Isoflurane and urethane impact neuronal and astroglial metabolic activity differentially in mouse brain: An ex vivo 1H-[13C]-NMR study

Background and Purpose

Isoflurane and urethane are among the most routinely used anaesthetics to immobilise rodents in functional studies. However, the quantitative significance of their impacts on neuronal and astroglial activity is not very clear. This study evaluated the impacts of isoflurane and urethane on the metabolic activity of glutamatergic neurons, GABAergic neurons and astrocytes in different brain regions.

Experimental Approach

Male C57BL/6 mice were anaesthetised with either isoflurane (1.5%) or urethane (1.5 g kg⁻¹, intraperitoneal), and administered [1,6-¹³C₂]glucose or [2-¹³C]acetate intravenously for 10 or 15 min, respectively. The brain metabolism was arrested using Focussed Beam Microwave Irradiation, and the ¹³C labelling of neurometabolites in the brain tissue extracts was measured ex vivo using ¹H-[¹³C]-nuclear magnetic resonance (NMR) spectroscopy.

Results

The levels of aspartate and succinate were decreased, while alanine increased in the studied brain regions in mice exposed to isoflurane compared to awake mice. The labelling of Glu_C4/C3, GABA_C2 and Gln_C4 from [2-¹³C]acetate was decreased in the isoflurane group when compared with awake, suggesting that isoflurane suppresses the astroglial metabolic activity, particularly in the subcortical region. There was a severe reduction in the ¹³C labelling of brain amino acids from [1,6-¹³C₂]glucose in all the brain regions in isoflurane and urethane groups of mice, indicating a severe impact of both anaesthetics on the metabolic activity of glutamatergic and GABAergic neurons.

Conclusions and Implications

These findings demonstrate that isoflurane and urethane differentially reduce excitatory and inhibitory synaptic transmissions in the brain. Notably, isoflurane shifts cerebral metabolism towards anaerobic respiration.