Influence of different isoflurane anesthesia protocols on murine cerebral hemodynamics measured with pseudo-continuous arterial spin labeling

Abstract

Arterial spin labeling (ASL)-MRI can noninvasively map cerebral blood flow (CBF) and cerebrovascular reactivity (CVR), potential biomarkers of cognitive impairment and dementia. Mouse models of disease are frequently used in translational MRI studies, which are commonly performed under anesthesia. Understanding the influence of the specific anesthesia protocol used on the measured parameters is important for accurate interpretation of hemodynamic studies with mice. Isoflurane is a frequently used anesthetic with vasodilative properties. Here, the influence of three distinct isoflurane protocols was studied with pseudo-continuous ASL in two different mouse strains. The first protocol was a free-breathing set-up with medium concentrations, the second a free-breathing set-up with low induction and maintenance concentrations, and the third a set-up with medium concentrations and mechanical ventilation. A protocol with the vasoconstrictive anesthetic medetomidine was used as a comparison. As expected, medium isoflurane anesthesia resulted in significantly higher CBF and lower CVR values than medetomidine (median whole-brain CBF of 157.7 vs 84.4 mL/100 g/min and CVR of 0.54 vs 51.7% in C57BL/6 J mice). The other two isoflurane protocols lowered the CBF and increased the CVR values compared with medium isoflurane anesthesia, without obvious differences between them (median whole-brain CBF of 138.9 vs 131.7 mL/100 g/min and CVR of 10.0 vs 9.6%, in C57BL/6 J mice). Furthermore, CVR was shown to be dependent on baseline CBF, regardless of the anesthesia protocol used.

Keywords: anesthesia; arterial spin labeling (ASL)-MRI; brain; hemodynamics; isoflurane; mouse.

Figure 1

Absolute CBF values and CBF maps for the four different anesthesia protocols in C57BL/6 J mice. Mean and standard deviation of the absolute CBF profiles in (A) the full brain and in (B) the cortex. (C) Representative examples of images acquired at −0.75 mm from Bregma. In the columns from left to right: Anatomical images with cortical ROIs; mean CBF maps collected in the last two minutes before the onset of the CO₂ challenge; mean CBF maps collected in the last two minutes during CO₂ challenge; and CVR maps. All the images on a row are from the same mouse

Figure 2

CVR relative to the baseline CBF for the four different anesthesia protocols in C57BL/6 J mice. CVR estimates are computed in the full brain (A, C, E) and in the cortex (B, D, F)

Figure 3

CBF and CVR values for the “low isoflurane” protocol in C57BL/6 J mice (blue) vs B6C3 mice (red). Time‐profiles of the CBF acquired in (A) the full brain and in (B) the cortex. (C, D) the CVR is significantly different between both strains. (E) the transcutaneous pCO₂ rise was significantly different at the time of maximum pCO₂ rise

Figure 4

CBF and CVR for the “standard isoflurane + mechanical ventilation” protocol: C57BL/6 J mice (blue) vs B6C3 mice (red). Time‐profiles of the CBF acquired in (A) the full brain and in (B) the cortex. CVR in (C) the full brain and in (D) the cortex, which are not significantly different in B6C3 vs C57BL/6 J mice. (E) Tc‐pCO₂ rise in B6C3 vs C57BL/6 J mice was not significantly different

Figure 5

CVR expressed as a function of the baseline CBF in C57BL/6 J mice. Each dot represents one mouse, where the colour indicates the anesthesia protocol used. Relations are given for (A) the full brain and (B) the cortex