Brain changes in BDNF and S100B induced by ketogenic diets in Wistar rats

AimsWe investigated the effects of ketogenic diet (KD) on levels of tumor necrosis factor alpha (TNF-α, a classical pro-inflammatory cytokine), BDNF (brain-derived neurotrophic factor, commonly associated with synaptic plasticity), and S100B, an astrocyte neurotrophic cytokine involved in metabolism regulation.Main methodsYoung Wistar rats were fed during 8 weeks with control diet or two KD, containing different proportions of omega 6 and omega 3 polyunsaturated fatty acids. Contents of TNF-α, BDNF and S100B were measured by ELISA in two brain regions (hippocampus and striatum) as well as blood serum and cerebrospinal fluid.Key findingsOur data suggest that KD was able to reduce the levels of BDNF in the striatum (but not in hippocampus) and S100B in the cerebrospinal fluid of rats. These alterations were not affected by the proportion of polyunsaturated fatty acids offered. No changes in S100B content were observed in serum or analyzed brain regions. Basal TNF-α content was not affected by KD.SignificanceThese findings reinforce the importance of this diet as an inductor of alterations in the brain, and such changes might contribute to the understanding of the effects (and side effects) of KD in brain disorders.     

GABAA Modulation of S100B Secretion in Acute Hippocampal Slices and Astrocyte Cultures

Astrocytes are the major glial cells in brain tissue and are involved, among many functions, ionic and metabolic homeostasis maintenance of synapses. These cells express receptors and transporters for neurotransmitters, including GABA. GABA signaling is reportedly able to affect astroglial response to injury, as evaluated by specific astrocyte markers such as glial fibrillary acid protein and the calcium-binding protein, S100B. Herein, we investigated the modulatory effects of the GABA_A receptor on astrocyte S100B secretion in acute hippocampal slices and astrocyte cultures, using the agonist, muscimol, and the antagonists pentylenetetrazol (PTZ) and bicuculline. These effects were analyzed in the presence of tetrodotoxin (TTX), fluorocitrate (FLC), cobalt and barium. PTZ positively modify S100B secretion in hippocampal slices and astrocyte cultures; in contrast, bicuculline inhibited S100B secretion only in hippocampal slices. Muscimol, per se, did not change S100B secretion, but prevented the effects of PTZ and bicuculline. Moreover, PTZ-induced S100B secretion was prevented by TTX, FLC, cobalt and barium indicating a complex GABA_A communication between astrocytes and neurons. The effects of two putative agonists of GABA_A, β-hydroxybutyrate and methylglyoxal, on S100B secretion were also evaluated. In view of the neurotrophic role of extracellular S100B under conditions of injury, our data reinforce the idea that GABA_A receptors act directly on astrocytes, and indirectly on neurons, to modulate astroglial response.

     

Effects of chronic caloric restriction on kidney and heart redox status and antioxidant enzyme activities in Wistar rats

Caloric restriction (CR) has been associated with health benefits and these effects have been attributed, in part, to modulation of oxidative status by CR; however, data are still controversial. Here, we investigate the effects of seventeen weeks of chronic CR on parameters of oxidative damage/modification of proteins and on antioxidant enzyme activities in cardiac and kidney tissues. Our results demonstrate that CR induced an increase in protein carbonylation in the heart without changing the content of sulfhydryl groups or the activities of superoxide dismutase and catalase (CAT). Moreover, CR caused an increase in CAT activity in kidney, without changing other parameters. Protein carbonylation has been associated with oxidative damage and functional impairment; however, we cannot exclude the possibility that, under our conditions, this alteration indicates a different functional meaning in the heart tissue. In addition, we reinforce the idea that CR can increase CAT activity in the kidney. [BMB Reports 2012; 45(11): 671-676]     

Phase-Dependent Astroglial Alterations in Li–Pilocarpine-Induced <Emphasis Type="Italic">Status Epilepticus</Emphasis> in Young Rats

