16p11.2 haploinsufficiency reduces mitochondrial biogenesis in brain endothelial cells and alters brain metabolism in adult mice

Neurovascular abnormalities in mouse models of 16p11.2 deletion autism syndrome are reminiscent of alterations reported in murine models of glucose transporter deficiency, including reduced brain angiogenesis and behavioral alterations. Yet, whether cerebrovascular alterations in 16p11.2^df/+ mice affect brain metabolism is unknown. Here, we report that anesthetized 16p11.2^df/+ mice display elevated brain glucose uptake, a phenomenon recapitulated in mice with endothelial-specific 16p11.2 haplodeficiency. Awake 16p11.2^df/+ mice display attenuated relative fluctuations of extracellular brain glucose following systemic glucose administration. Targeted metabolomics on cerebral cortex extracts reveals enhanced metabolic responses to systemic glucose in 16p11.2^df/+ mice that also display reduced mitochondria number in brain endothelial cells. This is not associated with changes in mitochondria fusion or fission proteins, but 16p11.2^df/+ brain endothelial cells lack the splice variant NT-PGC-1α, suggesting defective mitochondrial biogenesis. We propose that altered brain metabolism in 16p11.2^df/+ mice is compensatory to endothelial dysfunction, shedding light on previously unknown adaptative responses.

Environmental enrichment alters LPS-induced changes in BDNF and PSD-95 expressions during puberty

Puberty is a critical period of cortical reorganization and increased synaptogenesis. Healthy cortical reorganization and synaptic growth require sufficient environmental stimuli and minimalized stress exposure during pubertal development. Exposure to impoverished environments or immune challenges impact cortical reorganization and reduce the expression of proteins associated with neuronal plasticity (BDNF) and synaptogenesis (PSD-95). Environmentally enriched (EE) housing includes improved social-, physical-, and cognitive stimulation. We hypothesized that enriched housing environment would mitigate pubertal stress-induced decreases in BDNF and PSD-95 expressions. Three-week-old male and female CD-1 mice (n = 10 per group) were housed for three weeks in either EE, social or deprived housing conditions. At 6 weeks of age, mice were treated with either lipopolysaccharide (LPS) or saline eight hours prior to tissue collection. Male and female EE mice displayed greater BDNF and PSD-95 expressions in the medial prefrontal cortex and hippocampus compared to socially housed and deprived housed mice. LPS treatment decreased BDNF expression in all the brain regions examined in EE mice, except for the CA3 region of the hippocampus, where EE housing successfully mitigated the pubertal LPS-induced decrease in BDNF expression. Interestingly, LPS-treated mice housed in deprived conditions displayed unexpected increases in BDNF and PSD-95 expressions throughout the medial prefrontal cortex and hippocampus. Both enriched and deprived housing conditions moderate how an immune challenge influences BDNF and PSD-95 expressions in a region-specific manner. These findings also emphasize the vulnerability of brain plasticity during puberty to various environmental factors.

Voluntary Behavior and Training Conditions Modulate in vivo Extracellular Glucose and Lactate in the Mouse Primary Motor Cortex

Learning or performing new behaviors requires significant neuronal signaling and is metabolically demanding. The metabolic cost of performing a behavior is mitigated by exposure and practice which result in diminished signaling and metabolic requirements. We examined the impact of novel and habituated wheel running, as well as effortful behaviors on the modulation of extracellular glucose and lactate using biosensors inserted in the primary motor cortex of mice. We found that motor behaviors produce increases in extracellular lactate and decreases in extracellular glucose in the primary motor cortex. These effects were modulated by experience, novelty and intensity of the behavior. The increase in extracellular lactate appears to be strongly associated with novelty of a behavior as well as the difficulty of performing a behavior. Our observations are consistent with the view that a main function of aerobic glycolysis is not to fuel the current neuronal activity but to sustain new bio-infrastructure as learning changes neural networks, chiefly through the shuttling of glucose derived carbons into the pentose phosphate pathway for the biosynthesis of nucleotides.

Chronic sleep disruption induces depression-like behavior in adolescent male and female mice and sensitization of the hypothalamic-pituitary-adrenal axis in adolescent female mice

Depression is a prevalent mood disorder responsible for reduced quality of life for over 264 million people. Depression commonly develops during adolescence and becomes twice as prevalent in females than in males. However, the mechanisms underlying adolescent depression onset and sex differences in the prevalence rate remain unclear. Adolescent exposure to stress and subsequent sensitization of the hypothalamic-pituitary-adrenal (HPA) axis contributes to mood disorder development, and females are particularly vulnerable to HPA sensitization. Repeated exposure to stressors common to adolescent development, like sleep disruption, could partially be responsible for adolescent female susceptibility to depression. To address this possibility, 80 adolescent and adult CD-1 mice (Male, n = 40; Female, n = 40) were manually sleep disrupted for the first four hours of each rest cycle or allowed normal rest for eight consecutive days. Depression-like behavior was assessed with the forced swim test. 5-HT_1A and glucocorticoid receptor expression and concurrent cellular activation via glucocorticoid receptor/c-Fos colocalization were examined in various brain regions to assess cellular correlates of depression and HPA-axis activation. Both adolescent male and female mice displayed significantly greater depression-like behavior and prelimbic c-Fos expression after chronic sleep disruption than non-sleep disrupted adolescent and sleep disrupted adult counterparts. However, sleep disrupted adolescent females demonstrated greater dorsal raphe 5-HT_1A expression than sleep disrupted adolescent males. Adolescent females and males had decreased medial prefrontal 5-HT_1A expression after chronic sleep disruption, but only adolescent females expressed decreased hippocampal 5-HT_1A expression compared to controls. Chronic sleep disruption significantly increased corticosterone release, glucocorticoid expression in the CA1, and activation of glucocorticoid immunoreactive cells in the prelimbic cortex of adolescent females but not in adolescent males. These findings suggest that chronic sleep disruption during adolescence could give rise to depressive symptoms in male and female adolescents through differing signaling mechanisms.

Brain and muscle adaptation to high-fat diets and exercise: Metabolic transporters, enzymes and substrates in the rat cortex and muscle

There is evidence suggesting that the effects of diet and physical activity on physical and mental well-being are the result of altered metabolic profiles. Though the central and peripheral systems work in tandem, the interactions between peripheral and central changes that lead to these altered states of well-being remains elusive. We measured changes in the metabolic profile of brain (cortex) and muscle (soleus and plantaris) tissue in rats following 5-weeks of treadmill exercise and/or a high-fat diet to evaluate peripheral and central interactions as well as identify any common adaptive mechanisms. To characterize changes in metabolic profiles, we measured relative changes in key metabolic enzymes (COX IV, hexokinase, LDHB, PFK), substrates (BHB, FFA, glucose, lactate, insulin, glycogen, BDNF) and transporters (MCT1, MCT2, MCT4, GLUT1, GLUT3). In the cortex, there was an increase in MCT1 and a decrease in glycogen following the high-fat diet, suggesting an increased reliance on monocarboxylates. Muscle changes were dependent muscle type. Within the plantaris, a high-fat diet increased the oxidative capacity of the muscle likely supported by increased glycolysis, whereas exercise increased the oxidative capacity of the muscle likely supported via increased glycogen synthesis. There was no effect of diet on soleus measurements, but exercise increased its oxidative capacity likely fueled by endogenous and exogenous monocarboxylates. For both the plantaris and soleus, combining exercise training and high-fat diet mediated results, resulting in a middling effect. Together, these results indicate the variable adaptions of two main metabolic pathways: glycolysis and oxidative phosphorylation. The results also suggest a dynamic relationship between the brain and body.

