N. V. Bobkova

Effects of bulbectomy and subsequent antidepressant treatment on brain 5-HT2 and 5-HT1A receptors in mice

The effects of bilateral olfactory bulbectomy on serotonergic 5-HT2 and 5-HT1A receptor binding were studied in the frontal cortex (FC), limbic structures (LS), including the hippocampus, amygdala, olfactory tubercule, and piriform cortex, and hypothalamus (HTH) in mice. Bulbectomy resulted in the increase of Bmax for [3H]spiperone binding with 5-HT2 receptors in FC in C57Bl/6j. The receptors in LS and HTH remained unchanged. Subchronic treatment of the bulbectomized mice with antidepressant trazodone (20 mg/kg/day, IP, 14 days) induced downregulation of 5-HT2 receptors in FC and LS. The other two antidepressants used, amitriptyline (20 mg/kg/day, IP, 14 days) and imipramine (10 mg/kg/day, IP, 14 days), did not alter these receptors. [3H]8-OH-DPAT binding with 5-HT1A receptors was not altered by bulbectomy in any brain area in C57Bl/6j mice. Amitriptyline and trazodone decreased Bmax for these receptors in FC in the bulbectomized mice while imipramine was ineffective. Amitriptyline and imipramine significantly increased Bmax and decreased Kd in HTH, and trazodone displayed the same tendency. Bulbectomy did not alter 5-HT2 receptors in DBA/2j mice. Amitriptyline increased Kd in the all brain areas without changing Bmax in the bulbectomized DBA/2j mice. Trazodone significantly decreased Bmax in FC and increased Kd in FC and LS. Imipramine decreased Bmax while increasing Kd in LS. The possible involvement of the serotonin receptor subtypes in the bulbectomy-induced behavioral deficits and in the restorative action of the antidepressants is discussed.

Morphofunctional state of neurons in the temporal cortex and hippocampus in relation to the level of spatial memory in rats after ablation of the olfactory bulbs

Ablation of the olfactory bulbs (bulbectomy) in mice and guinea pigs evokes a neurodegenerative process which, in terms of its morphological, biochemical, and behavioral features, is similar to Alzheimer’s disease. We report here studies of the long-term sequelae of bulbectomy in rats. One year after surgery, testing of spatial memory in bulbectomized rats (BER) allowed the animals to be divided into two groups-those with good memory (BER-gm) and those with poor memory (BER-pm). Quantitative analysis of the morphofunctional state of neurons showed that BER-pm, as compared with the BER-gm group, had more marked pathological lesions in neurons of the temporal cortex and hippocampus, with significant increases in the numbers of cells showing pyknosis, karyolysis, cytolysis, and vacuolization. Both groups showed decreases in the distribution density of cells in the cortex. In terms of the level of brain β-amyloid, the study groups fell in the order: BER-pm > BER-gm > control sham-operated rats. These results provide evidence of the long-term nature of changes in the morphofunctional state of neurons in the brains of BER, correlating with their levels of spatial memory.

The State of Cholinergic Structures in Forebrain of Bulbectomized Mice

The effects of bulbectomy on the state of basal forebrain cholinergic structures and spatial memory in Morris water maze were studied. Immunostaining with polyclonal antibodies to choline acetyltransferase AB144P revealed decreased density of immunoreactive cells in the horizontal limb of the diagonal band of Broca (55% of control), basal magnocellular preoptic nucleus (58.9%), and the caudate nucleus-putamen complex (68.2%). No significant changes in the vertical limb of the diagonal band of Broca and globus pallidus were observed. These findings and published data allow us to assume that pathology of the olfactory bulb can underlie memory impairment during Alzheimers disease associated with dysfunction of acetylcholine-synthesizing structures in the forebrain.