Epilepsy prevalence is high in infancy and in the elderly population. Lithium–pilocarpine is widely used to induce experimental animal models of epilepsy, leading to similar neurochemical and morphological alterations to those observed in temporal lobe epilepsy. As astrocytes have been implicated in epileptic disorders, we hypothesized that specific astroglial changes accompany and contribute to epileptogenesis. Herein, we evaluated time-dependent astroglial alterations in the hippocampus of young (27-day-old) rats at 1, 14 and 56 days after Li–pilocarpine-induced status epilepticus (SE), corresponding to different phases in this model of epilepsy. We determined specific markers of astroglial activation: GFAP, S100B, glutamine synthetase (GS), glutathione (GSH) content, aquaporin-4 (AQP-4) and potassium channel Kir 4.1; as well as epileptic behavioral, inflammatory and neurodegenerative changes. Phase-dependent signs of hippocampal astrogliosis were observed, as demonstrated by increments in GFAP, S100B and GS. Astrocyte dysfunction in the hippocampus was characterized, based on the decrease in GSH content, AQP-4 and Kir 4.1 channels. Degenerating neurons were identified by Fluoro-Jade C staining. We found a clear, early (at SE1) and persistent (at SE56) increase in cerebrospinal fluid (CSF) S100B levels. Additionally, serum S100B was found to decrease soon after SE induction, implicating a rapid-onset increase in the CSF/serum S100B ratio. However, serum S100B increased at SE14, possibly reflecting astroglial activation and/or long-term increase in cerebrovascular permeability. Moreover, we suggest that peripheral S100B levels may represent a useful marker for SE in young rats and for follow up during the chronic phases of this model of epilepsy. Together, results reinforce and extend the idea of astroglial involvement in epileptic disorders.     

Disruption of Amyloid Plaques Integrity Affects the Soluble Oligomers Content from Alzheimer Disease Brains

The implication of soluble Abeta in the Alzheimer’s disease (AD) pathology is currently accepted. In fact, the content of soluble extracellular Abeta species, such as monomeric and/or oligomeric Abeta, seems to correlate with the clinico-pathological dysfunction observed in AD patients. However, the nature (monomeric, dimeric or other oligomers), the relative abundance, and the origin (extra-/intraneuronal or plaque-associated), of these soluble species are actually under debate. In this work we have characterized the soluble (defined as soluble in Tris-buffered saline after ultracentrifugation) Abeta, obtained from hippocampal samples of Braak II, Braak III–IV and Braak V–VI patients. Although the content of both Abeta40 and Abeta42 peptides displayed significant increase with pathology progression, our results demonstrated the presence of low, pg/µg protein, amount of both peptides. This low content could explain the absence (or below detection limits) of soluble Abeta peptides detected by western blots or by immunoprecipitation-western blot analysis. These data were in clear contrast to those published recently by different groups. Aiming to explain the reasons that determine these substantial differences, we also investigated whether the initial homogenization could mobilize Abeta from plaques, using 12-month-old PS1xAPP cortical samples. Our data demonstrated that manual homogenization (using Dounce) preserved the integrity of Abeta plaques whereas strong homogenization procedures (such as sonication) produced a vast redistribution of the Abeta species in all soluble and insoluble fractions. This artifact could explain the dissimilar and somehow controversial data between different groups analyzing human AD samples.     

Molecular and cellular characterization of the age-related neuroinflammatory processes occurring in normal rat hippocampus: potential relation with the loss of somatostatin GABAergic neurons

Increased neuroinflammatory reaction is frequently observed during normal brain aging. However, a direct link between neuroinflammation and neurodegeneration during aging has not yet been clearly shown. Here, we have characterized the age-related hippocampal inflammatory processes and the potential relation with hippocampal neurodegeneration. The mRNA expression of the pro-inflammatory cytokines IL-1beta and tumor necrosis factor-alpha (TNF-alpha), and the iNOs enzyme was significantly increased in aged hippocampus. Accordingly, numerous activated microglial cells were observed in aged rats. These cells were differentially distributed along the hippocampus, being more frequently located in the hilus and the CA3 area. The mRNA expression of somatostatin, a neuropeptide expressed by some GABAergic interneurons, and the number of somatostatin-immunopositive cells decreased in aged rats. However, the number of hippocampal parvalbumin-containing GABAergic interneurons was preserved. Interestingly, in aged rats, the mRNA expression of somatostatin and IL-1beta was inversely correlated and, the decrease in the number of somatostatin-immunopositive cells was higher in the hilus of dentate gyrus than in the CA1 region. Finally, intraperitoneal chronic lipopolysaccharide (LPS) injection in young animals mimicked the age-related hippocampal inflammation as well as the decrease of somatostatin mRNA expression. Present results strongly support the neuroinflammation as a potential factor involved in the age-related degeneration of somatostatin GABAergic cells.     

Heterogeneity in the Allosteric Interaction Between the γ-Aminobutyric Acid (GABA) Binding Site and Three Different Benzodiazepine Binding Sites of the GABAA/Benzodiazepine Receptor Complex in the Rat Nervous System

