Animal model of posterior cingulate cortex hypometabolism implicated in amnestic MCI and AD

Comparison of maternal versus postweaning ingestion of a high fat, high sucrose diet on depression-related behavior, novelty reactivity, and corticosterone levels in young, adult rat offspring

Consumption of a Western-type diet, high in fat and sugar, by mothers as well as maternal weight gain and obesity during gestation and lactation may impact offspring risk for mood and cognitive disorders. The objective of this study was to determine if ingestion of a high fat, high sucrose (HFS) diet by rat dams during gestation and lactation or by their pups after weaning impacted these behaviors and stress responsivity in young, adult offspring. To accomplish this, dams consumed either a 45% fat/high sucrose (HFS) diet or the AIN93G control diet during gestation and lactation. At weaning, pups from dams that consumed the HFS diet were weaned to the control diet. Pups from dams assigned to the control diet were weaned to either the control or HFS diet. Pup behavioral testing began at 10 weeks of age. Pups whose dams consumed the HFS diet during gestation and lactation exhibited increased depression-related behavior and baseline serum corticosterone levels, but no difference in peak levels in response to stress. Male pups of these dams displayed increased working memory during acquisition of the holeboard task and tended to exhibit more anxiety-related behavior in the elevated O-maze test. Regardless of when consumed, the HFS diet increased novelty reactivity in the open field test. These data indicate that diet but not maternal weight gain during gestation impacts offspring behavior and elevates stress hormone levels. Also, regardless of when consumed, the HFS diet increases novelty reactivity, a risk factor for depression and addiction.

Plasma DNA Mediate Autonomic Dysfunctions and White Matter Injuries in Patients with Parkinson's Disease

Background. Cardiovascular autonomic dysfunction is well known in Parkinson's disease (PD) presentation and it produces hypoperfusion of vital organs. The association between cardiovascular autonomic dysfunction and oxidative stress was examined in previous animal models. Oxidative stress and neuroinflammation were thought to have roles in PD pathogenesis. Owing to the relative low intrinsic antioxidative properties, brain white matter (WM) is vulnerable to the oxidative stress. This study is conducted to examine possible relationships by using a hypothesis-driven mediation model. Methods. Twenty-nine patients with PD and 26 healthy controls participated in this study, with complete examinations of cardiac autonomic parameters, plasma DNA level, and WM integrity. A single-level three-variable mediation model was used to investigate the possible relationships. Results. The elevated serum oxidative stress biomarkers include plasma nuclear DNA and mitochondrial DNA, and poorer cardiac autonomic parameters and multiple regional microstructural WM changes are demonstrated. Further mediation analysis shows that plasma nuclear DNA served as the mediators between poorer baroreflex sensitivity and mean diffusivity changes in cingulum. Conclusions. These results provide a possible pathophysiology for how the poor baroreflex sensitivity and higher oxidative stress adversely impacted the WM integrity. This model could provide us with a piece of the puzzle of the entire PD pathogenesis.

Behavioral effects of bovine lactoferrin administration during postnatal development of rats

We tested the hypothesis that rats consuming bovine lactoferrin (bLf) during postnatal development would show better performance of stressful tasks during adolescence. In the first study, we orally administered bLf (750 mg/kg) once daily between postnatal days 16-34. Rats then underwent a battery of behavioral tests: open field (forced exploration of risky environment), light-dark emergence (voluntary exploration of risky environment), baited holeboard (working and reference memory), food neophobia (preference for familiar versus novel food), forced swim (test for antidepressant efficacy), and shuttle-box escape (learning to escape footshock). bLf-supplemented rats showed less exploration of the risky environment, greater preference for the familiar food odor, and faster escape responses. The effect of bLf on forced-swim behavior depended on sex: immobility increased for males and decreased for females. In the next study, we replaced the forced-swim test with an escape-swim test in which rats learned to use a visual cue to locate an escape platform, and we tested the dose response of bLf on this and the shuttle-box escape test, with subjects receiving vehicle or bLf at 500, 1,000, or 2,000 mg/kg. Under this modified testing battery, improvement of escape from footshock was not observed at any dose. However, males, but not females, showed a significant dose-dependent effect of bLf on acquisition of the water-escape task. On average, males receiving a higher dose mastered the task 20-25 % sooner than rats receiving a lower dose or vehicle. These results offer preliminary evidence that bLf supplementation during development can improve subsequent cognitive performance during stress.