The impact of lactic acid and medium chain triglyceride on blood glucose, lactate and diurnal motor activity: A re-examination of a treatment of major depression using lactic acid

While investigating the effect of alternative energy substrates on extracellular brain glucose or lactate, Béland-Millar (2017) noted a reduction of physical activity after intraperitoneal administration of lactate and ketone bodies. These observations were similar to an older study that examined the impact of drinking a sodium lactate/lactic acid solution before sleep in hospitalized patients with major depression. Patients and control participants self-reported drowsiness, early sleep onset and better overall sleep after consumption. Some patients showed improved mood after several days of treatment. We re-evaluated the effects of the solution used (0.59 g/kg) as well as several smaller doses (0.47, 0.35, 0.24 and 0.12 g/kg) on blood lactate and glucose in CD-1 mice and on sleep onset associated activity reduction. Because of adverse effects with the lactate/lactic acid solution, we also examined the effects of a medium chain triglyceride (MCT) solution (10, 5, 2.5, and 1 ml/kg) on blood lactate and glucose. Oral gavage administration of lactic acid/lactate produced adverse effects particularly for the largest doses. However consumption of 10 and 5 ml/kg volumes of MCT oils significantly increased blood lactate concentration to levels comparable to Lowenbach's solution without piloerection indicative of adverse effects. To evaluate pre-sleep activity reduction produced by lactate, mice were intraperitoneally administered diluted sodium lactate (2.0 g/kg, 1.0 g/kg, 0.5 g/kg, 0.25 g/kg, or saline) for 6 days, 120 min before their sleep period and their running activity was measured. Larger lactate doses reduced pre-sleep running each day up to 60 min post injection. Smaller doses reduced running after a single treatment only. These results suggest that the modulation of blood lactate levels may be useful in treating sleep onset problems associated with depression.

Utility of the Hebb-Williams Maze Paradigm for Translational Research in Fragile X Syndrome: A Direct Comparison of Mice and Humans

To generate meaningful information, translational research must employ paradigms that allow extrapolation from animal models to humans. However, few studies have evaluated translational paradigms on the basis of defined validation criteria. We outline three criteria for validating translational paradigms. We then evaluate the Hebb–Williams maze paradigm (Hebb and Williams, 1946; Rabinovitch and Rosvold, 1951) on the basis of these criteria using Fragile X syndrome (FXS) as model disease. We focused on this paradigm because it allows direct comparison of humans and animals on tasks that are behaviorally equivalent (criterion #1) and because it measures spatial information processing, a cognitive domain for which FXS individuals and mice show impairments as compared to controls (criterion #2). We directly compared the performance of affected humans and mice across different experimental conditions and measures of behavior to identify which conditions produce comparable patterns of results in both species. Species differences were negligible for Mazes 2, 4, and 5 irrespective of the presence of visual cues, suggesting that these mazes could be used to measure spatial learning in both species. With regards to performance on the first trial, which reflects visuo-spatial problem solving, Mazes 5 and 9 without visual cues produced the most consistent results. We conclude that the Hebb–Williams mazes paradigm has the potential to be utilized in translational research to measure comparable cognitive functions in FXS humans and animals (criterion #3).

Fluctuations of extracellular glucose and lactate in the mouse primary visual cortex during visual stimulation

We measured the extracellular glucose and lactate in the primary visual cortex in the CD-1 mouse using electrochemical electrodes. To gain some additional information on brain metabolism, we examined the impact of systemic injections of lactate and fructose on the brain extracellular glucose and lactate changes observed during visual stimulation. We found that simple stimulation using a flashlight produced a decrease in visual cortex extracellular glucose and an increase in extracellular lactate. Similar results were observed following visual stimulation with an animated movie without soundtrack or the presentation of a novel object. Specificity of these observations was confirmed by the absence of extracellular glucose and lactate changes when the mice were presented a second time with the same object. Previous experiments have shown that systemic injections of fructose and lactate lead to an increase in blood lactate but no change in blood glucose while they both increase brain extracellular glucose but they do not increase brain extracellular lactate. When mice were visually stimulated after they had received these injections, we found that lactate, and to a slightly lesser degree fructose, both reduced the amplitude of the changes in extracellular glucose and lactate that accompanied visual stimulation. Thus, neural activation leads to an increase in extracellular lactate and a decrease in extracellular glucose. Novelty, attentional resources and availability of metabolic fuels modulate these fluctuations. The observations are consistent with a modified view of brain metabolism that takes into account the blood and brain glucose availability.

Oligodendrocyte progenitor cells are paired with GABA neurons in the mouse dorsal cortex: Unbiased stereological analysis

Oligodendrocyte progenitor cells (OPC) are glial cells that differentiate into myelinating oligodendrocytes during early stages of post-natal life. However, OPCs persist beyond developmental myelination and represent an important population of cycling cells in the gray and white matter of the adult brain. While adult OPCs form unique territories that are maintained through self-avoidance, some cortical OPCs appear to position their cell body very close to that of a neuron, forming what are known as OPC-neuron pairs. We used unbiased systematic stereological analysis of the NG2-CreER^TM:EYFP reporter mouse to determine that close to 170,000 OPC-neuron pairs can be found in the dorsal portion of the adult neocortex, with approximately 40% of OPCs and 4% of neurons in pairs. Through stereological analysis, we also determined that reference memory training does not change the prevalence of OPC-neuron pairs or the proportion of OPCs and neurons that form them. GABAergic agent administration did not affect the proportion of OPCs and neurons that can be found in pairs. However, the GABA_B-receptor agonist baclofen and the GABA_A receptor antagonist picrotoxin significantly increased the estimated number of pairs when compared to the control group and the GABA_B-receptor antagonist (i.e. saclofen) group. Density of OPC-neuron pairs was increased by the GABA_A receptor antagonist picrotoxin. Finally, histological analysis of OPC-neuron pairs suggested that in the dorsal portion of the cortex, GABAergic interneurons represent the most common neuronal component of the pairs, and that calbindin, calretinin and parvalbumin GABAergic interneurons found in the cortex take part in these pairs. Using previous estimates of the number of GABAergic neurons in the rodent cortex, we estimate that roughly one in four GABAergic neurons are paired with an OPC.

