Guanosine, a guanine-based purine nucleoside, has been described as a neuromodulator that exerts neuroprotective effects in animal and cellular ischemia models. However, guanosine's exact mechanism of action and molecular targets have not yet been identified. Here, we aimed to elucidate a role of adenosine receptors (ARs) in mediating guanosine effects. We investigated the neuroprotective effects of guanosine in hippocampal slices from A 2A R-deficient mice (A 2A R −/− ) subjected to oxygen/glucose deprivation (OGD). Next, we assessed guanosine binding at ARs taking advantage of a fluorescent-selective A 2A R antagonist (MRS7396) which could engage in a bioluminescence resonance energy transfer (BRET) process with NanoLuc-tagged A 2A R. Next, we evaluated functional AR activation by determining cAMP and calcium accumulation. Finally, we assessed the impact of A 1 R and A 2A R co-expression in guanosine-mediated impedance responses in living cells. Guanosine prevented the reduction of cellular viability and increased reactive oxygen species generation induced by OGD in hippocampal slices from wild-type, but not from A 2A R −/− mice. Notably, while guanosine was not able to modify MRS7396 binding to A 2A R-expressing cells, a partial blockade was observed in cells co-expressing A 1 R and A 2A R. The relevance of the A 1 R and A 2A R interaction in guanosine effects was further substantiated by means of functional assays (i.e., cAMP and calcium determinations), since guanosine only blocked A 2A R agonist-mediated effects in doubly expressing A 1 R and A 2A R cells. Interestingly, while guanosine did not affect A 1 R/A 2A R heteromer formation, it reduced A 2A R agonist-mediated cell impedance responses. Our results indicate that guanosine-induced effects may require both A 1 R and A 2A R co-expression, thus identifying a molecular substrate that may allow fine tuning of guanosine-mediated responses.

Intracerebroventricular (icv) amyloid-beta (Aβ) infusion to mice has been demonstrated to cause neurotoxicty and depressive-like behavior and it can be used to evaluate antidepressant and neuroprotective effect of drugs. Atorvastatin is a widely used statin that has demonstrated antidepressant-like effect in predictable animal behavioral models and neuroprotective effect against Aβ infusion. The purpose of this study was to determine the effect of in vivo atorvastatin treatment against Aβ-induced changes in mood-related behaviors and biochemical parameters in ex vivo hippocampal slices from mice. Atorvastatin treatment (10 mg/kg, p.o., once a day for seven consecutive days) abolished depressive-like and anhedonic-like behaviors induced by Aβ (400 pmol/site, icv) infusion. Aβ-induced hippocampal cell damage was reversed by atorvastatin treatment. Aβ infusion decreased glutamate uptake in hippocampal slices, and atorvastatin did not altered it. Glutamine synthetase activity was not altered by any treatment. Atorvastatin also increased hippocampal mature brain-derived neurotrophic factor (mBDNF)/precursor BDNF (proBDNF) ratio, suggesting an increase of proBDNF to mBDNF cleavage. Accordingly, increased tissue-type plasminogen activator (tPA) and p11 genic expression were observed in hippocampus of atorvastatin-treated mice. Atorvastatin displays antidepressant-like and neuroprotective effects against Aβ-induced toxicity, and these effects may involve tPA- and p11-mediated cleavage of proBDNF to mBDNF.

Guanosine (GUO) is a guanine-based purine nucleoside with important trophic functions and promising neuroprotective properties. Although the neuroprotective effects of GUO have been corroborated in cellular models of Parkinson’s disease (PD), its efficacy as an antiparkinsonian agent has not been fully explored in PD animal models. Accordingly, we evaluated the effectiveness of GUO in reversing motor impairments in several rodent movement disorder models, including catalepsy, tremor, and hemiparkinsonism. Our results showed that orally administered GUO antagonized reserpine-mediated catalepsy, reduced reserpine-induced tremulous jaw movements, and potentiated the number of contralateral rotations induced by L-3,4-dihydroxyphenylalanine in unilaterally 6-hydroxidopamine-lesioned rats. In addition, at 5 and 7.5 mg/kg, GUO inhibited L-DOPA-induced dyskinesia in rats chronically treated with a pro-dopaminergic agent. Overall, we describe the therapeutic potential of GUO, which may be effective not only for reversing parkinsonian motor impairments but also for reducing dyskinesia induced by treatment for PD.

Atorvastatin has been shown to exert a neuroprotective action by counteracting glutamatergic toxicity. Recently, we have shown atorvastatin also exerts an antidepressant-like effect that depends on both glutamatergic and serotonergic systems modulation. Excitotoxicity is involved in several brain disorders including depression; thus, it is suggested that antidepressants may target glutamatergic system as a final common pathway. In this study, a comparison of the mechanisms involved in the putative neuroprotective effect of a repetitive atorvastatin or fluoxetine treatment against glutamate toxicity in hippocampal slices was performed. Adult Swiss mice were treated with atorvastatin (10 mg/kg, p.o.) or fluoxetine (10 mg/kg, p.o.), once a day during seven consecutive days. On the eighth day, animals were killed and hippocampal slices were obtained and subjected to an in vitro protocol of glutamate toxicity. An acute treatment of atorvastatin or fluoxetine was not neuroprotective; however, the repeated atorvastatin or fluoxetine treatment prevented the decrease in cellular viability induced by glutamate in hippocampal slices. The loss of cellular viability induced by glutamate was accompanied by increased D-aspartate release, increased reactive oxygen species (ROS) and nitric oxide (NO) production, and impaired mitochondrial membrane potential. Atorvastatin or fluoxetine repeated treatment also presented an antidepressant-like effect in the tail suspension test. Atorvastatin or fluoxetine treatment was effective in protecting mice hippocampal slices from glutamate toxicity by preventing the oxidative stress and mitochondrial dysfunction.

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