Amyloid-β load predicts medial temporal lobe dysfunction in Alzheimer dementia

Amyloid-β (Aβ) deposition is a pathologic hallmark of Alzheimer disease (AD). Although the typical spatial distribution pattern of Aβ deposition in early AD mainly involves regions distant from the hippocampus, the predominant clinical feature is impairment of hippocampus-dependent memory. We aimed at elucidating the relationship between neocortical Aβ load, regional neuronal function, and memory impairment.

METHODS

Thirty patients with early AD underwent combined (11)C-Pittsburgh compound B ((11)C-PIB) and (18)F-FDG PET and memory assessments. Composite measures of hemispheric Aβ load were calculated by volume-weighted mean values of neocortical (11)C-PIB binding. Voxelwise (18)F-FDG uptake was used as a measure of regional glucose metabolism reflecting neuronal activity. We investigated the relationship between left- and right-hemispheric Aβ load and regional glucose metabolism (voxelwise analyses). In addition, we assessed the correlations of hemispheric Aβ load (region-of-interest-based analyses) and regional glucose metabolism (voxelwise analysis) with memory performance. Analyses were corrected for age and sex.

RESULTS

Higher Aβ load in the left hemisphere was associated with reduced glucose metabolism of the left medial temporal lobe (MTL; r(2) = 0.38) and correlated with worse wordlist recall (r = -0.37; partial correlation controlled for sex and age). Furthermore, wordlist recall correlated with regional glucose metabolism in the bilateral MTL and precuneus-posterior cingulate cortex and right lingual gyrus (r(2) = 0.24).

CONCLUSION

We demonstrated an association between the left-hemispheric Aβ load and impairment of the left MTL in AD at 2 different levels: regional hypometabolism and verbal memory. This correlation suggests that neocortical amyloid deposition is connected to or even drives neuronal dysfunction and neurodegeneration of the MTL, which is associated with impaired episodic memory processing as a clinical core symptom of AD.

Neurometabolic mechanisms for memory enhancement and neuroprotection of methylene blue

This paper provides the first review of the memory-enhancing and neuroprotective metabolic mechanisms of action of methylene blue in vivo. These mechanisms have important implications as a new neurobiological approach to improve normal memory and to treat memory impairment and neurodegeneration associated with mitochondrial dysfunction. Methylene blue's action is unique because its neurobiological effects are not determined by regular drug-receptor interactions or drug-response paradigms. Methylene blue shows a hormetic dose-response, with opposite effects at low and high doses. At low doses, methylene blue is an electron cycler in the mitochondrial electron transport chain, with unparalleled antioxidant and cell respiration-enhancing properties that affect the function of the nervous system in a versatile manner. A major role of the respiratory enzyme cytochrome oxidase on the memory-enhancing effects of methylene blue is supported by available data. The memory-enhancing effects have been associated with improvement of memory consolidation in a network-specific and use-dependent fashion. In addition, low doses of methylene blue have also been used for neuroprotection against mitochondrial dysfunction in humans and experimental models of disease. The unique auto-oxidizing property of methylene blue and its pleiotropic effects on a number of tissue oxidases explain its potent neuroprotective effects at low doses. The evidence reviewed supports a mechanistic role of low-dose methylene blue as a promising and safe intervention for improving memory and for the treatment of acute and chronic conditions characterized by increased oxidative stress, neurodegeneration and memory impairment.

