Background. Exposure of infant animals to clinically used anaesthetics is associated with acute structural brain abnormalities and development functional alterations. The α₂-adrenoceptor agonist dexmedetomidine (DEX) induces sedation, analgesia, and provides neuroprotection in experimental brain injury models. However, it is unknown whether DEX also affords protection in the developing brain against anaesthesia using sevoflurane (SEVO), which is commonly used in paediatric anaesthesia. Methods. Infant rats were exposed on postnatal day seven for six h to 2.5% SEVO and were given i.p. injections of saline or DEX (1–50 µg kg⁻¹) three times during the exposure. Level of anaesthesia, respiratory rates, and arterial blood gasses were assessed for each animal. Apoptosis was determined in brain slices immunostained for activated caspase-3 (AC-3) using a computerised approach. Results. SEVO alone induced a surgical plane of anaesthesia, and all animals survived the study. SEVO induced an approximately 10-fold increase in AC-3 positive cells in several cortical and subcortical brain regions compared with untreated control animals. Co-administration of DEX 1 µg kg⁻¹ with SEVO significantly reduced apoptosis in all brain areas, affording the highest protection in the thalamus (84% reduction) and lowest in the hippocampus and cortical areas (∼50% reduction). DEX 5–25 µg kg⁻¹ plus SEVO dose-dependently increased infant rat mortality. Conclusions. SEVO anaesthesia induced widespread apoptosis in infant rat brain. Co-administration of DEX (1 µg kg⁻¹) provided significant protection, whereas DEX (5 µg kg⁻¹ or higher) plus SEVO increased mortality. Our findings suggest that DEX could be an attractive therapeutic for future studies investigating its neuroprotective potential in a translational animal model.

Retrospective clinical studies suggest there is a risk for neurodevelopmental impairment following early childhood exposure to anaesthesia. In the developing animal brain, including those of non-human primates (NHPs), anaesthetics induce apoptotic cell death. We previously reported that a 5 h isoflurane (ISO) exposure in infant NHPs increases apoptosis 13-fold compared with control animals. However, the majority of paediatric surgeries requiring anaesthesia are of shorter durations. We examined whether 3 h ISO exposure similarly increases neuroapoptosis in the NHP developing brain. Six-day-old NHP infants ( Macaca mulatta ) were exposed to 3 h of a surgical plane of ISO ( n =6) or to room air ( n =5). Following exposure, NHP brains were screened for neuronal and oligodendrocyte apoptosis using activated caspase-3 immunolabelling and unbiased stereology. ISO treatment increased apoptosis (neurones + oligodendrocyte) to greater than four times that in the control group [mean density of apoptotic profiles: 57 (SD 22) mm -3 vs 14 (SD 5.2) mm -3 , respectively]. Oligodendrocyte apoptosis was evenly distributed throughout the white matter whereas neuroapoptosis occurred primarily in the cortex (all regions), caudate, putamen and thalamus. A 3 h exposure to ISO is sufficient to induce widespread neurotoxicity in the developing primate brain. These results are relevant for clinical medicine, as many surgical and diagnostic procedures in children require anaesthesia durations similar to those modelled here. Further research is necessary to identify long-term neurobehavioural consequences of 3 h ISO exposure.