Objective:

To investigate the impact of tribromoethanol, isoflurane, and ketamine/xylazine on neuronally- and hemodynamically-based functional connectivity. 

Background:

Resting-state functional connectivity (RSFC) captures correlated signals among brain regions while at rest. In humans, RSFC is imaged using fMRI by tracking spontaneous blood-oxygen-level-dependent (BOLD) fluctuations. Although distinct anesthetics have been shown to modulate RSFC in mice via a BOLD-like hemodynamic signal, the exploration of their effects on the neuronally based signals is less well known. 

Design/Methods:

We used Thy1-GCaMP6f mice with a genetically encoded calcium indicator in excitatory pyramidal neurons, to detect neuronal calcium activity. We implanted a chronic imaging window, followed by GCaMP fluorescence and optical intrinsic signal imaging. Each mouse sequentially received each of the anesthetics—tribromoethanol, isoflurane, or ketamine/xylazine—in random order. We calculated several connectivity metrics including a bihemispheric connectivity index (BCI) to determine the overall connectivity between homotopic regions on each hemisphere. Correlation coefficients were z-transformed to enable comparisons between groups. 

Results:

Tribromoethanol consistently exhibited the highest BCI values. Tribromoethanol's z-transformed BCI for neuronal GCaMP and hemodynamic connectivity was significantly higher than the metrics for ketamine/xylazine and isoflurane (tribromoethanol 1.06, ketamine/xylazine 0.67, isoflurane 0.80, p < 0.01 for tribromoethanol vs. others). Ketamine/xylazine displayed reduced variability when compared to tribromoethanol and isoflurane. All anesthetics had high correlations between the GCaMP signal and the oxy-hemoglobin signal, with ketamine/xylazine displaying the highest z-transformed correlation of the group (ketamine/xylazine 1.33, tribromoethanol 1.09, isoflurane 1.01), p < 0.01 for KX vs. others). 

Conclusions:

While all three anesthetics demonstrate varied effects, tribromoethanol notably optimized BCI compared to ketamine/xylazine and iso. Isoflurane displayed marked variability. This study underscores the importance of anesthetic selection for studies involving functional connectivity.