Tiziana Bonifacino

Acute Stress Increases Depolarization-Evoked Glutamate Release in the Rat Prefrontal/Frontal Cortex: The Dampening Action of Antidepressants

Background Behavioral stress is recognized as a main risk factor for neuropsychiatric diseases. Converging evidence suggested that acute stress is associated with increase of excitatory transmission in certain forebrain areas. Aim of this work was to investigate the mechanism whereby acute stress increases glutamate release, and if therapeutic drugs prevent the effect of stress on glutamate release. Methodology/Findings Rats were chronically treated with vehicle or drugs employed for therapy of mood/anxiety disorders (fluoxetine, desipramine, venlafaxine, agomelatine) and then subjected to unpredictable footshock stress. Acute stress induced marked increase in depolarization-evoked release of glutamate from synaptosomes of prefrontal/frontal cortex in superfusion, and the chronic drug treatments prevented the increase of glutamate release. Stress induced rapid increase in the circulating levels of corticosterone in all rats (both vehicle- and drug-treated), and glutamate release increase was blocked by previous administration of selective antagonist of glucocorticoid receptor (RU 486). On the molecular level, stress induced accumulation of presynaptic SNARE complexes in synaptic membranes (both in vehicle- and drug-treated rats). Patch-clamp recordings of pyramidal neurons in the prefrontal cortex revealed that stress increased glutamatergic transmission through both pre- and postsynaptic mechanisms, and that antidepressants may normalize it by reducing release probability. Conclusions/Significance Acute footshock stress up-regulated depolarization-evoked release of glutamate from synaptosomes of prefrontal/frontal cortex. Stress-induced increase of glutamate release was dependent on stimulation of glucocorticoid receptor by corticosterone. Because all drugs employed did not block either elevation of corticosterone or accumulation of SNARE complexes, the dampening action of the drugs on glutamate release must be downstream of these processes. This novel effect of antidepressants on the response to stress, shown here for the first time, could be related to the therapeutic action of these drugs.

Intravenous mesenchymal stem cells improve survival and motor function in experimental amyotrophic lateral sclerosis.

Despite some advances in the understanding of amyotrophic lateral sclerosis (ALS) pathogenesis, significant achievements in treating this disease are still lacking. Mesenchymal stromal (stem) cells (MSCs) have been shown to be effective in several models of neurological disease. To determine the effects of the intravenous injection of MSCs in an ALS mouse model during the symptomatic stage of disease, MSCs (1 × 106) were intravenously injected in mice expressing human superoxide dismutase 1 (SOD1) carrying the G93A mutation (SOD1/G93A) presenting with experimental ALS. Survival, motor abilities, histology, oxidative stress markers and [3H]d-aspartate release in the spinal cord were investigated. MSC injection in SOD1/G93A mice improved survival and motor functions compared with saline-injected controls. Injected MSCs scantly home to the central nervous system and poorly engraft. We observed a reduced accumulation of ubiquitin agglomerates and of activated astrocytes and microglia in the spinal cord of MSC-treated SOD1/G93A mice, with no changes in the number of choline acetyltransferase- and glutamate transporter type 1-positive cells. MSC administration turned around the upregulation of metallothionein mRNA expression and of the activity of the antioxidant enzyme glutathione S-transferase, both associated with disease progression. Last, we observed that MSCs reverted both spontaneous and stimulus-evoked neuronal release of (3H)d-aspartate, a marker of endogenous glutamate, which is upregulated in SOD1/G93A mice. These findings suggest that intravenous administration of MSCs significantly improves the clinical outcome and pathological scores of mutant SOD1/G93A mice, thus providing the rationale for their exploitation for the treatment of ALS.

Enriched experience and recovery from amblyopia in adult rats: Impact of motor, social and sensory components

Amblyopia is one of the most common forms of visual impairment, arising from an early functional imbalance between the two eyes. It is currently accepted that, due to a lack of neural plasticity,amblyopia is an untreatable pathology in adults. Environmental enrichment (EE) emerged as a strategy highly effective in restoring plasticity in adult animals, eliciting recovery from amblyopia through a reduction of intracortical inhibition. It is unknown whether single EE components are able to promote plasticity in the adult brain, crucial information for designing new protocols of environmental stimulation suitable for amblyopic human subjects. Here, we assessed the effects of enhanced physical exercise,increased social interaction, visual enrichment or perceptual learning on visual function recovery in adult amblyopic rats. We report a complete rescue of both visual acuity and ocular dominance in exercised rats, in animals exposed to visual enrichment and in animals engaged in perceptual learning.These effects were accompanied by a reduced inhibition/excitation balance in the visual cortex. In contrast, we did not detect any sign of recovery in socially enriched rats or in animals practicing a purely associative visual task. These findings could have a bearing in orienting clinical research in the field of amblyopia therapy.

Stress and corticosterone increase the readily releasable pool of glutamate vesicles in synaptic terminals of prefrontal and frontal cortex.

Stress and glucocorticoids alter glutamatergic transmission, and the outcome of stress may range from plasticity enhancing effects to noxious, maladaptive changes. We have previously demonstrated that acute stress rapidly increases glutamate release in prefrontal and frontal cortex via glucocorticoid receptor and accumulation of presynaptic SNARE complex. Here we compared the ex vivo effects of acute stress on glutamate release with those of in vitro application of corticosterone, to analyze whether acute effect of stress on glutamatergic transmission is mediated by local synaptic action of corticosterone. We found that acute stress increases both the readily releasable pool (RRP) of vesicles and depolarization-evoked glutamate release, while application in vitro of corticosterone rapidly increases the RRP, an effect dependent on synaptic receptors for the hormone, but does not induce glutamate release for up to 20 min. These findings indicate that corticosterone mediates the enhancement of glutamate release induced by acute stress, and the rapid non-genomic action of the hormone is necessary but not sufficient for this effect.

