Table 1.
Schedule of chronic exposure to escalating doses of heroin, extended withdrawal and chronic re-exposure to escalating doses of heroin (Heroin/Heroin group)
| Dose (mg/kg) per injectiona | Chronic Exposure to Escalating-Dose Heroinb | Spontaneous Withdrawalc | Chronic Exposure to Escalating-Dose Heroin | |||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
| ||||||||||||||||||||||
| Time(h) | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | Day 11–20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 |
| 0900 | 2.5 | 2.5 | 5 | 5 | 10 | 10 | 15 | 15 | 25 | 25 | -- | 2.5 | 2.5 | 5 | 5 | 10 | 10 | 15 | 15 | 25 | 25 | ** |
| 1300 | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | 0 | 0* | 0 | 0* | 0 | 0* | 0 | 0* | 0 | 0* | |
| 1500 | 2.5 | 2.5 | 5 | 5 | 10 | 10 | 15 | 15 | 25 | 25 | -- | 2.5* | 2.5 | 5* | 5 | 10* | 10 | 15* | 15 | 25* | 25 | |
| 2100 | 2.5 | 2.5 | 5 | 5 | 10 | 10 | 15 | 15 | 25 | 25 | -- | 2.5 | 2.5 | 5 | 5 | 10 | 10 | 15 | 15 | 25 | 25 | |
| Total | 7.5 | 7.5 | 15 | 15 | 30 | 30 | 45 | 45 | 75 | 75 | -- | 7.5 | 7.5 | 15 | 15 | 30 | 30 | 45 | 45 | 75 | 75 | |
Administered via intraperitoneal injection by the experimenter. Injections of saline vehicle are denoted by 0.
A separate group of rats (Saline/Heroin) received saline injections, rather than heroin injections, on an identical schedule on Days 1–10, followed by an injection-free period from Days 11–20. Heroin and saline injections, as well as timing of conditioning sessions, occurring on Days 21–30 were identical to those received by the Heroin/Heroin group.
Autoradiographic analyses were performed on rats that received chronic heroin exposure (Days 1–10) and extended withdrawal (Days 11–20), when they were sacrificed.
Injection was administered immediately before the rat was placed in the associated conditioning chamber of the place preference apparatus.
Conditioned place preference testing