Table 2.
Summary of Experimental Design for Experiment 2.
| Experimental Condition
|
|||
|---|---|---|---|
| Conditioning Weeks (each of 4) | Test Week (week 5) | ||
| Paired | Unpaired | Paired and Unpaired | |
| Monday | |||
| Injection at T = 0 (HC) | ------ | ------ | ------ |
| Pre-CS Session (10 min) a | ------ | NO CS | ------ |
| Injection at T = 4 hr | ------ | ------ | ------ |
| CS Session (20 min) | ------b | NO CS b | ------ |
|
| |||
| Tuesday | |||
| Injection at T = 0 (HC) | ------ | ------ | ------ |
| Pre-CS Session (10 min) a | NO CS | NO CS | NO CS |
| Injection at T = 4 hr | ------ | ------ | ------ |
| CS Session (20 min) | NO CS | NO CS | NO CS |
|
| |||
| Wednesday | |||
| Injection at T = 0 (HC) | VEH | VEH | VEH |
| Pre-CS Session (10 min) a | NO CS | NO CS | NO CS |
| Injection at T = 4 hra | VEH | VEH | VEH |
| CS Session (20 min) | NO CS | CS b | NO CS |
|
| |||
| Thursday (BASELINE DAY) | |||
| Injection at T = 0 (HC) | VEH | VEH | VEH |
| Pre-CS Session (10 min) a | NO CS | NO CS | NO CS |
| Injection at T = 4 hra | VEH | VEH | VEH |
| CS Session (20 min) | NO CS | NO CS | NO CS |
|
| |||
| Friday | |||
| Injection at T = 0 (HC) | MOR | MOR | MOR or VEH c |
| Pre-CS Session (10 min) a | NO CS | ------ | NO CS |
| Injection at T = 4 hra | NAL | NAL | VEH |
| CS Session (20 min) | CS | ------b | CS |
Abbreviations: MOR = morphine, NAL = naloxone, VEH = vehicle, HC = home cage injection, CS = conditioned stimulus present in 20-min session, NO CS = no CS in 20-min session.
Each injection at t = 4 hr was preceded by a 10 min operant session (Pre-CS) that started at t= 3:45; the CS was NEVER presented during the Pre-CS Session
During Conditioning Weeks, the Unpaired group received an operant session on Monday to ensure 4 sessions/week, just like Paired group. The Unpaired group required this Monday session since it was not given an operant session on Friday, the day of morphine/naloxone treatment, to preclude any possible association of treatment with operant context or CS. Instead the CS was presented to the Unpaired group on Wednesday, following VEH injections.
On the Test Day, rats from both the Paired and Unpaired groups were further sub-divided into cohorts that received morphine (MOR) or vehicle (VEH) 4 hr prior to the CS session.