Lipopolysaccharide (LPS) blocks the acquisition of LiCl-induced gaping in a rodent model of anticipatory nausea

Lipopolysaccharide (LPS) attenuates the primary conditioning of lithium chloride (LiCl)-induced context aversion but not the secondary conditioning of context aversion or taste avoidance

A first-order association can be formed between toxin-induced nausea and a context, as well as nausea and a taste cue. However, comparatively little is understood about second-order associations. The present study examined if the bacterial endotoxin, LPS, could impair the first- and second-order conditioning of context aversion (anticipatory nausea paradigm) and subsequent conditioned taste avoidance (two-bottle task). Adult male Long Evans rats were treated with LiCl (127 mg/kg, intraperitoneal [i.p.]) or vehicle control (NaCl) and then exposed to a distinct context for 4 first-order conditioning trials. LPS (200 μg/kg, i.p.) or NaCl were administered 24 h after each trial. Seventy-two h after the final first-order conditioning trial, rats underwent 2 second-order conditioning trials where they were treated with 2% saccharin (i.p.) and then exposed to the same context. Twenty-four h after the final second-order conditioning trial, rats were tested in a two-bottle task (2 trials), where they were given a choice between water and a palatable 0.2% saccharin solution. LiCl-treated rats demonstrated a context aversion by the 3rd conditioning trial in the anticipatory nausea paradigm. Rats previously exposed to LiCl also displayed a conditioned taste avoidance of saccharin within the two-bottle task. LPS attenuated first-order context aversion but did not alter either second-order context aversion or conditioned taste avoidance in the two-bottle task. This study demonstrated that a secondary association formed within an aversive context could result in a conditioned taste avoidance. Further, LPS may be able to attenuate primary conditioning, but not secondary conditioning.

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.

Immune activation attenuates memory acquisition and consolidation of conditioned disgust (anticipatory nausea) in rats

Anticipatory nausea is a classically conditioned response to cues (e.g. contexts) that have been previously paired with a nauseating stimulus, such as chemotherapy in humans. In rodents, anticipatory nausea can be modeled by pairing a novel context with lithium chloride (LiCl), which leads to conditioned disgust behaviours (such as gaping) when exposed to the context alone. Growing evidence suggests that selective immune activation attenuates various forms of learning and memory. The present study investigated the effects of the endotoxin lipopolysaccharide (LPS) on LiCl-induced anticipatory nausea across critical stages of associative memory including acquisition, consolidation, and extinction. Adult male Long Evans rats were subject to intraperitoneal (i.p.) LiCl (127 mg/kg) or vehicle control (NaCl) paired with a 30 min conditioning trial in a distinct context for a total of 4 trials. To study acquisition, rats were administered either LPS or NaCl (200 μg/kg, i.p.) 90 mins before the conditioning trials. To study consolidation, different rats were administered either LPS or NaCl (200 μg/kg, i.p.) immediately after the conditioning trials. These trials were followed by 4 drug-free extinction trials within the same context. LPS significantly reduced conditioned gaping behaviours by the 4th conditioning trial and on the 1st drug-free extinction trial when administered 90 mins before or immediately after the conditioning trials. LPS had no significant effect on extinction. The present study provides strong evidence for the attenuating effects of LPS exposure on the acquisition and consolidation of LiCl-induced anticipatory nausea.

Infection, Learning, and Memory: Focus on Immune Activation and Aversive Conditioning

Here we review the effects of immune activation primarily via lipopolysaccharide (LPS), a cell wall component of Gram-negative bacteria, on hippocampal and non-hippocampal-dependent learning and memory. Rodent studies have found that LPS alters both the acquisition and consolidation of aversive learning and memory, such as those evoking evolutionarily adaptive responses like fear and disgust. The inhibitory effects of LPS on the acquisition and consolidation of contextual fear memory are discussed. LPS-induced alterations in the acquisition of taste and place-related conditioned disgust memory within bottle preference tasks and taste reactivity tests (taste-related), in addition to conditioned context avoidance tasks and the anticipatory nausea paradigm (place-related), are highlighted. Further, conditioned disgust memory consolidation may also be influenced by LPS-induced effects. Growing evidence suggests a central role of immune activation, especially pro-inflammatory cytokine activity, in eliciting the effects described here. Understanding how infection-induced immune activation alters learning and memory is increasingly important as bacterial and viral infections are found to present a risk of learning and memory impairment.

