Effects of postnatal lead exposure on open field behavior in monkeys

Nursery-reared rhesus monkeys were treated with either no lead or moderate levels of lead from day eight or nine until day 365 after birth. All subjects were at or below 5 micrograms/dl blood lead levels for at least 1.5 years by the time of the present study conducted at 4 years of age. Data were collected in a primate version of the open field test which proved sensitive to several behavioral alterations in the lead-treated monkeys. These significant differences included a failure to habituate as evidenced by number of sectors entered, increased durations of activity and environmental exploration, and a longer latency to enter the open field. Most of these effects were compatible with a hypothesis of hippocampal dysfunction in the lead-treated monkeys and appeared to indicate enduring lead-induced alterations. These results provide further support for a correlation between early lead exposure and hippocampal dysfunction. Additionally, the utility of a primate version of the open field test for behavioral toxicological studies is substantiated.