Abstract Cannabinoid receptors (CBr) stimulation induces numerous central and peripheral effects. A growing interest in the beneficial properties of manipulating the endocannabinoid system has led to ...the possible involvement of CBr in the control of brain inflammation. In the present study we examined the effect of the CBr agonist, (R)-(+)-2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)-pyrrolo1,2,3-de-1,4benzoxazin-6-yl-1-naphthalenyl-methanone mesylate (WIN-55212-2), on microglial activation and spatial memory performance, using a well-characterized animal model of chronic brain inflammation produced by the infusion of lipopolysaccharide (LPS, 250 ng/h for 3 weeks) into the fourth ventricle of young rats. WIN-55212-2 (0.5 or 1.0 mg/kg/day, i.p.) was administered for 3 weeks. During the third week of treatment, spatial memory ability was examined using the Morris water-maze task. We found that 0.5 and 1 mg/kg WIN-55212-2 reduced the number of LPS-activated microglia, while 1 mg/kg WIN-55212-2 potentiated the LPS-induced impairment of performance in the water maze task. Cannabinoid receptors 1 were not expressed by microglia and astrocytes, suggesting an indirect effect of WIN-55212-2 on microglia activation and memory impairment. Our results emphasize the potential use of CBr agonists in the regulation of inflammatory processes within the brain; this knowledge may lead to the use of CBr agonists in the treatment of neurodegenerative diseases associated with chronic neuroinflammation, such as Alzheimer disease.
The cognitive symptoms of Alzheimer's disease (AD) are believed to be caused not only by the loss of neurons in the cholinergic and glutamatergic neural systems but also by the irregular functioning ...of surviving neurons in these 2 systems. Aberrant cholinergic functioning in AD has been linked to deficits in the neurotransmitter acetylcholine, while AD-related abnormalities in glutamatergic signaling have been attributed to excitotoxicity caused by the persistent, low-level stimulation of glutamatergic neurons via the chronic influx of Ca(2+) ions through the N-methyl-D-aspartate (NMDA) receptor calcium channel. Glutamatergic abnormalities in AD can be corrected to some extent by the NMDA receptor antagonist memantine, an agent whose therapeutic efficacy is believed to be related to its low to moderate level of affinity for the NMDA receptor calcium channel, a characteristic that allows memantine to prevent excessive glutamatergic stimulation while still permitting normal glutamate-mediated neurotransmission to take place. Although the mechanism underlying the chronic stimulation of glutamatergic neurons in AD has yet to be elucidated, one hypothesis is that the characteristic neuropathologic features of AD -- beta-amyloid deposits and neurofibrillary tangles -- induce brain inflammation, which in turn impairs glutamatergic receptor function in such a way that the ability of these receptors to prevent the influx of Ca(2+) in the absence of an appropriate presynaptic signal is compromised. If this hypothesis is correct, and if it is correct that beta-amyloid deposits and neurofibrillary tangles arise long before the symptomatic onset of AD, then memantine, with its ability to alleviate glutamatergic receptor overstimulation, would be expected to provide therapeutic benefits beginning from the earliest stages of the disease.
Understanding how the hippocampus processes episodic memory information during neuropathological conditions is important for treatment and prevention applications. Previous data have shown that ...during chronic neuroinflammation the expression of the plasticity related behaviourally-induced immediate early gene Arc is altered within the CA3 and the dentate gyrus; both of these hippocampal regions show a pronounced increase in activated microglia. Low doses of memantine, a low to moderate affinity open channel uncompetitive N-Methyl-d-aspartate receptor antagonist, reduce neuroinflammation, return Arc expression to control levels and attenuate cognitive deficits induced by lipopolysaccharide. Here we investigate whether neuroinflammation affects the accuracy of information processing in the CA3 and CA1 hippocampal regions and if this is modified by memantine treatment. Using the immediate early gene-based brain-imaging method called cellular analysis of temporal activity by fluorescence in situ hybridization, it is possible to detect primary transcripts at the genomic alleles; this provides exceptional temporal and cellular resolution and facilitates the mapping of neuronal activity. Here, we use this method to compare the neuronal populations activated by two separate experiences in CA1 and CA3 and evaluate the accuracy of information processing during chronic neuroinflammation. Our results show that the CA3 pyramidal neuron activity is not stable between two exposures to the same environment context or two different contexts. CA1 networks, however, do not differ from control conditions. These data suggest that during chronic neuroinflammation, the CA3 networks show a disrupted ability to encode spatial information, and that CA1 neurons can work independently of CA3. Importantly, memantine treatment is able to partially normalize information processing in the hippocampus, suggesting that when given early during the development of the pathology memantine confers neuronal and cognitive protection while indirectly prevents pathological microglial activation.
