Involvement of PKA-dependent upregulation of nNOS-CGRP in adrenomedullin-initiated mechanistic pathway underlying CFA-induced response in rats.

We have previously shown that intrathecal administration of the adrenomedullin (AM) receptor antagonist AM(22-52) produces a long-lasting anti-hyperalgesia effect. This study examined the hypothesis that AM recruits other pronociceptive mediators in complete Freund's adjuvant (CFA)-induced inflammation. Injection of CFA in the hindpaw of rat produced an increase in the expression of nNOS in dorsal root ganglion (DRG) and the spinal dorsal horn. An intrathecal administration of AM(22-52), but not the CGRP antagonist BIBN4096BS, abolished the CFA-induced increase of nNOS. Moreover, AM-induced increase of CGRP was inhibited by the nNOS inhibitors L-NAME and 7-nitroindazole in cultured ganglion explants. Addition of AM to ganglion cultures induced an increase in nNOS protein, which was attenuated by the PKA inhibitor H-89. Treatment with AM also concentration-dependently increased cAMP content and pPKA protein level, but not its non-phosphorylated form, in cultured ganglia. In addition, nNOS was shown to be co-localized with the AM receptor components calcitonin receptor-like receptor and receptor activity-modifying protein 2- and 3 in DRG neurons. The present study suggests that the enhanced activity of nitric oxide (NO) mediates the biological action of AM at the spinal level and that AM recruits NO-CGRP via cAMP/PKA signaling in a mechanistic pathway underlying CFA-induced hyperalgesia.

Comparative neuroprotective properties of stilbene and catechin analogs: action via a plasma membrane receptor site?

Various studies have reported on the neuroprotective effects of polyphenols, widely present in food, beverages, and natural products. For example, we have shown that resveratrol, a polyphenol enriched in red wine and other foods such as peanuts, protects hippocampal cells against beta-amyloid (Abeta)-induced toxicity, a key protein involved in the neuropathology of Alzheimer disease. This effect involves, at least in part, the capacity of resveratrol to activate the phosphorylation of delta isoform of protein kinase C (PKC-delta). The neuroprotective action of resveratrol is shared by piceatannol, a stilbene derivative, as well as by tea-derived catechin gallate esters. The thioflavin T assay indicated that all these polyphenols inhibited the formation of Abeta fibrils, suggesting that this action likely also contributes to their neuroprotective effects. Binding and autoradiographic studies revealed that the effects of polyphenols might involve specific binding sites that are particularly enriched in the choroid plexus in the rat brain. Interestingly, the choroid plexus secretes transthyretin, a protein that has been shown to modulate Abeta aggregation and that may be critical to the maintenance of normal learning capacities in aging. Taken together, these data suggest that polyphenols target multiple enzymes/proteins, leading to their neuroprotective actions, possibly through action via specific plasma membrane binding sites.

Prototypical antipsychotic drugs protect hippocampal neuronal cultures against cell death induced by growth medium deprivation.

BACKGROUND: Several clinical studies suggested that antipsychotic-based medications could ameliorate cognitive functions impaired in certain schizophrenic patients. Accordingly, we investigated the effects of various dopaminergic receptor antagonists--including atypical antipsychotics that are prescribed for the treatment of schizophrenia--in a model of toxicity using cultured hippocampal neurons, the hippocampus being a region of particular relevance to cognition. RESULTS: Hippocampal cell death induced by deprivation of growth medium constituents was strongly blocked by drugs including antipsychotics (10(-10)-10(-6) M) that display nM affinities for D2 and/or D4 receptors (clozapine, haloperidol, (+/-)-sulpiride, domperidone, clozapine, risperidone, chlorpromazine, (+)-butaclamol and L-741,742). These effects were shared by some caspases inhibitors and were not accompanied by inhibition of reactive oxygen species. In contrast, (-)-raclopride and remoxipride, two drugs that preferentially bind D2 over D4 receptors were ineffective, as well as the selective D3 receptor antagonist U 99194. Interestingly, (-)-raclopride (10(-6) M) was able to block the neuroprotective effect of the atypical antipsychotic clozapine (10(-6) M). CONCLUSION: Taken together, these data suggest that D2-like receptors, particularly the D4 subtype, mediate the neuroprotective effects of antipsychotic drugs possibly through a ROS-independent, caspase-dependent mechanism.

Neuroprotective effects of green and black teas and their catechin gallate esters against beta-amyloid-induced toxicity.

