personalized-needles-for-microinjections-in-the-rodent-brain

Personalized Needles for Microinjections in the Rodent Brain

Microinjections have been used for a long time for the delivery of drugs or toxins within specific brain areas and, more recently, they have been used to ...

University of ferrara

We have investigated the relevance of d-aspartate oxidase, the only enzyme known to selectively degrade d-aspartate (d-Asp), in modulating glutamatergic system homeostasis. Interestingly, the lack of the Ddo gene, by raising d-Asp content, induces a substantial increase in extracellular glutamate (Glu) levels in Ddo-mutant brains. Consistent with an exaggerated and persistent N-methyl-d-aspartate receptor (NMDAR) stimulation, we documented in Ddo knockouts severe age-dependent structural and functional alterations mirrored by expression of active caspases 3 and 7 along with appearance of dystrophic microglia and reactive astrocytes. In addition, prolonged elevation of d-Asp triggered in mutants alterations of NMDAR-dependent synaptic plasticity associated to reduction of hippocampal GluN1 and GluN2B subunits selectively located at synaptic sites and to increase in the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-to-N-methyl-d-aspartate ratio. These effects, all of which converged on a progressive hyporesponsiveness at NMDAR sites, functionally resulted in a greater vulnerability to phencyclidine-induced prepulse inhibition deficits in mutants. In conclusion, our results indicate that d-aspartate oxidase, by strictly regulating d-Asp levels, impacts on the homeostasis of glutamatergic system, thus preventing accelerated neurodegenerative processes.

d-Aspartate oxidase influences glutamatergic system homeostasis in mammalian brain.

Preclinical and clinical evidence that the serotonergic system plays a major role in levodopa-induced dyskinesias has been provided. Selective serotonin (5-hydroxytryptamine; 5-HT) 5-HT1A or 5-HT1B receptor agonists, and, very recently, the mixed 5-HT1A /5-HT1B receptor agonist, eltoprazine, proved effective in inhibiting L-dopa-induced dyskinesias in experimental animals and parkinsonian patients. Here, we investigate the mechanisms underlying this effect.

Eltoprazine prevents levodopa-induced dyskinesias by reducing striatal glutamate and direct pathway activity.

D-aspartate levels in the brain are regulated by the catabolic enzyme D-aspartate oxidase (DDO). D-aspartate activates NMDA receptors, and influences brain connectivity and behaviors relevant to schizophrenia in animal models. In addition, recent evidence reported a significant reduction of D-aspartate levels in the post-mortem brain of schizophrenia-affected patients, associated to higher DDO activity. In the present work, microdialysis experiments in freely moving mice revealed that exogenously administered D-aspartate efficiently cross the blood brain barrier and stimulates L-glutamate efflux in the prefrontal cortex (PFC). Consistently, D-aspartate was able to evoke L-glutamate release in a preparation of cortical synaptosomes through presynaptic stimulation of NMDA, mGlu5 and AMPA/kainate receptors. In support of a potential therapeutic relevance of D-aspartate metabolism in schizophrenia, in vitro enzymatic assays revealed that the second-generation antipsychotic olanzapine, differently to clozapine, chlorpromazine, haloperidol, bupropion, fluoxetine and amitriptyline, inhibits the human DDO activity. In line with in vitro evidence, chronic systemic administration of olanzapine induces a significant extracellular release of D-aspartate and L-glutamate in the PFC of freely moving mice, which is suppressed in Ddo knockout animals. These results suggest that the second-generation antipsychotic olanzapine, through the inhibition of DDO activity, increases L-glutamate release in the PFC of treated mice.

Article	Year
d-Aspartate oxidase influences glutamatergic system homeostasis in mammalian brain. Neurobiology of aging\| PubMed ID: 25771393	2015
Eltoprazine prevents levodopa-induced dyskinesias by reducing striatal glutamate and direct pathway activity. Movement disorders : official journal of the Movement Disorder Society\| PubMed ID: 26207892	2015
Olanzapine, but not clozapine, increases glutamate release in the prefrontal cortex of freely moving mice by inhibiting D-aspartate oxidase activity. Scientific reports\| PubMed ID: 28393897	2017

Giovanna Paolone

Biography

JoVE Journal Publications

Other Publications