Serotonin Depletion Does not Modify the Short-Term Brain Hypometabolism and Hippocampal Neurodegeneration Induced by the Lithium-Pilocarpine Model of Status Epilepticus in Rats.

It has been reported that fluoxetine, a selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitor, has neuroprotective properties in the lithium-pilocarpine model of status epilepticus (SE) in rats. The aim of the present study was to investigate the effect of 5-HT depletion by short-term administration of p-chlorophenylalanine (PCPA), a specific tryptophan hydroxylase inhibitor, on the brain hypometabolism and neurodegeneration induced in the acute phase of this SE model. Our results show that 5-HT depletion did modify neither the brain basal metabolic activity nor the lithium-pilocarpine-induced hypometabolism when evaluated 3 days after the insult. In addition, hippocampal neurodegeneration and astrogliosis triggered by lithium-pilocarpine were not exacerbated by PCPA treatment. These findings point out that in the early latent phase of epileptogenesis, non-5-HT-mediated actions may contribute, at least in some extent, to the neuroprotective effects of fluoxetine in this model of SE.

Subacute administration of fluoxetine prevents short-term brain hypometabolism and reduces brain damage markers induced by the lithium-pilocarpine model of epilepsy in rats.

The role of serotonin (5-hydroxytryptamine; 5-HT) in epileptogenesis still remains controversial. In this regard, it has been reported that serotonergic drugs can alter epileptogenesis in opposite ways. The main objective of this work was to investigate the effect of the selective 5-HT selective reuptake inhibitor (SSRI) fluoxetine administered subacutely (10mg/kg/day×7 days) on the eventual metabolic impairment induced by the lithium-pilocarpine model of epilepsy in rats. In vivo 2-deoxy-2-[(18)F]fluoro-d-glucose ([(18)F] FDG) positron emission tomography (PET) was performed to assess the brain glucose metabolic activity on days 3 and 30 after the insult. In addition, at the end of the experiment (day 33), several histochemical and neurochemical assessments were performed for checking the neuronal functioning and integrity. Three days after the insult, a marked reduction of [(18)F] FDG uptake (about 30% according to the brain region) was found in all brain areas studied. When evaluated on day 30, although a hypometabolism tendency was observed, no statistically significant reduction was present in any region analyzed. In addition, lithium-pilocarpine administration was associated with medium-term hippocampal and cortical damage, since it induced neurodegeneration, glial activation and augmented caspase-9 expression. Regarding the effect of fluoxetine, subacute treatment with this SSRI did not significantly reduce the mortality rate observed after pilocarpine-induced seizures. However, fluoxetine did prevent not only the short-term metabolic impairment, but also the aforementioned signs of neuronal damage in surviving animals to lithium-pilocarpine protocol. Finally, fluoxetine increased the density of GABAA receptor both at the level of the dentate gyrus and CA1-CA2 regions in pilocarpine-treated animals. Overall, our data suggest a protective role for fluoxetine against pilocarpine-induced brain damage. Moreover, this action may be associated with an increase of GABAA receptor expression in hippocampus.

Longitudinal assessment of a transgenic animal model of tauopathy by FDG-PET imaging.

Abnormal levels and hyperphosphorylation of tau protein have been proposed as the underlying cause of a group of neurodegenerative disorders collectively known as 'tauopathies'. The detrimental consequence is the loss of affinity between this protein and the microtubules, increased production of fibrillary aggregates, and the accumulation of insoluble intracellular neurofibrillary tangles. A similar phenotype can be observed in various preclinical models, which have been generated to study the role of tau protein in neurodegenerative disorders. In this study, we have analyzed the brain metabolic activity in an animal model of tauopathy (tauVLW transgenic mice), which has been previously reported to mimic some of the phenotypic features of these disorders. By using a non-invasive technique, positron emission tomography (PET), a longitudinal non-clinical follow up study was carried out during most of the lifespan of these transgenic mice, from the youth to the senescence stages. The results obtained point out to an aging-dependent decrease in 18F-fluoro-deoxyglucose (FDG) uptake in the cerebral areas analyzed, which was already significant at the adult age, i.e., 11 months, and became much more prominent in the oldest animals (19 months old). This observation correlates well with the histopathological observation of neurodegeneration in brain areas where there is overexpression of tau protein.

A longitudinal FDG-PET study of transgenic mice overexpressing GSK- 3ß in the brain.

Increased Glycogen synthase kinase-3 (GSK-3) activity is believed to contribute to the etiology of chronic disorders such as Alzheimer's disease, one of the earliest diseases linked to GSK-3 dysfunction. Numerous mouse models with modified GSK-3 have been generated in order to study the physiology of GSK-3, its implication in diverse pathologies and the potential effect of GSK-3 inhibitors. In this study we have characterised and evaluated the brain metabolic changes induced by GSK-3ß overexpression in transgenic mice throughout their lifespan. The conditional Tet/GSK-3ß transgenic line used in this study has been previously extensively characterized at the pathological, biochemical and cognitive levels. Now we have investigated the effect GSK-3ß overexpression on the (18)F-fluoro-deoxyglucose (FDG) uptake by positron emission tomography (PET), taking advantage from this non-invasive technique which has allowed us to track individually the same animals throughout their lives. The results obtained during the longitudinal analysis showed a reduction of metabolic activity in several brain regions, such as cortex, striatum and hippocampus, consistent with the areas where the transgene is being expressed. The reduction of the metabolic activity in these mice is observed from the first time point, performed at the age of 3 months, and maintained throughout the whole study, until the oldest age tested (19 months). This effect seems to be reverted in a satellite group of 3-month transgenic animals treated with the classical GSK-3 inhibitor lithium, as they show higher FDG uptake values compared with untreated age-matched transgenic animals.