Teas represent a large family of plants containing high amounts of polyphenols that may confer health benefits in various diseases. Recently, it has been hypothesized that tea consumption may also reduce the risk of age-related neurodegenerative pathologies. Considering the deleterious role of beta-amyloid (Abeta) in the aetiology of Alzheimer's disease (AD), we investigated green and black tea extracts and flavan-3-ols (present as monomers and dimers in green and black forms, respectively) against toxicity induced by Abeta-derived peptides using primary cultures of rat hippocampal cells as model. Both green and black tea extracts (5-25 microg/mL) displayed neuroprotective action against Abeta toxicity. These effects were shared by gallic acid (1-20 microm), epicatechin gallate (ECG; 1-20 microM) and epigallocatechin gallate (EGCG; 1-10 microM), the former being the most potent flavan-3-ol. In contrast, epicatechin and epigallocatechin were ineffective in the same range of concentrations. Moreover, only tea flavan-3-ol gallate esters (i.e. ECG, EGCG) and gallic acid inhibited apoptotic events induced by Abeta(25-35). Interestingly, EGCG and gallic acid inhibited Abeta aggregation and/or the formation of Abeta-derived diffusible neurotoxin ligands. Taken together, these results indicate that the catechin gallates (through the galloyl moiety) contribute to the neuroprotective effects of both green and black teas. Moreover, the protective effect of EGCG is likely to be associated, at least in part, with its inhibitory action on Abeta fibrils/oligomers formation. These data also support the hypothesis that not only green but also black teas may reduce age-related neurodegenerative diseases, such as AD.

Aged neuropeptide Y transgenic rats are resistant to acute stress but maintain spatial and non-spatial learning.

The behavioral phenotype of five-month-old rats overexpressing neuropeptide Y (NPY) has previously been described [Proc Natl Acad Sci USA 97 (2000) 12852]. In this transgenic rat model, there is central overexpression of prepro-NPY mRNA and NPY peptide in the hippocampus and hypothalamus and decreased Y1 binding sites within the hippocampus. These molecular and neurochemical events led to altered anxiety profile and learning abilities in NPY-overexpressing rats. In the present study, anxiety and learning/memory related behaviors were examined in one-year-old NPY-transgenic rats in order to assess any behavioral changes that may have occurred during the aging process. As observed in 5-month-old overexpressing rats, aged NPY-transgenic animals are resistant to acute physical restraint stress measured by the elevated-plus maze and demonstrate anxiolytic-like activity in the open field. However, in contrast to data in young rats, there was no significant difference between aged wildtype and NPY-transgenic animals in relation to spatial and non-spatial memory as indicated by the (allo- and ego-centric) Morris water maze and object recognition test. It would thus appear that the anxiolytic-like profile observed in young NPY-overexpressing rats is maintained in older animals providing further evidence for a role for NPY in anxious behaviors. However, the cognitive deficits observed in young rats do not appear to occur in older animals suggesting the existence of compensatory mechanisms leading to a reversal of the learning deficits noted in younger animals. These results also provide additional evidence for the mechanistic dissociation between anxiety and cognition-related behaviors modulated by NPY.

Estradiol valerate and alcohol intake: a comparison between Wistar and Lewis rats and the putative role of endorphins.

Studies show that estrogens can influence alcohol consumption; however, findings are variable and an etiology remains unknown. Furthermore, estrogen administration can alter several neurotransmitter systems implicated in alcohol consumption, including the beta-endorphin (beta-EP) system. The present studies investigate (a) whether estradiol valerate (EV) alters voluntary alcohol consumption in Wistar and Lewis rats, (b) if an effect of EV on drinking is associated with changes in hypothalamic or pituitary beta-EP content, and (c) whether differences in alcohol drinking between treatment and rat groups are related to locomotor or defensive behavior/anxiety scores. Of 30 Wistar and 30 Lewis rats used in this study, half were injected with 2 mg EV in 0.2 ml sesame oil, while the remainder were injected with the vehicle only. After 8 weeks, all animals were tested in the open field and elevated plus maze. A week later, 4-6 animals in each group were sacrificed. The remaining animals were tested for voluntary alcohol drinking for 24 days prior to being sacrificed on the last day. Radioimmunoassay was used to estimate hypothalamic and pituitary beta-EP content. Wistar and Lewis rats injected with EV showed an increase in alcohol drinking, but their behavior scores and beta-EP levels remained unaltered. This result suggests that any EV effect on drinking is unrelated to changes in beta-EP or behavioral performance. Furthermore, Wistar rats show higher alcohol drinking, locomotor and defensive behavior scores, and hypothalamic beta-EP than Lewis rats. Higher alcohol drinking by Wistar rats might be due to higher behavioral scores or endogenous opioid activity/sensitivity.

Neuropeptide Y (NPY) and depression: from animal studies to the human condition.