Morphofunctional Changes in Neurons in the Temporal Cortex of the Brain in Relation to Spatial Memory in Bulbectomized Mice After Treatment with Mineral Ascorbates

The effects of an antioxidant mixture of mineral ascorbates (MA) on the state of neurons in the temporal area of the cortex and the behavior of mice subjected to bulbectomy (BE) were studied; these mice, as demonstrated previously, are characterized by deficiency of spatial memory and the development of a neurodegenerative process in brain structures showing pathological changes in Alzheimers disease. One month after BE, there were abnormalities in the cytoarchitectonics of the temporal area of the cortex, with loss of clarity of the boundaries between its layers because of dystrophy of pyramidal neurons and foci of loss of these cells. There were sharp increases in the numbers of neurons showing pyknosis, karyolysis, and vacuolysis on the background of decreases in neuronal density. Three weeks of treatment by addition of MA to the diet prevented the degradation of spatial memory in mice after BE and protected neurons in the temporal area of the cortex from degenerative changes. These results provide evidence for the possibility of prophylaxis of neurodestructive changes of the Alzheimers type.

Immunization with either prion protein fragment 95-123 or the fragment-specific antibodies rescue memory loss and neurodegenerative phenotype of neurons in olfactory bulbectomized mice

Epidemiological studies demonstrated association between head injury (HI) and the subsequent development of Alzheimers disease (AD). Certain hallmarks of AD, e.g. amyloid-β (Aβ) containing deposits, may be found in patients following traumatic BI (TBI). Recent studies uncover the cellular prion protein, PrP(C), as a receptor for soluble polymeric forms of Aβ (sAβ) which are an intermediate of such deposits. We aimed to test the hypothesis that targeting of PrP(C) can prevent Aβ related spatial memory deficits in olfactory bulbectomized (OBX) mice utilized here to resemble some clinical features of AD, such as increased level of Aβ, memory loss and deficit of the CNS cholin- and serotonin-ergic systems. We demonstrated that immunization with the a.a. 95-123 fragment of cellular prion (PrP-I) recovered cortical and hippocampus neurons from OBX induced degeneration, rescued spatial memory loss in Morris water maze test and significantly decrease the Aβ level in brain tissue of these animals. Affinity purified anti-PrP-I antibodies rescued pre-synaptic biomarker synaptophysin eliciting similar effect on memory of OBX mice, and protected hippocampal neurones from Aβ25-35-induced toxicity in vitro. Immunization OBX mice with a.a. 200-213 fragment of cellular prion (PrP-II) did not reach a significance in memory protection albeit having similar to PrP-I immunization impact on Aβ level in brain tissue. The observed positive effect of targeting the PrP-I by either active or passive immunization on memory of OBX mice revealed the involvement of the PrP(C) in AD-like pathology induced by olfactory bulbectomy. This OBX model may be a useful tool for mechanistic and preclinical therapeutic investigations into the association between PrP(C) and AD.

Vaccination with Peptide 173-193 of Acetylcholine Receptor α7-Subunit Prevents Memory Loss in Olfactory Bulbectomized Mice

We studied the ability of four non-conjugated alpha7-subunit fragments of the nicotinic acetylcholine receptor to induce an immune response and to protect memory in olfactory bulbectomized mice which demonstrate abnormalities similar to Alzheimers disease (AD). Vaccination only with the alpha7-subunit fragment 173-193 was shown to rescue spatial memory, to restore the level of alpha7 acetylcholine receptors in the cortex, and to prevent an increase in the amyloid-beta (Abeta) level in brain tissue in these animals. Antibodies against the peptide 173-193 were revealed in blood serum and cerebrospinal liquid in the bulbectomized mice. Passive immunization with mouse blood sera containing antibodies to the peptide 173-193 also restored memory in bulbectomized animals. The observed positive effect of both active and passive immunization with the fragment of alpha7-subunit on memory of bulbectomized mice provides a new insight into an anti-AD drug design.

