Environmental contaminants and learning and memory

A number of environmental contaminants are known to cause a reduction in IQ in children exposed prenatally or early in life. These effects are well documented for exposure to lead, methylmercury, polychlorinated biphenyls (PCBs), and cigarette smoke, all of which can reduce IQ by up to 5–7 IQ points. Similar effects may result from exposure to dioxins and some pesticides. In most or all of these situations there are also behavioral changes as a result of exposure, including shortened attention span and hyperactivity. Recent studies have shown that adverse effects of contaminants such as lead and cigarette smoke on IQ occur at lower levels of exposure than previously thought, and that the dose–response relationship is actually steeper at lower concentrations than what is seen at higher levels. While adults are not as sensitive as children, there is evidence for a rather selective loss of memory function in adults exposed to the same substances. Our group has attempted to determine the mechanisms whereby these effects occur using long-term potentiation (LTP), an electrophysiological measure known to be related to learning and memory, studied in rodent brain slices. We find that lead and PCBs both reduce LTP whether given during gestation and lactation or acutely applied to brain slices of unexposed animals. Surprisingly, these very different contaminants appear to have a similar mechanism of action, that being alteration of the activity of protein kinase C.