Accelerated Extracellular Nucleotide Metabolism in Brain Microvascular Endothelial Cells in Experimental Hypercholesterolemia.

Hypercholesterolemia affects the neurovascular unit, including the cerebral blood vessel endothelium. Operation of this system, especially in the context of energy metabolism, is controlled by extracellular concentration of purines, regulated by ecto-enzymes, such as e-NTPDase-1/CD39, ecto-5'-NT/CD73, and eADA. We hypothesize that hypercholesterolemia, via modulation of the activity of nucleotide metabolism-regulating ecto-enzymes, deteriorates glycolytic efficiency and energy metabolism of endothelial cells, which may potentially contribute to development of neurodegenerative processes. We aimed to determine the effect of hypercholesterolemia on the concentration of purine nucleotides, glycolytic activity, and activity of ecto-enzymes in the murine brain microvascular endothelial cells (mBMECs). We used 3-month-old male LDLR-/-/Apo E-/- double knockout mice to model hypercholesterolemia and atherosclerosis. The age-matched wild-type C57/BL6 mice were a control group. The intracellular concentration of ATP and NAD and extracellular activity of the ecto-enzymes were measured by HPLC. The glycolytic function of mBMECs was assessed by means of the extracellular acidification rate (ECAR) using the glycolysis stress test. The results showed an increased activity of ecto-5'-NT and eADA in mBMECs of the hypercholesterolemic mice, but no differences in intracellular concentration of ATP, NAD, and ECAR between the hypercholesterolemic and control groups. The changed activity of ecto-5'-NT and eADA leads to increased purine nucleotides turnover and a shift in their concentration balance towards adenosine and inosine in the extracellular space. However, no changes in the energetic metabolism of the mBMECs are reported. Our results confirm the influence of hypercholesterolemia on regulation of purine nucleotides metabolism, which may impair the function of the cerebral vascular endothelium. The effect of hypercholesterolemia on the murine brain microvascular endothelial cells (mBMECs). An increased activity of ecto-5'-NT and eADA in mBMECs of the LDLR-/-/Apo E-/- mice leads to a shift in the concentration balance towards adenosine and inosine in the extracellular space with no differences in intracellular concentration of ATP. Figure was created with Biorender.com.

The extent of damage to the blood-brain barrier in the hypercholesterolemic LDLR-/-/Apo E-/- double knockout mice depends on the animal's age, duration of pathology and brain area.

One of the effects of hypercholesterolemia (Hch) exerted on the central nervous system (CNS) is damage to the blood-brain barrier (BBB). Increased permeability of BBB results from structural changes in the vascular wall, loss of the tight junctions and barrier function, as well as alterations in the concentration of proteins located in the layers of the vascular wall. These changes occur in the course of metabolic and neurodegenerative diseases. The important role in the course of these processes is attributed to agrin, matrix metalloproteinase-9, and aquaporin-4. In this study, we aimed to determine: 1) the extent of Hch-induced damage to the BBB during maturation, and 2) the distribution of the above-mentioned markers in the vascular wall. Immunohistochemical staining and confocal microscopy were used for vascular wall protein assessment. The size of BBB damage was studied based on perivascular leakage of fluorescently labeled dextran. Three- and twelve-month-old male LDLR-/-/Apo E-/- double knockout mice (EX) developing Hch were used in the study. Age-matched male wild-type (WT) C57BL/6 mice were used as a control group. Differences in the concentration of studied markers coexisted with BBB disintegration, especially in younger mice. A relationship between the maturation of the vascular system and reduction of the BBB damage was also observed. We conclude that the extent of BBB permeability depends on animal age, duration of Hch, and brain region. These may explain different susceptibility of various brain areas to Hch, and different presentation of this pathology depending on age and its duration.

The Effect of Simvastatin on the Dynamics of NF-κB-Regulated Neurodegenerative and Neuroprotective Processes in the Acute Phase of Ischemic Stroke.

