Animal models of cognitive dysfunction

Genetic deletion of TRPA1 receptor attenuates amyloid beta- 1-42 (Aβ1-42)-induced neurotoxicity in the mouse basal forebrain in vivo

Amyloid β 1-42 peptide (Aβ_1-42) accumulates in Alzheimer's disease (AD) that is toxic to the basal forebrain cholinergic (BFC) neurons in substantia innominata-nucleus basalis magnocellularis complex (SI-NBM). Transient Receptor Potential Ankyrin1 (TRPA1) receptor is present in murine brain, however its role in neurotoxic processes is unclear. We investigated the Aβ_1-42-induced neurotoxicity in TRPA1 wild-type (TRPA1^+/+) and knockout (TRPA1^-/-) mice. Expression and neuroanatomical localization of TRPA1 receptor were examined using RT qPCR. Cholinergic fibre loss was determined on acetylcholinesterase (AChE) stained brain slices, and choline acetyltransferase (ChAT) immunohistochemistry was used to assess the cholinergic cell loss. Novel object recognition (NOR), radial arm maze (RAM) and Y-maze tests were used to investigate memory loss. Aβ_1-42-injected WT mice showed marked loss of cholinergic fibres and cell bodies, which was significantly attenuated in TRPA1^-/- animals. According to the NOR and RAM tests, pronounced memory loss was detected in Aβ_1-42-injected TRPA1^+/+ mice, but not in TRPA1^-/- group. Our findings demonstrate that TRPA1 KO animals show substantially reduced morphological damage and memory loss after Aβ_1-42 injection in the SI-NBM. We conclude that TRPA1 receptors may play an important deteriorating role in the Aβ_1-42-induced cholinergic neurotoxicity and the consequent memory loss in the murine brain.

Characterization of aged male BALB/ccenp mice as a model of dementia

Dementia is defined as cognitive impairment in more than one cognitive area and leads to an abnormal degree of impairment in the ability to remember past events. Among mice models of dementia the most used strains are SAMP8 and C57BL/6. There is no reference to characterizing a model of dementia in naturally aged mice of the BALB/c strain, or to the minimum age at which these animals can be used. The aim of this study was the characterization of aged male BALB/ccenp mice as a model of dementia from the evaluation of behavioural, pathological and biochemical markers. One hundred and twenty mice were used and 10 of these were analysed from 8 to 9 months of age, and every 4 months, in a comparative way to young control animals from 4 to 5 months. At the age of 12-13 months there was cognitive impairment in the animals from the Y-maze and object recognition tests and this impairment was maintained at 16-17 months of age. An increase in oxidative damage to proteins in the brains of aged animals was also found in relation to young animals; as well as a decrease in the concentration of triglycerides. At the age of 16-17 months, a significant decrease in the size of the thymus and brain was obtained. We consider that it's a very useful option to use animals 12-13 months of age where there are symptoms of cognitive deficiency, histopathological and biochemical elements characteristic of dementia.

Pharmacotherapy of Down’s Syndrome: When and Which?

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Down Syndrome (DS) is an essential genetic disease that involves many other body systems along with cerebral functions. The postnatal approach to treat this genetic disease includes intervention on various related disorders (e.g., heart failure, respiratory, oral, ear, and hearing disorders). However, different proposed treatments do not significantly improve the quality of life of these subjects. Another approach to the treatment of DS considering the possibility to intervene on the embryo was recently introduced. As of this, the current study has reviewed different outcomes regarding DS treatment in an animal model, namely the Ts65Dn mouse. The obtained results encouraged spending more time, efforts, and resources in this field. Besides, various treatment strategies were tried to include genetic modification, treatment with vasoactive intestinal peptide derivatives or fluoxetine. However, the main obstacle to the use of these possible treatments is the ethical issues it raises. The progression of the pregnancy in spite of awareness that DS affects the unborn and prenatal treatment of DS injured embryo are relevant dilemmas. Thus, talented researchers should spend more efforts to improve the quality of life for people affected by DS, which will allow probably a better approach to the ethical issues.

Toxin-Induced Experimental Models of Learning and Memory Impairment

Animal models for learning and memory have significantly contributed to novel strategies for drug development and hence are an imperative part in the assessment of therapeutics. Learning and memory involve different stages including acquisition, consolidation, and retrieval and each stage can be characterized using specific toxin. Recent studies have postulated the molecular basis of these processes and have also demonstrated many signaling molecules that are involved in several stages of memory. Most insights into learning and memory impairment and to develop a novel compound stems from the investigations performed in experimental models, especially those produced by neurotoxins models. Several toxins have been utilized based on their mechanism of action for learning and memory impairment such as scopolamine, streptozotocin, quinolinic acid, and domoic acid. Further, some toxins like 6-hydroxy dopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and amyloid-β are known to cause specific learning and memory impairment which imitate the disease pathology of Parkinson's disease dementia and Alzheimer's disease dementia. Apart from these toxins, several other toxins come under a miscellaneous category like an environmental pollutant, snake venoms, botulinum, and lipopolysaccharide. This review will focus on the various classes of neurotoxin models for learning and memory impairment with their specific mechanism of action that could assist the process of drug discovery and development for dementia and cognitive disorders.

