Differential Influence of Amyloid-β on the Kinetics of Dopamine Release in the Dorsal and Ventral Striatum of Rats

Dopaminergic dysfunction is a part of Alzheimer's disease pathology. The brain accumulation of amyloid-β of toxic form is a key link of the pathology, which, according to the literature, is also true for dopaminergic dysfunction. An increase in the amyloid-β level in the brain changes the maximum of the evoked dopamine release in the dorsal and ventral parts of the striatum of the experimental animals. Theoretically, this may be due to the change in the intensity of dopamine release from the nerve terminals or its reuptake. However, it has not been studied. To fill this gap, we examined the amyloid-β induced changes in the kinetics of the evoked dopamine release in the dorsal striatum and the nucleus accumbens core and shell. Amyloid-β solution (fragments 25-35) was injected into the ventricular system of the anesthetized male Wistar rats. Before and after injection, electrically evoked dopamine kinetics was registered with fast-scan cyclic voltammetry. The results had shown that the amount of dopamine release decreases in the dorsal striatum and increases in the nucleus accumbens shell. No changes were found in the intensity of dopamine reuptake.

Losartan Improves Memory, Neurogenesis and Cell Motility in Transgenic Alzheimer's Mice

Angiotensin receptor blockers (ARBs) have demonstrated multiple neuroprotective benefits in Alzheimer’s disease (AD) models. However, their beneficial effects on memory deficits, cholinergic activity, neurogenesis and Amyloid beta (Aβ) clearance reveal significant interstudy variability. The delivery route can impact not only delivery but also targeting and therapeutic efficacy of ARBs. Our previous findings on the beneficial effects of intranasally delivered losartan in the APP/PS1 model of AD prompted us to explore the influence of the delivery route by employing here the systemic administration of losartan. Consistent with our previous results with intranasal losartan, repeated intraperitoneal administration (10 mg/kg) resulted in a remarkable decrease in Aβ plaques and soluble Aβ42, as well as inflammatory cytokines (IL-2, IL-6 and TNFα). The Aβ reduction can be ascribed to its facilitated degradation by neprilysin and diminished generation by BACE1. Losartan increased neurogenesis in vivo and in vitro and improved migratory properties of astrocytes isolated from adult transgenic AD mice. In summary, this data together with our previous results suggest therapeutic features of losartan which are independent of delivery route. The improvement of cell motility of Aβ-affected astrocytes by losartan deserves further in vivo investigation, which may lead to new strategies for AD treatment.

ATP-sensitive potassium-channel inhibitor glibenclamide attenuates HPA axis hyperactivity, depression- and anxiety-related symptoms in a rat model of Alzheimer's disease

Affective disorders including depression and anxiety are among the most prevalent behavioral abnormalities in patients with Alzheimer's disease (AD), which affect the quality of life and progression of the disease. Dysregulation of the hypothalamic-pituitary-adrenal-(HPA) axis has been reported in affective disorders and AD. Recent studies revealed that current antidepressant drugs are not completely effective for treating anxiety- and depression-related disorders in people with dementia. ATP-sensitive-potassium-(K_ATP) channels are well-known to be involved in AD pathophysiology, HPA axis function and the pathogenesis of depression and anxiety-related behaviors. Thus, targeting of K_ATP channel may be a potential therapeutic strategy in AD. Hence, we investigated the effects of intracerebroventricular injection of Aβ25-35 alone or in combination with glibenclamide, K_ATP channel inhibitor on depression- and anxiety-related behaviors as well as HPA axis response to stress in rats. To do this, non-Aβ25-35- and Aβ25-35-treated rats were orally treated with glibenclamide, then the behavioral consequences were assessed using sucrose preference, forced swim, light-dark box and plus maze tests. Stress-induced corticosterone levels following forced swim and plus maze tests were also evaluated as indicative of abnormal HPA-axis-function. Aβ25-35 induced HPA axis hyperreactivity and increased depression- and anxiety-related symptoms in rats. Our results showed that blockade of K_ATP channels with glibenclamide decreased depression- and anxiety-related behaviors by normalizing HPA axis activity in Aβ25-35-treated rats. This study provides additional evidence that Aβ administration can induce depression- and anxiety-like symptoms in rodents, and suggests that K_ATP channel inhibitors may be a plausible therapeutic strategy for treating affective disorders in AD patients.

Early Effect of Amyloid β-Peptide on Hippocampal and Serum Metabolism in Rats Studied by an Integrated Method of NMR-Based Metabolomics and ANOVA-Simultaneous Component Analysis

Amyloid β (Aβ) deposition has been implicated in the pathogenesis of Alzheimer's disease. However, the early effect of Aβ deposition on metabolism remains unclear. In the present study, thus, we explored the metabolic changes in the hippocampus and serum during first 2 weeks of Aβ25-35 injection in rats by using an integrated method of NMR-based metabolomics and ANOVA-simultaneous component analysis (ASCA). Our results show that Aβ25-35 injection, time, and their interaction had statistically significant effects on the hippocampus and serum metabolome. Furthermore, we identified key metabolites that mainly contributed to these effects. After Aβ25-35 injection from 1 to 2 weeks, the levels of lactate, N-acetylaspartate, creatine, and taurine were decreased in rat hippocampus, while an increase in lactate and decreases in LDL/VLDL and glucose were observed in rat serum. Therefore, we suggest that the reduction in energy and lipid metabolism as well as an increase in anaerobic glycolysis may occur at the early stage of Aβ25-35 deposition.