De-risking in Tier I CNS safety assessments is the primary function of study design and technical training of laboratory staff observers

Derisking is not a pharmaceutical industry strategy to reduce time, effort, or costs in drug development. Derisking strategies originated within the National Institutes of Health as a predicate to good science. There is a growing sentiment within drug development programs to diminish the importance of behavioral measures in toxicological studies and in the Tiered Safety assessment plans of the U.S. Regulatory Agencies and the International Commission on Harmonization. The validity and reliability of the Functional Observational Batter (FOB) is critically dependent on consistency and technical quality in each risk assessment plan. US Federal and International drug approval organizations have universally adopted the concept of principles of test construction rather than delineating specific behavioral assay endpoints for inclusion of the FOB in nonclinical safety protocols. The validity and reliability of behavioral observations in standardized neurotoxicity screening is critically dependent on the FOB developed by the Study Director with the Sponsor throughout all stages of testing.. The individual risk factors selected for observation to be included in the early Tier 1 safety program should be determined by the mechanism and mode of action of the test article. The results of Tier I testing are the basis for Tier II testing designs. Critical to the compliance with Good Laboratory Practices is the documentation of training of the operational staff scheduled to conduct all aspects of the established protocol.

Regulation of nausea and vomiting by cannabinoids and the endocannabinoid system

Nausea and vomiting (emesis) are important elements in defensive or protective responses that animals use to avoid ingestion or digestion of potentially harmful substances. However, these neurally-mediated responses are at times manifested as symptoms of disease and they are frequently observed as side-effects of a variety of medications, notably those used to treat cancer. Cannabis has long been known to limit or prevent nausea and vomiting from a variety of causes. This has led to extensive investigations that have revealed an important role for cannabinoids and their receptors in the regulation of nausea and emesis. With the discovery of the endocannabinoid system, novel ways to regulate both nausea and vomiting have been discovered that involve the production of endogenous cannabinoids acting centrally. Here we review recent progress in understanding the regulation of nausea and vomiting by cannabinoids and the endocannabinoid system, and we discuss the potential to utilize the endocannabinoid system in the treatment of these frequently debilitating conditions.

Anticipatory nausea and vomiting due to chemotherapy

As a specific variation of chemotherapy-induced nausea and vomiting, anticipatory nausea and vomiting (ANV) appears particularly linked to psychological processes. The three predominant factors related to ANV are classical conditioning; demographic and treatment-related factors; and anxiety or negative expectancies. Laboratory models have provided some support for these underlying mechanisms for ANV. ANV may be treated with medical or pharmacological interventions, including benzodiazepines and other psychotropic medications. However, behavioral treatments, including systematic desensitization, remain first line options for addressing ANV. Some complementary treatment approaches have shown promise in reducing ANV symptoms. Additional research into these approaches is needed. This review will address the underlying models of ANV and provide a discussion of these various treatment options.

Conditioned flavor avoidance and conditioned gaping: rat models of conditioned nausea

Although rats are incapable of vomiting, they demonstrate profound avoidance of a flavor previously paired with an emetic drug. They also display conditioned gaping reactions during re-exposure to the flavor. This robust learning occurs in a single trial and with long delays (hours) between consumption of a novel flavor and the emetic treatment. However, conditioned flavor avoidance learning is not a selective measure of the emetic properties of drugs, because non-emetic treatments (even highly rewarding treatments) produce conditioned avoidance, and anti-emetic treatments are generally ineffective in suppressing conditioned avoidance produced by an emetic drug. On the other hand, conditioned gaping reactions are consistently produced by emetic drugs and are prevented by anti-emetic drugs, indicating that they may be a more selective measure of conditioned malaise in rats. Here we review the literature on the use of conditioned flavor avoidance and conditioned gaping reactions as rat measures of conditioned nausea, as well as the neuropharmacology and neuroanatomy of conditioned gaping reactions in rats.

Impairment of lithium chloride-induced conditioned gaping responses (anticipatory nausea) following immune system stimulation with lipopolysaccharide (LPS) occurs in both LPS tolerant and LPS non-tolerant rats

