Type of Anesthesia Influences Positron Emission Tomography Measurements of Dopamine D2/3 Receptor Binding in the Rat Brain
Rats are often anesthetized prior to positron emission tomography (PET) brain imaging in order to prevent head movements. Anesthesia can be administered by inhalation agents, such as isoflurane (Forene), or injection mixtures, such as fentanyl-fluanisone-midazolam (Hypnorm-Dormicum). Unfortunately, anesthesia affects a variety of physiological variables, including those in the brain. The aim of this study was to compare the effects of inhalation and injection anesthesia on the binding potential of the dopaminergic D2/3 tracer [11C]raclopride used for PET brain imaging in human and animal studies. Male Lewis rats were assigned to either inhalation (isoflurane; N=4) or injection (fentanyl-fluanisone-midazolam; N=5) anesthesia. Isoflurane was given continuously, and fentanyl-fluanisone-midazolam was supplemented every 30-60 minutes when the tail reflex was positive. Catheters were surgically placed in femoral arteries and veins for blood sampling and tracer injection. After a short attenuation scan, the rats were PET scanned for 90 minutes after injection of [11C]raclopride. We found that rats anesthetized with isoflurane had double the binding potential in the striatum compared with fentanyl-fluanisone-midazolam anesthetized rats. Our results are in agreement with other studies showing that anesthesia may have a major influence on brain imaging studies involving tracer kinetics in rats.