Statins are lipid-lowering drugs that act by inhibiting 3-hydroxy-3-methylglutaryl coenzyme A reductase, a rate-limiting enzyme in cholesterol biosynthesis. Animal studies have shown neuroprotective effects of statins in cerebral stroke. However, the underlying mechanisms are not fully understood. The nuclear factor-kappa B (NF-κB) transcription factor is involved in the regulation of apoptosis in stroke. Different dimers of NF-κB regulate the gene expression of proteins involved in both neurodegeneration and neuroprotection. We aimed to determine whether simvastatin improves stroke outcome via inhibition of the RelA/p65-containing subunit and downregulation of stroke-induced pro-apoptotic genes or via activation of NF-κB dimers containing the c-Rel subunit and upregulation of anti-apoptotic genes during the acute stroke phase. Eighteen-month-old Wistar rats, subjected to permanent MCAO or sham surgery, were administered simvastatin (20 mg/kg b.w.) or saline for 5 days before the procedure. Stroke outcome was determined by measuring cerebral infarct and assessing motor functions. The expression of NF-κB subunits in various cell populations was investigated using immunofluorescence/confocal microscopy. RelA and c-Rel were detected by WB. The NF-κB-DNA binding activity was investigated using EMSA, and expression of Noxa, Puma, Bcl-2, and Bcl-x genes was analyzed by qRT-PCR. Results showed a 50% infarct size reduction and significant motor function improvement in the simvastatin-treated animals which correlated with a decrease in RelA and a transient increase in the c-Rel level in the nucleus, normalization of the NF-κB-DNA binding activity, and downregulation of the NF-κB-regulated genes. Our results provide new insights into the statin-mediated neuroprotective action against stroke based on NF-κB pathway inhibition.

Transient cerebral ischemia induces the neuroglial proliferative activity and the potential to redirect neuroglial differentiation.

Brain injury triggers a complex response involving morphological changes, cellular proliferation, and differentiation of newly formed neuroglial subpopulations. These processes have been extensively studied in animal stroke models with permanent large vessel occlusion. However, less is known about neuroglial response after transient cerebral ischemia. Herein, we aimed to determine an astrocytic and NG2 glial proliferative response, potential changes in expression of developmental neuroglial markers: vimentin, nestin, oligodendrocyte transcription marker (Olig2), and a role of neuroglial subpopulations as a source of cells replenishing structural deficiencies in the ischemic brain. Results showed an induction of a proliferative neuroglial response in the peri-infarct area reflected in an increased percentage of GFAP/Ki67 + and NG2/Ki67 + cells within 4 weeks after transient MCAO. The peak of GFAP+ astrocytes proliferation of 30.3 ± 10.3% was observed in the first week, and a peak of NG2 + cells proliferation of 23.1 ± 11.8% in the second week after stroke. The presence of GFAP/Vimentin+ and GFAP/Nestin+ cells, as well as GFAP/Olig2 + and NG2/Olig2 + cells indicated an induction of developmental phenotypes with a differentiation potential. Finally, observed between day 1 and week 3 transient GFAP/NG2 + colocalization suggests the heterogeneous source of the reactive neuroglia after transient MCAO. Altogether, one-hour MCAO is a sufficient pathological stimulus to trigger a strong proliferative response of GFAP+ and NG2 + neuroglial cells and induce their early developmental phenotype. Our results suggest that transient ischemia may initiate a change in the direction of differentiation within the neuroglia cell population.

DPP-4 Inhibitor and Sulfonylurea Differentially Reverse Type 2 Diabetes-Induced Blood-Brain Barrier Leakage and Normalize Capillary Pericyte Coverage.

