2.2. Cocaine self-administration
Rats were anesthetized with a ketamine/xylazine mixture
(100 mg/kg and 8 mg/kg, respectively, i.p.) and implanted with
intrajugular catheters. All incisions were sutured, stapled, and
sealed with Vetbond (3M). After surgery, catheters were flushed
daily with a sterile solution of heparin (2.5 units/mL) to maintain
catheter patency. Five to seven days following catheterization, animals
were trained to nose poke for intravenous cocaine HCl
(0.5 mg/kg/infusion; National Institute on Drug Abuse) during daily
3-h sessions (65 infusion max) over 7 days. The 65-infusion limit
was chosen to prevent adverse effects of the drug. Prior to the start
of each session, rats were placed into self-administration chambers
(20 20 26 cm) that were equipped with two nose-poke portals
located 5 cm above the floor on opposite walls. A protective cap was
removed from the catheter and its external end was connected via
tubing (0.02 inch inner diameter; Saint-Gobain Performance Plastics)
to a single-channel liquid swivel mounted in the ceiling of the
self-administration chamber. Nose pokes into one of the ports
(designated active) resulted in a cocaine infusion over 5 s on a
fixed-ratio 1 (FR1) schedule of reinforcement. Each reinforced
response resulted in a 20-s timeout period, during which time the
active port was illuminated with a white LED positioned at the back
of the port. Nose pokes made in the other port (designated inactive)
were recorded but had no programmed consequence. At the end of
the 7 days of self-administration training, the criteria for achieving
stable responding were a) minimum of 30 reinforcers earned; b)
preference for the active port greater than 70%; and c) no more than
20% variation (both number of reinforcers and active port preference)
for at least two of the final three self-administration sessions.
2.2. Cocaine self-administrationRats were anesthetized with a ketamine/xylazine mixture(100 mg/kg and 8 mg/kg, respectively, i.p.) and implanted withintrajugular catheters. All incisions were sutured, stapled, andsealed with Vetbond (3M). After surgery, catheters were flusheddaily with a sterile solution of heparin (2.5 units/mL) to maintaincatheter patency. Five to seven days following catheterization, animalswere trained to nose poke for intravenous cocaine HCl(0.5 mg/kg/infusion; National Institute on Drug Abuse) during daily3-h sessions (65 infusion max) over 7 days. The 65-infusion limitwas chosen to prevent adverse effects of the drug. Prior to the startof each session, rats were placed into self-administration chambers(20 20 26 cm) that were equipped with two nose-poke portalslocated 5 cm above the floor on opposite walls. A protective cap wasremoved from the catheter and its external end was connected viatubing (0.02 inch inner diameter; Saint-Gobain Performance Plastics)to a single-channel liquid swivel mounted in the ceiling of theself-administration chamber. Nose pokes into one of the ports(designated active) resulted in a cocaine infusion over 5 s on afixed-ratio 1 (FR1) schedule of reinforcement. Each reinforcedresponse resulted in a 20-s timeout period, during which time theactive port was illuminated with a white LED positioned at the backof the port. Nose pokes made in the other port (designated inactive)were recorded but had no programmed consequence. At the end of
the 7 days of self-administration training, the criteria for achieving
stable responding were a) minimum of 30 reinforcers earned; b)
preference for the active port greater than 70%; and c) no more than
20% variation (both number of reinforcers and active port preference)
for at least two of the final three self-administration sessions.
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