be the product of multiple factors, both internal (e.g., animal sex, strain, hormone cycles, or circadian rhythms) and external (e.g., housing conditions, social status, and light/dark phases). Each of these factors has the potential to influence experimental outcomes, either independently or via interactions with others, and yet there is little consistency across laboratories in terms of the weight with which they are considered in experimental design. Such discrepancies-both in practice and in reporting-likely contribute to the perception of a reproducibility crisis in the field of behavioral neuroscience. In this review, we discuss how several of these sources of variability can impact outcomes within the realm of common learning and memory paradigms. Expected final online publication date for the Annual Review of Neuroscience, Volume 45 is July 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Social factors and the neurobiology of pathogen avoidance

Although the evolutionary causes and consequences of pathogen avoidance have been gaining increasing interest, there has been less attention paid to the proximate neurobiological mechanisms. Animals gauge the infection status of conspecifics and the threat they represent on the basis of various sensory and social cues. Here, we consider the neurobiology of pathogen detection and avoidance from a cognitive, motivational and affective state (disgust) perspective, focusing on the mechanisms associated with activating and directing parasite/pathogen avoidance. Drawing upon studies with laboratory rodents, we briefly discuss aspects of (i) olfactory-mediated recognition and avoidance of infected conspecifics; (ii) relationships between pathogen avoidance and various social factors (e.g. social vigilance, social distancing (approach/avoidance), social salience and social reward); (iii) the roles of various brain regions (in particular the amygdala and insular cortex) and neuromodulators (neurotransmitters, neuropeptides, steroidal hormones and immune components) in the regulation of pathogen avoidance. We propose that understanding the proximate neurobiological mechanisms can provide insights into the ecological and evolutionary consequences of the non-consumptive effects of pathogens and how, when and why females and males engage in pathogen avoidance.

Toxin-induced aversive context conditioning: Assessing active aversive behaviors conditioned to the context of an automated activity monitor

Lithium chloride (LiCl) is an emetic drug that has been used to create animal models of anticipatory nausea and conditioned place aversion. In this study we examined escape behaviours from a context in which rats experienced the aversive effects of LiCl treatments. The experiment had two phases: acquisition of context conditioning, which consisted of pairing a distinct context with the pharmacological effects of a moderate dose of the toxin LiCl, and extinction of context conditioning, which consisted of placement in the distinct context in a drug free state. During context conditioning, 16 adult male Long-Evans rats were injected intraperitoneally with 96 mg/kg lithium chloride (LiCl; n = 8) or 0.9% saline (NaCl; n = 8) and placed individually in an automated locomotor activity apparatus for 30 min every other day for 4 days. During the extinction phase, rats were placed in the apparatus for 30 min every other day without injections during a 4 day extinction phase. A significant Drug x Trial interaction was found for the time spent in vertical position in the open field apparatus during trials 1-3 of the extinction phase. The LiCl treated rats exhibited significantly increased rearing behavior, relative to the control rats, indicative of conditioned aversion. The results of this study suggest that escape behavior (vertical activity) occurs in rats experiencing the aversive conditioned effects of LiCl in a distinct context. In the context of current theoretical accounts, the LiCl-conditioned increase in apparent escape behaviors can be considered a reflection of anticipatory nausea.

Pathogens, odors, and disgust in rodents

All animals are under the constant threat of attack by parasites. The mere presence of parasite threat can alter behavior before infection takes place. These effects involve pathogen disgust, an evolutionarily conserved affective/emotional system that functions to detect cues associated with parasites and infection and facilitate avoidance behaviors. Animals gauge the infection status of conspecific and the salience of the threat they represent on the basis of various sensory cues. Odors in particular are a major source of social information about conspecifics and the infection threat they present. Here we briefly consider the origins, expression, and regulation of the fundamental features of odor mediated pathogen disgust in rodents. We briefly review aspects of: (1) the expression of affective states and emotions and in particular, disgust, in rodents; (2) olfactory mediated recognition and avoidance of potentially infected conspecifics and the impact of pathogen disgust and its' fundamental features on behavior; (3) pathogen disgust associated trade-offs; (4) the neurobiological mechanisms, and in particular the roles of the nonapeptide, oxytocin, and steroidal hormones, in the expression of pathogen disgust and the regulation of avoidance behaviors and concomitant trade-offs. Understanding the roles of pathogen disgust in rodents can provide insights into the regulation and expression of responses to pathogens and infection in humans.