Unbiased stereological analysis of the fate of oligodendrocyte progenitor cells in the adult mouse brain and effect of reference memory training

Oligodendrocyte progenitor cells (OPCs) are glial cells that differentiate into myelinating oligodendrocytes during early stages of post-natal life. However, OPCs persist beyond developmental myelination and represent an important population of cycling cells in the gray and white matter of the adult brain. Here, we used unbiased systematic stereological analysis to determine the total number of OPCs in the neocortex and corpus callosum of the adult mouse. We found that the ratio of OPCs to neurons is of 1:10 in the adult neocortex. Likewise, the ratio of OPCs to oligodendrocytes is of 1:1 in the cortex and 1:7 in the corpus callosum. We also used BrdU labeling and the NG2-CreER™:EYFP reporter mouse to determine the proportion of proliferating adult OPCs and their fate. We show that OPCs continue to differentiate into oligodendrocytes in adulthood, with white matter OPCs being more likely to differentiate into an oligodendrocyte phenotype than gray matter OPCs. The differentiation of OPCs into an oligodendrocyte phenotype can occur either directly from a spontaneous differentiation by an OPC or following OPC cell division. We also provide evidence for the neuronal differentiation of adult OPCs in the cortical gray matter. Although activity-dependent neural network activity has been hypothesized to serve as a modulator of OPC proliferation and differentiation, we found that reference memory training did not affect the proportion of proliferating and differentiated OPCs in the adult mouse brain.

Doublecortin in Oligodendrocyte Precursor Cells in the Adult Mouse Brain

Key Points

Oligodendrocyte precursor cells express doublecortin, a microtubule-associated protein.

Oligodendrocyte precursor cells express doublecortin, but at a lower level of expression than in neuronal precursor.

Doublecortin is not associated with a potential immature neuronal phenotype in Oligodendrocyte precursor cells.

Oligodendrocyte precursor cells (OPC) are glial cells that differentiate into myelinating oligodendrocytes during embryogenesis and early stages of post-natal life. OPCs continue to divide throughout adulthood and some eventually differentiate into oligodendrocytes in response to demyelinating lesions. There is growing evidence that OPCs are also involved in activity-driven de novo myelination of previously unmyelinated axons and myelin remodeling in adulthood. Considering these roles in the adult brain, OPCs are likely mobile cells that can migrate on some distances before they differentiate into myelinating oligodendrocytes. A number of studies have noted that OPCs express doublecortin (DCX), a microtubule-associated protein expressed in neural precursor cells and in migrating immature neurons. Here we describe the distribution of DCX in OPCs. We found that almost all OPCs express DCX, but the level of expression appears to be much lower than what is found in neural precursor. We found that DCX is downregulated when OPCs start expressing mature oligodendrocyte markers and is absent in myelinating oligodendrocytes. DCX does not appear to signal an immature neuronal phenotype in OPCs in the adult mouse brain. Rather, it could be involved either in cell migration, or as a marker of an immature oligodendroglial cell phenotype.

Effects of Systemic Metabolic Fuels on Glucose and Lactate Levels in the Brain Extracellular Compartment of the Mouse

Classic neuroenergetic research has emphasized the role of glucose, its transport and its metabolism in sustaining normal neural function leading to the textbook statement that it is the necessary and sole metabolic fuel of the mammalian brain. New evidence, including the Astrocyte-to-Neuron Lactate Shuttle hypothesis, suggests that the brain can use other metabolic substrates. To further study that possibility, we examined the effect of intraperitoneally administered metabolic fuels (glucose, fructose, lactate, pyruvate, ß-hydroxybutyrate, and galactose), and insulin, on blood, and extracellular brain levels of glucose and lactate in the adult male CD1 mouse. Primary motor cortex extracellular levels of glucose and lactate were monitored in freely moving mice with the use of electrochemical electrodes. Blood concentration of these same metabolites were obtained by tail vein sampling and measured with glucose and lactate meters. Blood and extracellular fluctuations of glucose and lactate were monitored for a 2-h period. We found that the systemic injections of glucose, fructose, lactate, pyruvate, and ß-hydroxybutyrate increased blood lactate levels. Apart for a small transitory rise in brain extracellular lactate levels, the main effect of the systemic injection of glucose, fructose, lactate, pyruvate, and ß-hydroxybutyrate was an increase in brain extracellular glucose levels. Systemic galactose injections produced a small rise in blood glucose and lactate but almost no change in brain extracellular lactate and glucose. Systemic insulin injections led to a decrease in blood glucose and a small rise in blood lactate; however brain extracellular glucose and lactate monotonically decreased at the same rate. Our results support the concept that the brain is able to use alternative fuels and the current experiments suggest some of the mechanisms involved.

A simple histological technique to improve immunostaining when using DNA denaturation for BrdU labelling

The typical immunohistochemistry technique used to reveal 5-bromo-2'-deoxyuridine (BrdU) incorporation requires denaturation of the DNA by heat and acid to permeabilize the cell nucleus. This treatment can damage tissue and reduce the antigenicity of several proteins, which then leads to weak immunostaining and/or false negatives. We show that an overnight post-fixation step following immunohistochemistry for antigens of interest protects immunostaining during the acid/heat denaturation treatment for subsequent BrdU staining. We used this technique to study the differentiation of recently divided oligodendrocyte progenitor cells in NG2CreER:EYFP reporter mice. We used a GFP anti-EYFP antibody to maximize visualization of the EYFP-containing oligodendrocyte progenitor cells, Olig1, and GST-pi to confirm the cell phenotype. Immunostaining for GFP, Olig1, and GST-pi is reduced by DNA denaturation. We found that incorporating a post-fixation step after double immunostaining for GFP/Olig1 and GFP/GST-pi prior to DNA denaturation prevented the fading and false negatives associated with this treatment. This simple addition to BrdU immunohistochemistry protocols extends the range of proteins that can be detected in combination with BrdU, along with the number of antibodies that can be used successfully in the study of cell proliferation.

Translating the impact of exercise on cognition: methodological issues in animal research

Physical exercise and fitness have been proposed as potential factors that promote healthy cognitive aging. Some of the support for this hypothesis has come from animal research. Animal studies are also used to propose the physiological mechanisms underlying the cognitive performance improvement associated with exercise. In the present review and meta-analysis, we discuss several methodological problems that limit the contribution of animal studies to the understanding of the putative effects of exercise on cognitive aging. We suggest that the most likely measure to equate exercise intensity in rodent and humans may be oxygen consumption (VO2) because observed values are surprisingly similar in young and older rodents and humans. For practical reasons, several animal studies use young rodents kept in social isolation. We show that social isolation is associated with an enhanced impact of exercise on cognitive performance but not on some physiological measures thought to mediate the effect of exercise. Surprisingly, two months or more of exercise intervention appeared to be ineffective to promote cognitive performance compared to shorter durations. We argue that impact of exercise in socially isolated animals is explained by an alleviation of environmental impoverishment as much as an effect of physical exercise. It is possible that the introduction of exercise in rodents is partly mediated by environmental changes. It may explain why larger effects are observed for the shorter durations of exercise while much smaller effects are found after longer periods of exercise.

