Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 67-89).

No description available.

We have recently established that aberrant alkylacylglycerophosphocholine metabolism results in the increased tissue concentration of platelet activating factors (PAFs) in the temporal cortex of Alzheimer Disease (AD) patients and in TgCRND8 mice over-expressing mutant human amyloid precursor protein. PAF lipids activate a G-protein coupled receptor (PAFR) reported to be expressed by microglia and subsets of neurons in rat. It is not known whether this same expression pattern is recapitulated in mice however, as the expression has only been inferred by use of pharmacological PAFR antagonists, many of which impact on both PAFR-dependent and PAFR-independent signalling pathways. PAFR plays a role in long term potentiation (LTP) induction in rats. PAFR has also been implicated in behavioural indices of spatial learning and memory in rats. Contradictory reports using mice provide ambiguity regarding the role of PAFR in LTP induction in mice. To assess whether PAFR is expressed in murine neurons, I localized PAFR mRNA in wild-type C57BL/6 mice using PAFR KO mice as a negative control. I further showed that the loss of PAFR did not impair learning and memory although this assessment must be considered preliminary as the behavioural test employed was not optimized to detect changes in learning and memory of C57BL/6 mice over time adequately.Finally, I showed that the loss of PAFR in TgCRND8 mouse model of AD had no impact upon Aβ plaque number. My observations suggest that PAFR is restricted to microglial-like cells in mouse hippocampus and as such, it may not play a role in learning and memory.

Diss. (sammanfattning) Göteborg : Göteborgs universitet, 2006. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 94-116).

Dendritic spines are the major sites for receiving excitatory synaptic inputs and play important roles in neuronal signal transduction, memory storage and neuronal circuit organization. Structural plasticity of dendritic spines is correlated with functional plasticity, and is critical for learning and memory. Visualization of the changes of dendritic spines at the ultrastructural level that specifically correlated with their function changes in high throughput would shed light on detailed mechanisms of synaptic plasticity. Here we developed a correlative light and electron microscopy workflow which combines two-photon MNI-glutamate uncaging, pre-embedding immunolabeling, Automatic Tape-collecting Ultramicrotome sectioning and scanning electron microscopy imaging. This method bridges two different visualization platforms, directly linking ultrastructure and function at the level of individual synapses. With this method, we successfully relocated single dendritic spines that underwent long-term potentiation (LTP) induced by two-photon MNI-glutamate uncaging, and visualized their ultrastructures and AMPA receptors distribution at different phases of LTP in high throughput. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

The ventral tegmental area (VTA) is an important component of the mesolimbic dopamine circuit and processes reward and motivational behaviors. In response to drug exposure, synaptic connections of this circuit can be rewired via synaptic plasticity—a phenomenon thought be responsible for the pathology of addiction. While much is known about dopamine neuron plasticity, less is known regarding plasticity exhibited by VTA GABA cells, specifically inhibitory inputs from outside the VTA. Expanding on the work of Bocklisch et al. (2013), we investigated the plasticity of inhibitory inputs to VTA GABA neurons. Using whole cell electrophysiology in GAD67 GFP mice, we observed that these VTA GABA cells can experience either long-term potentiation (LTP) or long-term depression (LTD) in response to a 5 Hz stimulus. While neither the LTP nor LTD appear to be mediated by the cannabinoid-1 receptor (CB1), the nitric oxide synthase (NOS) pathway, or the dopamine-2 (D2) receptor, the LTP is blocked by APV, an NMDA receptor antagonist, and the LTD is blocked by CGP 54626, an antagonist of the GABAB receptor. Additionally, µ-opioid and adenosine-1 receptors modulated plasticity at this synapse, but chronic morphine administration (10mg/kg) did not block the observed LTP or LTD. Furthermore, we used an optogenetic approach in VGAT-Cre mice to target inhibitory inputs from the lateral hypothalamus (LH) to the VTA. An optical stimulus (5 Hz) caused these inputs to depress, which has not been previously described and may be behaviorally important in reward processing. These novel findings increase our understanding of VTA neural circuitry, ultimately increasing our capacity to better comprehend and treat the pathology of addiction. Additionally, changes in synaptic strength in hippocampal CA1 pyramidal cells are thought to be responsible for the acquisition and retention of short-term memory. Feedforward stratum radiatum interneurons of many subtypes experience LTD, short-term depression (STD), or lack of plasticity, but it is not known whether plasticity correlates with specific interneuron subtypes. Using whole cell electrophysiology and qPCR, we characterized the plasticity expressed by hippocampal interneurons in correlation with their mRNA expression patterns to determine cell subtype. We also assessed the expression of endocannabinoid (eCB) biosynthetic enzymes as well as metabotropic glutamate receptor subunits known to mediate plasticity. Cells exhibiting LTD tended to express mRNA for at least one of the eCB biosynthetic enzymes and the metabotropic glutamate receptor subunit mGluR5. mGluR5 was not expressed by cells exhibiting STD or no plasticity. Cells that exhibited short-term depression tended to express mRNA for at least one of the eCB biosynthetic enzymes, but not mGluR5. This suggests that stratum radiatum interneuron plasticity can be predicted based on mGluR expression, and that these different types of plasticity may have some importance in hippocampal function.