Diffusion tensor imaging of incentive effects in prospective memory after pediatric traumatic brain injury

Few studies exist investigating the brain-behavior relations of event-based prospective memory (EB-PM) impairments following traumatic brain injury (TBI). To address this, children with moderate-to-severe TBI performed an EB-PM test with two motivational enhancement conditions and underwent concurrent diffusion tensor imaging (DTI) at 3 months post-injury. Children with orthopedic injuries (OI; n=37) or moderate-to-severe TBI (n=40) were contrasted. Significant group differences were found for fractional anisotropy (FA) and apparent diffusion coefficient for orbitofrontal white matter (WM), cingulum bundles, and uncinate fasciculi. The FA of these WM structures in children with TBI significantly correlated with EB-PM performance in the high, but not the low motivation condition. Regression analyses within the TBI group indicated that the FA of the left cingulum bundle (p=0.003), left orbitofrontal WM (p<0.02), and left (p<0.02) and right (p<0.008) uncinate fasciculi significantly predicted EB-PM performance in the high motivation condition. We infer that the cingulum bundles, orbitofrontal WM, and uncinate fasciculi are important WM structures mediating motivation-based EB-PM responses following moderate-to-severe TBI in children.

Beneficial network effects of methylene blue in an amnestic model

Posterior cingulate/retrosplenial cortex (PCC) hypometabolism is a common feature in amnestic mild cognitive impairment and Alzheimer's disease. In rats, PCC hypometabolism induced by mitochondrial dysfunction induces oxidative damage, neurodegeneration and memory deficits. USP methylene blue (MB) is a diaminophenothiazine drug with antioxidant and metabolic-enhancing properties. In rats, MB facilitates memory and prevents neurodegeneration induced by mitochondrial dysfunction. This study tested the memory-enhancing properties of systemic MB in rats that received an infusion of sodium azide, a cytochrome oxidase inhibitor, directly into the PCC. Lesion volumes were estimated with unbiased stereology. MB's network-level mechanism of action was analyzed using graph theory and structural equation modeling based on cytochrome oxidase histochemistry-derived metabolic mapping data. Sodium azide infusions induced PCC hypometabolism and impaired visuospatial memory in a holeboard food-search task. Isolated PCC cytochrome oxidase inhibition disrupted the cingulo-thalamo-hippocampal effective connectivity, decreased the PCC functional networks and created functional redundancy within the thalamus. An intraperitoneal dose of 4 mg/kg MB prevented the memory impairment, reduced the PCC metabolic lesion volume and partially restored the cingulo-thalamo-hippocampal network effects. The effects of MB were dependent upon the local sub-network necessary for memory retrieval. The data support that MB's metabolic-enhancing effects are contingent upon the neural context, and that MB is able to boost coherent and orchestrated adaptations in response to physical alterations to the network involved in visuospatial memory. These results implicate MB as a candidate intervention to improve memory. Because of its neuroprotective properties, MB may have disease-modifying effects in amnestic conditions associated with hypometabolism.

The depressive phenotype induced in adult female rats by adolescent exposure to THC is associated with cognitive impairment and altered neuroplasticity in the prefrontal cortex

We recently demonstrated that Delta(9)-tetrahydrocannabinol (THC) chronic administration in female adolescent rats induces alterations in the emotional circuit ending in depressive-like behavior in adulthood. Since cognitive dysfunction is a major component of depression, we assessed in these animals at adulthood different forms of memory. Adolescent female rats were treated with THC or its vehicle from 35 to 45 post-natal days (PND) and left undisturbed until their adulthood (75 PND) when aversive and spatial memory was assessed using the passive avoidance and radial maze tasks. No alteration was found in aversive memory, but in the radial maze THC pre-treated animals exhibited a worse performance than vehicles, suggesting a deficit in spatial working memory. To correlate memory impairment to altered neuroplasticity, level of marker proteins was investigated in the hippocampus and prefrontal cortex, the most relevant areas for learning and memory. A significant decrease in synaptophysin and PSD95 proteins was found in the prefrontal cortex of THC pre-treated rats, with no alterations in the hippocampus. Finally, proteomic analysis of the synapses in the prefrontal cortex revealed the presence of less active synapses characterized by reduced ability in maintaining normal synaptic efficiency. This picture demonstrates the presence of cognitive impairment in THC-induced depressive phenotype.