Acquisition of a shuttlebox avoidance task with high and low shock following different durations of treatment with dl parachlorophenylalanine

This study investigated acquisition of a shuttlebox avoidance task using high (1.00 ma) and low (0.25 ma) shock levels, following different durations of treatment with dl- parachlorophenylalanine (PCPA), a depletor of brain serotonin. Subjects were 80 female albino rats of the Fisher strain. The four durations of treatment investigated wore 3 days, 7 days, 15 days and 28 days. Rats in each of these duration . groups received daily injections (100 mg/kg, i.p.) of PCPA. The corresponding control groups received daily injections of the vehicle only (0.2% agar). On the day following the last day of treatment the animals were trained for 50 trials in a two way shuttlebox avoidance task. At the time of training each of the eight treatment groups was further subdivided into a high shock and a low shock group, resulting in a total of 16 groups (N=5) for the experimental procedure. Comparison of the two treatments, irrespective of duration of treatment and shock level, indicates that performance of animals treated with PCPA was inferior to that of control animals, as measured by the number of avoidance responses occurring during acquisition. The high shock level resulted in more avoidance responses than the low shock level. A significant difference between animals treated with PCPA and animals treated with agar was obtained only for a treatment duration of 15 days. However, the direction of the differences obtained suggests that acute treatment may result in facilitation of avoidance acquisition whereas chronic treatment results in impaired acquisition. With further investigation this relationship might account for disagreements among studies concerning the effects of treatment with PCPA on avoidance learning.