Pre-clinical models of human cerebral small vessel disease: utility for clinical application

Small vessel disease (SVD) is a frequent cause of vascular cognitive impairment (VCI), encompassing vascular dementia. SVD is characterised by vasculopathy in deep penetrating arteries, diffuse white matter lesions (seen radiologically as leukoaraiosis) and focal, lacunar infarcts. Risk factors are age and hypertension but the pathogenic mechanism is unknown. Recent systematic reviews assessed experimental models of SVD or VCI. Chronically hypertensive animals (e.g. stroke-prone spontaneously hypertensive rats) display some features of SVD vasculopathy, such as vessel wall thickening. White matter lesions are seen in chronic hypoperfusion states (e.g. carotid occlusion/stenosis models). Small focal infarcts are induced by targeted ischemic challenge (surgical occlusion of a small artery, or stereotaxic endothelin-1 injection). Some degree of cognitive impairment is detectable in most cerebrovascular models, probably reflecting the broad neuroanatomical mapping of cognitive function. Important confounds to be considered in animal models of VCI are somatosensory impairment and hippocampal damage. Advances in clinical understanding will come from targeting specific questions on some aspect of SVD (e.g. vasculopathy, white matter damage) to the appropriate model in vivo. In vivo models of SVD are likely to benefit experimental studies of pathological processes, interactions with other brain disease states (such as Alzheimer disease), and therapeutic strategies.

Comparative protective action of curcumin, memantine and diclofenac against scopolamine-induced memory dysfunction

The comparative preventive effect of curcumin, memantine, and diclofenac on scopolamine-induced memory dysfunction was investigated in a controlled study. A group of male and female rats was treated with one of these compounds for 15 days, after which a single dosage of scopolamine was administered. The preventive activity of curcumin on memory dysfunction was higher than that of diclofenac or memantine, that was, however, administered at lower dosages. Gender differences were observed.

Brain mitochondrial dysfunction in ovariectomized mice injected with D-galactose

Our previous studies reveal that long-term exposure of ovariectomized rodents to D: -galactose results in pathophysiologic alterations associated with Alzheimer's disease. The current study was to address whether mitochondrial dysfunction was involved in the pathogenesis of this model. Ovariectomized mice were administered intraperitoneally with D: -galctose (100 mg/kg body weight) once a day for 8 weeks. Brain tissues from model mice showed decreases in reduced glutathione level, total antioxidative capabilities, total superoxide dismutase activity and glutathione peroxidase activity but an increase in malondialdehyde level, compared with those from sham-operated plus saline-injected mice. Activities of brain mitochondrial respiratory chain (complex I, II, III and IV) were reduced in model group. In contrast, ATP synthase (F(1)F(0)-ATPase) activity was not significantly different between the two groups. Moreover, electron microscopy identified ultrastructural impairments of hippocampal mitochondria in model mice. These results demonstrated that brain mitochondrial degeneration caused by oxidative stress participated in the etiology of ovarian hormone deprivation and D-galactose-induced neurodegeneration.

Microanatomical evidences for potential of mesenchymal stem cells in amelioration of striatal degeneration

Huntington's disease is an inherited neurodegenerative disorder, characterized by loss of spiny neurons in the striatum and cortex, which usually happens in the third or fourth decades of life. In advanced form of the disease, progressive striatum atrophy happens and medium spiny neurons, which occupy more than 80% of the striatum, become atrophic. Gradually, the atrophy expands to the neocortex and other regions of the brain. To our knowledge, there is no effective therapeutic strategy for diminishing the motor disorders of Huntington's disease. In recent years, cellular transplantation has been an effective therapeutic method for neurodegenerative diseases. In the present study, the potential of bone marrow derived mesenchymal stem cells in amelioration of striatal degeneration was assessed in animal model of Huntington's disease. After unilateral lesion in striatum was caused by quinolinic acid (QA), bone marrow derived mesenchymal stem cells, which were isolated and purified from 4-6 weeks old rats, were transplanted into the damaged striatum. After 9 weeks of transplantation, the volume of striatum, lateral ventricles and hemispheres were measured in control (normal) and test (QA injected + cell transplanted) groups. After volume determination, the atrophy percentage of both striatum and damaged hemisphere and volume extension of lateral ventricles were calculated. Histologic results showed significant difference in amount of striatum atrophy between sham (only QA injected) and test groups. These results confirm the potential of bone marrow derived mesenchymal stem cells in treatment of microanatomical defects in motor disorders of Huntington's disease. According to our results, cell therapy by means of bone marrow derived adult stem cells could be considered as a good candidate for treatment of neurodegenerative diseases, especially Huntington's disease.

Long-term d-galactose injection combined with ovariectomy serves as a new rodent model for Alzheimer's disease

Estrogen deprivation and oxidative stress have been well established as two main factors closely related to the pathological development of Alzheimer's disease (AD). The aim of the present study is to investigate whether these two components act synergistically to accelerate the pathophysiological course of AD. To do this, we examined the effect of long-term intraperitoneal administration of D-galactose (D-gal) into ovariectomized (OVX) rats. Six weeks later, the OVX and d-gal-injected rats exhibited a higher degree of cognitive and memory impairment. This was accompanied by cholinergic neuronal loss in the forebrain and synaptic degeneration in the hippocampus and cerebral cortex which was not observed in intact controls, animals receiving injections of d-gal alone, untreated OVX animals or OVX animals receiving both D-gal and 17-beta estradiol. The typical histopathological alterations associated with AD, including intracellular deposition of amyloid beta peptide and the appearance of intracellular neurofibrillary tangles and nuclear granulovacuolar bodies, were observed in the hippocampus of OVX and D-gal-injected rats but not in other control groups. These results strongly suggest that estrogen deprivation and oxidative stress behave synergistically to enhance the development and progression of AD. Long-term OVX combined with D-gal injection serves as an ideal AD rodent model capable of mimicking pathological, neurochemical and behavioral alterations in AD.