Abstract
Recent animal studies have drawn concerns regarding most commonly used anesthetics and their long-term cytotoxic effects, specifically on the nervous tissue. It is therefore imperative that the search continues for agents that are non-toxic at both the cellular and behavioural level. One such agent appears to be dexmedetomidine (DEX) which has not only been found to be less neurotoxic but has also been shown to protect neurons from cytotoxicity induced by other anesthetic agents. However, DEX’s effects on the growth and synaptic connectivity at the individual neuronal level, and the underlying mechanisms have not yet been fully resolved. Here, we tested DEX for its impact on neuronal growth, synapse formation (in vitro) and learning and memory in a rodent model. Rat cortical neurons were exposed to a range of clinically relevant DEX concentrations (0.05–10 µM) and cellular viability, neurite outgrowth, synaptic assembly and mitochondrial morphology were assessed. We discovered that DEX did not affect neuronal viability when used below 10 µM, whereas significant cell death was noted at higher concentrations. Interestingly, in the presence of DEX, neurons exhibited more neurite branching, albeit with no differences in corresponding synaptic puncta formation. When rat pups were injected subcutaneously with DEX 25 µg/kg on postnatal day 7 and again on postnatal day 8, we discovered that this agent did not affect hippocampal-dependent memory in freely behaving animals. Our data demonstrates, for the first time, the non-neurotoxic nature of DEX both in vitro and in vivo in an animal model providing support for its utility as a safer anesthetic agent. Moreover, this study provides the first direct evidence that although DEX is growth permissive, causes mitochondrial fusion and reduces oxygen reactive species production, it does not affect the total number of synaptic connections between the cortical neurons in vitro.
Highlights
Recent animal studies have drawn concerns regarding most commonly used anesthetics and their long-term cytotoxic effects, on the nervous tissue
Since most anesthetics exert their actions by suppressing neuronal activity and shutting off synaptic communications, it is believed that their neurotoxic effects likely involve both structures and functions that are deemed essential for neuronal excitability
Most previous studies have shown DEX to be non-toxic and neuroprotective against cytotoxicity induced by other anesthetics[17,18,20]
Summary
Recent animal studies have drawn concerns regarding most commonly used anesthetics and their long-term cytotoxic effects, on the nervous tissue. It is imperative that the search continues for agents that are non-toxic at both the cellular and behavioural level One such agent appears to be dexmedetomidine (DEX) which has been found to be less neurotoxic but has been shown to protect neurons from cytotoxicity induced by other anesthetic agents. While a complete understanding of the neurotoxic mechanisms underlying these potential deficits in humans is yet to be deduced, recent research has shown that most commonly used anesthetics, such as sevoflurane, propofol and ketamine, are neurotoxic in various animal m odels[5] These agents are being supplemented with a number of other compounds in anticipation that they might stem the anesthetic-induced neurotoxicity[5], though the evidence and the underlying mechanisms remain to be fully defined. The DEX-induced effects have either been examined over a shorter time p eriod[29] or at one time point[30], and they have failed to identify the potential target sites for DEX-mediated e ffects[31]
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