Immunohistochemical Analysis of Mitochondrial Dynamics in Different Zones of the Hippocampus during Experimental Modeling of Alzheimer's Disease

We performed a comparative assessment of the immunohistochemical distribution of markers of mitochondrial fission (Drp-1), mitochondrial fusion (Mfn-2), and mitochondrial biogenesis (PGC-1α) in pyramidal neurons of different zones of the hippocampus in mice with intrahippocampal administration of β-amyloid peptide 25-35. The most pronounced changes in the dynamics associated with a decrease in the amount of the fission marker and an increase in the amount of the fusion marker were observed in the CA3 field on day 38 after peptide administration. In the CA1 field, a significant decrease in the marker of mitochondrial biogenesis PGC-1α was found on day 38, which can indicate a decrease in the intensity of mitochondrial biogenesis. Early mitochondrial changes can play an important role in the pathogenesis of all types of memory impairment in Alzheimer's disease.

Glial Reaction in a Neuroinflammatory Model of Parkinson's Disease

Sixty and 90 days after unilateral intranigral injection of LPS to Wistar rats (10 μg), activation of microglia, neuronal death, and formation of synuclein-positive inclusions were observed in the substantia nigra, but not in dopaminergic neurons. Astrocytes were characterized by increased expression of gliofibrillary protein GFAP, vimentin, complement protein C3, aquaporin-4, and connexin-43. At later stages, GFAP expression decreased, but the distribution of aquaporin-4 and connexin-43 remained disordered, and neuronal degeneration deteriorated. Thus, reactive changes in astrocytes after LPS administration can cause long-term disturbances of the neurogliovascular coupling. The observed functional and morphological alterations in the astroglia can be the cause of progressive disturbances in the substantia nigra.

[Morphochemical study of alpha-synuclein, iron and iron-containing proteins in the substantia nigra of the brain in Parkinson's disease]

OBJECTIVE

To study, using a complex morphochemical approach, the localization of alpha-synuclein, iron compounds and iron-containing proteins in the structures of the substantia nigra of the brain in Parkinson's disease (PD).

MATERIAL AND METHODS

Histochemistry and immunohistochemistry methods have been used to study the localization of pathological alpha-synuclein (α-Syn-p129), iron compounds and iron-containing proteins - transferrin receptor and ferritin in neurons and neuroglia in the substantia nigra of the brain of deceased PD patients and persons with no neurological symptoms detected during life (control).

RESULTS

In the substantia nigra of PD patients, in comparison with the control, a stable accumulation of pathological alpha-synuclein (α-Syn-p129) in the bodies and processes of neurons was found, and in the neuroglia and neuropil - the accumulation of iron (II) and ferritin heavy chain, the reaction of microglia to protein CD68 was moderately elevated. The transmembrane protein CD71 was detected equally in the brains of PD patients and in controls.

CONCLUSION

Synaptic protein alpha-synuclein in PD turns into a pathological metabolite that accumulates in the structures of substantia nigra, and probably disrupts the conduction of nervous excitation. Excessive accumulation of the ferritin heavy chain in neuroglia can increase the concentration of reactive forms of iron and increase neurotoxicity. The uniform distribution of the transmembrane glycoprotein CD71 in the of substantia nigra structures both in the control and in PD patients indicates the preservation of non-heme iron transport during the neurodegenerative process.

[The role of mercury and arsenic in the etiology and pathogenesis of Parkinson's and Alzheimer's diseases]

A critical review of literature data on the toxic effects of mercury and arsenic on the human brain and their relationship with the etiology and pathogenesis of neurodegenerative diseases such as Parkinson's and Alzheimer's diseases is presented. In the first case, the toxic effect of mercury and arsenic on the brain stimulates oxidative stress, which leads to the formation of free oxygen species and a decrease in the antioxidant defense of neurons. In the second case, the harmful effect of mercury changes the structure and properties of β-amyloid, and the toxic effect of arsenic contributes to its accumulation. In the pathogenesis of the diseases under consideration, particular importance is attached to the reaction of astrocytes that initiate neuroinflammation, which is also characteristic of mercury and arsenic intoxication. Considering that the symptoms recorded during intoxication with mercury and arsenic are in many respects similar to those of Parkinson's and Alzheimer's diseases, and their pathogenetic mechanisms (oxidative stress and neuroinflammation) coincide, then the toxic effects of mercury and arsenic in neurodegenerative diseases analyzed in this review can be characterized as the influence of the most significant risk factors.

