Boys born to fathers who are addicted to cocaine develop resistance to the drug, a new research has found.

The latest study shows that cocaine-induced changes in the body are passed from father to son, making the son resistant to addictive behavior associated with cocaine.

"This study is the first to show that the chemical effects of cocaine use can be passed down to future generations to cause a resistance to addictive behavior, indicating that paternal exposure to toxins such as cocaine can have profound effects on gene expression and behavior in their offspring," said senior author R. Christopher Pierce, PhD, associate professor of Neuroscience in Psychiatry at Penn, according to a news release.

Researchers analyzed the effects of cocaine on rats. 60 rats were kept on cocaine while the controls were administered saline. The rats were then allowed to mate with female rats that weren't exposed to the drug. The female rats were separated immediately after mating.

Researchers then analyzed behavior of the offspring to see whether they would self-administer cocaine when it was offered to them. They discovered that male rats, but not female rats, were less likely to self-administer cocaine and had fewer levels of the drug in the body than other rats.

Even the rewarding effect of cocaine was decreased in rats whose fathers were kept on the drug as these rats were also less likely to work harder to get another dose of the drug.

Researchers then analyzed the brains of these rats and found that males born to rats that were addicted to cocaine had higher levels of a protein called brain-derived neurotrophic factor (BDNF) in the prefrontal cortex. The protein is known to reduce the behavioral effects of cocaine.

"We were quite surprised that the male offspring of sires that used cocaine didn't like cocaine as much. While we identified one change in the brain that appears to underlie this cocaine resistance effect, there are undoubtedly other physiological changes as well and we are currently performing more broad experiments to identify them. We also are eager to perform similar studies with more widely used drugs of abuse such as nicotine and alcohol," said Pierce.

The study results showed that cocaine causes epigenetic changes in the sperms that reprogram the information that's passed between two generations. The fact that only males showed the changes in cocaine resistance leaves many questions unanswered about why females don't get the cocaine resistance trait from the father. Researchers say that sex-hormones like testosterone, estrogen and/or progesterone may play a role.

The study is published in the journal Nature Neuroscience.