Yu. V. Moiseeva

Single intracerebroventricular administration of amyloid-beta (25-35) peptide induces impairment in short-term rather than long-term memory in rats.

Ample experimental evidence indicates that intracerebral injection or infusion of amyloid-beta peptides (Abeta) to rodents induces learning and memory impairments as well as neurodegeneration in brain areas related to cognitive function. In the present study, we assessed the effects of a single intracerebroventricular (i.c.v.) injection of aggregated Abeta fragment (25-35) at a dose of 15nmol/rat on short-term and long-term memory in rats during the 6-month post-surgery period. The results demonstrate that Abeta(25-35)-induced memory impairments in spontaneous alternation behavior in a Y-maze at 17, 36, and 180 days after the surgery as well as in a social recognition task 110 days post-surgery. Abeta(25-35) also impaired spatial memory in an 8-arm radial maze, but did not influence performance of the step-down passive avoidance task. These results suggest that Abeta(25-35) preferably induces impairments of spatial and non-spatial short-term (working) memory rather than long-term memory in rats.

Studies of the effects of fragment (25-35) of beta-amyloid peptide on the behavior of rats in a radial maze.

Decreases in cognitive functions, particularly long-term (episodic) and working memory, are among the earliest prognostic signs of Alzheimer’s disease. The toxicity of β-amyloid peptide is regarded as a major cause of neurodegeneration and cognitive impairment in this disease. The present report describes studies of the effects of intracerebroventricular administration of β-amyloid peptide (25–35) (Aβ(25–35)) on the reproduction of a previously assimilated habit consisting of finding food in an eight-arm radial maze in rats. Aβ (25–35) was given bilaterally at doses of 15 and 30 nmol/animal seven days after preliminary training. Testing was performed 60 days after peptide administration. The results showed that Aβ(25–35) impaired working memory in rats without having any significant effect on the retention of responses. We were unable to demonstrate any relationship between memory impairment and the dose of peptide given. These data provide evidence of the ability of Aβ(25–35) to produce greater degradation of working memory function than long-term memory function.

Effects of doses of fragment (25-35) of beta-amyloid peptide on behavior in rats.

Studies of the mechanisms of development and methods of treatment of Alzheimers disease (AD) are among the most relevant areas of contemporary biology and medicine. The major cognitive and neuropathological signs of AD include senile dementia, the formation of neurofibrillary tangles in neurons, the presence of deposits of/~-amyloid peptide in the form of amyloid plaques in the cerebral cortex and various subcortical structures (especially the hippocampus), and intensive neurodegenerative processes [6]. Neurodegenerative changes in AD primarily affect cholinergic neurons, especially in the region of the septohippocampal tract. The cholinergic deficit characteristic of AD is associated with disturbances in shortterm as well as in so-called working memory. Understanding of the mechanisms of development of AD is critically dependent on the production of an etiological model of the disease in animals, which would combine the cognitive and neuropathological signs. This is a complex task because of the multifactorial etiology of AD, including both genetic and nongenetic factors. Several different approaches to developing a model of AD in animals, especially rodents, have been addressed. First is the use of specific neurotoxins which predominantly kill cholinergic neurons [2]. This approach produces socalled analogous models, which model the behavioral and cholinergic deficit in animals, albeit without the characteristic pathomorphological picture of the course of AD. Second is a frequently used approach to modeling AD -creation of transgenic mice in which there is an additional copy of a gene (i.e., overexpression of the gene) encoding the protein precursor of amyloid peptide [4]. These animals usually show disturbances in spatial working memory, though the formation of plaques and neurofibrillary tangles has not been described in transgenic animals. These models can be used for studies of the mechanisms of development of AD and for searching for therapeutic substances for its treatmem. At the same time, transgenic animals cannot be used for developing prophylactic measures. The third approach consists of treating animals with fragments of amyloid peptide with the aim of triggering amyloidogenesis and cholinergic neurodegeneration. One study [3] showed that central administration of neurotoxic fragment (25-35) of B-amyloid peptide leads to Alzheimers-like amnesia in mice, accompanied by neurodegeneration and cholinergic dysfunction. The aim of the present work was to study the behavior of rats given intracerebroventricular doses of fragment (25-35) of/3-amyloid peptide. Studies were carried out on adult male Wistar rats weighing 230-290 g, kept in an animal house in conditions of natural illumination in groups of five per cage, with free access to water and food. Rats were divided randomly into two groups: a sham-operated (SO, n = 13) group and an experimental group given amyloid peptide (AM, n = 14). Animals were anesthetized with ketamine HCI (150 mg/kg), placed in a stereotaxic apparatus, and the skin on the head was incised in the region of the sagittal suture. Rats were scalped and two openings were drilled in the skull bone at the following coordinates: 0.8 mm posterior to the bregma, 1.5 mm lateral to the sagittal suture, and 3.8 mm beneath the level of the skull bone. Animals of group AM were given 7.5 nmol of aqueous aggregated fragment (25-35) of/3-amyloid peptide (RBI, USA) at 1 #I/min into each ventricle. The syringe needle was left in situ for 3 min after injections. Peptide was aggregated as described in [3]. Animals of group SO received the same quantity of distilled water.