From precursors to myelinating oligodendrocytes: contribution of intrinsic and extrinsic factors to white matter plasticity in the adult brain

Oligodendrocyte precursor cells (OPC) are glial cells that metamorphose into myelinating oligodendrocytes during embryogenesis and early stages of post-natal life. OPCs continue to divide throughout adulthood and some eventually differentiate into oligodendrocytes in response to demyelinating lesions. There is growing evidence that OPCs are also involved in activity-driven de novo myelination of previously unmyelinated axons and myelin remodeling in adulthood. In this review, we summarize the interwoven factors and cascades that promote the activation, recruitment and differentiation of OPCs into myelinating oligodendrocytes in the adult brain based mostly on results found in the study of demyelinating diseases. The goal of the review was to draw a complete picture of the transformation of OPCs into mature oligodendrocytes to facilitate the study of this transformation in both the normal and diseased adult brain.

2-Methyl-6-(phenylethynyl) pyridine (MPEP) reverses maze learning and PSD-95 deficits in Fmr1 knock-out mice

Fragile X Syndrome (FXS) is caused by the lack of expression of the fragile X mental retardation protein (FMRP), which results in intellectual disability and other debilitating symptoms including impairment of visual-spatial functioning. FXS is the only single-gene disorder that is highly co-morbid with autism spectrum disorder and can therefore provide insight into its pathophysiology. Lack of FMRP results in altered group I metabotropic glutamate receptor (mGluR) signaling, which is a target for putative treatments. The Hebb-Williams (H-W) mazes are a set of increasingly complex spatial navigation problems that depend on intact hippocampal and thus mGluR-5 functioning. In the present investigation, we examined whether an antagonist of mGluR-5 would reverse previously described behavioral deficits in fragile X mental retardation 1 knock-out (Fmr1 KO) mice. Mice were trained on a subset of the H-W mazes and then treated with either 20 mg/kg of an mGluR-5 antagonist, 2-Methyl-6-(phenylethynyl) pyridine (MPEP; n = 11) or an equivalent dose of saline (n = 11) prior to running test mazes. Latency and errors were dependent variables recorded during the test phase. Immediately after completing each test, marble-burying behavior was assessed, which confirmed that the drug treatment was pharmacologically active during maze learning. Although latency was not statistically different between the groups, MPEP treated Fmr1 KO mice made significantly fewer errors on mazes deemed more difficult suggesting a reversal of the behavioral deficit. MPEP treated mice were also less perseverative and impulsive when navigating mazes. Furthermore, MPEP treatment reversed post-synaptic density-95 (PSD-95) protein deficits in Fmr1 KO treated mice, whereas levels of a control protein (β-tubulin) remained unchanged. These data further validate MPEP as a potentially beneficial treatment for FXS. Our findings also suggest that adapted H-W mazes may be a useful tool to document alterations in behavioral functioning following pharmacological intervention in FXS.

Voluntary Out-of-Body Experience: An fMRI Study

The present single-case study examined functional brain imaging patterns in a participant that reported being able, at will, to produce somatosensory sensations that are experienced as her body moving outside the boundaries of her physical body all the while remaining aware of her unmoving physical body. We found that the brain functional changes associated with the reported extra-corporeal experience (ECE) were different than those observed in motor imagery. Activations were mainly left-sided and involved the left supplementary motor area and supramarginal and posterior superior temporal gyri, the last two overlapping with the temporal parietal junction that has been associated with out-of-body experiences. The cerebellum also showed activation that is consistent with the participant’s report of the impression of movement during the ECE. There was also left middle and superior orbital frontal gyri activity, regions often associated with action monitoring. The results suggest that the ECE reported here represents an unusual type of kinesthetic imagery.

Abstract P3-15-09: Impact of granulocyte colony-stimulating factors on febrile neutropenia risk during early-stage breast cancer treatment

Febrile neutropenia (FN) is a significant cause of both mortality and morbidity in patients undergoing adjuvant or neoadjuvant chemotherapy for early-stage breast cancer (ESBC). The risk of FN varies with respect to the type of chemotherapy used and patient-specific characteristics. Granulocyte colony-stimulating factors (G-CSF) are recommended, but not mandatory, as primary prophylaxis for patients at high-risk of FN. This study aimed to evaluate the impact of filgrastim and pegfilgastrim on the incidence of FN during adjuvant and neoadjuvant chemotherapy for ESBC. Risk factors for FN were also assessed.

We conducted a retrospective cohort study that included 297 consecutive patients undergoing adjuvant or neoadjuvant chemotherapy for ESBC between May 2010 and May 2012. Patients on clinical trials were excluded. 173 patients (58%) received primary G-CSF prophylaxis whereas 124 (42%) did not. In patients receiving G-CSF prophylaxis, filgrastim was more commonly prescribed (59.9%), due to reimbursement reasons in Quebec. In total, 38 patients (12.8%) manifested at least one episode of FN. The incidence of FN was significantly reduced in patients receiving primary prophylaxis with G-CSF (p = 0.012).

The most commonly prescribed chemotherapy protocols were FEC-D (5-Fluorouracil, epirubicin, cyclophosphamide followed by docetaxel), AC-T (Adriamycin, cyclophosphamide followed by paclitaxel), and TC (docetaxel and cyclophosphamide). The use of G-CSF as primary prophylaxis was associated with a decrease in FN incidence in patients receiving FEC-D and TC.

Table 1 Incidence of febrile neutropenia in early-stage breast cancer chemotherapy G-CSF primary prophylaxis N = 173Absence of G-CSF prophylaxis N = 124  N (%)N (%) Febrile neutropenia (all chemotherapy)15 (9)23 (19)p = 0.012*TC4/51 (8)5/11 (45)p = 0.01*FEC-D6/59 (10)8/27 (30)p = 0.023*AC-T3/31 (10)8/63 (13)p = 0.668* denotes statistical significance at p < 0.05

One death occurred in a patient receiving FEC-D who had not received prophylaxis. There was no significant difference in the dosing of filgrastim between patients with FN (mean dose received = 5.289 mcg/kg) and those without FN (mean = 5.167mcg/kg) (p = 0.742). Furthermore, previously described risk factors for FN such as age, comorbidities and decreased baseline albumin were not associated with an increased of FN in our study.

Although this was a retrospective study with inherent limitations, our cohort included, to our knowledge, the largest number of patients in a study of G-CSF use in ESBC. We found a statistically significant reduction of FN in patients receiving primary G-CSF prophylaxis. Primary prophylaxis should be routinely offered to patients undergoing chemotherapy for ESBC and in particular, to those receiving docetaxel-containing regimens.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-15-09.

Older people's attitudes toward interactive voice response systems

BACKGROUND

Interactive voice response (IVR) systems are computer programs that interact with people to provide a number of services from business to healthcare. The healthcare applications are particularly relevant to older adults because they are important consumers of medical services. However, research has found that older adults can experience significant difficulties with IVR and have more negative attitudes toward the technology.

SUBJECTS AND METHODS

Seniors' attitudes appear to be related to their most recent experiences with IVR systems. The objective of this study was to examine attitudes toward four commercial or governmental IVR systems and how these attitudes relate to participants' ability to interact with the technology in a sample of 185 community-dwelling older (>65-year-old) adults. We also examined the effects of several demographic factors on both success and attitudes toward automated systems.

