This post was written by Nicki Herald.
Introduction
Alcoholism is a disease that millions of people suffer from, worldwide. It is a “roller coaster” sort of lifestyle, with periods of abstinence followed by relapses. Each time an affected individual drinks, they must drink more than they did the last time to get the “reward” they are looking for. As it turns out, other animals exhibit this pattern when exposed to ethanol, as well. Mice, for example, possessed a type of dependence when they were chronically exposed to ethanol, in this study. The control and experimental groups were placed in an identical environment, with the same opportunity to consume ethanol. As expected, and explained in greater detail below, the experimental mice consumed much more ethanol.
Methods
This study involved three experiments, but some of the variables were the same in all three. All of the control mice (CTL) were given saline and pyrazole injections, whereas all of the experimental mice (EtOH) were given 1.6 g/kg ethanol and pyrazole injections. All mice were placed into a chronic ethanol exposure chamber, basically a gas chamber, for sixteen hours a day, four days at a time. The gas was turned off for three days, and the mice had no access to ethanol. After this period of abstinence, no gas was turned on for five days, but the mice had a choice to drink either tap water or ethanol. This cycle was repeated multiple times during the study.
In experiment one, the goal was to find out how much ethanol the mice were voluntarily consuming. The sucrose fading procedure was employed to establish a 15% baseline ethanol. Four separate tests were conducted.
In experiment two, the goal was to compare voluntary ethanol consumption and the ethanol concentrations in the brain. In vivo microdialysis was used to measure the ethanol concentration in the brain. Probes were implanted into the brains of seventeen EtOH mice and ten CTL mice, the day before the dialysis was needed (Figure 6 illustrates the placement of the probes). When dialysis was ready to be collected, .22 micrometers of artificial cerebral spinal fluid was diffused through the probes. The dialysate was collected into tubes containing six microliters of .75 M perchloric acid. After each twenty minute collection interval, two microliters of dialysate was removed to be tested for ethanol. This was done using gas chromatography with flame detection.
In experiment three, ethanol concentrations in the blood and brain were tested immediately after being taken out of the gas chamber. These results were compared with those found after the mice had drunk voluntarily for four cycles. A baseline ethanol of 15% was set, again, using the sucrose fading test. Four test cycles were done under drinking-only sessions. After the fourth cycle, thirteen of the mice had blood drawn from behind their eyes to test the ethanol concentration. Fourteen of the mice went through one more cycle in the gas chamber, and had blood and cortex tissue removed immediately after the cycle was finished. This was used to test ethanol concentration solely from the ethanol gas.
Results
As expected, in experiment one, voluntary drinking increased with time spent in an environment filled with ethanol. The control mice stayed constant at the baseline of 2.1 g/kg, but the experimental mice reached 4.1 g/kg by the end of the experiment. Again, just like humans, the mice that went into the chambers with ethanol already in their bloodstream were much more likely to keep drinking more and more. An individual struggling with alcoholism would have a much harder time not drinking when it was freely available, than someone who did not have a drinking problem. Once the affected individual started drinking, it would be harder for him/her to stop until he/she reached the euphoria he/she was looking for. Figures 1a and b make it easy to see that the EtOH mice were much more vulnerable to the ethanol. As time went on, they increased their voluntary consumption. This is supported by post-hoc tests. Though it may seem like common sense that with increased exposure to alcohol, the EtOH mice would voluntarily drink, but this is a valid experiment. This had to be shown and proven in order for experiments two and three to make sense.
In experiment two, the same trend was seen. As test cycles went on, voluntary consumption increased in the EtOH mice, as shown in figure 5a. This part of the experiment, in my opinion, was not necessary to include in the article again. It is essentially a repeat of experiment one. The second half of the experiment, however, is valid. The microdialysis procedure proved that the EtOH mice had significantly higher concentrations of ethanol in their nucleus accumbens than the CTL mice. Four samples were tested, and in each one the concentration increased (figure 5c).
In experiment three, the first part was, once again, testing ethanol concentration in the blood and brain after a drinking session. Obviously, EtOH mice had much higher levels. Again, I feel like this part of the article was redundant. The second half of the experiment was valid, and yielded surprising results. The EtOH mice that were tested immediately after coming out of the gas chamber had blood and brain concentrations with no significant difference than those tested in the first part of this experiment (table 2). This goes to show that, during drinking sessions, they were trying to obtain as much ethanol as they were receiving in the gas chambers.
Discussion
I think that this was a very valid experiment, overall. Alcoholism is a real disease, and humans share many of the relapsing and dependent characteristics with the mice. Since humans are not ethically able to be researched on, experiments such as this one may lead to a remedy for alcoholism.
