Oral self-administration of methohexital in baboons.

Oral self-administration of methohexital was generated in baboons that were food-restricted but not water-deprived. Stable intake of an 8% ethanol solution (two baboons) or water (two baboons) was first established in 3-h-sessions. Increasing concentrations of methohexital (0.005-10 mg/ml) then were substituted with a return to the ethanol or water baseline condition between methohexital conditions. For one baboon in the ethanol baseline condition, drinking was initially suppressed by methohexital substitution, but increased under a food-induced drinking procedure. For all baboons, an inverted U-shaped function generally described the relation between methohexital concentration and volume consumed. Anesthetization was observed at concentrations of 1.6 mg/ml and above. In two-bottle choice tests, three baboons generally drank greater volumes of methohexital than water at concentrations of 0.8 mg/ml and above. After a methohexital-free period of 1-3 months methohexital self-administration was readily reestablished.