RESULTS

We found a significant positive correlation between IVR success and attitudes toward IVR. However, a large subset of our sample gave high ratings despite experiencing significant difficulties with the systems. These participants tended to have lower full scale IQ. No gender differences emerged in terms of attitudes and ability to interact with IVR systems.

CONCLUSIONS

Results also indicated that older adults in our sample viewed the IVR interaction as particularly demanding on attention and concentration abilities.

Administration of neuropsychological tests using interactive voice response technology in the elderly: validation and limitations

Interactive voice response (IVR) systems are computer programs, which interact with people to provide a number of services from business to health care. We examined the ability of an IVR system to administer and score a verbal fluency task (fruits) and the digit span forward and backward in 158 community dwelling people aged between 65 and 92 years of age (full scale IQ of 68–134). Only six participants could not complete all tasks mostly due to early technical problems in the study. Participants were also administered the Wechsler Intelligence Scale fourth edition (WAIS-IV) and Wechsler Memory Scale fourth edition subtests. The IVR system correctly recognized 90% of the fruits in the verbal fluency task and 93–95% of the number sequences in the digit span. The IVR system typically underestimated the performance of participants because of voice recognition errors. In the digit span, these errors led to the erroneous discontinuation of the test: however the correlation between IVR scoring and clinical scoring was still high (93–95%). The correlation between the IVR verbal fluency and the WAIS-IV Similarities subtest was 0.31. The correlation between the IVR digit span forward and backward and the in-person administration was 0.46. We discuss how valid and useful IVR systems are for neuropsychological testing in the elderly.

Confirmatory Factor Analysis of the WAIS-IV and WMS-IV in Older Adults

New editions of the Wechsler Adult Intelligence and Memory scales are now available. Yet, given the significant changes in these new releases and the skepticism that has met them, independent evidence on their psychometric properties is much needed but currently lacking. We administered the WAIS-IV and the Older Adult version of the WMS-IV to 145 older adults. We examined how closely our data matched the normative sample by comparing our scaled scores with those of the publisher and by evaluating interrelations among subtests using confirmatory factor analysis. Not surprisingly, scaled scores from our sample were somewhat higher than those from the normative sample on some tests. Factor analysis on our sample provided support for a higher-order model of the WAIS-IV/WMS-IV Older Adults battery combined. In addition, allowing some subtests to load on more than one factor significantly improved model fit. The best fitting model for our sample was also the best for the normative sample. Overall, the data suggest that the factor analysis models generated from the normative samples for the new WAIS-IV and WMS-IV are reliable.

Plastic changes in the astrocyte GLUT1 glucose transporter and beta-tubulin microtubule protein following voluntary exercise in mice

Glucose, the predominant energy substrate of the central and peripheral nervous system, is delivered to neurons via a family of facilitative glucose transporters (GLUT). The majority of glucose is transported to the brain via glucose transporter 1 (GLUT1) located on epithelial cells of capillaries and on the astrocytes that wrap around them. Changes in neuronal activity are linked to increases in glucose demand and local cerebral glucose utilization. Current research has indicated a corresponding change in GLUT1 expression in response to increased metabolic demand in operant tasks. The purpose of this study was to examine, in the mouse brain, the effects of neuronal activation induced by voluntary running on the plastic expression of vascular GLUT1 and neuronal plasticity as measured by the microtubule protein beta-tubulin III (Tuj). The results showed that access to a running wheel for 48h induced plastic changes in the expression of GLUT1, Tuj and GLUT1-associated estimate of astrocyte vascular endfeet in motor regions. The results tend to support the plastic association between mechanisms of energy supply and plastic reorganization of neurons following a new training experience.

Predictors of successful communication with interactive voice response systems in older people

OBJECTIVES

Interactive voice response (IVR) systems are computer programs that can interact with people to provide a number of services from business to health care. However, surveys examining people's attitudes toward these systems have consistently found that people in general and older people in particular strongly dislike these systems. We wanted to determine the memory and cognitive abilities that predict successful IVR interactions for older people.

METHOD

We compared the performance of 185 older adults (aged 65 and older) on normed cognitive tests (the Wechsler Adult Intelligence Scale fourth edition and the Wechsler Memory Scale fourth edition) with their performance on 4 real-life IVR systems that included fact-finding at governmental agencies and plane ticket reservation.

RESULTS

The results indicated that adults aged 65 and older experience significant difficulties in interacting with IVR systems. A significant number of people (20.5%) could not complete any of the tasks. Participants who could not complete any task were older and had the lowest full-scale IQ. However, there was little difference between the age of participants who completed 1, 2, 3, or 4 tasks. Rather, auditory memory and working memory were the best overall predictors for success in IVR tasks.

DISCUSSION

The impact of poorer auditory memory and working memory is compounded by programming practices that increase the demand on these abilities and create unnecessary difficulties. Successful use of IVR systems could eventually complement in person health services.

Snf2l regulates Foxg1-dependent progenitor cell expansion in the developing brain

Balancing progenitor cell self-renewal and differentiation is essential for brain development and is regulated by the activity of chromatin remodeling complexes. Nevertheless, linking chromatin changes to specific pathways that control cortical histogenesis remains a challenge. Here we identify a genetic interaction between the chromatin remodeler Snf2l and Foxg1, a key regulator of neurogenesis. Snf2l mutant mice exhibit forebrain hypercellularity arising from increased Foxg1 expression, increased progenitor cell expansion, and delayed differentiation. We demonstrate that Snf2l binds to the Foxg1 locus at midneurogenesis and that the phenotype is rescued by reducing Foxg1 dosage, thus revealing that Snf2l and Foxg1 function antagonistically to regulate brain size.

Licorice and its potential beneficial effects in common oro-dental diseases

Licorice, the name given to the roots and stolons of Glycyrrhiza species, has been used since ancient times as a traditional herbal remedy. Licorice contains several classes of secondary metabolites with which numerous human health benefits have been associated. Recent research suggests that licorice and its bioactive ingredients such as glycyrrhizin, glabridin, licochalcone A, licoricidin, and licorisoflavan A possess potential beneficial effects in oral diseases. This paper reviews the effects of licorice and licorice constituents on both the oral microbial pathogens and the host immune response involved in common ora-dental diseases (dental caries, periodontitis, candidiasis, and recurrent aphthous ulcers). It also summarizes results of clinical trials that investigated the potential beneficial effects of licorice and its constituents for preventing/treating oro-dental diseases.

Improving older adults' experience with interactive voice response systems

BACKGROUND

Interactive voice response (IVR) systems use computer-based voice recognition and software algorithms to conduct human/computer interactions. In recent years, there has been a proliferation of IVR applications in business and healthcare. The available evidence suggests that older people have negative attitudes towards IVR and experience significant difficulties using these systems.

OBJECTIVE

The goal of this project was to identify areas of difficulties in IVR use by older people and propose strategies for improvement.

