Self-administration is a common method in behavioral pharmacological, reward-seeking and addiction behavior research. It provides perfect scientific research protocol for the qualitative and quantitative analysis and evaluation of drug psycho-dependence.
In this article, we will introduce you one of the drug self administration protocol.
1. SA Test Materials and Methods
1.1 Experimental Animals
The experimental animals selected for this study were adult male Sprague-Dawley rats, weighing 350-400 g. The animal housing room was maintained at a temperature of 22 ± 2 ℃ and a humidity of approximately 60%. All rats were housed individually in cages. The animal room was equipped with an automatic light control system, with light exposure from 7 a.m. to 7 p.m. All rats were acclimated to the housing conditions for one week before the formal experiment began.
1.2 Self-administration System
The bottom of the SA214 self-administration box is a metal grid, and there are two levers on the box walls, left and right. When the rat presses the lever, the system can receive the lever signal. Above the soundproof box is a house light, and there is a cue light above each of the two levers on the sides. There is also a buzzer on the middle panel. On the top of the box is the intravenous drug delivery device. The tube is covered with a spring tube to protect it. The upper end of the tube is connected to the intravenous injection pump, and the lower end can be connected to the catheter device implanted in the rat’s jugular vein. In addition, there is a camera on the top of the box that can record the rat’s training process. According to the experiment, an appropriate experimental method (FR1) is edited. When the rat presses the lever, the system will pump in an addictive drug or offers one pellet as reward, accompanied by changes in environmental cues such as signal lights and sounds. After each effective lever pressing, the system immediately enters a refractory period of 20 seconds. During this period, the rat’s lever pressing behavior (considered as ineffective event) is also recorded, but it does not trigger any system response or reward. After the effective refractory period, the system completes one cycle and enters the next cycle. When the rat performs a control lever pressing, the system only records the number of control lever pressing, not offer the liquid reward through syringe pump, and does not have changes in cues such as lights and sounds.
1.3 Intravenous Drug Infusion & Food Pellet Dispenser
Intravenous Drug Infusion Device: For precise administration of fluids and drugs through programmable control. Suitable for multiple flow rates continuous or when flow rates need to vary during experiments. Applicable on drug testing, catheters flushing, electrolyte therapy, and sucrose gradients etc. Injection time is calculated automatically by the speed and the dosage of a single dose. Configurable pump speeds 0.5 – 60 RPM. Syringe diameter range: 1-60mm. Single dose, range 0.001ml-1ml.
Food Pellet Dispenser: Support 20mg or 45mg Bio-Serv pellet, 45 mg pellet dispenser is the default choice. 20mg pellet is available. Food detection function to ensure perfect delivery of one standard pellet. Support manual feeding training, and manual feeding stop. With food shortage feedback function, if no detect after three deliveries, missing food data will be uploaded to remind the researchers to add pellet.
1.4 Drugs
Cocaine hydrochloride powder (1 g/bottle) was used in the experiment. It was dissolved in sterile physiological saline to prepare a solution with a concentration of 8 mg/mL. The drug was properly stored by designated laboratory staff at room temperature and away from light.
1.5 Jugular Vein Catheterization Surgery
The jugular vein catheterization surgery protocol utilized 10% chloral hydrate. A longitudinal skin incision of approximately 1 cm was made in the scapular region, and the subcutaneous tissue was appropriately separated. A subcutaneous tunnel needle was used to insert the jugular vein catheter from the back incision into the neck incision. The position of the jugular vein catheter was adjusted appropriately, and a positioning pin was placed on the silicone tube. The tightness of the jugular vein catheter was adjusted, and the fixation position of the positioning pin was adjusted according to the length of the subcutaneous tunnel. The positioning pin was firmly tightened with appropriate force, and the length of the silicone tube was trimmed so that the distance from the positioning pin to the end of the catheter was approximately 3.7 cm (confirmed through multiple dissections that this length corresponds to the junction of the superior vena cava and the right atrium). Then, the end of the catheter was trimmed into a fish-mouth shape. Three suture lines were placed horizontally across the jugular vein. One suture was used to ligate the distal end of the jugular vein (where the internal jugular vein and the external jugular vein converge to form the common jugular vein). Approximately 0.3 mm away from this point, a 20 mL syringe needle was inserted longitudinally along the vein into the rat’s jugular vein, and the catheter was inserted into the jugular vein to the positioning pin. The other two suture lines were used to fix the catheter and the proximal end of the vein. Subsequently, the positioning pin was fixed in the adjacent subcutaneous tissue to prevent the silicone tube from being dislodged from the jugular vein. The anterior neck and the scapular region incision were thoroughly rinsed with hydrogen peroxide, disinfected, and the incision was sutured. The surgery was completed. The jugular vein catheter required daily effective care, which involved flushing with physiological saline containing heparin (10 U/mL) and penicillin (200,000 IU/animal) to prevent infection and catheter blockage. One week after the surgery, the next step of the experiment could be conducted.
1.6 Training of Rat Cocaine Self-Administration Model
The classic animal self-administration model is an effective method for studying drug addiction. Seven days after the catheterization surgery in the rat’s jugular vein, the self-administration training stage can be initiated. Generally, the following steps are required:
(1) Selecting an appropriate experimental training method:
This experiment adopts a fixed ratio (FR = 1) procedure. That is, when the rat presses the effective lever (left lever, L-signal) once, the system will inject 0.05 ml of addictive drug (cocaine, 8 mg/mL) within 3-5 seconds, accompanied by changes in signal lights, sounds, etc. Each time the rat presses the effective lever, the system immediately enters a refractory period, which lasts for 20 seconds. During this period, the rat’s lever pressing behavior will be recorded, but no reward response will be triggered. After the effective refractory period, the system completes one cycle and enters the next cycle (note: the left lever touched by the rat during the refractory period is an ineffective lever). When the rat presses the control lever (right lever, R-signal), our self-administration device only records the number of right lever presses, does not inject the drug, and does not accompany changes in lights, sounds, etc. The training lasts for 2 hours each day, and the number of lever presses (effective lever, ineffective lever, and control lever) and drug administration times of the rats are recorded.
(2) Drug addiction training (1-15 days):
Place normal-fed rats into their own drug administration boxes for drug addiction training. That is, when the rat presses the lever successfully, the addictive drug is pumped in, accompanied by changes in lights, sounds, etc. The drug addiction training lasts for 2 hours each day, and the number of lever presses (successful lever presses, ineffective lever presses, and control lever presses), as well as the number of drug administrations, are recorded for the rats.
1.7 Statistical Analysis
The relevant data were analyzed and processed using statistical software. The measurement data were expressed as mean ± standard error (Mean ± SEM). The test method employed was the independent sample t-test. A P value less than 0.05 was considered statistically significant.
2 Results
The classic animal self-administration model is an effective method for studying drug addiction and drug dependence. The rats were placed in their own administration boxes for training. When the rats performed an effective lever, the addictive drug was pumped in, accompanied by changes in lights, sounds, etc. The training lasted for 2 hours each day, and the number of lever presses (effective lever, ineffective lever, and control lever) and the number of drug administrations were recorded for the rats. After approximately 2 weeks of continuous training, the addiction effect of the rats basically stabilized. In the addiction training group, after the rats underwent cocaine self-administration training, the number of drug pump in (effective lever) significantly increased. In the later stage of training, the number of effective lever presses reached a certain stable value. The data of the last three days were statistically analyzed. While for the control training group, the number of effective lever presses was significantly lower than that of the addiction training group (P < 0.01), indicating that the training group had effectively established the cocaine self-administration model.