Microvascular pathology in the brain is one of the suggested mechanisms underlying the increased incidence and progression of neurodegenerative diseases in people with type 2 diabetes (T2D). Although accumulating data suggest a neuroprotective effect of antidiabetics, the underlying mechanisms are unclear. Here, we investigated whether two clinically used antidiabetics, the dipeptidyl peptidase-4 inhibitor linagliptin and the sulfonylurea glimepiride, which restore T2D-induced brain vascular pathology. Microvascular pathology was examined in the striatum of mice fed for 12 months with either normal chow diet or a high-fat diet (HFD) to induce T2D. A subgroup of HFD-fed mice was treated with either linagliptin or glimepiride for 3 months before sacrifice. We demonstrate that T2D caused leakage of the blood-brain barrier (BBB), induced angiogenesis, and reduced pericyte coverage of microvessels. However, linagliptin and glimepiride recovered the BBB integrity and restored the pericyte coverage differentially. Linagliptin normalized T2D-induced angiogenesis and restored pericyte coverage. In contrast, glimepiride enhanced T2D-induced angiogenesis and increased pericyte density, resulting in proper vascular coverage. Interestingly, glimepiride reduced microglial activation, increased microglial-vascular interaction, and increased collagen IV density. This study provides evidence that both DPP-4 inhibition and sulfonylurea reverse T2D-induced BBB leakage, which may contribute to antidiabetic neurorestorative effects.

More than Addiction-The Nucleus Accumbens Contribution to Development of Mental Disorders and Neurodegenerative Diseases.

Stress and negative emotions evoked by social relationships and working conditions, frequently accompanied by the consumption of addictive substances, and metabolic and/or genetic predispositions, negatively affect brain function. One of the affected structures is nucleus accumbens (NAc). Although its function is commonly known to be associated with brain reward responses and addiction, a growing body of evidence also suggests its role in some mental disorders, such as depression and schizophrenia, as well as neurodegenerative diseases, such as Alzheimer's, Huntington's, and Parkinson's. This may result from disintegration of the extensive connections based on numerous neurotransmitter systems, as well as impairment of some neuroplasticity mechanisms in the NAc. The consequences of NAc lesions are both morphological and functional. They include changes in the NAc's volume, cell number, modifications of the neuronal dendritic tree and dendritic spines, and changes in the number of synapses. Alterations in the synaptic plasticity affect the efficiency of synaptic transmission. Modification of the number and structure of the receptors affects signaling pathways, the content of neuromodulators (e.g., BDNF) and transcription factors (e.g., pCREB, DeltaFosB, NFκB), and gene expression. Interestingly, changes in the NAc often have a different character and intensity compared to the changes observed in the other parts of the basal ganglia, in particular the dorsal striatum. In this review, we highlight the role of the NAc in various pathological processes in the context of its structural and functional damage, impaired connections with the other brain areas cooperating within functional systems, and progression of the pathological processes.

A High-Fat Diet Increases Activation of the Glucagon-Like Peptide-1-Producing Neurons in the Nucleus Tractus Solitarii: an Effect that is Partially Reversed by Drugs Normalizing Glycemia.

Glucagon-like peptide-1 (GLP-1) is a peripheral incretin and centrally active peptide produced in the intestine and nucleus tractus solitarii (NTS), respectively. GLP-1 not only regulates metabolism but also improves cognition and is neuroprotective. While intestinal GLP-1-producing cells have been well characterized, less is known about GLP-1-producing neurons in NTS. We hypothesized that obesity-induced type 2 diabetes (T2D) impairs the function of NTS GLP-1-producing neurons and glycemia normalization counteracts this effect. We used immunohistochemistry/quantitative microscopy to investigate the number, potential atrophy, and activation (cFos-expression based) of NTS GLP-1-producing neurons, in non-diabetic versus obese/T2D mice (after 12 months of high-fat diet). NTS neuroinflammation was also assessed. The same parameters were quantified in obese/T2D mice treated from month 9 to 12 with two unrelated anti-hyperglycemic drugs: the dipeptidyl peptidase-4 inhibitor linagliptin and the sulfonylurea glimepiride. We show no effect of T2D on the number and volume but increased activation of NTS GLP-1-producing neurons. This effect was partially normalized by both anti-diabetic treatments, concurrent with decreased neuroinflammation. Increased activation of NTS GLP-1-producing neurons could represent an aberrant metabolic demand in T2D/obesity, attenuated by glycemia normalization. Whether this effect represents a pathophysiological process preceding GLP-1 signaling impairment in the CNS, remains to be investigated.