The stress effects of a single injection of isotonic saline solution: systemic (blood) and central (frontal cortex and dorsal and ventral hippocampus)

In experiments with animals, a group that is injected with the vehicle in which a drug of interest is dißsolved is often used as a control. However, even a single injection of a vehicle is a stressor, i.e., “treatment stress,” which may significantly affect some stress-sensitive indices. In the present study, we report some data on the effects of a single intraperitoneal injection of isotonic saline solution on the contents of corticosterone, nitric oxide metabolites, and oxidative capacity, as well as on the expression of proteins and mRNAs of proinflammatory cytokines in the blood and brain regions of rats within one day after the injection as compared to intact animals. At the early time points after the injection, corticosterone contents were substantially elevated in the blood and ventral hippocampus. The content of nitric oxide metabolites decreased in the blood and remained stably low within 2–24 h after the injection. The injection did not affect the contents of proinflammatory cytokines in the blood; however, early after the injection the expression of IL-1ß mRNA decreased in the ventral hippocampus and frontal cortex, whereas 24 h after this treatment, the expression of TNF-a mRNA increased by a factor of 4 in the frontal cortex. Thus, a single injection of isotonic saline solution had a clear stress-producing effect, which was observed at the systemic level and in stress-sensitive brain regions. The strength of this stressful event was sufficient to activate the hypothalamus–pituitary–adrenal axis but not sufficient to induce a significant inflammatory response. The frontal cortex was most sensitive to this treatment; the alterations in the ventral hippocampus were less expressed, whereas the dorsal hippocampus was most stress resistant. Our data show that it is important to consider and thoroughly analyze the effects of “treatment stress” in experiments using injections of biologically active substances.

Increased anxiety level induced by social crowding stress in rats is not related to changes in the nitrergic system of the brain

In our previous studies, we have shown that stress induced by early social deprivation or total isolation, increases nitric oxide synthase activity in the brain regions of laboratory animals, and possible links between this phenomenon and stress-induced psychoemotional disturbances have been discussed. In the present study, we studied the effects of chronic psychosocial stress (housing under crowding conditions for 6 weeks) on the anxiety behavior and the indices of nitrergic system and intensity of free radical-mediated processes. Stress significantly increased anxiety levels, primarily influencing the exploratory components of animal behavior. Nitric oxide synthase activity and the levels of nitric oxide stable metabolites did not differ in the cerebral cortex, hippocampus, striatum and cerebellum of the control and stressed rats. Stress moderately increased the content of lipid peroxidation products in the cerebellum, whereas the levels of protein- and nonprotein thiol groups remained unchanged. Thus, the increased anxiety level in rats subjected to a long-term crowding was not accompanied by changes in the nitrergic system in the brain.

Accumulation of corticosterone and interleukin-1β in the hippocampus after focal ischemic damage of the neocortex: Selective vulnerability of the ventral hippocampus

Most ischemic strokes are caused by the occlusion of the middle cerebral artery (MCAO), which results in focal brain lesions in different areas of the neocortex. Secondary damage develops in brain regions located out of the infarct area, including the hippocampus. Hippocampal lesion may lead to cognitive impairments and post-stroke depression. Here, we studied the time course of changes in the levels of corticosterone and proinflammatory cytokine interleukine-1β (IL-1β) in the blood and hippocampus of rats after transient focal brain ischemia. Activation of the hypothalamo–pituitary–adrenal axis, which causes a release of corticosterone into blood, was observed at the early stage after MCAO and was accompanied by the presence of the stress hormone in the hippocampi of both the ischemic and contralateral hemispheres. We show for the first time that this effect was observed only in the ventral hippocampus (VH) but not in the dorsal hippocampus (DH). MCAO induced accumulation of the proinflammatory cytokine IL-1β, which coexisted with the elevated level of corticosterone at the early and delayed stages after reperfusion and was also observed in the VH of both hemispheres. Our data show that the VH is more vulnerable to remote damage induced by MCAO compared to the DH and corticosteroid response and neuroinflammation may be detected in the VH of both ischemic and contralateral hemispheres.