MATERIALS AND METHODS

During two focus groups, we examined older people's perceptions of IVR systems and the most common difficulties experienced by seniors in interacting with these systems. We also recorded their suggestions for improvement of IVR.

RESULTS

Frequency and chi square analyses were performed on the focus groups data. Some of the difficulties reported by participants in this study were congruent with previous findings, but we also uncovered some additional problems, such as frustration for not being able to reach an operator, being asked to wait too long on hold, being unable to recover from mistakes, and an absence of shortcuts in the systems. In addition, significant number of participants indicated that they prefer a system that adjusts to them automatically as opposed to a system that allows for adjustment.

CONCLUSION

Generally, our findings suggest that the poor acceptability of IVR systems by older people could be improved by designing IVR algorithms that detect difficulties during an ongoing IVR exchange and direct people to different algorithms adapted for each person.

Measuring the impact of exercise on cognitive aging: methodological issues

Physical exercise and fitness have been proposed as potential factors that promote healthy cognitive aging. Support for this hypothesis has come from cross sectional, longitudinal, and intervention studies. In the present review, we discuss several methodological problems that limit the conclusions of many studies. The lack of consensus on how to retrospectively measure exercise intensity is a major difficulty for all studies that attempt to estimate lifelong impact of exercise on cognitive performance in older adults. Intervention studies have a much better capacity to establish causality, but still suffer from difficulties arising from inadequate control groups and the choice and modality of administration of cognitive measures. We argue that, while the association between exercise and preserved cognition during aging is clearly demonstrated, the specific hypothesis that physical exercise is a cause of healthy cognitive aging has yet to be validated. A number of factors could mediate the exercise-cognition association, including depression, and social or cognitive stimulation. The complex interactions among these 3 factors and the potential impact of exercise on cognition remain to be systematically studied. At this time, the best prescription for lifestyle interventions for healthy cognitive aging would be sustained physical, social, and mental activities. What remains unknown is which type of activity might be most useful, and whether everyone benefits similarly from the same interventions.

Comparing the Rey and Taylor Complex Figures: A Test-Retest Study in Young and Older Adults

The Rey and Taylor figures, two visual perception and memory tests, are not equivalent in terms of their difficulty. The purpose of this study was to examine factors such as age, gender, order of administration, copy time, and copy score that could account for the variability in recall performance. Copy score was shown to be the best overall predictor of recall. Younger participants recalled more units than older participants on both complex figures. Furthermore, older participants appeared to benefit more from the presentation of the Taylor figure first compared to when they were presented with the Rey figure first. The present findings reveal the importance of test order and provide equations that can be used to facilitate the comparison of scores derived from the two figures in test-retest situations.

Explicit and Objective Scoring Criteria for the Taylor Complex Figure Test

The Rey and Taylor figures are two constructional and visual memory tests used interchangeably. The purpose of this study was to develop a scoring system for the Taylor figure based on the explicit guidelines established by Meyers and Meyers (1995) for the Rey figure. Younger (n = 97; mean age = 21 years) and older (n = 61; mean age = 72 years) participants' performance on the Taylor figure was scored according to the proposed scoring system and the original scoring system devised by Taylor (1989). Both scoring systems yielded comparable scores on the Taylor figure as well as comparable patterns of validity and good interrater reliabilities (0.85-0.98). Although the present system does not further improve scoring reliability, it renders both tests similar in methodology and simplifies training to evaluate the two figures. The present study also reveals the limitations of the use of the Taylor and the Rey in test-retest situations but suggests that administering the Taylor first would improve the comparability of the two figures in a test-retest situation.

Effect of age and glucoregulation on cognitive performance

Type 2 diabetes has been associated with a number of physiological consequences including neuropathy, retinopathy, and incidence of vascular disease. Less is known about the effect on cognition of prediabetes, a period when glucose regulation is abnormal. It is not clear which aspect of impaired glucoregulation is most predictive of cognitive deterioration. In the present experiment, we measured cognitive function in 93 healthy male and female nondiabetic older participants who ranged in age from 55 to 88 years. Various biological measures were obtained including a glucose tolerance test during which glucose and insulin were measured. Participants were evaluated twice, once after drinking a saccharin solution and on another occasion after drinking a glucose solution (50 g). The analysis of the correlations between the biological measures and the results of the cognitive tasks revealed that evoked glucose measures such as peak glucose and glucose at 1 hour were most often correlated with cognitive performance. We observed that progressively worse glucose regulation predicted poorer performance on measures of working memory and executive function-that is, on the Arithmetic, Digit Span Backward, Letter-Number Sequencing, Spatial Span Forward, Spatial Span Backward (trend), and Modified Brown-Peterson tasks. Although, there was no significant facilitative effect of glucose on cognitive performance, it reduced the association between glucose regulation and cognition, apparently by slightly improving performance. These results suggest that cognitive functions may be impaired before glucoregulatory impairment reaches levels consistent with a type 2 diabetes diagnosis.

A comparative study of the performance of individuals with fragile X syndrome and Fmr1 knockout mice on Hebb-Williams mazes

Fragile X syndrome (FXS) is the most prevalent form of heritable mental retardation. It arises from a mutation in the FMR1 gene on the X chromosome that interferes with expression of fragile X mental retardation protein (FMRP) and leads to a wide range of behavioural and cognitive deficits. Previous studies have shown a deficit in basic visual perceptual processing as well as spatial abilities in FXS. How such a deficit may impact spatial navigation remains unknown. The current study extended previous research by evaluating spatial learning and memory using both virtual and physical versions of Hebb-Williams mazes, which allows for testing of humans and animals under comparable conditions. We compared the performance of individuals affected by FXS to typically developing individuals of equivalent mental age as well as the performance of Fmr1 knockout mice to wild-type control mice on the same maze problems. In human participants, performance of the comparison group improved across trials, showing expected significant decreases in both errors and latency. In contrast, the performance of the fragile X group remained at similar levels across trials. Although wild-type control mice made significantly fewer errors than the Fmr1 knockout mice, latencies were not statistically different between the groups. These findings suggest that affected humans and mice show similar spatial learning deficits attributable to the lack of FMRP. The implications of these data are discussed including the notion that Hebb-Williams mazes may represent a useful tool to examine the impact of pharmacological interventions on mitigating or reversing the symptoms associated with FXS.