Neuroplasticity and Multilevel System of Connections Determine the Integrative Role of Nucleus Accumbens in the Brain Reward System.

A growing body of evidence suggests that nucleus accumbens (NAc) plays a significant role not only in the physiological processes associated with reward and satisfaction but also in many diseases of the central nervous system. Summary of the current state of knowledge on the morphological and functional basis of such a diverse function of this structure may be a good starting point for further basic and clinical research. The NAc is a part of the brain reward system (BRS) characterized by multilevel organization, extensive connections, and several neurotransmitter systems. The unique role of NAc in the BRS is a result of: (1) hierarchical connections with the other brain areas, (2) a well-developed morphological and functional plasticity regulating short- and long-term synaptic potentiation and signalling pathways, (3) cooperation among several neurotransmitter systems, and (4) a supportive role of neuroglia involved in both physiological and pathological processes. Understanding the complex function of NAc is possible by combining the results of morphological studies with molecular, genetic, and behavioral data. In this review, we present the current views on the NAc function in physiological conditions, emphasizing the role of its connections, neuroplasticity processes, and neurotransmitter systems.

The Stroke-Induced Increase of Somatostatin-Expressing Neurons is Inhibited by Diabetes: A Potential Mechanism at the Basis of Impaired Stroke Recovery.

Type 2 diabetes (T2D) hampers recovery after stroke, but the underling mechanisms are mostly unknown. In a recently published study (Pintana et al. in Clin Sci (Lond) 133(13):1367-1386, 2019), we showed that impaired recovery in T2D was associated with persistent atrophy of parvalbumin+ interneurons in the damaged striatum. In the current work, which is an extension of the abovementioned study, we investigated whether somatostatin (SOM)+ interneurons are also affected by T2D during the stroke recovery phase. C57Bl/6j mice were fed with high-fat diet or standard diet (SD) for 12 months and subjected to 30-min transient middle cerebral artery occlusion (tMCAO). SOM+ cell number/density in the striatum was assessed by immunohistochemistry 2 and 6 weeks after tMCAO in peri-infarct and infarct areas. This was possible by establishing a computer-based quantification method that compensates the post-stroke tissue deformation and the irregular cell distribution. SOM+ interneurons largely survived the stroke as seen at 2 weeks. Remarkably, 6 weeks after stroke, the number of SOM+ interneurons increased (vs. contralateral striatum) in SD-fed mice in both peri-infarct and infarct areas. However, this increase did not result from neurogenesis. T2D completely abolished this effect specifically in the in the infarct area. The results suggest that the up-regulation of SOM expression in the post-stroke phase could be related to neurological recovery and T2D could inhibit this process. We also present a new and precise method for cell counting in the stroke-damaged striatum that allows to reveal accurate, area-related effects of stroke on cell number.

Western Diet Accelerates the Impairment of Odor-Related Learning and Olfactory Memory in the Mouse.

Olfactory dysfunction could be an early indicator of cognitive decline in type 2 diabetes (T2D). However, whether obesity affects olfaction in people with T2D is unclear. This question needs to be addressed, because most people with T2D are obese. Importantly, whether different contributing factors leading to obesity (e.g., different components of diet or gain in weight) affect specific olfactory functions and underlying mechanisms is unknown. We examined whether two T2D-inducing obesogenic diets, one containing a high proportion of fat (HFD) and one with moderate fat and high sugar (Western diet, WD), affect odor detection/discrimination, odor-related learning, and olfactory memory in the mouse. We also investigated whether the diets impair adult neurogenesis, GABAergic interneurons, and neuroblasts in the olfactory system. Here, we further assessed olfactory cortex volume and cFos expression-based neuronal activity. The WD-fed mice showed declined odor-related learning and olfactory memory already after 3 months of diet intake (p = 0.046), although both diets induced similar hyperglycemia and weight gain compared to those of standard diet-fed mice (p = 0.0001 and p < 0.0001, respectively) at this time point. Eight months of HFD and WD diminished odor detection (p = 0.016 and p = 0.045, respectively), odor-related learning (p = 0.015 and p = 0.049, respectively), and olfactory memory. We observed no changes in the investigated cellular mechanisms. We show that the early deterioration of olfactory parameters related to learning and memory is associated with a high content of sugar in the diet rather than with hyperglycemia or weight gain. This finding could be exploited for understanding, and potentially preventing, cognitive decline/dementia in people with T2D. The mechanisms behind this finding remain to be elucidated.