Alterations in tanycytes and related cell populations of arcuate nucleus in streptozotocin-induced Alzheimer disease model

It is assumed that dysfunction of tanycytes could be one of the components of pathogenesis of both Alzheimer disease and type 2 diabetes mellitus. The study was aimed to assess alterations in the tanycyte morphology in the Alzheimer disease model. The 3 mg/kg streptozotocin dose was injected in the lateral ventricles of Wistar rats in order to model the Alzheimer disease. Alterations in hypothalamic tanycytes were assessed 2 weeks, 4 weeks, 3 months and 6 months after administration of the toxin. Immunohistochemistry was used to identify the protein markers of tanycytes (vimentin, nestin), astrocytes (GFAP, glutamine synthetase) and neurons (HuC/D), as well as to assess cell proliferation (with the use of Ki67 protein) and mitochondrial alterations (mitochondrial complex IV, PGC1a). Administration of streptozotocin lead to β-amyloid accumulation in hypothalamus and ventricular enlargement (p < 0.001). Streptozotocin damaged both α1/α2 tanycytes and β1 tanycytes. The intensity of vimentin staining in α1/α2 tanycytes decreased by week 4 (p = 0.003), and in β1 tanycytes it decreased in three months (p < 0.001). The same trend was observed for nestin. The number of Ki67+ nuclei decreased (p < 0.05), and the expression of proteins associated with mitochondria changed. The density of hypothalamic tanycytes decreased by week 4 after administration of the toxin. Moreover, astrocyte activation was revealed. However, no prominent damage to both astrocytes and neurons was observed within four weeks after administration of streptozotocin. The revealed high tanycyte vulnerability to streptozotocin is in line with the hypothesis of the role of damage to hypothalamic structures in both local and systemic metabolic disorders occurring in the Alzheimer disease models.

[Streptozocin-induced Alzheimer's disease as an independent risk factor for the development of hyperglycemia in Wistar rats]

BACKGROUND

In recent years the theme of the relationship of Alzheimers disease (AD) and metabolic disorders has been widely discussed. Nevertheless, it remains unclear whether AD is a direct cause of carbohydrate metabolism disorders or it is the presence of classical risk factors for type 2 diabetes mellitus (DM 2), primarily obesity, that significantly increases the risk of AD.

AIM

To evaluate the separate contribution of two factors to the development of disorders of carbohydrate metabolism: (1) weight gain due to a high-calorie diet and (2) experimental-induced AD.

METHODS

Male Wistar rats were injected with streptozocin (STZ) in the lateral ventricles of the brain to induce AD or saline (sham operated animals - SO) during stereotactic operations. After 2 weeks, the animals were divided into four groups: 1) the SO group, which was assigned to the normal calorie (NCD) diet (SO NCD); 2) the SO group, which was assigned to the high-calorie diet (SO HCD); 3) the group to which the norm-calorie diet was prescribed after the administration of STZ into the lateral ventricles of the brain (STZ NCD); 4) the group to which the HCD was assigned after the administration of STZ (STZ HCD). The animals were on a diet for 3 months. Intraperitoneal glucose tolerance tests were carried out before the diet and after 3 months. At the end of the study, a morphological assessment of brain tissue, pancreas, and liver was performed.

RESULTS

3 months after surgical interventions and the appointment of diets, the glycemic curves significantly differed in the 4 studied groups: normoglycemia persisted only in the SO + NCD group, while HCD and the STZ administration were accompanied by the development of hyperglycemia (p = 0.0001). The STZ + NСD group, which represented the isolated effect of AD, was also characterized by impaired carbohydrate metabolism. A morphological study showed that HCD leads to a more pronounced ectopic accumulation of fat in the liver and pancreas tissue than NCD. The administration of STZ, regardless of the diet, led to changes typical for the AD model an increase in the size of the ventricles of the brain, degeneration of white matter, and the accumulation of -amyloid in the hypothalamus.

