PULLMAN – A team of WSU professors and students is working to prove environmental factors, such as the light/dark cycle, may dictate pleasure-seeking behavior – even in rodents.

“Behavior, whether in humans or animals, is organized partly by environmental surroundings,” said Heiko Jansen, associate professor in the veterinary and comparative anatomy, pharmacology and physiology department (VCAPP). “We are studying the way rats respond to environmental factors, and how drug behavior changes when external factors are manipulated.”

Jansen and his team specifically are focusing on circadian rhythms – 24-hour cycles – in the lives of most organisms. They give a treatment group, approximately four to five rats, cocaine while manipulating the daily light and dark cycles and the time the rats receive the drug.
     
“By giving rats cocaine and manipulating the time of day they receive it, we will have a better understanding of when drug addictions emerge most strongly,” said Jansen.

A reason for rodents
 
Jansen and his team have chosen rats for their experiment because their systems work similarly to those of humans. The rats’ desire for cocaine is monitored by activity level and body temperature.

“We think, in many respects, rats become addicted to drugs like people do,” said Jansen. “They can tie experiences together with their surroundings just as easily.” This includes the ability to use time as a cue.
 
Furthermore, rats seem to actively work to obtain cocaine – and willingly ignore repercussions.

“Rats seem to do things in spite of the negative consequences, as humans do,” said Jansen. “If you provide them with a self-injecting lever for cocaine, they will likely develop an addiction and never know when to stop.”

Life application
 
From their own study and others, team members have concluded that circadian rhythms play a role in drug use. Day length and seasonal rhythms also seem to play a role.
 
“There’s an overlap between the brain’s timing system and a section of the brain known as the ‘reward system’ – it engages when something feels good or satisfying to you,” Jansen said. “The rats’ desire for cocaine emerged more strongly during certain times of the light and dark cycles – depending on what time of day they were trained.” Manipulating day length also suppressed the rats’ behavior.

This is affirmed in a recent study done in Alaska, where day and night vary drastically by season.
 
“The study concluded that during the winter, when days are very short, inhabitants were more concerned with stimulants – such as cocaine – and in the summer were more prone to other drugs, such as marijuana,” Jansen said. “Day length likely contributes to this seasonal difference.

 “This experiment emphasizes how dangerous drugs can be, because they can override parts of the brain that identify necessity,” he said. “These drugs, in combination with daily and seasonal cycles, may cause development of habits that will shape our behaviors – and will be hard to alter.”

Looking to future research, Jansen hopes to use his team’s findings to develop a way to override an individual’s desire for drugs.
 
“We hope to find a point in the day where light or dark treatment could override the ‘reward system’ and resynchronize the individual so they’re less apt to suffer from withdrawal,” he said.