Anticipatory nausea is a classically conditioned response to a context that has been previously paired with toxin-induced nausea and/or vomiting. When injected with a nausea-inducing drug, such as lithium chloride (LiCl), rats will show a distinctive conditioned gaping response that has been suggested to be an index of nausea. Previous studies have found that immune system activation with an endotoxin, such as lipopolysaccharide (LPS), attenuates LiCl-induced conditioned gaping in rats. The present study examined the acquisition of LiCl-induced conditioned gaping in rats that were either LPS tolerant or LPS non-tolerant, as little is known about the effects of endotoxin tolerance on learning and memory. Male Long-Evan rats were given four systemic injections of LPS (200 μg/kg) or isotonic saline (NaCl) to induce LPS tolerance, indexed with 24 h changes in body weight following treatment. The animals were then given 4 acquisition trials in a LiCl-induced conditioned gaping paradigm. On conditioning days animals were treated with LPS (200 μg/kg) or saline followed 90 min later by injection of LiCl (127 mg/kg) or saline and then placed in a distinctive context for 30 min and their behavior video-recorded. On a drug free test day all animals were again placed in the distinctive context for 10 min and behavior was video-recorded. Gaping responses were scored for all acquisition days and the test day. Spleen and body weights were also obtained for all rats at the end of the experiment. Gaping responses were attenuated in rats treated with LPS in both the LPS tolerant and LPS non-tolerant groups. There were significant negative correlations between spleen weight as well as spleen/body weight ratios, and levels of conditioned gaping responses in LiCl treated rats, but not control rats. These results show that LPS interferes with learning/memory in the anticipatory nausea paradigm in rats that are both LPS tolerant and LPS non-tolerant.

Lipopolysaccharide inhibits the simultaneous establishment of LiCl-induced anticipatory nausea and intravascularly conditioned taste avoidance in the rat

This study examined the effects of the bacterial endotoxin, lipopolysaccharide (LPS), on the establishment of anticipatory nausea and conditioned taste avoidance in a simultaneous conditioning paradigm using an intravascular/intraperitoneal saccharin taste. 83 naïve adult male Long-Evans rats were injected (intraperitoneal) with either 200 μg/kg LPS or 0.9% saline (NaCl), 90 min prior to ip treatment with either 64 mg/kg LiCl, 64 mg/kg LiCl+2.0% saccharin, 0.9% NaCl, or 0.9% NaCl+2.0% saccharin, and immediately placed into a distinctive context for 30 min (repeated over 4 conditioning days, spaced 72 h apart). 72 h following the final conditioning day, each animal was re-exposed to the context on a drug-free test day where orofacial responding was recorded. The next day, animals received a 24 h 2-bottle preference test with a choice between water and a palatable 0.2% saccharin solution. Results showed that LPS exposure, prior to LiCl or LiCl+Saccharin treatment, inhibited the establishment of anticipatory nausea, as evidenced by significantly lower conditioned gaping frequencies relative to animals pre-treated with NaCl followed by LiCl or LiCl+Saccharin. LPS pre-treatment also inhibited the formation of LiCl-induced taste avoidance, as evidence by significantly higher saccharin preferences in Group LPS-LiCl+Saccharin relative to Group NaCl-LiCl+Saccharin. The results of the current study provide additional evidence for the deleterious effects of LPS on learning and memory in aversive conditioning.

Alteration of embryonic AT(2)-R and inflammatory cytokines gene expression induced by prenatal exposure to lipopolysaccharide affects renal development

Prenatal exposure to LPS(lipopolysaccharide) results in renal damage in offspring rats, but the mechanism is unknown. The present study was to explore the role of angiotensin II and inflammation in the development of renal damage induced by prenatal exposure to LPS. The pregnant rats were randomly divided into two groups, i.e., control group, LPS group. The rats in the two groups were administered intraperitoneally with vehicle or 0.79 mg/kg LPS on 8th, 10th and 12th day during gestation. The mRNA expression of angiotensinogen, renin, AT(1)-R, AT(2)-R, TNF-α and IL-6 in embryos were assessed. Renal Ang II-positive cells, monocytes/macrophages, lymphocytes, collagen I and TUNEL-positive cells were identified by immunohistochemical staining in newborn and 7-week-old offspring rats. The number of glomeruli and creatinine clearance rate were determined in offspring at 7 weeks of age. The results showed that prenatal LPS decreased AT(2)-R mRNA expression but increased TNF-α and IL-6 mRNA expression in embryos. Prenatal LPS decreased renal angiotensin II-positive cells in newborn offspring rats, while these increased in 7-week-old offspring rats. Prenatal LPS decreased glomerular number and creatinine clearance rate but increased renal infiltrating monocytes/macrophages and lymphocytes at 7 weeks of age. Prenatal LPS also increased TUNEL-positive cells and collagen I expressions in newborn rats and 7-week-old offspring rats.

CONCLUSION

Alteration of embryonic AT(2)-R and inflammatory cytokines gene expression induced by prenatal exposure to lipopolysaccharide affects renal development.