Dipeptidyl peptidase-4 inhibitors and sulfonylureas prevent the progressive impairment of the nigrostriatal dopaminergic system induced by diabetes during aging.

The nigrostriatal dopaminergic system (NDS) controls motor activity, and its impairment during type 2 diabetes (T2D) progression could increase Parkinson's disease risk in diabetics. If so, whether glycemia regulation prevents this impairment needs to be addressed. We investigated whether T2D impairs the NDS and whether dipeptidyl peptidase-4 inhibition (DPP-4i; a clinical strategy against T2D but also neuroprotective in animal models) prevents this effect, in middle-aged mice. Neither T2D (induced by 12 months of high-fat diet) nor aging (14 months) changed striatal dopamine content assessed by high-performance liquid chromatography. However, T2D reduced basal and amphetamine-stimulated striatal extracellular dopamine, assessed by microdialysis. Both the DPP-4i linagliptin and the sulfonylurea glimepiride (an antidiabetic comparator unrelated to DPP-4i) counteracted these effects. The functional T2D-induced effects did not correlate with NDS neuronal/glial alterations. However, aging itself affected striatal neurons/glia, and the glia effects were counteracted mainly by DPP-4i. These findings show NDS functional pathophysiology in T2D and suggest the preventive use of two unrelated anti-T2D drugs. Moreover, DPP-4i counteracted striatal age-related glial alterations suggesting striatal rejuvenation properties.

Neurovascular Unit as a Source of Ischemic Stroke Biomarkers-Limitations of Experimental Studies and Perspectives for Clinical Application.

Cerebral stroke, which is one of the most frequent causes of mortality and leading cause of disability in developed countries, often leads to devastating and irreversible brain damage. Neurological and neuroradiological diagnosis of stroke, especially in its acute phase, is frequently uncertain or inconclusive. This results in difficulties in identification of patients with poor prognosis or being at high risk for complications. It also makes difficult identification of these stroke patients who could benefit from more aggressive therapies. In contrary to the cardiovascular disease, no single biomarker is available for the ischemic stroke, addressing the abovementioned issues. This justifies the need for identifying of effective diagnostic measures characterized by high specificity and sensitivity. One of the promising avenues in this area is studies on the panels of biomarkers characteristic for processes which occur in different types and phases of ischemic stroke and represent all morphological constituents of the brains' neurovascular unit (NVU). In this review, we present the current state of knowledge concerning already-used or potentially applicable biomarkers of the ischemic stroke. We also discuss the perspectives for identification of biomarkers representative for different types and phases of the ischemic stroke, as well as for different constituents of NVU, which concentration levels correlate with extent of brain damage and patients' neurological status. Finally, a critical analysis of perspectives on further improvement of the ischemic stroke diagnosis is presented.

Obesity-induced type 2 diabetes impairs neurological recovery after stroke in correlation with decreased neurogenesis and persistent atrophy of parvalbumin-positive interneurons.

