Are there specific freediving skills? A comparative study of training in voluntary apnea in Sprague Dawley and Long-Evans rats

Although Sprague Dawley (SD) and Long-Evans (LE) rats are commonly used in a variety of behavioral studies, their specific abilities are rarely compared. The aim was to compare the apneic abilities of SD and LE male rats for future studies on brain adaptability to apnea using a voluntary apnea training protocol in a serpentine-shaped maze. This training is conducted in such a way as to reduce as much as possible any stressfulness, making it under the full will of the rat. It consists of a pre-training swimming phase, starting at weaning, followed by an apnea training over a 8 week duration, where distance, and thus time in apnea, increases progressively (from 5m to 11m). Four behavioral indexes were measured: (1) proportions of willing rats and dropouts, (2) reliability, (3) time to start and (4) confidence. The main findings showed that LE rats were more inclined to freedive than SD rats (e.g. higher proportion of freedivers in LE than SD groups), with LE rats waiting less time in the start zone before diving, compared to SD rats. LE rats were also more variable in several aspects, such as the number of U-turns in the maze or distance traveled in apnea. These results show that LE rats spent more time in apnea than SD rats, rendering this strain a better model for the study of brain adaptability in voluntary apnea.