This method can help to address some key questions in the drug addiction field about drug use cravings and the incubation of craving response. With only six days of morphine conditioning, the conditioned place preference memory response can be extended to 18 days for observation of the craving phenomena in the rat model. The implications of this rat morphine conditioning model extend toward the furthering of our understanding underlying mechanisms of the incubation of cravings.
Before beginning the procedure, construct a three chamber conditioned place preference apparatus consisting of two large, black 30 by 25 by 30 centimeter side chambers. And one white 11 by 25 by 30 centimeter middle chamber, with a smooth, white PVC floor. Then add different tactile cues to the side chambers for testing of the rat's initial preferences.
For pre-conditioning of the animals, remove the guillotine doors to allow free access to the entire apparatus. And place a rat into the middle chamber. Record the activity of the animal for 15 minutes, calculating the time spent in the two side chambers on day three as a baseline.
For conditioning of the animals, inject the morphine conditioned rat group with one milliliter per kilogram of 10 milligrams per milliliter morphine hydrochloride IP in the morning. And with one milliliter per kilogram saline 10 hours later, every day for six days. Placing each rat into its appropriate drug paired, non-preferred or saline paired, preferred chamber for 45 minutes immediately after each injection.
For testing of the morphine conditioned animals, on days two, 10, and 18 after the last conditioning session, remove the guillotine doors to allow free access to the entire apparatus. And record the activity of each animal for 15 minutes after placement into the middle chamber for free exploration of the entire apparatus in a morphine free state. The memory retention of conditioned place preference in the morphine and saline groups is assessed by measuring the conditioned place preference score at multiple time points after the last conditioning session.
The number of entries to the side chambers is analogous to the number of active responses in the self-administration paradigm, reflecting the reinforcing property of the morphine and with an increased number of entries indicating the incubation of craving. As illustrated, a morphine conditioned place preference can be successfully established using this protocol. Inducing a long-term morphine reward memory for up to 18 days after the last conditioning session.
When attempting this procedure, it's important to remember to choose to balance the tactile cues. Following this procedure, other measures like reinstatement after each conditioning can be performed. To answer additional questions about whether reinstatement under the incubation of craving have similar underlying mechanisms.
After reinstatement, this technique paved the way for researchers in the field of drug addition to explore the incubation of craving in rats'conditioned place preference paradigms.
