Dose-related sex differences in the establishment of conditioned disgust (anticipatory nausea), and the effect of peripubertal and adult immune system stimulation with the endotoxin lipopolysaccharide (LPS) on learning and memory in the rat

This thesis examined sex differences in the establishment of lithium chloride (LiCl) – induced conditioned disgust behavior (anticipatory nausea) to a distinct context, as well as, the establishment of conditioned place avoidance (CPA) using rodent models. Also examined were potential sex differences in response to treatment with the bacterial endotoxin, lipopolysaccharide (LPS), and its effect on learning and memory. In Chapter 2, male and female naïve Long-Evans rats were injected (intraperitoneally; i.p.) with either 200 µg/kg LPS or 0.9% (NaCl), 90 minutes prior to i.p. injections of either 128 mg/kg LiCl or 0.9% NaCl, and immediately placed into a distinctive context for 30 minutes (repeated over 4 conditioning days, spaced 72 h apart). 72 h following the final conditioning day, each subject was re-exposed to the context on a drug-free test day where orofacial and somatic behaviors were recorded. Results showed that LiCl-treated females conditioned stronger disgust reactions, relative to LiCl-treated males, as evidenced by significantly higher frequencies of conditioned “gaping” behavior and forelimb flailing in females. Pre-treatment with LPS during conditioning led to strong inhibition of conditioned disgust behavior, to levels that did not significantly differ from controls. Although there was no apparent sex difference in the degree of inhibition produced by LPS in this context-based rodent disgust model, males did exhibit significantly greater 24 h body weight losses following LPS injections on the first two conditioning days, relative to females. In Chapter 3, the sex difference in conditioned gaping behavior found in Chapter 2 was explored further by examining potential dose-related effects. Once again, females displayed significantly higher frequencies of conditioned “gaping” behavior relative to males, in a dose-dependent manner. The results from Chapters 2 and 3 provide strong support for a sex difference in the onset and severity of nausea-related symptoms which is also observed among the human population. This provides a preclinical tool for testing the efficacy of anti-nausea treatments and noxious drug side-effects. In Chapter 4, the effects of LPS pretreatment on the establishment of conditioned place avoidance (CPA) were examined. Female rats were also injected with LPS or saline during the peripubertal phase of development (6 weeks of age) and later pretreated with LPS again or saline in the classic two-chamber CPA paradigm. Results showed that while peripubertal LPS had no long-term effect on establishing CPA, it did interfere with the ability of a second LPS challenge in adulthood to block CPA, as was shown in subjects pretreated with LPS in adulthood only. The results of this study provide support for previous findings that suggest that stressors and/or immune challenges during this sensitive period of development can lead to long-lasting alterations in behavior

Magnetic Field Effects On The Neuroprocessing Of Pain

Magnetic fields can affect behaviour in a variety of ways, in a manner that is dependent on the particulars of the magnetic field exposure. A specific pulsed magnetic field with analgesic properties was investigated using functional magnetic resonance imaging with acute thermal pain. The functional activation of pain was significantly different pre/post exposure vs. a sham condition within areas of the brain associated with the affective component of pain, in particular the anterior cingulate and the right insula. Sleep was found to be a significant confound with a 45-minute exposure. This was the first time fMRI has been used as a tool to investigate bioelectromagnetics effects, and demonstrates that an MR system can be used for both image acquisition and exposure. This technique will have applications to functional tasks beyond the acute thermal pain tested here

SIMULTANEOUS CONDITIONING OF ANTICPATORY NAUSEA AND TASTE AVOIDANCE AND THE INFLUENCE OF IMMUNE SYSTEM STIMULATION

Immune system stimulation with lipopolysaccharide (LPS) elicits a specific set of physiological and behavioral responses termed “sickness behavior”. LPS treatment has been found to impair learning and memory in a variety of learning paradigms, including those for anticipatory nausea and conditioned taste avoidance. Traditional conditioning paradigms typically employ a single conditioned stimulus (CS) and unconditioned stimulus (US). This thesis used an intravascular (intraperitoneal) saccharin “taste” cue, together with the toxin LiCl, given immediately prior to anticipatory nausea context conditioning, in order to simultaneously condition responses to both internal (taste) and external (context) conditioning stimuli. The effects of LPS on the simultaneous acquisition of anticipatory nausea and taste avoidance were then examined. In addition to the establishment of a concurrent conditioning model, the present findings suggest that LPS pre-treatment was effective in disrupting both conditioned nausea and taste avoidance