Neuropeptide Y (NPY) is widely distributed throughout the central nervous system (CNS) and is one of the most conserved peptides in evolution, suggesting an important role in the regulation of basic physiological functions. In addition, both pre-clinical and clinical evidence have suggested that NPY, together with its receptors, may have a direct implication in several psychiatric disorders, including depression and related illnesses. NPY-like immunoreactivity and NPY receptors are expressed throughout the brain, with varying concentrations being found throughout the limbic system. Such brain structures have been repeatedly implicated in the modulation of emotional processing, as well as in the pathogenesis of depressive disorders. This review will concentrate on the distribution of NPY, its receptors, and the putative role played by this peptide in depressive illness based on both pre-clinical and clinical evidence.

EGb 761 is a neuroprotective agent against beta-amyloid toxicity.

Beta-amyloid (Abeta) deposition likely plays a causal role in the lesions that occur in Alzheimer's disease (AD). The Ginkgo biloba extract EGb 761 is widely prescribed in the treatment of cognitive deficits that are associated with normal and pathological brain aging such as AD. We have investigated here the potential effectiveness of EGb 761 against cell death produced by Abeta fragments on primary cultures of hippocampal cells, these cells being severely damaged in AD. A co-treatment with EGb 761 protected cells against toxicity induced by Abeta fragments in a concentration dependent manner. The effect of EGb 761 was even significant if added up to 8 hr to cells and was shared by its flavonoid fraction CP 205, whereas the terpenes bilobalide and ginkgolide B were ineffective. EGb 761 also displayed protective effects against toxicity produced by either H2O2 or nitric oxide, two neurotoxic agents that possibly mediate Abeta toxicity. Moreover, EGb 761, and to a lesser extent CP 205, completely blocked Abeta-induced events, such as reactive oxygen species accumulation and apoptosis. Taken together, these results and those obtained by other groups highlight the neuroprotective abilities of EGb 761 against dysfunction and death of neurons caused by Abeta deposits.

Natural extracts as possible protective agents of brain aging.

A growing number of studies suggest that natural extracts and phytochemicals have a positive impact on brain aging. We examined the potential of the Ginkgo biloba extract EGb 761 and red wine-derived constituents on cell death produced by beta-amyloid (Abeta) peptides and oxidative stress, with respect to their possible deleterious role in age-related neurological disorders. We found that EGb 761, possibly through the antioxidant properties of its flavonoids, was able to protect hippocampal cells against toxic effects induced by Abeta peptides. Moreover, we showed that an exposure of rat hippocampal cells to the nitric oxide (NO) donor sodium nitroprusside (SNP) resulted in a decrease in cell survival and increase in reactive oxygen species (ROS) accumulation. However, EGb 761 and red wine-derived polyphenols protected against these events, due to their antioxidant activities, and their ability to block SNP-stimulated activity of protein kinase C (PKC). Taken together, these results support the hypothesis that dietary intake of natural substances may be beneficial in normal aging of the brain.

The neuropeptide Y (NPY) Y1 receptor subtype mediates NPY-induced antidepressant-like activity in the mouse forced swimming test.

The present study was undertaken to investigate the possible antidepressant-like effects of neuropeptide Y (NPY) in the mouse forced swimming test, an animal model widely used for the screening of potential antidepressant drugs. In addition, experiments were performed, using agonists and selective antagonists, to assess the potential role of NPY Y(1) and Y(2) receptor subtypes in this model. Complementary studies were performed in an open field apparatus to rule out any changes in locomotor activity that might have interfered with the interpretation of data from the mouse forced swimming test. Intracerebroventricular injections (0.03 nmole-3 nmole) of NPY, [Leu(31)Pro(34)]PYY (Y(1) agonist), NPY(13-36) (Y(2) agonist), BIBP3226, BIBO3304 (Y(1) antagonists) and BIIE0246 (Y(2) antagonist) were performed 30 min prior to testing in the mouse forced swimming test and open field. NPY administration significantly reduced immobility time in a dose dependent manner (p <.01 vs. control group), as did [Leu(31)Pro(34)]PYY (p <.01 vs. control group) and BIIE0246 (p <.05 vs. control group). In contrast, BIBO3304, BIBP3226 and NPY(13-36) did not display any activity at the doses tested. However, pretreatment with BIBO3304 or BIBP3226 significantly blocked the anti-immobility effects of NPY. Data from the open field demonstrated that BIIE0246 increased horizontal ambulation at the dose found to be active in the forced swimming test. Taken together, our results demonstrate that NPY displays antidepressant-like activity in the mouse forced swimming test, and suggest that this activity is mediated by the NPY Y(1) receptor subtype.