Complex maze performance during carbon monoxide exposure in rats

Abstract

Most human victims of residential fires die of smoke inhalation. The cause of death of the victims is attributed to high levels of carboxyhemoglobin, but it is not clear why the victims are unable to escape even from locations remote from flaming combustion. In an attempt to provide a model of escape from toxic gases using animals, a complex maze was built for rats with 8 choice points. The animals were 24 hr water deprived and trained to remain in the start box for 15 min. Following this period, a rat was released in the maze and had to learn to avoid blind alleys and reach the goal box for water reinforcement within 15 min. Total time to traverse and total distance in the maze were recorded. Each animal was given one trial per day. After stable running times were established, different groups of six rats were exposed to 2000, 3000, 3500, and 4000 ppm of carbon monoxide (CO) when placed in the maze. Each animal was exposed to CO only once. On the day after CO exposure the rats were implanted with an arterial cannula and on the next day each animal was exposed to the same CO concentration it had previously experienced for 30 min. Blood samples were taken every 5 min. The effect of increasing CO concentrations was to increase maze running times as well as to decrease the number of animals reaching the goal. At 3500 ppm no animal reached the goal. At 2000 ppm, the animals that failed to reach the goal moved a greater distance than animals that reached the goal. At 3000 ppm, animals that did not reach the goal still moved enough total distance to reach it, but their movement was not goal directed after entry into the maze, Carboxyhemoglobin concentrations reached asymptote sooner at high CO concentrations, but were not markedly higher at high CO concentrations. The behavior of the rats in this situation may be similar to human behavior prior to collapse in residential fires.