Social Factors Modulate Toxin (LICL)-Induced Conditioned Disgust Responses in Male Rats

Rats, which are a non-emetic species, display conditioned disgust responses when re-exposed to a context previously associated with sickness. These conditioned disgust responses can be used to model anticipatory nausea in humans, a growing problem faced by numerous chemotherapy patients. This thesis found that social factors, in addition to contextual factors, can play a role in the expression of toxin (LiCl)-induced conditioned disgust in rats. The results show that a familiar, but not unfamiliar, social partner can serve as a cue for the display of conditioned gaping. Further, a variety of sensory cues may play a role in the development of socially-mediated conditioned disgust, as an odour cue (urine) alone was incapable of causing significant conditioned disgust. It was also found that socially-mediated conditioned disgust can be modulated by oxytocin, as an oxytocin receptor antagonist, L-368,899, significantly decreased the display of conditioned gaping. Therefore, these findings suggest that social factors can lead to the development and expression of toxin-elicited conditioned disgust responses in rats. This has implications for chemotherapy patients, as the development and expression of anticipatory nausea may also be impacted by social factors

Oxytocin’s Effects on Sickness Behaviours, Anxiety Responses, and Immune Function in Adult Male Mice

The nonapeptide, oxytocin (OT), is implicated in a range of behavioural and physiological functions. However, OT\u27s role in sickness behaviours remains unclear. This thesis examined effects of the OT agonist, carbetocin (CBT), and OT antagonist, L-368,899, on anxiety and locomotor sickness-related behaviours and pro-inflammatory cytokines, TNF-a and IL-6, in adult male CD-1 mice. Animals received 2 intraperitoneal treatment injections. The first treatment was carbetocin, L-368,899, or saline, while the second was lipopolysaccharide (LPS) or saline. Behaviours were evaluated via the light-dark test, and cytokines via immunoassay. OT antagonist treatment attenuated LPS induced perturbations in locomotor and anxiety-like behaviour, but produced no significant effects on cytokines. The 10 mg/kg CBT-saline treatment suppressed locomotion and augmented anxiogenic behaviour, while OT antagonist treatment enhanced locomotor behaviour, and decreased anxiety-like behaviour. The present findings suggest that OT antagonist treatment has anxiolytic effects on basal anxiety-like behaviours, and attenuates the expression of sickness behaviour

The effects of pre- and postnatal administration of propionic acid and lipopolysaccharide on the behaviour of adolescent male and female rats

The gut microbiome plays an important role in immune functioning and neurodevelopment. Altered microbiome composition, leading to short chain fatty acid, and/or immune system dysfunction has been observed in children with autism spectrum disorders (ASD). This thesis describes the developmental influence of prenatal exposure to propionic acid (PPA), a metabolic fermentation product of enteric bacteria, or prenatal exposure to lipopolysaccharide (LPS), a bacterial mimetic and product of enteric bacteria, on a range of behaviours in male and female neonatal, adolescent and adult rats. Study one evaluated the effects of prenatal PPA and LPS, and postnatal PPA, on developmental milestones in early life and on subsequent locomotor activity and anxiety-related behaviours. Study two examined acoustic startle response (ASR) and prepulse inhibition, while the third examined social behaviours. Overall, prenatal and postnatal treatments subtly altered behaviour in a sex- and test-specific manner. Male and female rats showed developmental delay in the day of eye opening and in acquiring a nest seeking odor discrimination. Prenatal and postnatal PPA treatments increased anxiety-related behaviour and altered ASR. Male rats displayed alterations in social behaviour and locomotor activity that was not observed in female rats, supporting the male bias seen in autism. However, female rats also showed augmented sensitivity to PPA, displaying repetitive behaviour, altered ASR, and decreased prepulse inhibition, in agreement with the evidence that these behaviours are more severe in females with ASD. Together, these findings demonstrate that the metabolic products of enteric bacteria, PPA and LPS, may alter development in ways resembling ASD

Emerging Synergisms Between Drugs and Physiologically-Patterned Weak Magnetic Fields: Implications for Neuropharmacology and the Human Population in the Twenty-First Century

