Male adult mice with heterozygous knockdown of vesicular acetylcholine transporter in the brain or homozygous knockout of the transporter in the basal forebrain were compared with wild-type mice. Hippocampal and frontal cortical electrographic activity and righting reflex were studied in response to isoflurane and ketamine doses.
The loss-of-righting-reflex dose for isoflurane was lower in knockout (mean ± SD, 0.76 ± 0.08%, n = 18, P = 0.005) but not knockdown (0.78 ± 0.07%, n = 24, P = 0.021), as compared to wild-type mice (0.83 ± 0.07%, n = 23), using a significance criterion of P = 0.017 for three planned comparisons. Loss-of-righting-reflex dose for ketamine was lower in knockout (144 ± 39 mg/kg, n = 14, P = 0.006) but not knockdown (162 ± 32 mg/kg, n = 20, P = 0.602) as compared to wild-type mice (168 ± 24 mg/kg, n = 21). Hippocampal high-gamma (63 to 100 Hz) power after isoflurane was significantly lower in knockout and knockdown mice compared to wild-type mice (isoflurane-dose and mouse-group interaction effect, F[8,56] = 2.87, P = 0.010; n = 5 to 6 mice per group). Hippocampal high-gamma power after ketamine was significantly lower in both knockout and knockdown mice when compared to wild-type mice (interaction effect F[2,13] = 6.06, P = 0.014). The change in frontal cortical gamma power with isoflurane or ketamine was not statistically different among knockout, knockdown, and wild-type mice.
These findings suggest that forebrain cholinergic neurons modulate behavioral sensitivity and hippocampal gamma activity during isoflurane and ketamine anesthesia.
- Acetylcholine plays a major role in arousal, and pharmacologic interventions that raise the concentrations of this neurotransmitter reduce anesthetic potency
- Forebrain cholinergic neurons are a major source of acetylcholine, but their role in the modulation of anesthetic sensitivity is incompletely understood
- In genetically modified mice lacking the vesicular acetylcholine transporter in the forebrain, lower doses of isoflurane and ketamine were necessary to induce the loss of the righting reflex, a surrogate for loss of consciousness, when compared to wild-type counterparts
- Hippocampal gamma power was lower in genetically modified mice lacking forebrain acetylcholine than in the wild-type mice during both isoflurane and ketamine anesthesia
- These observations suggest that forebrain cholinergic neurons modulate anesthetic sensitivity during isoflurane and ketamine anesthesia