Assessment of Substance Abuse Liability in Rodents: Self‐Administration, Drug Discrimination, and Locomotor Sensitization

Neil E. Paterson1

1 PsychoGenics, Inc., Tarrytown, New York
Publication Name:  Current Protocols in Pharmacology
Unit Number:  Unit 5.62
DOI:  10.1002/0471141755.ph0562s58
Online Posting Date:  September, 2012
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Abstract

Assessing abuse liability is a crucial step in the development of a novel chemical entity (NCE) with central nervous system (CNS) activity or with chemical or pharmacological properties in common with known abused substances. Rodent assessment of abuse liability is highly attractive due to its relatively low cost and high predictive validity. Described in this unit are three rodent assays commonly used to provide data on the potential for abuse liability based on the acute effects of NCEs: specifically, self‐administration, drug discrimination, and locomotor sensitization. As these assays provide insight into the potential abuse liability of NCEs as well as in vivo pharmacological mechanism(s) of action, they should form a key part of the development process for novel therapeutics aimed at treating CNS disorders. Curr. Protoc. Pharmacol. 58:5.62.1‐5.62.22. © 2012 by John Wiley & Sons, Inc.

Keywords: abuse liability; self‐administration; drug discrimination; locomotor sensitization; rat; mouse

     
 
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Table of Contents

  • Introduction
  • Basic Protocol 1: Drug Self‐Administration in Rats
  • Alternate Protocol 1: Self‐Administration in Drug‐Naïve Rats
  • Basic Protocol 2: Drug Discrimination in Rats
  • Basic Protocol 3: Locomotor Sensitization
  • Reagents and Solutions
  • Commentary
  • Literature Cited
  • Figures
     
 
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Materials

Basic Protocol 1: Drug Self‐Administration in Rats

  Materials
  • Rats: male Wistar or Sprague‐Dawley rats, 300 to 324 g upon arrival
  • Standard rat chow
  • Standard rat bedding
  • 70% ethanol
  • Dustless purified precision pellets (45 mg) for food‐shaping (Bio‐Serv, cat. no. F0165; http://www.bio‐serv.com/)
  • Catheter flushing solution (see recipe)
  • Isoflurane
  • Oxygen
  • Saline: 0.9% (w/v) NaCl
  • Swabs (povidone‐iodine and alcohol)
  • Tissue glue
  • Topical antibiotic ointment
  • Carprofen solution (see recipe)
  • Drug solutions:
    • Nicotine injection solution (see recipe)
    • Cocaine injection solution (see recipe)
    • Morphine injection solution (see recipe)
  • Novel chemical entity (NCE) solution for testing
  • Standard rat cages
  • Animal balance
  • Sound‐attenuating chamber equipped with an exhaust fan (MED Associates, http://www.med‐associates.com/)
  • Operant conditioning box (Fig. ), equipped with a balance arm located on the exterior surface of the roof and a food hopper for delivery of food pellets; the interior of the operant box is equipped with 2 retractable levers, 2 cue‐lights, a food pellet magazine (located between the two levers), a grid floor, and a house light located at the top of the opposite wall (MED Associates, cat. no. Med008‐062; http://www.med‐associates.com/)
  • Catheters (Model IVSA28/1350; CamCaths, http://www.camcaths.com/index.html)
  • 50‐ml beaker
  • Vaporizer for isoflurane anesthesia (Single Animal Vaporizer Unit and Induction Chamber; Braintree Scientific, cat. no. EZ 17 85)
  • Scavenger (a pass‐through charcoal canister filter in the exhaust gas line to collect vaporized isoflurane), oxygen
  • Hair clippers/shaver
  • Surgical tools: small sharp‐tipped scissors 12 cm long with 4‐cm‐long blades; blunt‐tipped hemostatic forceps 15 cm long with 5‐cm‐long blades, two curved blunt‐tip forceps, one fine‐tipped forceps (tip: 0.05 × 0.01 mm), scalpel, and blades (#10)
  • Sterile gauze
  • Hemostats
  • Syringe and flusher (blunted 22‐G needle tip with attached 8‐ to 15‐cm length of Tygon tubing)
  • Syringe (3‐ to 5‐ml) and needle for irrigation (18‐G for high flow)
  • 1‐ml syringes and 25‐G needles for carprofen administration (for s.c. injection)
  • Wound stapler and wound clips
  • Cotton swabs (Q‐tips)
  • Sutures (silk and chromic gut)
  • Plastic tubing (Tygon tubing is an excellent option in terms of flexibility and durability: 0.05 mm internal diameter, 0.5 mm outer diameter)
  • Syringe pump (MED Associates, cat. no. PHM‐111‐EC; http://www.med‐associates.com/)
  • Blunted 22‐G needle tips for attachment of tubing to syringe.
  • Syringe: 10 ml (ensure that syringe pump is calibrated correctly for syringe size)
  • Single‐channel fluid swivel (Fig. ) mounted on balance arm located on the roof of the operant conditioning box
  • A steel spring sleeve to sheath the Tygon tubing inside the operant box, with a threaded connector to attach to the catheter exit port [PlasticsOne (http://www.plastics1.com/PCR/Preclinical‐Research‐Components.php) manufactures a suitable connector, which they will provide at the specified length (Model C313CS/SP]; the length depends on the internal dimensions of the operant box: ideally, there is sufficient tubing and spring to allow connection with the catheter exit port on the rat's back (mid‐scapulae) at all times during the test session; excessive extra length tends to distract animals or get tangled as the animal moves around the box
  • Data acquisition and analysis software (MED PC, MED Associates; http://www.med‐associates.com/)
  • Computer and interface to allow control of apparatus and software, and collection and storage of data (MED‐SYST‐8 for 8 operant chambers or MED‐SYST‐16 for 16 operant chambers, MED Associates; http://www.med‐associates.com/)
  • Additional reagents and equipment for parenteral injection of the rat (Donovan and Brown, )