Tau-knockout mice show reduced GSK3-induced hippocampal degeneration and learning deficits.

It has been proposed that deregulation of neuronal glycogen synthase kinase 3 (GSK3) activity may be a key feature in Alzheimer disease pathogenesis. We have previously generated transgenic mice that overexpress GSK3beta in forebrain regions including dentate gyrus (DG), a region involved in learning and memory acquisition. We have found that GSK3 overexpression results in DG degeneration. To test whether tau protein modified by GSK3 plays a role in that neurodegeneration, we have brought GSK3 overexpressing mice to a tau knockout background. Our results indicate that the toxic effect of GSK3 overexpression is milder and slower in the absence of tau. Thus, we suggest that the hyperphosphorylated tau mediates, at least in part, the pathology observed in the brain of GSK3 overexpressing mice.

Inhibition of glutamate release by delaying ATP fall accounts for neuroprotective effects of antioxidants in experimental stroke.

Excitotoxic neuronal injury related to excessive glutamate release is believed to play a key role in the pathogenesis of focal cerebral ischemia. Reversal of neuronal glutamate transporters caused by ATP fall and subsequent imbalance of membrane ionic gradients accounts for most glutamate release after cerebral ischemia. ATP synthesis from oxidative phosphorylation derives from the coupled functioning of the mitochondrial respiratory chain (MRC) and the ATP synthase; interestingly, the MRC is one of the main sites of cellular reactive oxygen species (ROS) generation even in physiological circumstances. Hence, we have studied the effect of the antioxidants glutathione, superoxide dismutase, and alpha-tocopherol on infarct outcome, brain ATP, and glutamate levels after permanent middle cerebral artery occlusion (MCAO) in Fischer rats; we have also characterized the actions of antioxidants on MRC complexes. Our results show that intraperitoneal administration of antioxidants 2 h before MCAO enhances ATP synthesis and causes a neuroprotective effect concomitant to inhibition of ischemia-induced increase in brain glutamate. Antioxidants also increased mitochondrial ATP and MRC complex I-III activity and respiration, suggesting that these actions are due to removal of the inhibition caused by endogenous ROS on MRC. These findings may possess important therapeutic repercussions in the management of ischemic stroke.

Aspirin inhibits stress-induced increase in plasma glutamate, brain oxidative damage and ATP fall in rats.

The precise mechanisms by which stress induces brain damage are still being elucidated. The high-output, inducible isoform of nitric oxide (NO) synthase (iNOS) is expressed in rat brain after immobilisation stress and its inhibition protects against cell damage in this condition. We have hereby explored some mechanisms involved in iNOS expression and studied the effects of aspirin, a NSAID with neuroprotective actions, in this model. Acute (6 h) stress exposure in rats caused brain expression of iNOS, an increase in plasma glutamate and brain TNF-alpha, induction of oxidative indicators in brain and a fall in brain ATP levels. Prior administration of aspirin (10 mg/kg i.p.) inhibited all these effects caused by stress, suggesting possible therapeutic implications of this drug in this condition.

Inhibition of glutamate release via recovery of ATP levels accounts for a neuroprotective effect of aspirin in rat cortical neurons exposed to oxygen-glucose deprivation.

BACKGROUND AND PURPOSE: Aspirin is preventive against stroke not only because of its antithrombotic properties but also by other direct effects. The aim of this study was to elucidate its direct neuroprotective effects. METHODS: Viability parameters, glutamate release and uptake, and ATP levels were measured in cultured cortical neurons exposed to oxygen-glucose deprivation (OGD). In addition, ATP levels and oxygen consumption were studied in isolated brain mitochondria or submitochondrial particles. RESULTS: Aspirin inhibited OGD-induced neuronal damage at concentrations lower (0.3 mmol/L) than those reported to act via inhibition of the transcription factor nuclear factor-kappaB (which are >1 mmol/L), an effect that correlated with the inhibition caused by aspirin on glutamate release. This effect was shared by sodium salicylate but not by indomethacin, thus excluding the involvement of cyclooxygenase. A pharmacological dissection of the components involved indicated that aspirin selectively inhibits the increase in extracellular glutamate concentration that results from reversal of the glutamate transporter, a component of release that is due to ATP depletion. Moreover, aspirin-afforded neuroprotection occurred in parallel with a lesser decrease in ATP levels after OGD. Aspirin elevated ATP levels not only in intact cortical neurons but also in isolated brain mitochondria, an effect concomitant with an increase in NADH-dependent respiration by brain submitochondrial particles. CONCLUSIONS: Taken together, our present findings show a novel mechanism for the neuroprotective effects of aspirin, which takes place at concentrations in the antithrombotic-analgesic range, useful in the management of patients with high risk of ischemic events.