Type 2 diabetes (T2D) hampers stroke recovery though largely undetermined mechanisms. Few preclinical studies have investigated the effect of genetic/toxin-induced diabetes on long-term stroke recovery. However, the effects of obesity-induced T2D are mostly unknown. We aimed to investigate whether obesity-induced T2D worsens long-term stroke recovery through the impairment of brain's self-repair mechanisms - stroke-induced neurogenesis and parvalbumin (PV)+ interneurons-mediated neuroplasticity. To mimic obesity-induced T2D in the middle-age, C57bl/6j mice were fed 12 months with high-fat diet (HFD) and subjected to transient middle cerebral artery occlusion (tMCAO). We evaluated neurological recovery by upper-limb grip strength at 1 and 6 weeks after tMCAO. Gray and white matter damage, stroke-induced neurogenesis, and survival and potential atrophy of PV-interneurons were quantitated by immunohistochemistry (IHC) at 2 and 6 weeks after tMCAO. Obesity/T2D impaired neurological function without exacerbating brain damage. Moreover, obesity/T2D diminished stroke-induced neural stem cell (NSC) proliferation and neuroblast formation in striatum and hippocampus at 2 weeks after tMCAO and abolished stroke-induced neurogenesis in hippocampus at 6 weeks. Finally, stroke resulted in the atrophy of surviving PV-interneurons 2 weeks after stroke in both non-diabetic and obese/T2D mice. However, after 6 weeks, this effect selectively persisted in obese/T2D mice. We show in a preclinical setting of clinical relevance that obesity/T2D impairs neurological functions in the stroke recovery phase in correlation with reduced neurogenesis and persistent atrophy of PV-interneurons, suggesting impaired neuroplasticity. These findings shed light on the mechanisms behind impaired stroke recovery in T2D and could facilitate the development of new stroke rehabilitative strategies for obese/T2D patients.

Dipeptidyl Peptidase-4 Inhibitors for the Potential Treatment of Brain Disorders; A Mini-Review With Special Focus on Linagliptin and Stroke.

Cerebral stroke is a leading cause of death and persistent disability of elderly in the world. Although stroke prevention by targeting several risk factors such as diabetes and hypertension has decreased the stroke incidence, the total number of strokes is increasing due to the population aging and new preventive therapies are needed. Moreover, post-stroke acute pharmacological strategies aimed to reduce stroke-induced brain injury have failed in clinical trials despite being effective in animal models. Finally, approximately 30% of surviving stroke patients do not recover from stroke and remain permanently dependent on supportive care in activities of daily living. Therefore, strategies to improve stroke recovery in the post-acute phase are highly needed. Linagliptin is a dipeptidyl peptidase-4 inhibitor which is clinically approved to reduce hyperglycemia in type 2 diabetes. The regulation of glycemia by dipeptidyl peptidase-4 inhibition is mainly achieved by preventing endogenous glucagon-like peptide-1 (GLP-1) degradation. Interestingly, linagliptin has also shown glycaemia-independent beneficial effects in animal models of stroke, Parkinson's disease and Alzheimer's disease. In some case the preclinical data have been supported with some clinical data. Although potentially very interesting for the development of new strategies against stroke and neurodegenerative disorders, the mode of action of linagliptin in the brain is still largely unknown and seems to occur in a GLP-1R-independent manner. The purpose of this mini-review is to summarize and discuss the recent experimental and clinical work regarding the effects of linagliptin in the central nervous system, with special emphasis on acute neuroprotection, stroke prevention and post-stroke recovery. We also highlight the main questions in this research field that need to be addressed in clinical perspective.

The effect of DPP-4 inhibition to improve functional outcome after stroke is mediated by the SDF-1α/CXCR4 pathway.