Alternate Protocol 1: Self‐Administration in Drug‐Naïve Rats

  Materials
  • Rats: male Wistar or Sprague‐Dawley rats, 300 to 324 g upon arrival
  • Standard rat chow
  • Standard rat bedding
  • Dustless purified precision pellets (45 mg) for food‐shaping (Bio‐Serv, cat. no. F0165; http://www.bio‐serv.com/)
  • Training drugs:
    • Nicotine solution (for protocol 3; see recipe)
    • Cocaine solution (for protocol 3; see recipe)
  • 70% ethanol
  • Novel chemical entity (NCE) solution for testing
  • Standard rat cages
  • Animal balance
  • Sound‐attenuating chamber equipped with an exhaust fan
  • Operant conditioning box (Fig. ), equipped with a balance arm located on the exterior surface of the roof, and a food hopper for delivery of food pellets; the interior of the operant box is equipped with 2 retractable levers, 2 cue‐lights, a food pellet magazine (located between the two levers), a grid floor, and a house light located at the top of the opposite wall
  • Data acquisition and analysis software (MED PC, MED Associates; http://www.med‐associates.com/)
  • Computer and interface to allow control of apparatus and software, and collection and storage of data

Basic Protocol 2: Drug Discrimination in Rats

  Materials
  • 10‐ to 12‐week‐old C57Bl6/J mice (male mice are preferable because there is no requirement to consider estrus cycle as a potential factor in the effects of the test compounds)
  • Standard lab mouse chow
  • Cleaning agent: e.g., Nolvasan (Fort Dodge Animal Health)
  • Test solutions dissolved in saline or sterile water, and administered in a volume of 10 ml/kg.
  • Light meter
  • OF (open‐field) test chamber: approximately 25 cm (l) × 25 cm (w) × 20 cm (h) with infra‐red (I/R) array (Med‐OFA‐MS; MED Associates, http://www.med‐associates.com/)
  • Animal balance
  • Data acquisition and analysis software (MED PC, MED Associates; http://www.med‐associates.com/)
  • Computer
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Figures

Videos

Literature Cited

Literature Cited
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