The Effects of Developmental Lead Poisoning on the Adult Rat's Freezing and Exploration Behaviors in a Hole Board Test

Abstract

Lead poisoning is a well-established neurotoxicant that produces developmental neuropathologies that persist across the lifespan. However, how these early neurodeveloprnental insults impair sensorimotor, emotional, and cognitive behavioral systems later on in life remain to be elucidated. The present study examined Long Evans hooded rats that were exposed to 1,000 ppm lead acetate perinatally or Control rats that were not exposed to lead (i.e., 0 ppm). The male offspring from at least 5 different litters were randomly selected to form the treatment conditions. The perinatal group was exposed to lead 1-month prior to pairing, throughout gestation, birth, and ceased exposure at postnatal day (PND) 22. At PND 22 rats were subjected to a two-day hole board test whereby Day 1 served as an anxiogenic assessment and Day 2 served as a habituated and odor evoked novel exploration test within the identical apparatus. The only difference was that on Day 2 four novel odor extracts were positioned under the apparatus. The total time mobile, number of head pokes, and duration of head poking were recorded across both test days. The hole board test revealed that male Perinatal lead-exposed rats on Day I froze more and exhibited elevated emotional fear responses, when compared to the Control rats. Interestingly, on Day 2 Control rats engaged in significantly more head poking than they did on Day 1. Thus, evidencing the ability to emotionally habituate to t.he prior anxiogenic stimulus and engage in sensorimotor dependent exploratory behaviors. However, the Perinatal lead-exposed rats exhibited difficulty in shifting from their anxiogenic responses, showed little habituation, and a delayed on-set to sensorimotor dependent exploration of the novel odors. The data suggest that perinatal lead poisoning impairs sensory processes required for contextual adaptations, efficiency, and ongoing environmental changes directed by the prefrontal cortical through goal directed behaviors.