Age-dependent modifications in the mRNA levels of the rat excitatory amino acid transporters (EAATs) at 48hour reperfusion following global ischemia

Bicuculline Reverts the Neuroprotective Effects of Meloxicam in an Oxygen and Glucose Deprivation (OGD) Model of Organotypic Hippocampal Slice Cultures

We previously demonstrated that the non-steroidal anti-inflammatory agent meloxicam has neuroprotective effects in an oxygen and glucose deprivation model (OGD) of rat organotypic hippocampal slice cultures. We wondered if GABAergic transmission changed the neuroprotective effects of meloxicam and if meloxicam was able to modulate endoplasmic reticulum stress (ER stress) in this model. Mortality was measured using propidium iodide. Western blot assays were performed to measure levels of cleaved and non-cleaved caspase-3 to quantify apoptosis, while levels of GRP78, GRP94 and phosphorylated eIF2α were used to detect unfolded protein response (UPR). Transcript levels of GRP78, GRP94 and GABAergic receptor α, β, and γ subunits were measured by real-time quantitative polymerase chain reaction (qPCR). In the present study, we show that the presence of meloxicam in a 30 min OGD assay, followed by 24 h of normoxic conditions, presented an antiapoptotic effect. The simultaneous presence of the GABA_A receptor antagonist, bicuculline, in combination with meloxicam blocked the neuroprotective effect provided by the latter. However, in light of its effects on caspase 3 and PARP, bicuculline did not seem to promote the apoptotic pathway. Our results also showed that meloxicam modified the unfolded protein response (UPR), as well as the transcriptional response of different genes, including the GABA_A receptor, alpha1, beta3 and gamma2 subunits. We concluded that meloxicam has a neuroprotective anti-apoptotic action, is able to enhance the UPR independently of the systemic anti-inflammatory response and its neuroprotective effect can be inhibited by blocking GABA_A receptors.

The importance of the excitatory amino acid transporter 3 (EAAT3)

The neuronal excitatory amino acid transporter 3 (EAAT3) is fairly ubiquitously expressed in the brain, though it does not necessarily maintain the same function everywhere. It is important in maintaining low local concentrations of glutamate, where its predominant post-synaptic localization can buffer nearby glutamate receptors and modulate excitatory neurotransmission and synaptic plasticity. It is also the main neuronal cysteine uptake system acting as the rate-limiting factor for the synthesis of glutathione, a potent antioxidant, in EAAT3 expressing neurons, while on GABAergic neurons, it is important in supplying glutamate as a precursor for GABA synthesis. Several diseases implicate EAAT3, and modulation of this transporter could prove a useful therapeutic approach. Regulation of EAAT3 could be targeted at several points for functional modulation, including the level of transcription, trafficking and direct pharmacological modulation, and indeed, compounds and experimental treatments have been identified that regulate EAAT3 function at different stages, which together with observations of EAAT3 regulation in patients is giving us insight into the endogenous function of this transporter, as well as the consequences of altered function. This review summarizes work done on elucidating the role and regulation of EAAT3.

Glutamate receptor and transporter modifications in rat organotypic hippocampal slice cultures exposed to oxygen-glucose deprivation: the contribution of cyclooxygenase-2

Meloxicam is a non-steroidal anti-inflammatory drug which has been reported to lessen the ischemic transcriptional effects in some of the glutamatergic system genes as well as to decrease the infarct volume in in vivo assays. In this study, we show how the presence of meloxicam decreases cell mortality in assays of oxygen-glucose deprivation (OGD) in rat organotypic hippocampal slices culture. Mortality was measured using propidium iodide. Transcript levels of some glutamatergic system genes, including vesicular and membrane glutamate transporters (VGLUT1, VGLUT2, GLAST-1A, GLT-1, and EAAC-1) and some glutamatergic receptor subunits (NMDA receptor, GluN1, GluN2A and GluN2B subunits and AMPA receptor, GluA1 and GluA2 subunits) were measured by real-time PCR (qPCR). The transcription of vesicular glutamate transporters and glutamatergic receptor subunits, but not membrane glutamate transporters, was modified by the presence of meloxicam. The study demonstrates the neuroprotective role of meloxicam in organotypic hippocampal slice cultures and shows how meloxicam is able to selectively increase or decrease the OGD-induced changes in the expression of the different glutamatergic system genes studied here. We suggest that the neuroprotective role of meloxicam could be due to a modification in the balance of the expression of some glutamatergic receptor subunits, leading to a different stoichiometry of receptors such as NMDA or AMPA. Thus, meloxicam would decrease the excitotoxicity induced by OGD.

Age-dependent modifications in vascular adhesion molecules and apoptosis after 48-h reperfusion in a rat global cerebral ischemia model

Stroke is one of the leading causes of death and permanent disability in the elderly. However, most of the experimental studies on stroke are based on young animals, and we hypothesised that age can substantially affect the stroke response. The two-vessel occlusion model of global ischemia by occluding the common carotid arteries for 15 min at 40 mmHg of blood pressure was carried out in 3- and 18-month-old male Sprague-Dawley rats. The adhesion molecules E- and P-selectin, cell adhesion molecules (CAMs), both intercellular (ICAM-1) and vascular (VCAM-1), as well as glial fibrillary acidic protein (GFAP), and cleaved caspase-3 were measured at 48 h after ischemia in the cerebral cortex and hippocampus using Western blot, qPCR and immunofluorescence techniques. Diametric expression of GFAP and a different morphological pattern of caspase-3 labelling, although no changes in the cell number, were observed in the neurons of young and old animals. Expression of E-selectin and CAMs was also modified in an age- and ischemia/reperfusion-dependent manner. The hippocampus and cerebral cortex had similar response patterns for most of the markers studied. Our data suggest that old and young animals present different time-courses of neuroinflammation and apoptosis after ischemic damage. On the other hand, these results suggest that neuroinflammation is dependent on age rather than on the different vulnerability described for the hippocampus and cerebral cortex. These differences should be taken into account in searching for therapeutic targets.

