The effects of chronic lead exposure on reactivity to frustrative nonreward in rats

Prior to straight runway training two groups of rats received lead exposure (500 ppm via the drinking water) for 106 days. Two additional groups of animals received access to plain tap water. An 80-trial runway acquisition phase followed an initial 60-day fluid exposure phase. During acquisition one lead-exposed group and one water-exposed group received 50% partial reinforcement training, while the remaining animals received continuous reinforcement training. An 80-trial extinction phase immediately followed acquisition. Acquisition results were characterized by superior performance by the continuous reinforcement animals. The partial reinforcement animals took significantly longer to extinguish the alleyway response than did the continuous reinforcement animals. Moreover, the lead-exposed, partial reinforcement animals took longer to extinguish in the goal section of the runway than did the water-exposed, partial reinforcement animals. Conversely, the lead-exposed, continuously reinforced animals displayed significantly more rapid goal-measure extinction than did the water-exposed, continuously reinforced animals. When interpreted by the classic frustration theory [1,2], these latter two findings are supportive of a heightened emotional reaction being promulgated by lead exposure.