Various facets of excitotoxicity

Abstract

Aim: Excitotoxicity results from unusually increased activation of excitatory amino acid receptors leading to neuronal death. Since glutamate is the main excitatory neurotransmitter in the central nervous system, it is also the most common excitotoxicity trigger. This uncontrolled neuronal response participates in various neurodegenerative diseases, such as ischemia, hypoglycemia, Huntington’s, Parkinson’s and Alzheimer’s disease. Thus, the investigation in the field expanded a lot in the past decade, leading to in vitro modelling adaptations. However, much performed work on glutamate-induced excitotoxicity is methodologically inconsistent in the literature. The field lacks reproducibility, which is one of the main fundaments of empirical science. In this regard, the literature was summarized and the main methodological features were critically evaluated, aiming to guide the researchers that are starting in the field. Methods: Published data since 1985 from PUBMED were collected and analyzed to observe which in vitro experimental conditions of excitotoxicity were reproducible. The suggested methods were based on the characteristics of excitotoxicity, such as abnormal intracellular calcium mediated signaling, mitochondria impairment, reactive oxygen species accumulation and cell death. Various conditions and comparative controls were used to design the standard investigation of excitotoxicity, such as culture medium content (presence of glutamate and aspartate), time interval of induction and the concentration of the inductor, based on the most reproducible published ones. Results: Our results and critical analysis point to some experimental conditions to consider, such as primary cultured neurons are more sensitive to glutamate and the response obtained is more robust than in other models; excitotoxicity mediated effects are better observed one hour following the stimulus; the culture medium should contain low levels of glutamate or aspartate or glycine. Online available phosphoproteomic data on excitotoxicity using the primary cortical neurons in vitro model supported the same conditions proposed by us. Conclusions: This manuscript will facilitate the design of any research for excitotoxic or neuroprotective compounds in physiological and pathophysiological conditions by standardizing and improving experimental conditions.

Keywords

• glutamate
• cell death
• calcium
• mitochondria
• neurodegeneration