CONCLUSIONS

The STZ-induced brain damage typical for AD led to impaired carbohydrate metabolism regardless of diet and was an independent risk factor for hyperglycemia.

[Lewy bodies in Parkinson's disease: histological, immunohistochemical, and interferometric examinations]

OBJECTIVE

To quantify the morphochemical characteristics of Lewy bodies detected in the substantia nigra in patients with Parkinson's disease (PD).

MATERIAL AND METHODS

The investigators studied the localization of alpha-synuclein (α-Syn) and the distribution of neurofilament protein and synaptophysin by immunohistochemical assas and compared with the results of interferometry and computer-assisted morphometry of Lewy bodies in the autopsy specimens of the substantia nigra from PD patients.

RESULTS

Three groups of synuclein-positive aggregates differing in shape were identified. Mature Lewy bodies had a rounded shape, a concentric structure, a poorly stained core, and, as compared with neuropil, a high phase difference value. Comparison of the localization of α-Syn, neurofilaments, and synaptophysin showed that immunostaining of neurofilaments in the peripheral layer of Lewy bodies was shifted closer to the nucleus and the localization of synaptophysin and α-Syn coincided.

CONCLUSION

Synuclein-positive protein aggregates showed heterogeneity in structure, shape, and protein composition in PD. The localization of neurofilament protein and synaptophysin in Lewy bodies attests that the cytoskeleton and neuronal synaptic vesicle trafficking in the substantia nigra are impaired in BP.

[Morphochemical changes in the substantia nigra cellular structures in Parkinson's disease]

AIM

to clarify the features of morphochemical changes in the substantia nigra cellular structures in Parkinson's disease.

MATERIAL AND METHODS

The structural characteristics of the substantia nigra were studied microscopically and quantified using computer morphometric methods at brain autopsies of individuals with Parkinson's disease who had died from intercurrent diseases and those who had no evidence of neurological disorders in their history (a control group).

RESULTS

This investigation could clarify the features of morphochemical changes in both the neural network structures and the glial populations of the substantia nigra in Parkinson's disease. The number of neurons containing tyrosine hydroxylase (a marker of dopamine neurons) in the compact part of the substantia nigra (a ventral region) was smaller and the density distribution of Lewy bodies was higher in the patients with Parkinson's disease than in the control group. The accumulation of iron (II) compounds in the cellular elements and neuropile and the increased expression of glial fibrillary acidic protein in Parkinson's disease were more pronounced than those in the controls.

CONCLUSION

Postmortem diagnosis in Parkinson's disease should be based on a full description of a set of neuronal and glial morphochemical and structural changes in the substantia nigra rather than on the identification of cellular markers for the neurodegenerative process.

[MORPHOMETRIC CHARACTERISTICS OF SUBSTANTIA NIGRA CELLULAR STRUCTURES OF THE HUMAN BRAIN]

Neurons and glial cells were studied by means of computerassisted morphometry in the segments of the ventral and dorsal regions of the compact part of the substantia nigra (CPSN) of the brain. The material obtained at autopsy from 6 males and 3 females aged from 52 to 87 years. It was found that in segments of the ventral CPSN region the neuronal cell bodies and nuclei were larger than those in the segments of the dorsal region. The numerical density of neurons and gliocytes in the ventrolateral segment was higher than in the segments of the dorsal region. In the ventromedial segment the glial index was lower than in the segments of the dorsal region. The morphometric differences found between CPSN segments must be taken into account in the assessment of the morphological changes in substantia nigra of the brain, due to both age involution or pathological process.

[Morphological parameters of the heterogeneity of the substantia nigra in elderly men and women]

OBJECTIVE

to define the quantitative characteristics of cell structures in the substantia nigra pars compacta of neurologically healthy elderly people (men and women).