In the present communication we have investigated the allosteric coupling between the gamma-aminobutyric acidA (GABAA) receptor and the pharmacologically different benzodiazepine (BZD) receptor subtypes in membranes from various rat nervous system regions. Two types of BZD receptors (type I and type II) have been classically defined using CL 218.872. However, using zolpidem, three different BZD receptors have been identified by binding displacement experiments in membranes. These BZD receptor subtypes displayed high, low, and very low affinity for zolpidem. The distribution of the high- and low-affinity binding sites for zolpidem was similar to that of type I and type II subtypes in cerebellum, prefrontal cortex, and adult cerebral cortex. On the other hand, the very-low-affinity binding site was localized in relative high proportion in spinal cord, hippocampus, and newborn cerebral cortex and, to a minor extent, in superior colliculus. The allosteric coupling between the GABAA receptor and the BZD receptor subtypes was different. The high- and low-affinity binding sites for zolpidem seemed to have a similar high degree of coupling, except in spinal cord. On the other hand, the very-low-affinity binding site for zolpidem displayed a low degree of coupling with the GABAA receptor. These results seem to indicate that the different efficacy of GABA in enhancing the [3H]flunitrazepam binding could be due to the different BZD receptor subtypes present in the GABAA/BZD receptor complex and, moreover, led us to speculate that the low GABA efficacy found in membranes from spinal cord, hippocampus, and newborn cerebral cortex might be due to the presence in relatively high proportion of the very-low-affinity binding site for zolpidem.     

A generalized pollination system in the tropics: bats, birds and Aphelandra acanthus

Background and Aims

A number of different types of flower-visiting animals coexist in any given habitat. What evolutionary and ecological factors influence the subset of these that a given plant relies on for its pollination? Addressing this question requires a mechanistic understanding of the importance of different potential pollinators in terms of visitation rate (pollinator ‘quantity’) and effectiveness at transferring pollen (pollinator ‘quality’) is required. While bat-pollinated plants typically are highly specialized to bats, there are some instances of bat-pollinated plants that use other pollinators as well. These generalized exceptions tend to occur in habitats where bat ‘quantity’ is poor due to low or fluctuating bat densities.

Methods

Aphelandra acanthus occurs in tropical cloud forests with relatively high densities of bat visitors, yet displays a mix of floral syndrome characteristics, suggesting adaptation to multiple types of pollinators. To understand its pollination system better, aspects of its floral phenology and the ‘quantity’ and ‘quality’ components of pollination by its floral visitors are studied here.

Key Results

Flowers were found to open and senesce throughout the day and night, although anther dehiscence was restricted to the late afternoon and night. Videotaping reveals that flowers are visited nocturnally by bats and moths, and diurnally by hummingbirds. Analysis of pollen deposition shows that bats regularly transfer large amounts of conspecific pollen, while hummingbirds occasionally transfer some pollen, and moths rarely do so.

Conclusions

Hummingbirds and bats were comparable in terms of pollination ‘quantity’, while bats were the most effective in terms of ‘quality’. Considering these components together, bats are responsible for approx. 70 % of A. acanthus pollination. However, bats also transferred remarkably large amounts of foreign pollen along with the conspecific grains (three of four grains were foreign). It is suggested that the negative effects of interspecific pollen transfer may decrease bat ‘quality’ for A. acanthus, and thus select for generalization on multiple pollinators instead of specialization on bats.Key words: Specialization, generalization, pollinator effectiveness, hummingbirds, floral syndrome, bat pollination, chiropterophily, ornithophily, cloud forest, heterospecific pollen transfer     

The Non-NMDA Glutamate Receptor Antagonists 6-Cyano-7-Nitroquinoxaline-2,3-dione and 2,3-Dihydroxy-6-Nitro-7-Sulfamoylbenzo(f)quinoxaline, but Not NMDA Antagonists, Block the Intrastriatal Neurotoxic Effect of MPP+

Altered glutamatergic neurotransmission appears to be central to the pathophysiology of Parkinson's disease; consequently, considerable effort has been made to elucidate neuroprotective mechanisms against such toxicity. In the present study, the possible neuroprotective effect of glutamate receptor antagonists against MPP+ neurotoxicity on dopaminergic terminals of rat striatum was investigated. Different doses of glutamate receptor antagonists were coinfused with 1.5 microg of MPP+ into the striatum; kynurenic acid, a nonselective antagonist of glutamate receptors (30 and 60 nmol), partially protected dopaminergic terminal degeneration in terms of rescue of dopamine levels and tyrosine hydroxylase immunohistochemistry. Dizocilpine, a channel blocker of the NMDA receptor (1, 4, and 8 nmol), and 7-chlorokynurenic acid, a selective antagonist at the glycine site of the NMDA receptor (1 and 10 nmol), failed to protect dopaminergic terminals from MPP+ toxicity. However, 6-cyano-7-nitroquinoxaline-2,3-dione (0.5 and 1 nmol) and 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline (1 nmol), two AMPA-kainate receptor antagonists, protected against MPP toxicity. Our findings suggest that the toxic effects of MPP+ on dopaminergic terminals are not mediated through a direct interaction with the NMDA subtype of glutamate receptor, but with the AMPA-kainate subtype.