Similar development of tolerance to barbital-induced inhibition of avoidance behavior and loss of righting reflex in rats.

In order to determine if tolerance develops to the inhibition of avoidance behavior by the barbiturates, the effects of barbital on avoidance were determined in rats given barbital in their sole source of drinking water for 7 or 33 days. For comparison tolerance to the loss of righting reflex was also determined in other rats at the same time. All rats were trained by one 60-min session in a one-way active avoidance task; they were then put on the chronic drug administration schedule and then tested on the appropriate day after a single IP injection of 250 mg/kg sodium barbital. To assess the degree of tolerance, the brain level of barbital found at the biological endpoint--the loss of avoidance or loss of righting reflex--was compared in the chronic barbital treated rats and controls. A similar degree of tolerance developed to both effects of the drug and it appeared to be as great after 7 as after 33 days of chronic barbital treatment.