Effect of Ozone Exposure on Dendritic Spines of CA1 Pyramidal Neurons of the Dorsal Hippocampus and on Object–place Recognition Memory in Rats

Abstract

The growth of many cities has generated an increase in the emission of environmental pollutants. Exposure to these pollutants has been associated with increased mortality worldwide. These pollutants, such as ozone, produce reactive oxygen species (ROS), which cause oxidative stress throughout the body. It has been observed that there is a relationship between chronic oxidative stress and the development of degenerative diseases typical of old age such as amyotrophic lateral sclerosis, Parkinson's disease, Alzheimer's disease, and Huntington's disease. The purpose of this research was to evaluate whether chronic exposure to ozone produces a deleterious effect on density and morphology of dendritic spines in CA1 of dorsal hippocampus and on learning and memory of object–place recognition. Rats were exposed to ozone or to ozone-free air for a period of 15, 30, 60, or 90 days. The principal results indicate that chronic oxidative stress induced by ozone produces a decrease in the density of dendritic spines, a decrease in thin and mushroom spine ratios, and an increase in stubby spine ratio, as well as a deficit in learning and memory of the object–place recognition task. These results indicate that chronic ozone exposure produces a loss in the inputs of CA1 neurons of the dorsal hippocampus, which may be the source of the cognitive deficits observed in the object–place recognition task, as indicated by the decrease in density of dendritic spines; these alterations are similar to those reported in some neurodegenerative diseases such as Alzheimer's disease.