Inhibition of LiCl-induced conditioning of anticipatory nausea in rats following immune system stimulation: comparing the immunogens lipopolysaccharide, muramyl dipeptide, and polyinosinic: polycytidylic acid

The effects of the bacterial endotoxins, lipopolysaccharide (LPS) and muramyl dipeptide (MDP; Experiment 1), and the viral mimetic, polyinosinic: polycytidylic acid (poly I:C; Experiment 2), on the acquisition of "conditioned gaping" behavior in the rodent model of LiCl-induced anticipatory nausea were examined. Experimentally naïve adult male Long-Evans rats were injected (intraperitoneal, i.p.) with either 200 μg/kg LPS, 1.6 mg/kg MDP, or 0.9% saline (Experiment 1), or 4.0 mg/kg poly I:C or 0.9% saline (Experiment 2), 90 min prior to treatment with 127 mg/kg LiCl or saline control and immediately placed into a distinctive context for 30 min (repeated over 4 conditioning days, spaced 72 h apart). On a drug-free test day (72 h following conditioning day 4), each animal was re-exposed to the context for 10 min, and orofacial and aversive behavioral responses were video recorded and analyzed. The results showed that pre-treatment with LPS, MDP (Experiment 1), or poly I:C (Experiment 2) prior to LiCl+context conditioning significantly impaired the establishment of conditioned gaping behavior, thus blocking the acquisition of anticipatory nausea. Results varied in regards to peripheral acute-phase response sickness behaviors, with significantly reduced weight loss in LPS-treated animals, less robust weight loss in poly I:C-treated animals, and no significant reductions in body weight in MDP-treated animals. The learning impairments observed in the current study suggest that endotoxin treatment with bacterial and viral endotoxin may have stronger central effects on learning and memory behavior, relative to peripheral effects on body weight and other sickness-related responses.

Peripheral bacterial endotoxin administration triggers both memory consolidation and reconsolidation deficits in mice

Peripherally administered inflammatory stimuli, such as lipopolysaccharide (LPS), induce the synthesis and release of proinflammatory cytokines and chemokines in the periphery and the central nervous system, and trigger a variety of neurobiological responses. Indeed, prior reports indicate that peripheral LPS administration in rats disrupts contextual fear memory consolidation processes, potentially due to elevated cytokine expression. We used a similar, but partially olfaction-based, contextual fear conditioning paradigm to examine the effects of LPS on memory consolidation and reconsolidation in mice. Additionally, interleukin-1β (IL-1β), brain-derived neurotrophic factor (BDNF), and zinc finger (Zif)-268 mRNA expression in the hippocampus and the cortex, along with peripheral cytokines and chemokines, were assessed. As hypothesized, LPS administered immediately or 2 h, but not 12 h, post-training impaired memory consolidation processes that support the storage of the conditioned contextual fear memory. Additionally, as hypothesized, LPS administered immediately following the fear memory trace reactivation session impaired memory reconsolidation processes. Four hours post-injection, both central cytokine and peripheral cytokine and chemokine levels were heightened in LPS-treated animals, with a simultaneous decrease in BDNF, but not Zif-268, mRNA. Collectively, these data reinforce prior work showing LPS- and cytokine-related effects on memory consolidation, and extend this work to memory reconsolidation.

Anticipatory nausea and vomiting

A commonly reported consequence of post-treatment nausea or vomiting is the development of anticipatory nausea and vomiting (ANV). In most published work, nausea is reported to occur before chemotherapy drugs are administered by approximately 20% of patients at any one chemotherapy cycle and by 25-30% of patients by their fourth chemotherapy cycle. Most studies in adult patients strongly support the view that the development of ANV involves elements of classical conditioning. The best method to avoid development of ANV is to adequately prevent both vomiting and nausea from the first exposure to chemotherapy. If anticipatory side effects develop, behavioral treatment techniques, such as systematic desensitization, have been shown effective. Benzodiazepines used in combination with behavioral techniques or antiemetics may also be useful. The evidence on which these conclusions are based is reviewed in this article.

Contributions of peripheral inflammation to seizure susceptibility: cytokines and brain excitability

Inflammation is an important factor in the pathophysiology of seizure generation and epileptogenesis. While the role of CNS inflammation is well acknowledged as an important factor in seizure pathophysiology, less is known about the role of peripheral inflammation. Systemic inflammation induces a mirror inflammatory response in the brain that might have transient or long-term effects on seizure susceptibility. The focus of our laboratory research is the study of the interaction of systemic inflammatory events with neuronal excitability and seizure susceptibility. In this paper we provide a review of our findings and discuss possible mechanisms.