Measures of cholinergic transmitter activity were investigated in patients with autism because of reported neuropathological abnormalities in cholinergic nuclei in the basal forebrain.
Levels of ...cholinergic enzyme and receptor activity were measured in the frontal and parietal cerebral cortex of deceased autistic adults, similarly aged normal adults without mental retardation, and nonautistic mentally retarded adults. The immunoreactivity levels of brain-derived neurotrophic factor and nerve growth factor were measured in the basal forebrain.
There were no differences between the autistic and comparison groups in choline acetyltransferase or acetylcholinesterase activity in the cerebral cortex and basal forebrain or in muscarinic M(2) receptor or alpha-bungarotoxin binding within the cortex. Cortical M(1) receptor binding was up to 30% lower than normal in the autistic subjects, and the difference reached significance in the parietal cortex. In both the parietal and frontal cortices, differences in nicotinic receptors assessed by (3)Hepibatidine binding were significant and extensive (65%-73% lower in the autistic group than in the normal subjects); there were no differences in nicotine binding in the basal forebrain. Immunochemical analysis indicated lower levels of both the alpha(4) and beta(2) nicotinic receptor subunits in the parietal cortex. The M(1) receptor abnormality was not evident in the nonautistic group with mental retardation, although the lower (3)Hepibatidine binding was apparent. In the basal forebrain, the level of brain-derived neurotrophic factor in the autistic group was three times as high as the level of the normal group.
These neurochemical abnormalities implicate the cholinergic system in developmental disorders such as autism and suggest the potential for intervention based on cholinergic receptor modulation.
•mTOR/p70S6K activation in area CA3 are involved in long term memory formation.•Rapamycin inhibited mTOR/p70S6K activation at 4h and impaired long term memory at 24h.•Scopolamine activated ...mTOR/p70S6K at 1h and impaired short but not long term memory.•Mecamylamine reduced the scopolamine-induced increase of mTOR/p70S6K activation at 1h.•Rapamycin increased mTORC2 activation in microglial cells in Stratum Radiatum.
The present study was aimed at establishing whether the mTOR pathway and its downstream effector p70S6K in CA3 pyramidal neurons are under the modulation of the cholinergic input to trigger the formation of long term memories, similar to what we demonstrated in CA1 hippocampus. We performed in vivo behavioral experiments using the step down inhibitory avoidance test in adult Wistar rats to evaluate memory formation under different conditions. We examined the effects of rapamycin, an inhibitor of mTORC1 formation, scopolamine, a muscarinic receptor antagonist or mecamylamine, a nicotinic receptor antagonist, on short and long term memory formation and on the functionality of the mTOR pathway. Acquisition was conducted 30min after i.c.v. injection of rapamycin. Recall testing was performed 1h, 4h or 24h after acquisition. We found that (1) mTOR and p70S6K activation in CA3 pyramidal neurons were involved in long term memory formation; (2) rapamycin significantly inhibited mTOR and of p70S6K activation at 4h, and long term memory impairment 24h after acquisition; (3) scopolamine impaired short but not long term memory, with an early increase of mTOR/p70S6K activation at 1h followed by stabilization at longer times; (4) mecamylamine and scopolamine co-administration impaired short term memory at 1h and 4h and reduced the scopolamine-induced increase of mTOR/p70S6K activation at 1h and 4h; (5) mecamylamine and scopolamine treatment did not impair long term memory formation; (6) unexpectedly, rapamycin increased mTORC2 activation in microglial cells. Our results demonstrate that in CA3 pyramidal neurons the mTOR/p70S6K pathway is under the modulation of the cholinergic system and is involved in long-term memory encoding, and are consistent with the hypothesis that the CA3 region of the hippocampus is involved in memory mechanisms based on rapid, one-trial object–place learning and recall. Furthermore, our results are in accordance with previous reports that selective molecular mechanisms underlie either short term memory, long term memory, or both. Furthermore, our discovery that administration of rapamycin increased the activation of mTORC2 in microglial cells supports a reappraisal of the beneficial/adverse effects of rapamycin administration.