Beta-Amyloid and Tau-Protein: Structure, Interaction, and Prion-Like Properties

During the last twenty years, molecular genetic investigations of Alzheimer’s disease (AD) have significantly broadened our knowledge of basic mechanisms of this disorder. However, still no unambiguous concept on the molecular bases of AD pathogenesis has been elaborated, which significantly impedes the development of AD therapy. In this review, we analyze issues concerning processes of generation of two proteins (β-amyloid peptide and Tau-protein) in the cell, which are believed to play the key role in AD genesis. Until recently, these agents were considered independently of each other, but in light of the latest studies, it becomes clear that it is necessary to study their interaction and combined effects. Studies of mechanisms of toxic action of these endogenous compounds, beginning from their interaction with known receptors of main neurotransmitters to specific peculiarities of functioning of signal intracellular pathways upon development of this pathology, open the way to development of new pharmaceutical substances directed concurrently on key mechanisms of interaction of toxic proteins inside the cell and on the pathways of their propagation in the extracellular space.

Immunization with a synthetic fragment 155–164 of neurotrophin receptor p75 prevents memory loss and decreases beta-amyloid level in mice with experimentally induced Alzheimer’s disease

Neurotoxic beta-amyloid peptide plays an important role in the pathology of Alzheimer’s disease. In aggregated form it binds to several proteins on the surface of the brain cells leading to their death. p75 receptor involved in supporting of cell balance is one of the targets for toxic beta-amyloid. We proposed that induction of antibodies against potential binding sites of p75 with beta-amyloid can be a promising approach towards development of new anti-Alzheimer’s disease treatment. Four potentially immunoactive fragments of p75 were chosen and chemically synthesized. Investigation of immunoprotective effect of the peptide fragments carried out in mice with experimentally induced form of Alzheimer’s disease helped to reveal two fragments effectively preserving murine memory from impairment. Results obtained by ELISA biochemical analysis showed that only immunization with fragment p75 155–164 led to significant decrease in beta-amyloid level in the brain of the experimental mice. Thus, immunization with both fragments of p75 receptor pro-vides a new insight into anti-Alzheimer’s disease drug design.

Molecular and cellular mechanisms of sporadic Alzheimer’s disease: Studies on rodent models in vivo

In this review, recent data are presented on molecular and cellular mechanisms of pathogenesis of the most widespread (about 95%) sporadic forms of Alzheimer’s disease obtained on in vivo rodent models. Although none of the available models can fully reproduce the human disease, several key molecular mechanisms (such as dysfunction of neurotransmitter systems, especially of the acetylcholinergic system, β-amyloid toxicity, oxidative stress, neuroinflammation, mitochondrial dysfunction, disturbances in neurotrophic systems) are confirmed with different models. Injection models, olfactory bulbectomy, and senescence accelerated OXYS rats are reviewed in detail. These three approaches to in vivo modeling of sporadic Alzheimer’s disease have demonstrated a considerable similarity in molecular and cellular mechanisms of pathology development. Studies on these models provide complementary data, and each model possesses its specific advantages. A general analysis of the data reported for the three models provides a multifaceted and the currently most complete molecular picture of sporadic Alzheimer’s disease. This is highly relevant also from the practical viewpoint because it creates a basis for elaboration and preclinical studies of means for treatment of this disease.

A fragment of the receptor for advanced glycation end products restores the spatial memory of animals in a model of Alzheimer’s disease

The ability of some synthetic peptides modeling the potentially important regions of four membrane proteins, known as cell targets for beta-amyloid, to restore the spatial memory of animals in an experimental model of Alzheimer’s disease has been studied. Nine fragments of the protein receptor for advanced glycation end products (RAGE), which, according to X-ray structure analysis data, repeat all its exposed nonstructural regions, have been synthesized. The effect of these peptides and of earlier synthesized immunoprotective fragments of three other proteins (alpha7-type acethylcholine receptor, the prion protein, and the neurotrophin receptor p75) has been studied on intranasal administration, which excludes the development of the immune response to the peptide. It has been shown that only one fragment, RAGE (60–76), exhibits a therapeutic activity, by restoring the spatial memory of bulbectomized mice and decreasing the level of the brain beta-amyloid.