Description

The magnetic self administration runway apparatus consists of parallel magnetic rails, set a few centimeters apart from each other, positioned directly above the center of a runway. A swivel carriage device rests freely between the rails with one of its end connected to the PE tubing to the subject and the other end connected to the syringe pump. The swivel assembly moves between the rails as the subject traverses the alley eliminating the need to disturb the sessions for drug administration. The apparatus can be fully automated upon request to provide location data about the subject.

Documentation

Introduction

Operant runways have been used for over a century to investigate the impact of incentive stimuli in animal models. A self-administration runway is an appropriate tool in the investigation of drug-seeking behavior in animal models of drug abuse. However, intravenous administration of drugs during the trial tends to be difficult, often disturbing the subject’s natural behavior during the task. Earlier approaches to drug administration on the runway task suggested using chronically implanted remote catheter pumps or employment of pulley systems that use a counterweight to suspend the tubing away from the subject during the session. Unfortunately, these approaches were not feasible for the large sample of subjects and resulted in drug-flow problems due to enormous strain at the joint between the cannula and the subject.

To overcome this methodological constraint Geist and Ettenberg (1990) developed the magnetic runway with a swivel-carriage device for delivery of drugs without interfering with the behavior of the subject. The magnetic runway is a device that permits free movement of the subject on the runway while the cannula tubing hovers right above the subject.

The apparatus consists of parallel magnetic rails, set a few centimeters apart from each other, positioned directly above the center of the runway. A swivel carriage device rests freely between the rails with one of its end connected to the PE tubing to the subject and the other end connected to the syringe pump. The swivel assembly moves between the rails as the subject traverses the alley eliminating the need to disturb the sessions for drug administration. The apparatus is fully automated and provides real-time data about the location and speed of the subject on the alley.

Apparatus and Equipment

The magnetic runway apparatus consists of two components: the runway and the magnetic rails. The runway is designed as a 155 x 15 cm straight-arm alley having a height of 40 cm. The floor of the runway is fitted with 3 mm diameter steel rods laid in parallel 1.2 cm apart and aligned perpendicular to the sidewalls. On either side of the runway are two 24 x 25 x 40 cm start and goal boxes. The floor is also equipped with 13 infrared photocell emitter-detector pairs connected to the computer and placed at approximately 15 cm apart along the inside walls, 2.5 cm above the floor.

The magnetic track is suspended approximately 53 cm above the straight-arm runway. It consists of two long bar magnets placed parallel to each other with a distance of about 2.5 cm between them to hold the swivel-carriage device. The swivel is custom built, collared with a flat circular disk that has a pot magnet attached to the underside to minimize the weight and the pull of the swivel on the subject. The polarity of the pot magnet is aligned such that it repels the polarity of the rails resulting in a floating swivel that produces minimal resistance. The cylindrical commutator has the top attached to the PE tubing to the 10 ml drug-filled syringe and the bottom to the guide cannula attached to the subject’s back.

Training Protocol

The sensors in the runway floor are attached to a computer that records the precise location of the subject in real-time on the track and controls the opening and closing of the start and goal box, and the delivery of the drug. A video and tracking software such as the Noldus Ethovision XT can also be used.

Before the test sessions, the animals undergo stereotaxic surgery to implant a chronic jugular catheter. After 10 days of the surgery, the subjects are tested on the runway. The subject is connected to the drug delivery system by threading the internal cannula into the guide cannula on the subject’s back, after which it is placed in the start box and released into the alley after 5 seconds. When the subject enters the goal box, it is confined to the goal box for 5 minutes after delivery of the drug dose. The timing and the dosage are dependent on the experiment being conducted. The subject is then removed from the goal box, detached from the drug delivery system and placed back in its housing.

The subjects are treated once every day on the runway until they develop retreat behaviors, that is, the subject returns towards the start box rather than moving forward towards the goal box. The trials are repeated and carried out in cycles depending on the aim and requirement of the investigation.

One day before the test session, the subjects are given 10 minutes to acclimate to the apparatus by individually placing them in the start box and allowing them to freely explore the runway, with the goal box closed. The apparatus should be well-lit and cleaned before and after every trial to avoid interference of any stimuli. The apparatus is not limited for use in drug self-administration and can also be adapted for other research purposes.

Evaluation of the co-administration of alcohol or heroin to overcome the anxiogenic properties of cocaine

The possible anxiolytic effects of co-administration of either alcohol or heroin to overcome the anxiogenic properties of cocaine are evaluated in the runway apparatus. Thirsty subjects are trained on the runway apparatus for IV cocaine and permitted to drink various solutions of ethanol or water after removal from the goal box, 5-minute post cocaine injection. Similarly, co-administration of heroin is tested for subjects that are trained to run a straight alley for IV cocaine reinforcement once each day until retreat behaviors have developed. On the development of retreat behavior, the subjects are divided into groups receiving between 0.0 to 0.1 mg/kg/injection dose of heroin added to the standard 0.75 mg/kg/injection dose of cocaine (Ettenberg 2004).

Evaluation of the anxiolytic-like actions of buspirone

Subjects are treated with single 1.0 mg/kg IV cocaine daily on the runway until consistent approach-avoidance retreats are observed. Once the consistency of retreats is reached, the subjects are pre-treated with the vehicle and either one of 1.0, 2.5 or 5.0 mg/kg IP buspirone doses. (Ettenberg & Bernardi 2006).

Sample Data

Following parameters are recorded during each test session:

1. Run Times: The time taken to travel from the start box to the goal box serves as the measure of the subject’s motivation to seek the reinforcing stimuli it had received in previous trials on entering the goal box.
2. Number of Retreats: Retreat is defined as heading back to the start box. This parameter is observed over trials and is an index of the approach-avoidance conflict.
3. Latency: The time taken to leave the start box.

The infrared photocell emitter-detector provide real-time data of the speed of the subject and the location of the subject, which can be plotted into a spatiotemporal graph.

Strengths & Limitations

Strengths

The magnetic runway provides a simple and cost-effective alternative to the expensive chronically implanted remote catheter pumps and inefficient pulley systems that uses a counterweight to suspend the tubing away from the subject during the session.  Additionally, the setup allows free movement in any directions with minimal force being exerted upon the catheter connection. The apparatus can also easily be adapted for tasks other than drug self-administration.

Limitations

Overtraining and handling procedures may affect performance during the task. The subjects own behavioral flexibility can also influence the results.

Summary and Key Points

• The magnetic runway is a simple and cost-effective apparatus
• The apparatus overcomes the shortcomings of remote catheter pumps and pulley systems in delivering drugs
• The cylinder swivel has a pot magnet attached under the collar with polarity repealing the magnetic bars to minimize the weight and pull exerted upon the animals
• The infrared photocell emitter-detector pairs provide real-time data about the speed and location of the subject on the alleyway
• The computer controls the doors to the goal and start box and the delivery of the drugs via the injection
• The apparatus can easily be adapted for tasks other than self-administration of drugs

References

Geist TD, Ettenberg A. A simple method for studying intravenous drug reinforcement in a runaway. Pharmacol Biochem Behav. 1990 Jul;36(3):703-6.

Ettenberg A, Bernardi RE. Anxiolytic-like actions of buspirone in a runway model of intravenous cocaine self-administration. Pharmacol Biochem Behav. 2006 Oct;85(2):393-9. Epub 2006 Oct 24.

Ettenberg A. Opponent process properties of self-administered cocaine. Neurosci Biobehav Rev. 2004 Jan;27(8):721-8.