Sampling of orbital sinus blood closely reflects brain ethanol content in rats

It was demonstrated that the aerial righting reflex can be used as an index of acute ethanol-induced impairment of motor coordination in rats, and was found to directly correlate with blood ethanol content from the infraorbital plexus. A study of ethanol within the blood and its distribution in brain regions showed that the ethanol content of orbital sinus blood closely reflected that in the cerebral cortex, midbrain, and cerebellum. Ethanol administration by intraperitoneal (IP) injection (2, 3 or 4 g/kg) produced the same distribution as 24 hr ethanol vapor inhalation (28 mg/l). Blood ethanol concentrations were slightly higher than brain ethanol concentrations when measured at 10, 30, and 60 min after IP injection and immediately following ethanol vapor administration. Also, in rats 48 hr following ethanol vapor inhalation when tolerance to ethanol is exhibited, the distribution and concentrations of ethanol in blood and brain from acute ethanol (2 g/kg, IP) were unaltered when compared with controls. These data suggest that ethanol distribution within the brain does not play a role in the phenomenon of tolerance to ethanol.