The effects of derivatives of pantothenic acid on free-radical processes and the corticosterone level in the hippocampus and neocortex of rats after interoceptive stress

In this study, the effects of interoceptive stress on the indices of free-radical oxidation and the corticosterone contents in the brain and blood of male rats were examined. In addition, we studied the effects of the GABA-like nootropic drug calcium hopanthenate and panthenol on these indices after stress. Interoceptive stress was induced by intraperitoneal injection of bacterial lipopolysaccharide and the studies were performed 24 h after injection. The derivatives of pantothenic acid substantially attenuated corticosterone accumulation in the hippocampus after interoceptive stress induced by systemic immune challenge but did not prevent a stress-induced increase in the level of substances that reacted with thiobarbituric acid in the blood of the animals.

The roles of monoamine oxidase form A (MAO A) and NO synthase in the mechanisms of the emergence from hibernation in the ground squirrel Citellus undulatus.

Emergence of hibernation is a short and rapid process that is completed within two to three hours. During this time, the animal body temperature increases from 3–4 to 37 ° C, the oxygen consumption increases by a factor of 100–150, and the heart rate becomes 200– 250 beats per minute instead of four to five in a state of hibernation. A lifeless, cold animal rapidly becomes active using only its own resources and escaping pathological consequences [9]. The Arctic ground squirrel ( Citellus undulatus ) has been found to restore cerebral integrative activity soon after hibernation. Its parameters reach the values characteristic of animal behavior during the active summer period within a day or even several hours after the emergence from hibernation [3, 14].

The Effects of Cortexin on Free-Radical Oxidation and Inflammatory Processes in Rats with Normal and Accelerated Aging

We studied the geroprotective properties of Cortexin and the systems of free-radical oxidation and inflammatory processes as potential targets of this drug. The study used 12-month-old male Wistar and OXYS rats with normal and accelerated aging, respectively. After preliminary assessment of their behavior in the open-field test, the rats were divided into homogenous groups according to behavioral indices. The animals were intraperitoneally injected with Cortexin (Geropharm, Russia) at a dose of 1 mg/kg daily for 30 days. The course of treatment with Cortexin did not substantially affect the general conditions and behavioral indices of both Wistar and OXYS rats and had a moderate positive effect on cognitive functions. Cortexin corrected the state of the systems of free-radical oxidation and cytokines. Specifically, in the brains of OXYS rats, Cortexin restored the ratio of the pro- and antioxidant systems primarily in the neocortex; however, a systemic effect was also observed. A significant anti-inflammatory effect was found at the systemic level and in the brain.

Changes in Cell Proliferation in the Subventricular Zone of the Brain in Adult Rats Given β-Amyloid Peptide (25-35)

The effects of intracerebroventricular administration of fragment (25–35) of β-amyloid peptide [Aβ(25–35)] on cell proliferation in the subventricular zone of the dentate gyrus of the hippocampus in adult rats were analyzed. Animals received doses of 15 nmol of pre-aggregated Aβ(25–35) or the Aβ(35–25) control peptide, or solvent (sterile water) into the lateral ventricles. On post-injection days 1–5, rats received intraperitoneal injections of the thymidine analog 5-bromo-2’-deoxyuridine (BrdU). BrdU incorporated into DNA was detected immunohistochemically on frontal brain sections six and 12 days after peptide administration. At six days, the numbers of BrdU-containing cells in the subventricular zone showed no differences between the study groups. At 12 days, the total number of BrdU-positive cells decreased significantly in all study groups. At the same time, the number of labeled cells in rats given Aβ(25–35) was significantly greater in this brain zone than in animals given water or the control peptide. Thus, Aβ(25–35) significantly increased cell proliferation in the subventricular zone after intracerebroventricular administration.