This is our 6th week working at Utrecht University in the Department of Animals, Science, and Society, Division of Behavioral Neuroscience. Our research here mostly focuses on the effects of adolescent alcohol consumption on later motivation to consume alcohol and the neurobiology of addiction. The rats we use to model addiction are male Lister-Hooded rats, which are an outbred strain characterized by their high intelligence.
We’re helping with two projects. The first is an experiment that is examining the correlation between adolescent (21-42 days after birth) play behavior, adolescent alcohol consumption, and consumption of alcohol in aversive conditions in adulthood.
Adolescent rats love to play, but to encourage them to exhibit this behavior during testing, they are isolated before all play tests. This makes the rats “hungry” for play and ensures that we will have plenty of play behavior to observe. Play sessions can last 5 or 10 minutes, sometimes longer. We can quantify the rats’ playfulness by counting the number of times they pounce on or pin their partner.
After play testing is completed, the adolescent rats are given either alcohol or water to drink so that we can relate adolescent alcohol exposure to alcohol consumption later in life. During the time between adolescent alcohol exposure and adult alcohol exposure, the rats complete a series of behavioral tests, including the elevated plus maze, the open field test, and the cognitive hole board test. Once the rats reach adulthood, they are given alcohol and water bottles to choose from for 24 hours, three days a week. We weigh both the alcohol and the water bottles before and after they are given to the rats so that we can measure their drinking preferences.
When the rats are finished with the alcohol self-administration period, they begin testing in the operant boxes. An operant box is used to assess motivation for reward. Inside, there are two levers. Pressing of one of the levers leads to the animal receiving a reward (alcohol in this case), while pressing the other lever does nothing. The inactive lever’s purpose is to control for general exploration. When the rats start training, they are on a “fixed ratio schedule”, meaning they receive one dose of alcohol for every active lever press. Once they seem to understand that there is an association between the active lever and the reward, they begin random interval training. In a random interval schedule, the rat can make as many lever presses as it wants, but they receive no reward until a random amount of time is up. In the first random interval (RI) test, the animals must wait an average of 5 seconds in between rewards. Eventually, the rats can be trained to respond even when the random interval is an average of 120 seconds. In a one-hour testing period, some rats on a 120 second RI schedule may press the lever 600 times! How many times the rat presses the lever to obtain alcohol indicates their level of motivation to obtain the alcohol.
Because this research is focused on alcohol addiction, we also measure the rats’ motivation to consume the drug in spite of aversive stimuli (a characteristic of addiction). To do this, we train the rats to associate a tone with a foot shock. After they have learned this association, we place them back in the operant boxes and measure how they adjust their alcohol consumption in the presence of the tone. The idea is that if the rat is truly addicted to the alcohol, it will continue to seek a reward by pressing the active lever even if it thinks that seeking a reward will also yield a foot shock. This system is intended to be analogous to a situation in which an addict continues abusing a substance despite aversive consequences, such as losing their job/straining their family.
The second project is one that uses optogenetics (stimulation of specific brain areas using fiber optic cables) to examine the effects of inhibition of different brain areas on alcohol seeking behavior. Optogenetics is very new to neuroscience research and we are still in the process of perfecting the techniques in this lab. It is very useful as it can allow us to see the effect of temporarily increasing or decreasing the activity of the selected brain region in real time, rather than studying the effects of permanent brain damage. To use this technique, we first must perform stereotaxic surgery on the rat to make a hole in the skull and brain through which we can insert the fiber optic cables. Then, a viral vector encoding a gene for a light-activated sodium (if excitatory stimulation is desired) or potassium (if inhibitory stimulation is desired) channel is administered. The brain cells that are infected with this virus can then be activated by shining a light through the fiber optic cables and into the brain. After surgery, the animals are trained in the operant boxes as explained above. Once they have been trained, we can place them in the operant boxes while they are connected to the fiber optic cables and record their reward-seeking behavior while we activate the brain areas expressing the ion channel genes. It is expected that inhibition of the dorsolateral striatum (DLS) will decrease responding. This is because the DLS promotes rewarding behavior.
This research is important in that it will provide information that can be used to understand the underlying causes and characteristics of addiction.