Abnormal exocytotic release of glutamate in a mouse model of amyotrophic lateral sclerosis.

J. Neurochem. (2011) 116, 1028–1042.

Blockade of stress-induced increase of glutamate release in the rat prefrontal/frontal cortex by agomelatine involves synergy between melatonergic and 5-HT2C receptor-dependent pathways

BackgroundAgomelatine is a melatonergic receptor agonist and a 5HT2C receptor antagonist that has shown antidepressant efficacy. In order to analyze separately the effect of the two receptorial components, rats were chronically treated with agomelatine, melatonin (endogenous melatonergic agonist), or S32006 (5-HT2C antagonist), and then subjected to acute footshock-stress.ResultsOnly chronic agomelatine, but not melatonin or S32006, completely prevented the stress-induced increase of glutamate release in the rat prefrontal/frontal cortex.ConclusionsThese results suggest a potential synergy between melatonergic and serotonergic pathways in the action of agomelatine.

Fluoxetine in adulthood normalizes GABA release and rescues hippocampal synaptic plasticity and spatial memory in a mouse model of Down syndrome.

Down syndrome (DS) is the most common genetic disorder associated with mental retardation. It has been repeatedly shown that Ts65Dn mice, the major animal model for DS, have severe cognitive and synaptic plasticity dysfunctions caused by excessive inhibition in their temporal lobe structures. Here we employed a multidisciplinary approach spanning from the behavioral to the electrophysiological and molecular level to investigate the effects elicited by fluoxetine on cognitive abilities, hippocampal synaptic plasticity and GABA release in adult Ts65Dn mice. We report that a chronic treatment with fluoxetine administered in the drinking water normalizes GABA release and promotes recovery of spatial memory abilities, spatial working memory for alternation, and hippocampal synaptic plasticity in adult Ts65Dn mice. Our findings might encourage new experimental attempts aimed at investigating the potential of fluoxetine for application in the treatment of major functional deficits in adult people with DS.

In vitro activation of GAT1 transporters expressed in spinal cord gliosomes stimulates glutamate release that is abnormally elevated in the SOD1/G93A(+) mouse model of amyotrophic lateral sclerosis

J. Neurochem. (2010) 113, 489–501.

Chronic treatment with agomelatine or venlafaxine reduces depolarization-evoked glutamate release from hippocampal synaptosomes.

BackgroundGrowing compelling evidence from clinical and preclinical studies has demonstrated the primary role of alterations of glutamatergic transmission in cortical and limbic areas in the pathophysiology of mood disorders. Chronic antidepressants have been shown to dampen endogenous glutamate release from rat hippocampal synaptic terminals and to prevent the marked increase of glutamate overflow induced by acute behavioral stress in frontal/prefrontal cortex. Agomelatine, a new antidepressant endowed with MT1/MT2 agonist and 5-HT2C serotonergic antagonist properties, has shown efficacy at both preclinical and clinical levels.ResultsChronic treatment with agomelatine, or with the reference drug venlafaxine, induced a marked decrease of depolarization-evoked endogenous glutamate release from purified hippocampal synaptic terminals in superfusion. No changes were observed in GABA release. This effect was accompanied by reduced accumulation of SNARE protein complexes, the key molecular effector of vesicle docking, priming and fusion at presynaptic membranes.ConclusionsOur data suggest that the novel antidepressant agomelatine share with other classes of antidepressants the ability to modulate glutamatergic transmission in hippocampus. Its action seems to be mediated by molecular mechanisms located on the presynaptic membrane and related with the size of the vesicle pool ready for release.

Knocking down metabotropic glutamate receptor 1 improves survival and disease progression in the SOD1G93A mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late-onset fatal neurodegenerative disease reflecting degeneration of upper and lower motoneurons (MNs). The cause of ALS and the mechanisms of neuronal death are still largely obscure, thus impairing the establishment of efficacious therapies. Glutamate (Glu)-mediated excitotoxicity plays a major role in MN degeneration in ALS. We recently demonstrated that the activation of Group I metabotropic Glu autoreceptors, belonging to both type 1 and type 5 receptors (mGluR1 and mGluR5), at glutamatergic spinal cord nerve terminals, produces excessive Glu release in mice over-expressing human superoxide-dismutase carrying the G93A point mutation (SOD1(G93A)), a widely used animal model of human ALS. To establish whether these receptors are implicated in ALS, we generated mice expressing half dosage of mGluR1 in the SOD1(G93A) background (SOD1(G93A)Grm1(crv4/+)), by crossing the SOD1(G93A) mutant mouse with the Grm1(crv4/+) mouse, lacking mGluR1 because of a spontaneous recessive mutation. SOD1(G93A)Grm1(crv4/+) mice showed prolonged survival probability, delayed pathology onset, slower disease progression and improved motor performances compared to SOD1(G93A) mice. These effects were associated to reduction of mGluR5 expression, enhanced number of MNs, decreased astrocyte and microglia activation, normalization of metallothionein and catalase mRNA expression, reduced mitochondrial damage, and decrease of abnormal Glu release in spinal cord of SOD1(G93A)Grm1(crv4/+)compared to SOD1(G93A) mice. These results demonstrate that a lower constitutive level of mGluR1 has a significant positive impact on mice with experimental ALS, thus providing the rationale for future pharmacological approaches to ALS by selectively blocking Group I metabotropic Glu receptors.