A Conflict Model of Reward-seeking Behavior in Male Rats

This conflict model can be used for revealing the impairment of inhibitory control after exposure to addictive drugs or other factors that may influence inhibitory control. The main advantage of this model is to provide a simple and a quick way to evaluate the ability of inhibitory control without a learning process. We draw the mastration of this method is critical because the operations in the conflict test are difficult to understand literally.

For the confict model, house four rats in each cage for at least 10 days before the tests. Perform all the tests under dim lighting during the dark phase. Prepare 120 milliliters of morphine, 10 milliliters of estradiol benzoate, and 10 milliliters of progesterone for artificial induction of estrus.

Handle the ovariectomized female rats at least three times over three days, each time for three minutes before mating screening. About 48 to 52 hours before mating screening or the conflict test, inject the estradiol benzoate at 25 micrograms per rat subcutaneously. Four to six hours before mating screening or the conflict test, subcutaneously inject progesterone at one milligram per rat.

To screen the rats for mating performance, place a male rat into the carton with pine wood shaving bedding and let it habituate for five minutes. Next introduce an estrus female rat into the carton and monitor the male copulatory behavior. After the male rat completes its first ejaculation, within 30 minutes or does not display intermission within 15 minutes, transfer the rat back to its home cage.

For binge-like morphine treatment, weigh the male rats and calculate the injection volume for each rat based on the body weight. Then inject the rats intraperineally with saline or morphine in a binge-like regimen. After at least six hours, give the rats a second injection in the same way.

On the day before testing, transfer the male rat to the conflict test room and allow it to habituate to the open-field reward proximity chamber for 15 minutes. On the testing day, transfer the rat to a chamber allowing free exploration for 10 minutes. Subsequently, place an estrus female rat in the stimulus cage as an incentive and allow the male subject to freely approach it and investigate the incentive rat for five minutes.

After five minutes of free approach, transfer the male subject from the stimulus cage to the other end of the arena and place an obstacle. Then start the first trial of the test. Remove the male rat from the stimulus cage about 15 to 20 seconds after each time it surmounts the obstacle.

End the trial if the male subject climbs or jumps over the obstacle three times within four minutes. Immediately start the next trial with increasing obstacle difficulty. If a male subject surmounts the obstacle less than three times within four minutes, end the test and record the number of times it surmounts the obstacle.

Afterward bring the male rat back to the home cage and scrub the open-field chamber with 05%glacial acetic acid. Score each surmounting and use the sum of the scores for all of the surmountings as a total score for a male subject in this conflict test. To explore whether this conflict model can reveal maladaptive, risky reward-seeking behavior induced by opiates, the reward-seeking behavior is displayed by the saline and morphine pretreated groups were compared after short-term and long-term withdrawal from morphine, respectively.

On both day seven and day 17 of withdrawal, the morphine pretreated rats showed significantly more approaching behaviors than the saline pretreated rats, suggesting that the morphine withdrawn rats displayed more perseverative behaviors upon aversive obstacle, and this maladaptive behavior persists for a long time after withdrawal. The repeated test showed a significant main effect of pretreatment. The correlation of the scores between day seven and day 14 of withdrawal, showed that the rats'reward-seeking behaviors were roughly stable over repeated tests.

To investigate the influence of stressful events on the ability of inhibitory control in animals, the drug naive rats were exposed to an intermittent foot-shock stress before the conflict test. Although there was no significant difference between the stress and control groups, the reward-seeking behaviors displayed a bimodal distribution within the stress group, suggesting the markedly differential effects of acute stress on risky reward-seeking behaviors among individuals. It's important that male rats to acquire sexual experience before entering follow-up conflict tasks.

And the stress factors should be tightly controlled throughout the experiment. In this conflict task, one can also investigate the impact of rewards value on reward-seeking behaviors. For example, changing some reward value by replacing the female rat with a male rat.

Don't forget that estrogen benzoate and progesterone are harmful to humans, so wear masks and gloves all the time when in contact with them.