Food restriction induces long-lasting recovery of spatial memory deficits following global ischemia in delayed matching and non-matching-to-sample radial arm maze tasks

Food restriction has been shown to be beneficial for a number of brain processes. In the current study, we characterized the impact of food restriction on hippocampal damage 70 days following ischemia. We assessed memory and cognitive flexibility of ad libitum fed (AL) and food-restricted (FR) animals using complex delayed non-matching- and matching-to-sample tasks in the radial arm maze. Our findings demonstrate that food restriction led to significant improvement of ischemia-induced memory impairments. FR ischemic animals rapidly reached comparable performance as both AL and FR sham animals in delayed-non-matching (win-shift) and matching (win-stay) radial arm maze tasks. They also made considerably fewer microchoices in the retention trials than AL ischemic animals. In contrast, AL ischemic rats showed persistent spatial memory impairments in the same paradigms. Assessment of basal and stress-induced corticosterone (CORT) secretion revealed no significant differences in baseline levels in AL and FR rats prior to or following global ischemia. However, FR animals showed a more pronounced attenuation of CORT secretion 45 min following restraint. Both FR and AL ischemic rats had comparable cell loss within CA1 and CA3 subfields of Ammon's horn (CA1 and CA3) at 70 days following reperfusion, although a trend toward increased CA3 cell survival was observed in FR ischemic rats. The functional sparing in the FR ischemic animals in the face of equivalent hippocampal cell loss suggests that food restriction somehow enhanced the efficacy of remaining hippocampal or extrahippocampal neurons following ischemia. In the current study, this phenomenon was not associated with diet- and or ischemia-related alterations of vesicular glutamate transporter 1 expression in various hippocampal regions although lower vesicular GABA transporter immunostaining was present in the CA1 stratum oriens and the CA3 stratum radiatum in FR sham and ischemic rats.

Food restriction attenuates ischemia-induced spatial learning and memory deficits despite extensive CA1 ischemic injury

The purpose of the present study was to examine whether short-term food restriction (40% less food over a 3-month period) can attenuate ischemia-induced CA1 neuronal degeneration, and whether this attenuation translated into improved recovery of functional impairments following global ischemia. There was a significant loss of pyramidal CA1 neurons in ischemic compared to sham-operated rats but no difference between the ad lib and food-restricted ischemic animals. Although the diet did not influence neuronal damage in ischemic animals, the performance of food-restricted ischemic rats in spatial task such as the radial arm maze was significantly better than that of ad lib fed ischemic rats. Food-restricted ischemic rats made equivalent numbers of working memory errors as sham-operated animals and took the same time to complete a standard 8-arm radial arm maze task. They also displayed higher activity level in the open field compared to ad libitum fed ischemic rats, and spent considerably more time in the open arms of the elevated plus maze compared to the other groups, suggesting decreased anxiety in these ischemic rats. The relative sparing of spatial memory performance in food-restricted ischemic animals suggests that food restriction facilitates functional recovery.

Exploratory factor analysis of neuropsychological tests and their relationship to the Brown-Peterson task

The interference condition of the Brown-Peterson task and the auditory consonant trigrams test was designed to evaluate working memory in that it required a division of attentional processes to complete two cognitive tasks. However, the specific cognitive functions contributing to the performance of this interference task have yet to be determined. The objective of this study was to determine what other tasks are comparable to the Brown-Peterson task and conduct an exploratory factor analysis that included the measures from the Brown-Peterson task and other neuropsychological measures. A neuropsychological battery was administered to younger participants (n=107, mean age=20.83) and older participants (n=93, mean age=70.14). Factor analysis yielded a two-factor solution. Performance after the intervening serial subtraction task loaded on an auditory/visual working memory and complex attention factor and had common loadings with working memory subtests of the WAIS-III and the spatial span subtest of the WMS-III. Results suggest that the performance after the intervening serial subtraction task evaluates dual information processing, complex attention, and working memory.

The effects of a high-fat, high-fructose, and combination diet on learning, weight, and glucose regulation in C57BL/6 mice

The objective of the study was to determine the effects of a high-fructose diet, a high-fat diet and a combination high-fructose/high-fat diet on weight gain, blood glucose regulation, and cognitive function in C57BL/6 mice. Thirty-eight male mice aged 7 weeks were placed on one of four different diets for 3 months: standard chow and water (n=8), standard diet and access to a fructose solution as the only intake of water (n=8), high-fat diet and water (n=11), and high-fat diet and fructose solution (n=11). Weights were measured 10 times over a 3-month period. Blood glucose regulation was measured using a glucose tolerance test. Cognitive testing consisted of learning an operant bar-pressing task and was performed in the absence of fructose intake. At the end of the experiment, the density of the fructose-specific glucose transporter GLUT5 was measured in the hippocampus, frontal cortex, sensori-motor cortex and cerebellum. The high-fat and the combined high-fat/high-fructose groups gained significantly more weight than the control group. The high-fat group and combined group had significantly higher levels of blood glucose than the control group. The high-fructose group learned the operant task faster than the control group, but the high-fat/high-fructose group was not different from control indicating that the facilitative effect of prior fructose intake was abolished when a high-fat diet was added. Addition of fructose to the diet did not result in an increase of brain GLUT5 density suggesting that the learning improvement were not dependent on plastic upregulation of GLUT5 fructose transporter. The results show that, contrary to high-fat diets, access to fructose in mice did not lead to increased weight and impaired glucose tolerance. The present experiment confirm the deleterious impact of high-fat diets on glucose regulation and weight but suggest that high-fructose diets, contrary to what has been observed in hamsters, do not have the same effect.

Longitudinal study of the effects of a high-fat diet on glucose regulation, hippocampal function, and cerebral insulin sensitivity in C57BL/6 mice

Although the increasing rate of obesity has stimulated interest in the effects of diet composition on peripheral systems, comparatively little work has been done to examine effects upon the brain. A diet high in fat is one of many factors that can promote obesity, and previous research has shown that such a diet can produce learning and memory impairment in rodents. In the present study, C57BL/6 mice were placed on either a high-fat (45% kcal fat) or regular (5% kcal fat) diet, and examined at different points during the subsequent year. The high-fat diet led to increased weight gain, significant impairment in glucoregulation, and altered insulin-mediated signaling within the hippocampus, an area of the brain believed to be important for the acquisition of memory. Following ten months on either diet, synaptic function in ex vivo hippocampal slices was examined, and neither stimulus-response curves nor electrically induced long-term potentiation were found to be different. As well, performance in the Morris water maze, a hippocampal-dependent test of spatial memory, was not influenced by diet. However, mice consuming a high-fat diet failed to perform an operant bar-pressing task, indicating a significant impairment to procedural learning and consolidation processes. Despite causing broad peripheral changes in C57BL/6 mice, consuming a large proportion of calories from saturated fat had only a limited effect upon learning and memory, which suggests that certain aspects of brain function are selectively vulnerable to the influences of diet.

Cerebral glucose transporters expression and spatial learning in the K-ATP Kir6.2(-/-) knockout mice

K-ATP channels formed of the Sur and Kir subunits are widely distributed in the brain. Sur1-Kir6.2 is the most common combination of K-ATP channel subunits in the brain and Kir6.2 plays an important role in glucose metabolism through pancreatic insulin secretion or hypothalamic glucose sensing. K-ATP channels have also been reported to play a role in memory processing. Therefore, the aim of the present experiment is to assess the gene and protein expression of GLUT1, GLUT3 and GLUT4 in various brain regions of Kir6.2(-/-) K-ATP knockout mice and to test their working memory performance. GLUT4 was measured using two antibodies, one recognizing an intracellular epitope and the other, an extracellular epitope. Relative to their corresponding wild type, semi-quantitative immunohistochemistry showed that GLUT4 protein expression as measured by a GLUT4 antibody recognizing an extracellular epitope was increased in the Kir6.2(-/-) K-ATP mice. However, there was only a small increase in GLUT4 labeling using the GLUT4 antibody recognizing the intracellular epitope. These results suggest a compensatory higher GLUT4 inclusion at the cellular neuronal membrane in the cerebral cortex, hippocampus and cerebellum of the Kir6.2(-/-) K-ATP knockout mice. However, there was no change in GLUT4 gene expression assessed by TaqMan PCR except for a decrease in the cerebellum of these mice. Working memory performance of the Kir6.2(-/-) K-ATP mice was disrupted at age of 12 weeks but not at 5 weeks. The mild glucose intolerance that is observed in the Kir6.2 knockout mice is unlikely to have created the memory deficits observed. Rather, in light of the effects of K-ATP channel modulators on memory, the memory deficits in the Kir6.2(-/-) K-ATP mice are more likely due to the absence of the Kir6.2 and possible disruption of the GLUT4 activity in the brain.