Neuroinflammation is reliably associated with the pathogenesis of a number of neurodegenerative diseases, and can be detected by the presence of activated microglia. Neuroinflammation can be induced ...by chronic lipopolysaccharide (LPS) infusion into the 4th ventricle of the rat resulting in region-selective microglia activation and impaired hippocampal-dependent memory. Furthermore, this treatment results in altered behaviorally-induced expression of the immediate early gene
Arc, indicating altered network activity. LPS is known to activate microglia directly, leading to increased glutamate release, and in enhanced
N-methyl-
d-aspartate (NMDA) -dependent signaling. Taken together, the foregoing suggests that decreasing NMDA receptor activation during early stages of chronic neuroinflammation should reduce a) microglia activation, b) overexpression of
Arc, and c) spatial memory deficits. Memantine, a low to moderate affinity open channel uncompetitive NMDA receptor antagonist, at low doses was used here to test these hypotheses. Rats were chronically infused into the 4th ventricle for 28 days with LPS alone, vehicle alone (via osmotic minipump) or LPS and memantine (10 mg/kg/day memantine s.c.). The results reported here demonstrate that memantine reduces OX6-immunolabeling for activated microglia, spares resident microglia, returns Arc (
activity-
regulated
cytoskeletal associated protein, protein) -expressing neuronal populations to control levels (as revealed by Arc immunolabeling and fluorescence
in situ hybridization), and ameliorates the spatial memory impairments produced by LPS alone. These data indicate that memantine therapy at low doses, recreating plasma levels similar to those of therapeutic doses in human, acts in part through its ability to reduce the effects of neuroinflammation, resulting in normal gene expression patterns and spatial learning.
Combined, these findings suggest that low, therapeutically relevant doses of memantine delivered early in the development of neuroinflammation-influenced diseases may confer neural and cognitive protection.
Alzheimer's disease is characterized by degenerative changes in a variety of neurotransmitter systems. These include alterations in the function of the monoaminergic neural systems that release ...glutamate, norepinephrine, and serotonin as well as a few neuropeptide-containing systems. Alzheimer's disease is also characterized by degenerative changes in selected brain regions, including the temporal and parietal lobes and restricted regions within the frontal cortex and cingulate gyrus. The degeneration of these systems may underlie specific aspects of the dementia associated with Alzheimer's disease. A major problem in Alzheimer's disease research today is that none of the current hypothesized mechanisms are able to explain the cellular and regional distribution pattern that characterizes the neuropathology of Alzheimer's disease. This article summarizes the nature and extent of the changes associated with neural systems, possible treatment approaches, and a potential mechanism involving chronic neuroinflammation to explain the pattern of neuropathologic changes in Alzheimer's disease.
3-4-(2-Fluoro-alpha-methyl-1,1'-biphenyl-4-acetyloxy)-3-methoxyphenyl-2-propenoic acid 4-nitrooxy butyl ester (NCX-2216), a nitric oxide (NO)-releasing derivative of the cyclooxygenase-1-preferring ...nonsteroidal anti-inflammatory drug (NSAID) flurbiprofen, dramatically reduced both beta-amyloid (Abeta) loads and Congo red staining in doubly transgenic (Tg) amyloid precursor protein plus presenilin-1 mice when administered at 375 ppm in diet between 7 and 12 months of age. This reduction was associated with a dramatic increase in the number of microglia expressing major histocompatibility complex-II antigen, a marker for microglial activation. In contrast, ibuprofen at 375 ppm in diet caused modest reductions in Abeta load but not Congo red staining, suggesting that the effects of this nonselective NSAID were restricted primarily to nonfibrillar deposits. We detected no effects of the cyclooxygenase-2-selective NSAID celecoxib at 175 ppm on amyloid deposition. In short-term studies of 12-month-old Tg mice, we found that the microglia-activating properties of NCX-2216 (7.5 mg small middle dot kg(-1) small middle dot d(-1), s.c.) were present after 2 weeks of treatment. Microglia were not activated by NCX-2216 in non-Tg mice lacking Abeta deposits, nor were microglia activated in Tg animals by flurbiprofen (5 mg small middle dot kg(-1) small middle dot d(-1)) alone. These data are consistent with the argument that activated microglia can clear Abeta deposits. We conclude that the NO-generating component of NCX-2216 confers biological actions that go beyond those of typical NSAIDs. In conclusion, NCX-2216 is more efficacious than ibuprofen or celecoxib in clearing Abeta deposits from the brains of Tg mice, implying potential benefit in the treatment of Alzheimer's dementia.
Alzheimer's disease (AD) is characterized by chronic neuroinflammation, significant temporal lobe cell loss, and dementia. We investigated the influence of chronic neuroinflammation produced by ...chronic infusion of lipopolysaccharide (LPS) into the fourth ventricle for 4 weeks upon the induction and maintenance of long-term potentiation (LTP) in the dentate gyrus of the hippocampus, a well-characterized model of cellular synaptic plasticity. We also examined for pyramidal cell loss within the entorhinal cortex an area of the brain that contains the cell bodies of the perforant path. The results demonstrate that chronic neuroinflammation results in the loss of pyramidal cells within layers II and III of the entorhinal cortex and a significant attenuation of LTP within the dentate gyrus. Similar changes may underlie the temporal lobe pathology and dementia associated with AD.
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