We have recently established that aberrant alkylacylglycerophosphocholine metabolism results in the increased tissue concentration of platelet activating factors (PAFs) in the temporal cortex of Alzheimer Disease (AD) patients and in TgCRND8 mice over-expressing mutant human amyloid precursor protein. PAF lipids activate a G-protein coupled receptor (PAFR) reported to be expressed by microglia and subsets of neurons in rat. It is not known whether this same expression pattern is recapitulated in mice however, as the expression has only been inferred by use of pharmacological PAFR antagonists, many of which impact on both PAFR-dependent and PAFR-independent signalling pathways. PAFR plays a role in long term potentiation (LTP) induction in rats. PAFR has also been implicated in behavioural indices of spatial learning and memory in rats. Contradictory reports using mice provide ambiguity regarding the role of PAFR in LTP induction in mice. To assess whether PAFR is expressed in murine neurons, I localized PAFR mRNA in wild-type C57BL/6 mice using PAFR KO mice as a negative control. I further showed that the loss of PAFR did not impair learning and memory although this assessment must be considered preliminary as the behavioural test employed was not optimized to detect changes in learning and memory of C57BL/6 mice over time adequately.Finally, I showed that the loss of PAFR in TgCRND8 mouse model of AD had no impact upon Aβ plaque number. My observations suggest that PAFR is restricted to microglial-like cells in mouse hippocampus and as such, it may not play a role in learning and memory.

The brain is one of the most energetically demanding organs within the human body and is cognitively susceptible to energetic deficits such that the rise in obesity, insulin resistance, and Alzheimer’s disease in recent decades pose a substantial threat to cognitive longevity. The therapeutic efficacy of ketones are well-established in epilepsy and are currently being applied to other disease states. Alzheimer’s disease is characterized by impairments in brain glucose uptake and metabolism in regions relevant to learning, memory, and cognition that progress with the disease. While brain glucose uptake is impaired, ketone uptake is unaltered, potentially enabling ketones to fuel the glucose-deficient brain. Using RNA-seq data acquired from multiple publicly available AD databases, we assessed glycolytic and ketolytic gene expression in post-mortem AD and cognitively normal control brains. Gene expression was normalized to brain region – parietal lobe, cerebellum, temporal cortex, frontal lobe, inferior frontal gyrus, parahippocampal gyrus, superior temporal gyrus – and cell type – neurons, astrocytes, oligodendrocytes, and microglia. We report impairments in glycolytic gene expression in regions of the brain relevant to memory and cognition in neurons and oligodendrocytes, but not ketolytic gene expression in neurons. The data are consistent with previous work and support clinical ketone intervention. The cognitive effects of ketogenic diets remain controversial, especially in healthy adults. To elucidate the effects of a ketogenic diet in healthy mice, C57BL6 mice were placed on a ketone-supplemented ketogenic diet for eight weeks. Recognition memory was assessed in a novel object recognition test and hippocampal bioenergetics were measured using high-resolution respirometry, western blot, and biochemical assays. The diet significantly improved recognition memory and enhanced hippocampal mitochondrial efficiency, measured by ATP production per unit of oxygen consumed, suggesting cognitive validity of the diet in middle-age. Long-term potentiation (LTP), the activity-dependent strengthening of synapses, within the hippocampus, is one of the molecular mechanisms of learning and memory formation. LTP of hippocampal Schaffer-collaterals was quantified in young adult C57BL/6 mice with field electrophysiology following ex vivo brain slice incubation with a β-hydroxybutyrate-rich ACSF. Mice were then placed on the ketone-supplemented diet for four weeks. Behavioral spatial memory was measured in the Morris water maze and Schaffer-collateral LTP was assessed with field electrophysiology. No meaningful changes in LTP and behavioral memory were observed with ketone treatment, suggesting ketogenic interventions may be more applicable in aging and pathologies that display cognitive deficits, rather than in healthy young adults. Together, these studies support the exploration of ketogenic interventions as a potential restorative measure in Alzheimer’s disease and preventative measure in aging, which may be impactful facing the rise of obesity and insulin resistance.

Endocannabinoids (eCBs) are small molecules that are capable of modulating synaptic plasticity of both excitatory and inhibitory synapses in the brain. While eCBs bind to transient receptor potential vanilloid 1 (TRPV1) and cannabinoid receptor 1 (CB1) in the central nervous system, we recently identified a form of non-CB1, non-TRPV1 mediated long term depression activated by the eCB anandamide at CA1 hippocampal stratum radiatum interneurons. GPR55, an orphan G-protein receptor, has been identified in the hippocampus and is capable of activation by eCBs, making it a good candidate for mediating this non-CB1, non-TRPV1 form of synaptic plasticity. Here we performed whole-cell patch clamp recordings from CA1 stratum radiatum interneurons in rat brain slices to investigate the effect of GPR55 agonist O-1602 on excitatory synapses. We also performed field recordings from CA1 pyramidal cells in rats and GPR55 knockout mice and littermate controls to investigate the effect of GPR55 agonists O-1602 and lysophosphatidylinositol (LPI) on both basal output and electrically induced long-term depression and long-term potentiation in the hippocampus. Application of O-1602 in rats depressed long-term potentiation in CA1 pyramidal cells, and depressed excitatory glutamatergic transmission onto some interneurons. O-1602 had no effect on long-term depression of CA1 pyramidal cells. GPR55 +/+ mice showed an increase in long-term potentiation in the presence of LPI compared to GPR55-/- littermates. GPR55-/-mice had no change in long-term potentiation when exposed to O-1602, though there was an increase in post-tetanic potentiation with O-1602. In order to examine whether GPR55 has a role in formation of spatial memory, GPR55 -/- mice were compared to littermate controls during a Morris water maze behavioral task, with a reversal task after 7 days of training. GPR55-/-mice did not perform in a different manner on either the training task or the reversal, though there may be a trend of difference in training worth investigating further. This study illustrates a novel pathway for synaptic plasticity modulation through GPR55 in the hippocampus, and may therefore provide valuable insight into both the effects of synthetic and endogenous cannabinoids on the brain and the processes underlying learning and memory.