MATERIAL AND METHODS

Autopsy brain materials from neurologically healthy men and women who had died from intercurrent diseases at the age of 72 to 87 years were examined for quantitative characteristics of the substantia nigra pars compacta, by applying computed morphometric methods.

RESULTS

In the elderly people (men and women), the compactness of arrangement of neurons, including those containing tyrosine hydroxylase (a marker of dopamine neurons), was much higher and the glial index was lower in the ventral area of the substantia nigra pars compacta than in the dorsal area. Comparing the structures in the substantia nigra pars compacta showed that the neurons were larger in the dorsal area and the variability of the compactness of their arrangement and the glial index were higher in the women than in the men.

CONCLUSION

In the elderly people, the cell structures in the substantia nigra pars compacta are typified by high morphometric heterogeneity.

Quantitative morphochemical characterization of the neurons in substantia nigra of rat brain and its volume reconstruction

Three cell compartments differing by size and proportion of neurons were identified by 3D reconstruction of the substantia nigra pars compacta of the rat brain based on immunohistochemical localization of tyrosine hydroxylase, a marker of dopamine neurons. Dopaminepositive neurons prevailed over dopamine-free neurons (1.45:1) in the most voluminous (75%) dorsal part, and in smaller lateral and ventral parts, inverse cell ratios were observed: 0.54:1 and 0.78:1, respectively. Morphometry characterized the substantia nigra pars compacta as a structure consisting not only of several parts, but of horizons and showed differences between the neurons both in several parts and in several layers within the part. The revealed morphochemical heterogeneity of the substantia nigra pars compacta provides better understanding of the selective damage to its structures in Parkinson's disease.

[Changes in neuroglial interactions in the cerebral nigrostriatal structures in a model of dopamine system dysfunction]

Hypofunction of the dopamine system was induced by haloperidol or reserpine in Wistar rats. Reserpine increased a number of glial fibrillary acidic protein (GFAP) containing astrocytes by 49% and reduced glutamine synthase astrocytes and monoamine oxidase activity by 23% and 1/3, respectively. Haloperidol had no effect on morpho-chemical characteristics of astrocytes but increased a number of oligodendrocytes. It has been supposed that the activation of astroglia by reserpine in a dopamine hypofunction model is caused by the dysfunction of the corticostriatal glutamatergic system as a result of inhibition of the dopaminergic transmission in the basal nuclei. The changes in the neuroglial interactions in the striatum that lead to the disbalance of neuromediator systems in the basal nuclei may underlie the dysfunction of the basal nuclei in some diseases including Parkinson's disease.

Immunohistochemical and morphological changes in neurons and neuroglia in the cerebral nigrostriatal structures under conditions of experimental nigral neurodegeneration

The count of dopamine-containing neurons decreased by 77%, the area of the remaining cells shrank by 75%, and the neuroglia doubled 4 weeks after injection of toxin (6-hydroxydopamine) into the compact part of the substantia nigra of the right cerebral hemisphere of rats, while no changes in the substantia nigra of the left hemisphere were observed. Neurons of the caudate nucleus were virtually unchanged in comparison with the intact control, while the neuroglia was activated: its total volume in the right hemisphere increased by 33% (50% increase in astrocyte count and a 25% increase of the rest neuroglia), while in the left hemisphere only astrocyte count increased by 20%. Astrocyte nuclei in the caudate nuclei of both hemispheres were enlarged by 22-23%. Hence, unilateral destruction of the nigral dopamine-containing neurons stimulated the neuroglia (particularly astroglia) in the caudate nuclei, especially on the side of damage.

[Glial satellites as the source of additional energy supply to the neurons during the increased frequency of firing activity]

Using surviving slices of guinea pig somatosensory cortex, it was shown that functionally different regulation of spontaneous firing activity in different neurons corresponded to irregular distribution of glial satellites. Maximal increase of spike activity induced by acetylcholine (up to 36 spikes per second) was detected in "silent" neurons which account for 37.2% of nerve cells in layer V. According to the morphometric analysis, the same relative number of neurons (38.6%) were surrounded with glial satellites. In spontaneously active neurons only a small elevation of firing activity (5-22 spikes per second) above the basal level was recorded. The results allow to suggest that M-cholinergic reaction, controlling the spontaneous activity level, requires the additional energy supply for its maximal expression in inactive neurons. This is achieved by contacts of neurons with the surrounding glial satellites.