Synergisms between pharmacological agents and endogenous neurotransmitters are familiar and frequent. The present review describes the experimental evidence for interactions between neuropharmacological compounds and the classes of weak magnetic fields that might be encountered in our daily environments. Whereas drugs mediate their effects through specific spatial (molecular) structures, magnetic fields mediate their effects through specific temporal patterns. Very weak (microT range) physiologically-patterned magnetic fields synergistically interact with drugs to strongly potentiate effects that have classically involved opiate, cholinergic, dopaminergic, serotonergic, and nitric oxide pathways. The combinations of the appropriately patterned magnetic fields and specific drugs can evoke changes that are several times larger than those evoked by the drugs alone. These novel synergisms provide a challenge for a future within an electromagnetic, technological world. They may also reveal fundamental, common physical mechanisms by which magnetic fields and chemical reactions affect the organism from the level of fundamental particles to the entire living system

Sharing an environment with sick conspecifics alters odors of healthy animals

Body odors change with health status and the odors of sick animals can induce avoidance behaviors in healthy conspecifics. Exposure to sickness odors might also alter the physiology of healthy conspecifics and modify the odors they produce. We hypothesized that exposure to odors of sick (but non-infectious) animals would alter the odors of healthy cagemates. To induce sickness, we injected mice with a bacterial endotoxin, lipopolysaccharide. We used behavioral odor discrimination assays and analytical chemistry techniques followed by predictive classification modeling to ask about differences in volatile odorants produced by two types of healthy mice: those cohoused with healthy conspecifics and those cohoused with sick conspecifics. Mice trained in Y-maze behavioral assays to discriminate between the odors of healthy versus sick mice also discriminated between the odors of healthy mice cohoused with sick conspecifics and odors of healthy mice cohoused with healthy conspecifics. Chemical analyses paired with statistical modeling revealed a parallel phenomenon. Urine volatiles of healthy mice cohoused with sick partners were more likely to be classified as those of sick rather than healthy mice based on discriminant model predictions. Sickness-related odors could have cascading effects on neuroendocrine or immune responses of healthy conspecifics, and could affect individual behaviors, social dynamics, and pathogen spread

Novel Object Test: Examining Nociception and Fear in the Rainbow Trout

This study aimed to assess fear responses to a novel object while experiencing a noxious event to determine whether nociception or fear will dominate attention in a fish in novel object testing paradigm. This experimentally tractable animal model was used to investigate (1) the degree of neophobia to a novel object while experiencing noxious stimulation, (2) the response of the fish after removing the fear-causing event by using a familiar object, and (3) the effects of removing the nociceptive response by morphine administration and examining the response to a novel object. Control animals displayed a classic fear response to the novel objects and spent most of their time moving away from this stimulus, as well as showing an increase in respiration rate when the novel object was presented. In contrast, noxiously stimulated animals spent most of their time in close proximity to the novel object and showed no additional increase in respiration rate to novel object presentation. There was evidence of a slight hypoalgesia in noxiously stimulated animals. The responses to familiar objects demonstrated that by familiarizing the animal with the object, fear was removed from the experiment. Both control and noxiously treated animals responded in similar ways to a novel object by spending the majority of their time in close proximity. Treatment with morphine reduced effects of noxious stimulation and appears to be an effective analgesic. After morphine administration, the acid-injected animals showed a neophobic response to a novel object and this was similar to the response of the control fish, with a similar amount of time spent moving away from the object and an increase in ventilation in response to the novel object. Morphine affected the fear response because both groups approached the novel object more quickly than the non-morphine controls. These results suggest that nociception captures the animal’s attention with only a relatively small amount of attention directed at responding to the fear of the novel object

The Effects of Early Adolescent Lipopolysaccharide or Cat Odour Exposure Followed by Propionic Acid Administration on Anxiety, Startle Response, and Sensorimotor Gating in Adolescence and Adulthood

Autism spectrum disorders (ASD) are caused by genetic factors and a complex set of risk factors including early stressors and alterations in the gut microbiome. The present thesis investigated whether environmental stressors during early adolescence predisposes rats administered another stressor in later adolescence and adulthood to produce altered anxiety-like behaviours, startle response, and percent prepulse inhibition. The early adolescent stressors used in this study included repeated administration of a bacterial endotoxin, lipopolysaccharide (LPS), or a stressful predator cat odour exposure. In later adolescence and adulthood, rats were administered with a gut microbial by-product, propionic acid (PPA), and subsequently tested on behaviour. Repeated early adolescent LPS exposure induced long-term anxiety-like behaviours and elevated startle response in adulthood. Repeated early adolescent cat odour exposure induced long-term anxiogenic effects. PPA exposure decreased activity and percent prepulse inhibition. Combined LPS and PPA exposure induced additive effects on activity, while prior cat odour exposure potentiated PPA’s reduction of vertical activity. The results of this thesis are important in evaluating the complex set of risk factors involved in the development of ASD