Rats may seek cannabis to cope with stress

PULLMAN, Wash. -- It isn’t just people – when given the chance rats may also use cannabis to cope with stress, according to a study by researchers at Washington State University.

Published in the journal Neuropsychopharmacology, the study was designed to examine cannabis-seeking behavior and found that rats with higher natural stress levels are far more likely to self-administer the popular recreational drug.

"We ran rats through this extensive battery of behavioral and biological tests, and what we found was that when we look at all of these different factors and all the variables that we measured, stress levels seem to matter the most when it comes to cannabis use,” said Ryan McLaughlin, associate professor in WSU’s College of Veterinary Medicine.

Looking at traits ranging from social behaviors to sex, cognition, reward, and arousal, McLaughlin and his team of undergraduate and graduate student researchers created a behavioral profile for each rat. Then, over the course of three weeks, rats were observed for one hour daily as they were given the option to self-administer cannabis by poking their nose in a vapor port to release a three-second dispersal of cannabis vapor in an air-tight chamber.

During that one-hour period, student researchers tracked the number of “nose-pokes” by each rat and found a direct correlation to the number of nose-pokes and baseline stress hormone levels. 

By measuring the stress hormone corticosterone in the rodents, the equivalent to the stress hormone cortisol in humans, the team found rats with higher natural stress hormone levels were far more likely to self-administer cannabis.

“If you want to really boil it down, there are baseline levels of stress hormones that can predict rates of cannabis self-administration, and I think that only makes sense given that the most common reason that people habitually use cannabis is to cope with stress,” McLaughlin said.

He said it’s important to note that it was a rat’s resting baseline stress levels that were associated with cannabis self-administration, not stress that fluctuates in real time with exercise or mentally challenging tasks. Stress hormone levels were also calculated after exposure to a stressor and showed no significant link to cannabis-seeking behavior.

There were also significant relationships between rates of cannabis self-administration and measures of “cognitive flexibility”, which is our ability to adapt to changing rules.

“Animals that were less flexible in shifting between rules, when we tested them in a cognitive task, tended to show stronger rates of cannabis-seeking behavior,” he said. “So, animals that rely more heavily on visual cues to guide their decision making, those rats, when we tested their motivation to self-administer cannabis vapor, were also very highly motivated rats.”

The study also identified a link between high morning corticosterone and low endocannabinoid levels to cannabis self-administration, although not as strongly as baseline stress.

Endocannabinoids are compounds produced on demand to help the body maintain a state of physiological balance, or homeostasis.

“There's some thought behind why people might be more prone to use cannabis, and that maybe THC serves as a reasonable substitute for endocannabinoids in individuals that have lower endocannabinoid levels,” McLaughlin said. “So, perhaps there's more of a drive to supplement that with cannabis.”

With more and more states decriminalizing cannabis and legalizing recreational cannabis, McLaughlin said it’s critical to understand the effects of the drug and the grips of drug abuse.

“Our findings highlight potential early or pre-use markers that could one day support screening and prevention strategies,” McLaughlin said. “I could certainly envision a scenario where having an assessment of baseline cortisol might provide some level of insight into whether there's an increased propensity for you to develop problematic drug use patterns later in life.”