Changes in the expression of the glutamate transporter EAAT3/EAAC1 in health and disease

Excitatory amino acid transporters (EAATs) are high-affinity Na(+)-dependent carriers of major importance in maintaining glutamate homeostasis in the central nervous system. EAAT3, the human counterpart of the rodent excitatory amino acid carrier 1 (EAAC1), is encoded by the SLC1A1 gene. EAAT3/EAAC1 is ubiquitously expressed in the brain, mostly in neurons but also in other cell types, such as oligodendrocyte precursors. While most of the glutamate released in the synapses is taken up by the "glial-type" EAATs, EAAT2 (GLT-1 in rodents) and EAAT1 (GLAST), the functional role of EAAT3/EAAC1 is related to the subtle regulation of glutamatergic transmission. Moreover, because it can also transport cysteine, EAAT3/EAAC1 is believed to be important for the synthesis of intracellular glutathione and subsequent protection from oxidative stress. In contrast to other EAATs, EAAT3/EAAC1 is mostly intracellular, and several mechanisms have been described for the rapid regulation of the membrane trafficking of the transporter. Moreover, the carrier interacts with several proteins, and this interaction modulates transport activity. Much less is known about the slow regulatory mechanisms acting on the expression of the transporter, although several recent reports have identified changes in EAAT3/EAAC1 protein level and activity related to modulation of its expression at the gene level. Moreover, EAAT3/EAAC1 expression is altered in pathological conditions, such as hypoxia/ischemia, multiple sclerosis, schizophrenia, and epilepsy. This review summarizes these results and provides an overall picture of changes in EAAT3/EAAC1 expression in health and disease.

Differences in neuronal damage and gliosis in the hippocampus between young and adult gerbils induced by long duration of transient cerebral ischemia

Response to cerebral ischemia in young animals was very different from that in the adult. The aim of this study was to investigate differences in neuronal death and gliosis in the hippocampal CA1 region (CA1) between adult and young gerbils following 5 and 15 min of transient cerebral ischemia. Delayed neuronal death (DND) of pyramidal cells occurred in the CA1 was similar in all the adult gerbils after 5 and 15 min of ischemia: the DND occurred 4 days after ischemia. In the young groups, DND of pyramidal cells in the CA1 region occurred 7 and 3 days after 5 and 15 min of ischemia, respectively. On the other hand, the activation of GFAP-immunoreactive ((+)) astrocytes and Iba-1(+) microglia was different in the young groups from the adult groups after ischemia. The change pattern of GFAP immunoreactivity in the adult groups was similar in both the adult groups after ischemia; in the young groups, the activation of GFAP(+) astrocytes after 5 min of ischemia was much delayed than that after 15 min of ischemia. Activated Iba-1(+) microglia were aggregated in the stratum pyramidale 4 days after ischemia in all the adult ischemia-operated groups; in the young groups, activated Iba-1(+) microglia were aggregated in the stratum pyramidale 7 days after 5 min of ischemia and 3 days after 15 min of ischemia. These observations indicate that DND in young animals is very different from the adult according to different duration of transient cerebral ischemia and glial activation is very different in young animals after different duration of transient ischemia.

The role of amino acid transporters in GSH synthesis in the blood-brain barrier and central nervous system

Glutathione (GSH) plays a critical role in protecting cells from oxidative stress and xenobiotics, as well as maintaining the thiol redox state, most notably in the central nervous system (CNS). GSH concentration and synthesis are highly regulated within the CNS and are limited by availability of the sulfhydryl amino acid (AA) l-cys, which is mainly transported from the blood, through the blood-brain barrier (BBB), and into neurons. Several antiporter transport systems (e.g., x(c)(-), x(-)(AG), and L) with clearly different luminal and abluminal distribution, Na(+), and pH dependency have been described in brain endothelial cells (BEC) of the BBB, as well as in neurons, astrocytes, microglia and oligodendrocytes from different brain structures. The purpose of this review is to summarize information regarding the different AA transport systems for l-cys and its oxidized form l-cys(2) in the CNS, such as expression and activity in blood-brain barrier endothelial cells, astrocytes and neurons and environmental factors that modulate transport kinetics.

Comparison of glial activation in the hippocampal CA1 region between the young and adult gerbils after transient cerebral ischemia

It has been reported that young animals are less vulnerable to brain ischemia. In the present study, we compared gliosis in the hippocampal CA1 region of the young gerbil with those in the adult gerbil induced by 5 min of transient cerebral ischemia by immunohistochemistry and western blot for glial cells. We used male gerbils of postnatal month 1 (PM 1) as the young and PM 6 as the adult. Neuronal death in CA1 pyramidal neurons in the adult gerbil occurred at 4 days post-ischemia; the neuronal death in the young gerbil occurred at 7 days post-ischemia. The findings of glial changes in the young gerbil after ischemic damage were distinctively different from those in the adult gerbil. Glial fibrillary acidic protein-immunoreactive astrocytes, ionized calcium-binding adapter molecule (Iba-1), and isolectin B4-immunoreactive microglia in the ischemic CA1 region were activated much later in the young gerbil than in the adult gerbil. In brief, very less gliosis occurred in the hippocampal CA1 region of the young gerbil than in the adult gerbil after transient cerebral ischemia.