Omega-3 fatty acids deprivation affects ontogeny of glutamatergic synapses in rats: Relevance for behavior alterations

Essential omega-3 polyunsaturated fatty acids (ω3) are crucial to brain development and function, being relevant for behavioral performance. In the present study we examined the influence of dietary ω3 in the development of the glutamatergic system and on behavior parameters in rats. Female rats received isocaloric diets, either with ω3 (ω3 group) or a ω3 deficient diet (D group). In ontogeny experiments of their litters, hippocampal immunocontent of ionotropic NMDA and AMPA glutamatergic receptors subunits (NR2 A\B and GluR1, respectively) and the alpha isoform of the calcium-calmodulin protein kinase type II (αCaMKII) were evaluated. Additionally, hippocampal [³H]glutamate binding and uptake were assessed. Behavioral performance was evaluated when the litters were adult (60 days old), through the open-field, plus-maze, inhibitory avoidance and flinch-jump tasks. The D group showed decreased immunocontent of all proteins analyzed at 02 days of life (P2) in comparison with the ω3 group, although the difference disappeared at 21 days of life (except for αCaMKII, which content normalized at 60 days old). The same pattern was found for [³H]glutamate binding, whereas [³H]glutamate uptake was not affected. The D group also showed memory deficits in the inhibitory avoidance, increased in the exploratory pattern in open-field, and anxiety-like behavior in plus-maze. Taken together, our results suggest that dietary ω3 content is relevant for glutamatergic system development and for behavioral performance in adulthood. The putative correlation among the neurochemical and behavioral alterations caused by dietary ω3 deficiency is discussed.     

Effects of 3 weeks GMP oral administration on glutamatergic parameters in mice neocortex

Overstimulation of the glutamatergic system (excitotoxicity) is involved in various acute and chronic brain diseases. Several studies support the hypothesis that guanosine-5′-monophosphate (GMP) can modulate glutamatergic neurotransmission. The aim of this study was to evaluate the effects of chronically administered GMP on brain cortical glutamatergic parameters in mice. Additionally, we investigated the neuroprotective potential of the GMP treatment submitting cortical brain slices to oxygen and glucose deprivation (OGD). Moreover, measurements of the cerebrospinal fluid (CSF) purine levels were performed after the treatment. Mice received an oral administration of saline or GMP during 3 weeks. GMP significantly decreases the cortical brain glutamate binding and uptake. Accordingly, GMP reduced the immunocontent of the glutamate receptors subunits, NR2A/B and GluR1 (NMDA and AMPA receptors, respectively) and glutamate transporters EAAC1 and GLT1. GMP treatment significantly reduced the immunocontent of PSD-95 while did not affect the content of Snap 25, GLAST and GFAP. Moreover, GMP treatment increased the resistance of neocortex to OGD insult. The chronic GMP administration increased the CSF levels of GMP and its metabolites. Altogether, these findings suggest a potential modulatory role of GMP on neocortex glutamatergic system by promoting functional and plastic changes associated to more resistance of mice neocortex against an in vitro excitotoxicity event.     

Intranasal guanosine administration presents a wide therapeutic time window to reduce brain damage induced by permanent ischemia in rats

In addition to its intracellular roles, the nucleoside guanosine (GUO) also has extracellular effects that identify it as a putative neuromodulator signaling molecule in the central nervous system. Indeed, GUO can modulate glutamatergic neurotransmission, and it can promote neuroprotective effects in animal models involving glutamate neurotoxicity, which is the case in brain ischemia. In the present study, we aimed to investigate a new in vivo GUO administration route (intranasal, IN) to determine putative improvement of GUO neuroprotective effects against an experimental model of permanent focal cerebral ischemia. Initially, we demonstrated that IN [³H] GUO administration reached the brain in a dose-dependent and saturable pattern in as few as 5 min, presenting a higher cerebrospinal GUO level compared with systemic administration. IN GUO treatment started immediately or even 3 h after ischemia onset prevented behavior impairment. The behavior recovery was not correlated to decreased brain infarct volume, but it was correlated to reduced mitochondrial dysfunction in the penumbra area. Therefore, we showed that the IN route is an efficient way to promptly deliver GUO to the CNS and that IN GUO treatment prevented behavioral and brain impairment caused by ischemia in a therapeutically wide time window.     

Effects of Depressive-Like Behavior of Rats on Brain Glutamate Uptake

Learned helplessness paradigm is a widely accepted animal model of depressive-like behavior based on stress. Glutamatergic system is closely involved with the stress-neurotoxicity in the brain and recently it is pointed to have a relevant role in the pathophysiology of depression disorder. Glutamate uptake is the main mechanism to terminate the glutamatergic physiological activity and to neuroprotection against excitotoxicity. We investigated the profile of glutamate uptake in female rats submitted to the learned helplessness paradigm and to different classes of stress related to the paradigm, in slices of brain cortex, striatum and hippocampus. Glutamate uptake in slices of hippocampus differ between learned helplessness (LH) and non-learned helplessness (NLH) animals immediately persisting up to 21 days after the paradigm. In addition, there were a decrease of glutamate uptake in the three brain structures analyzed at 21 days after the paradigm for LH animals. These results may contribute to better understand the role of the glutamatergic system on the depressive-like behavior.     

Effects of intranasal guanosine administration on brain function in a rat model of ischemic stroke

Ischemic stroke is a major cause of morbidity and mortality worldwide and only few affected patients are able to receive treatment, especially in developing countries. Detailed pathophysiology of brain ischemia has been extensively studied in order to discover new treatments with a broad therapeutic window and that are accessible to patients worldwide. The nucleoside guanosine (Guo) has been shown to have neuroprotective effects in animal models of brain diseases, including ischemic stroke. In a rat model of focal permanent ischemia, systemic administration of Guo was effective only when administered immediately after stroke induction. In contrast, intranasal administration of Guo (In-Guo) was effective even when the first administration was 3 h after stroke induction. In order to validate the neuroprotective effect in this larger time window and to investigate In-Guo neuroprotection under global brain dysfunction induced by ischemia, we used the model of thermocoagulation of pial vessels in Wistar rats. In our study, we have found that In-Guo administered 3 h after stroke was capable of preventing ischemia-induced dysfunction, such as bilateral suppression and synchronicity of brain oscillations and ipsilateral cell death signaling, and increased permeability of the blood-brain barrier. In addition, In-Guo had a long-lasting effect on preventing ischemia-induced motor impairment. Our data reinforce In-Guo administration as a potential new treatment for brain ischemia with a more suitable therapeutic window.