BACKGROUND: Dipeptidyl peptidase-4 (DPP-4) inhibitors (gliptins) are approved drugs for the treatment of hyperglycemia in patients with type 2 diabetes. These effects are mainly mediated by inhibiting endogenous glucagon-like peptide-1 (GLP-1) cleavage. Interestingly, gliptins can also improve stroke outcome in rodents independently from GLP1. However, the underlying mechanisms are unknown. Stromal cell-derived factor-1α (SDF-1α) is a DPP-4 substrate and CXCR4 agonist promoting beneficial effects in injured brains. However, SDF-1α involvement in gliptin-mediated neuroprotection after ischemic injury is unproven. We aimed to determine whether the gliptin linagliptin improves stroke outcome via the SDF-1α/CXCR4 pathway, and identify additional effectors behind the efficacy. METHODS: Mice were subjected to stroke by transient middle cerebral artery occlusion (MCAO). linagliptin was administered for 3 days or 3 weeks from stroke onset. The CXCR4-antagonist AMD3100 was administered 1 day before MCAO until 3 days thereafter. Stroke outcome was assessed by measuring upper-limb function, infarct volume and neuronal survival. The plasma and brain levels of active GLP-1, GIP and SDF-1α were quantified by ELISA. To identify additional gliptin-mediated molecular effectors, brain samples were analyzed by mass spectrometry. RESULTS: Linagliptin specifically increased active SDF-1α but not glucose-dependent insulinotropic peptide (GIP) or GLP-1 brain levels. Blocking of SDF-1α/CXCR4 pathway abolished the positive effects of linagliptin on upper-limb function and histological outcome after stroke. Moreover, linagliptin treatment after stroke decreased the presence of peptides derived from neurogranin and from an isoform of the myelin basic protein. CONCLUSIONS: We showed that linagliptin improves functional stroke outcome in a SDF-1α/CXCR4-dependent manner. Considering that Calpain activity and intracellular Ca2+ regulate neurogranin and myelin basic protein detection, our data suggest a gliptin-mediated neuroprotective mechanism via the SDF-1α/CXCR4 pathway that could involve the regulation of Ca2+ homeostasis and the reduction of Calpain activity. These results provide new insights into restorative gliptin-mediated effects against stroke.

Type 2 diabetes impairs odour detection, olfactory memory and olfactory neuroplasticity; effects partly reversed by the DPP-4 inhibitor Linagliptin.

Recent data suggest that olfactory deficits could represent an early marker and a pathogenic mechanism at the basis of cognitive decline in type 2 diabetes (T2D). However, research is needed to further characterize olfactory deficits in diabetes, their relation to cognitive decline and underlying mechanisms.The aim of this study was to determine whether T2D impairs odour detection, olfactory memory as well as neuroplasticity in two major brain areas responsible for olfaction and odour coding: the main olfactory bulb (MOB) and the piriform cortex (PC), respectively. Dipeptidyl peptidase-4 inhibitors (DPP-4i) are clinically used T2D drugs exerting also beneficial effects in the brain. Therefore, we aimed to determine whether DPP-4i could reverse the potentially detrimental effects of T2D on the olfactory system.Non-diabetic Wistar and T2D Goto-Kakizaki rats, untreated or treated for 16 weeks with the DPP-4i linagliptin, were employed. Odour detection and olfactory memory were assessed by using the block, the habituation-dishabituation and the buried pellet tests. We assessed neuroplasticity in the MOB by quantifying adult neurogenesis and GABAergic inhibitory interneurons positive for calbindin, parvalbumin and carletinin. In the PC, neuroplasticity was assessed by quantifying the same populations of interneurons and a newly identified form of olfactory neuroplasticity mediated by post-mitotic doublecortin (DCX) + immature neurons.We show that T2D dramatically reduced odour detection and olfactory memory. Moreover, T2D decreased neurogenesis in the MOB, impaired the differentiation of DCX+ immature neurons in the PC and altered GABAergic interneurons protein expression in both olfactory areas. DPP-4i did not improve odour detection and olfactory memory. However, it normalized T2D-induced effects on neuroplasticity.The results provide new knowledge on the detrimental effects of T2D on the olfactory system. This knowledge could constitute essentials for understanding the interplay between T2D and cognitive decline and for designing effective preventive therapies.

BDNF: A Key Factor with Multipotent Impact on Brain Signaling and Synaptic Plasticity.

