Continuous manganese delivery via osmotic pumps for manganese-enhanced mouse MRI does not impair spatial learning but leads to skin ulceration

Manganese-enhanced magnetic resonance imaging (MEMRI) is a widely used technique in rodent neuroimaging studies. Traditionally, Mn2+ is delivered to animals via a systemic injection; however, this can lead to toxic effects at high doses. Recent studies have shown that subcutaneously implanted mini-osmotic pumps can be used to continuously deliver manganese chloride (MnCl2), and that they produce satisfactory contrast while circumventing many of the toxic side effects. However, neither the time-course of signal enhancement nor the effect of continuous Mn2+ delivery on behaviour, particularly learning and memory, have been well-characterized. Here, we investigated the effect of MnCl2 dose and route of administration on a) spatial learning in the Morris Water Maze and b) tissue signal enhancement in the mouse brain. Even as early as 3 days after pump implantation, infusion of 25–50 mg/kg/day MnCl2 via osmotic pump produced signal enhancement as good as or better than that achieved 24 h after a single 50 mg/kg intraperitoneal injection. Neither route of delivery nor MnCl2 dose adversely affected spatial learning and memory on the water maze. However, especially at higher doses, mice receiving MnCl2 via osmotic pumps developed skin ulceration which limited the imaging window. With these findings, we provide recommendations for route and dose of MnCl2 to use for different study designs

The Role of Prostaglandin E2 on the Developing Hippocampus - Link to Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social communication, increased repetitive/restricted behaviours and anxiety. The prevalence of autism has been drastically increasing over the past few decades with an associated increase in socioeconomic burden, imposing hardship on many families. Currently, 1 in 66 Canadians are impacted by the disorder and males are four times as likely to be diagnosed with ASD. There is a growing need to understand the underlying mechanisms during development that are contributing to the pathology of ASD in both sexes. Clinical and epidemiological studies suggest exposure to environmental risk factors during pregnancy can impact lipid signaling during development, contributing to the pathology of ASD in children. Previous literature has provided evidence that a bioactive lipid signalling molecule in the brain, known as prostaglandin E2 (PGE2) can be perturbed due to exposure to environmental risk factors during pregnancy, impacting critical processes such as neuronal migration, differentiation and proliferation. Moreover, deficits in hippocampal function are known to contribute to the major symptoms that characterize ASD. In this study, we investigated how prenatal exposure to PGE2 impacts the developing hippocampus in males and females. We examined the effect of PGE2 exposure on dendritic morphology using Golgi-cox staining and proteins that may be driving these morphological changes using western blotting. Our findings suggest that prenatal PGE2 exposure impacts hippocampal dendritic morphology in a sex-dependent manner, which is associated with changes in the expression of proteins involved in cytoskeletal architecture. Ultimately, this study provides us with insight on how perturbed PGE2 signaling impacts cytoskeletal dynamics in the developing hippocampus, contributing to the pathology of autism

The Role of Prostaglandin E2 on the Developing Hippocampus - Link to Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social communication, increased repetitive/restricted behaviours and anxiety. The prevalence of autism has been drastically increasing over the past few decades with an associated increase in socioeconomic burden, imposing hardship on many families. Currently, 1 in 66 Canadians are impacted by the disorder and males are four times as likely to be diagnosed with ASD. There is a growing need to understand the underlying mechanisms during development that are contributing to the pathology of ASD in both sexes. Clinical and epidemiological studies suggest exposure to environmental risk factors during pregnancy can impact lipid signaling during development, contributing to the pathology of ASD in children. Previous literature has provided evidence that a bioactive lipid signalling molecule in the brain, known as prostaglandin E2 (PGE2) can be perturbed due to exposure to environmental risk factors during pregnancy, impacting critical processes such as neuronal migration, differentiation and proliferation. Moreover, deficits in hippocampal function are known to contribute to the major symptoms that characterize ASD. In this study, we investigated how prenatal exposure to PGE2 impacts the developing hippocampus in males and females. We examined the effect of PGE2 exposure on dendritic morphology using Golgi-cox staining and proteins that may be driving these morphological changes using western blotting. Our findings suggest that prenatal PGE2 exposure impacts hippocampal dendritic morphology in a sex-dependent manner, which is associated with changes in the expression of proteins involved in cytoskeletal architecture. Ultimately, this study provides us with insight on how perturbed PGE2 signaling impacts cytoskeletal dynamics in the developing hippocampus, contributing to the pathology of autism

The Effects of Ovarian Hormones and Reproductive Experience on Multiple Memory System Bias in Female Rats and Women.