Structural, functional, and biochemical changes in the brain during modeling of dopamine system disturbances in rats

Dysfunction of the dopamine system was modeled in Wistar rats by injection of 50 mg/kg L-dopa over 4 weeks. Experimental rats demonstrated considerably decreased locomotor activity and increased emotional strain compared to the control group. Structural changes consisted in a significant decrease in the size of neuronal bodies in the sensorimotor cortex (layers III and V) and caudate nucleus together with changed variability of these parameters compared to the corresponding values in the control. The neuroglial index increased by 22% in layer V, tended to decrease in layer III, and remained unchanged in the caudate nucleus. L-Dopa changed specific activity of enzymes: tyrosine hydroxylase activity in the sensorimotor cortex decreased by 25%, while monoamine oxidase B activity in the caudate nucleus increased by 33%. Thus, dysfunction of the dopamine system resulting in changes in dopamine metabolism not only leads to structural and functional rearrangements reducing functional capacities of the cell systems, but is also associated with compensatory and repair reactions in the brain.

Features of the expression of the c-Fos gene along the rostrocaudal axis of the hippocampus in common voles after rapid training to solve a spatial task

The level of expression of the c-Fos protein in neurons was used as a measure of the activation of transcription in the hippocampus of common voles (Microtus arvalis Pall.) after rapid spatial training. Stained Fos-positive cells were counted on 20 brain sections along the rostrocaudal axis of the hippocampus. Voles were trained to find the exit to their home cages through one of the arms of a modified eight-arm radial maze (using a 2-h series of six trials on one day). Animals were initially trained to leave the home cage via an arm not connected to the maze. Voles of the "active" control group were passed through the isolated arm into the home cage six times on the experimental day. Animals for the "passive" control for c-Fos levels were collected from their home cages. Significant increases in c-Fos expression in voles trained in the maze and the active control group, as compared with passive controls, were seen in all areas studied (hippocampal fields CA1 and CA3 and the dentate fascia). At the same time, a significant increase in the number of c-Fos-positive neurons in voles trained in the maze, as compared with the active controls, was noted only in the caudal hippocampus, no differences being seen in the rostral part. The greatest levels of activation were seen in the dentate fascia and field CA3. These results provide evidence for the heterogeneous functioning of the hippocampus along the rostrocaudal axis during training of voles to solve a spatial task.

A large outdoor radial maze for comparative studies in birds and mammals

For a comparative neurobiological analysis of spatial learning and memory, a large outdoor eight-arm radial maze was constructed which permits behavioral assessment of many avian and mammalian species both from the laboratory or the wild, using the same metric space and session schedules. It consists of a central part of 250cm diameter, and has arms of 650cm length, 170cm height and 80cm width. In order to determine appropriate training schedules for comparison of different species, we tested four mammalian and two avian species during 9-15 sessions: 18 albino rats (Rattus norvegicus), nine outdoors and nine in a conventional small indoor maze; six guinea pigs (Cavia porcellus); six rabbits (Oryctolagus cuniculus); five hedgehogs (Erinaceus europaeus); seven hooded crows (Corvus corone cornix) and six chickens (Gallus domesticus). Rats learned fast in both mazes yet significantly better in the large one. Good-to-excellent learning was also observed in juvenile rabbits and wild-caught crows, although the latter tended to avoid arms in the vicinity of the observer. Hedgehogs and chickens did not show significant learning as a group, but some individuals appeared to learn the task. Guinea pigs remained continuously passive and could not be trained. Thus, in spite of species-specific demands for reward, adaptation and pre-training, this type of radial maze permits to directly compare a wide variety of species. Such comparability is essential for an analysis of underlying neurobiological mechanisms.