Brain-derived neurotrophic factor (BDNF) is one of the most widely distributed and extensively studied neurotrophins in the mammalian brain. Among its prominent functions, one can mention control of neuronal and glial development, neuroprotection, and modulation of both short- and long-lasting synaptic interactions, which are critical for cognition and memory. A wide spectrum of processes are controlled by BDNF, and the sometimes contradictory effects of its action can be explained based on its specific pattern of synthesis, comprising several intermediate biologically active isoforms that bind to different types of receptor, triggering several signaling pathways. The functions of BDNF must be discussed in close relation to the stage of brain development, the different cellular components of nervous tissue, as well as the molecular mechanisms of signal transduction activated under physiological and pathological conditions. In this review, we briefly summarize the current state of knowledge regarding the impact of BDNF on regulation of neurophysiological processes. The importance of BDNF for future studies aimed at disclosing mechanisms of activation of signaling pathways, neuro- and gliogenesis, as well as synaptic plasticity is highlighted.

Nicotine-induced CREB and DeltaFosB activity is modified by caffeine in the brain reward system of the rat.

Coffee and nicotine consumption are frequently combined, indicating possible intensifying effect of caffeine on smoking behavior, although neurobiological background of this phenomenon remains unknown. We aimed at determining the effect of caffeine and nicotine, applied separately or simultaneously, on activation of six structures of the brain reward system: nucleus accumbens (NAc), ventral tegmental area (VTA), amygdala (Amg), hippocampus (Hip), medial prefrontal cortex (mPfr) and dorsal striatum (CdP) in the adult male Wistar rats. Activation of two transcription factors, the phosphorylated form of cyclic AMP-response element binding protein (pCREB) and DeltaFosB (ΔFosB) was assessed by immunohistochemistry after multiple-dose five-days psychostimulants administration followed by 20min and 24h survival, respectively. Nicotine evoked the highest increase of pCREB-immunoreactivity (-ir) in NAc, while caffeine exerted the weakest effect in mPfr and CdP. Nicotine/caffeine co-administration resulted in decrease of pCREB-ir in NAc and increase in Amg, compared with the effect of each psychostimulant used separately. Nicotine was the strongest psychostimulant activating ΔFosB-ir in Amg, whereas caffeine - in Hip. Nicotine/caffeine-exerted effect upon ΔFosB-ir in Amg was weaker, whereas in mPfr stronger, than nicotine-evoked effect in these structures. In summary, pCREB and ΔFosB activation is dependent on the type of stimulus, brain structure and functional context. Activation of both transcription factors is responsible for caffeine's modifying effect upon nicotine-related behaviors and must be taken into account while quitting cigarette smoking.

Type 2 diabetes alters hippocampal gamma oscillations: A potential mechanism behind impaired cognition.

Type 2 diabetes (T2D) has been associated with cognitive decline, dementia and Alzheimer's disease (AD). Remarkably, the pathophysiological mechanisms behind this are still mostly unknown. Cognition and memory formation are associated with gamma oscillations in hippocampal neuronal networks and fast-spiking, parvalbumin-expressing interneurons (PV+ IN) play a key role in these processes.

Cholesterol as a modifying agent of the neurovascular unit structure and function under physiological and pathological conditions.

The brain, demanding constant level of cholesterol, precisely controls its synthesis and homeostasis. The brain cholesterol pool is almost completely separated from the rest of the body by the functional blood-brain barrier (BBB). Only a part of cholesterol pool can be exchanged with the blood circulation in the form of the oxysterol metabolites such, as 27-hydroxycholesterol (27-OHC) and 24S-hydroxycholesterol (24S-OHC). Not only neurons but also blood vessels and neuroglia, constituting neurovascular unit (NVU), are crucial for the brain cholesterol metabolism and undergo precise regulation by numerous modulators, metabolites and signal molecules. In physiological conditions maintaining the optimal cholesterol concentration is important for the energetic metabolism, composition of cell membranes and myelination. However, a growing body of evidence indicates the consequences of the cholesterol homeostasis dysregulation in several pathophysiological processes. There is a causal relationship between hypercholesterolemia and 1) development of type 2 diabetes due to long-term high-fat diet consumption, 2) significance of the oxidative stress consequences for cerebral amyloid angiopathy and neurodegenerative diseases, 3) insulin resistance on progression of the neurodegenerative brain diseases. In this review, we summarize the current state of knowledge concerning the cholesterol influence upon functioning of the NVU under physiological and pathological conditions.