The role of insulin, insulin growth factor, and insulin-degrading enzyme in brain aging and Alzheimer's disease

Most brain insulin comes from the pancreas and is taken up by the brain by what appears to be a receptor-based carrier. Type 2 diabetes animal models associated with insulin resistance show reduced insulin brain uptake and content. Recent data point to changes in the insulin receptor cascade in obesity-related insulin resistance, suggesting that brain insulin receptors also become less sensitive to insulin, which could reduce synaptic plasticity. Insulin transport to the brain is reduced in aging and in some animal models of type 2 diabetes; brain insulin resistance may be present as well. Studies examining the effect of the hyperinsulinic clamp or intranasal insulin on cognitive function have found a small but consistent improvement in memory and changes in brain neuroelectric parameters in evoked brain potentials consistent with improved attention or memory processing. These effects appear to be due to raised brain insulin levels. Peripheral levels of Insulin Growth Factor-I (IGF-I) are associated with glucose regulation and influence glucose disposal. There is some indication that reduced sensitivity to insulin or IGF-I in the brain, as observed in aging, obesity, and diabetes, decreases the clearance of Aβ amyloid. Such a decrease involves the insulin receptor cascade and can also increase amyloid toxicity. Insulin and IGF-I may modulate brain levels of insulin degrading enzyme, which would also lead to an accumulation of Aβ amyloid.

Impact of impaired glucose tolerance and type 2 diabetes on cognitive aging

Type 2 diabetes is becoming increasingly common in most Westernized countries and it now occurs at a younger age. There are pathologies associated with diabetes, mostly systemic ones. However, a growing number of studies is also showing that diabetes is associated with impaired cognitive processes in older adults and hasten the progression to dementia. The most common cognitive deficits are decreases in processing speed and verbal memory; these may extend to other aspects of cognition with increasing age. The link between diabetes and cognitive decline is obscured by depression, hypertension, as well as cardio- and cerebrovascular diseases, all of which occur to varying degrees in diabetic patients. A few studies indicate that controlling blood glucose with anti-diabetic treatments may help prevent the cognitive decline in diabetic patients before they are 70 years old. After that age, diabetes appears to produce faster cognitive decline and may increase the occurrence of pathological changes associated with vascular dementia or Alzheimer's disease.

Longitudinal evaluation of memory performance and peripheral neuropathy in the Ins2C96Y Akita mice

Ins2C96Y Akita mice represent a model of spontaneous early-onset diabetes mellitus, expressing a mutant non-functional isoform of insulin. These mice are characterized by a reduced number of pancreatic beta cells resulting in hypoinsulinemia and hyperglycemia. We obtained longitudinal measures of morning fasting blood glucose levels and gait performance. Sciatic nerve electrophysiology was also performed and the performance of these mice on spatial memory tasks was measured longitudinally. We observed a progressive increase in fasting blood glucose levels that was proportionally associated with increased gait disturbances. Diabetes induced a decrease in the sensory nerve conduction velocity up to the age of 40 weeks. Glucose transporter (GLUT) 3 levels were reduced in the hippocampus of the aged Ins2C96Y Akita mice. However, we failed to detect any significant deficits during reference, reversal or probe tests in the Morris water maze or in a spontaneous alternation task up to the age of 34 weeks old. We found that, up to the age of 34 weeks old, uncontrolled hyperglycemia produced peripheral neuropathy and reduced hippocampal GLUT3 levels in the absence of any effect on spatial memory processing.

Glucose transporter plasticity during memory processing

Various types of learning, including operant conditioning, induce an increase in cellular activation concomitant with an increase in local cerebral glucose utilization (LCGU). This increase is mediated by increased cerebral blood flow or changes in brain capillary density and diameter. Because glucose transporters are ultimately responsible for glucose uptake, we examined their plastic expression in response to cellular activation. In vitro and in vivo studies have demonstrated that cerebral glucose transporter 1 (GLUT1) expression consistently parallels changes in LCGU. The present study is the first to investigate the effect of memory processing on glucose transporters expression. Changes in GLUT expression produced by training in an operant conditioning task were measured in the brain of CD1 mice. Using semi-quantitative immunohistochemistry, Western blot and real time RT-PCR the cerebral GLUT1 and GLUT3 expression was quantified immediately, 220 min and 24 h following training. Relative to sham-trained and naive controls, operant conditioning training induced an immediate increase in GLUT1 immunoreactivity level in the hippocampus CA1 pyramidal cells as well as in the sensorimotor cortex. At longer post-learning delays, GLUT1 immunoreactivity decreased in the sensorimotor cortex and putamen. Parallel to the changes in protein levels, hippocampus GLUT1 mRNA level also increased immediately following learning. No effect of learning was found on hippocampal GLUT3 protein or mRNA expression. Measures of changes in glucose transporters expression present a link between cellular activation and glucose metabolism. The learning-induced localized increases in GLUT1 protein as well as mRNA levels observed in the present study confirm the previous findings that GLUT1 expression is plastic and respond to changes in cellular metabolic demands.

The relationship between impaired glucose tolerance, type 2 diabetes, and cognitive function

The present review integrates findings of published studies that have evaluated the cognitive function of treated and untreated type 2 diabetic patients and provides a detailed overview of the neuropsychological assessments conducted. Cognitive deficits are observed in older people with glucose intolerance or untreated diabetes but these deficits appear to be attenuated by treatments that improve glycemic control. Cognitive decrements in treated type 2 diabetic patients are most consistently observed on measures of verbal memory (35% of the measures) and processing speed (45% of the measures) while preserved function is observed on measures of visuospatial, attention, semantic and language function. Some studies suggest that deficits in cognitive functions are associated with poorer glycemic control. A number of other factors, such as depression, cardiovascular and cerebrovascular disease, increase these deficits. We conclude that, in diabetic patients who achieve and maintain good glycemic control, type 2 diabetes only has a small impact on cognitive functions before the age of 70 years. However, early onset of type 2 diabetes, poor glycemic control and the presence of micro- and macrovascular disease may interact to produce early cognitive deficits. In older adults (70 years and over), diabetes likely interacts with other dementing processes such as vascular disease and Alzheimer's disease to hasten cognitive decline.