The present thesis examined the role of ovarian hormones and reproductive experience on multiple memory system bias in female rats and women. First, the effect of 17β-Estradiol (E2) and parity on learning in a dorsal striatum- (DS) mediated response task and a hippocampus- (HPC) mediated place task was investigated. Ovariectomized (OVX) nulliparous and primiparous female rats receiving low or high E2 replacement were trained on both tasks. Nulliparous rats in the low E2 group learned the response task significantly faster than the place task; this facilitatory effect of low E2 on response learning was not observed in primiparous rats, which suggests that the E2-induced effect on response learning disappears with parity. Dopamine (DA) D1 and D2 type receptor (D1R and D2R, respectively) binding was then investigated in the DS and NAcc core and shell of nulliparous and primiparous OVX rats receiving low or high E2 replacement. Primiparous rats had significantly lower D2R binding in the DS than nulliparous rats. These results hint at a possible DS D2R mechanism in altered response learning in reproductively experienced rats. Second, the effects of E2 and parity on memory bias in humans was investigated. Young, naturally cycling women with and without reproductive experience were tested on the 4-on-8 virtual maze (4/8 VM) task, which can be solved by using response or spatial memory, during the follicular phase (first half of the menstrual cycle) or the luteal phase (second half). Menstrual cycle results revealed predominant use of spatial memory in the luteal phase group, whereas response memory was associated with the follicular phase, showing that memory bias shifts with cyclic changes in ovarian hormones. Moreover, this pattern was also observed and found to be more pronounced in reproductively experienced women. However, mothers and non-mothers differed in terms of learning the 4/8 VM task, which indicates that there were parity-induced differences despite similar cycle-dependent memory bias. Finally, the role of E2, progesterone (P), and testosterone (T) on this cycle-dependent shift in strategy in mothers and non-mothers was investigated. Results revealed that the follicular phase was associated with low P levels, whereas the luteal phase was linked to a high P state, suggesting that the shift in strategy across the menstrual cycle could be P-mediated in humans. Though not significant, high E2 levels were associated with response memory. Also, the results revealed that P and T both play a significant role in multiple memory system bias; this effect is reversed with parity. Thus, memory bias changes across the menstrual cycle, P and T could have a larger impact than E2 on this shift in humans, and the hormonal profile that underlies this effect is different in reproductively experienced women

Understanding how age and biological sex influence the development of Alzheimer’s disease

Alzheimer’s disease is a highly complex neurodegenerative disease and multifactorial. Age is the most significant risk factor for Alzheimer’s disease (AD), with cases doubling every five years after 65. Thus, one of the most challenging areas in AD research is understanding what happens to the brain when it ages. Such insights could aid in distinguishing individuals who are more susceptible to developing AD during ageing. Over the last 25 years, brain ageing studies have looked at thousands of human brains to investigate the neuronal basis of agerelated cognitive decline. However, most of these studies enrolled adults over 60 years of age. Therefore, those studies overlooked the most significant period of neuroendocrine changes in a woman’s life, the menopause transition period. In the menopause phase, females undergo a significant decline in ovarian sex steroid production, including approximately 90% of oestrogen (E2) production. It is well documented that E2 has a neuroprotection function in the brain. Thus, the dramatic loss of sex steroids during menopause impacts multiple biological systems in the body, including the brain. In addition, despite documented sex disparities in the risk for dementia, the effect of biological sex and sex hormones on human brain ageing and AD development is understudied. Thus, in this thesis, it was hypothesized that an interrelationship between age and biological sex could impact brain structure and function during ageing and increase the susceptibility of women to develop AD. In this thesis, AD biomarkers and their processing proteins, along with E2-associated proteins expression, were investigated in frontal cortical brain samples from young (20-30), middle-aged (45-55), and elderly (70-90) males and females with no history of dementia, and in AD samples (70-90). A sex disparity during brain ageing and AD in the expression of AD biomarkers was reported in the first two experimental chapters, with females exhibiting agerelated upregulation in the levels of APP and its amyloidogenic enzymes. Also, Ab overproduction was observed in both sexes with advancing age, but its levels were significantly higher in aged female samples compared to aged males. In addition, higher levels of tau and GSK3b were found in the aged female frontal cortex compared to the male frontal cortex. In AD samples, these sex disparities in AD biomarkers were also visible in higher Ab levels and tau hyperphosphorylation in female AD patients compared to AD male patients. When E2- associated proteins were investigated, oestrogen receptor (ERa and ERb), in male samples only ERb and its downstream signalling molecules (Akt and ERK2) were upregulated in the VIII male frontal cortex with ageing, reported in chapter 5, while middle-aged female samples have shown a decline in the level of ERb and an age-related decrease in ERa in chapter 6. In AD samples, ERb expression declined in males in chapter 5, and in females, both ERa and ERb were decreased in chapter 6. Thus, the decline of ER in middle-aged females and AD of both sexes samples could indicate a reduction in E2 neuroprotection function; E2 can regulate Ab production, and it is the most significant neuroprotection function against AD. The neuroprotection of E2 against AD was illustrated in chapter 7, where the treatment of nontransfected female AD neuronal human induced pluripotent stem (hIPS) cells with E2 showed an apparent significant decline in Ab levels. An inter-relationship between brain ageing and biological sex in AD development was apparent in this project. The findings of this project could partly explain the sex-based variation in AD development. ER decline in the female frontal cortex during ageing and tremendous overproduction of Ab might highlight the differences between the sexes in the age of onset of AD. Preclinical AD could be initiated earlier in females because of losing the neuroprotective function of E2 during the menopause transition phase. Also, the thesis findings could indicate how important it is to investigate both sexes separately and not neglect to report female findings in preclinical and clinical studies where male samples were predominant