Effects of pain- and analgesia-related manipulations on intracranial self-stimulation in rats: further studies on pain-depressed behavior

Pain. 2009 Jul;144(1-2):170-7. doi: 10.1016/j.pain.2009.04.010. Epub 2009 May 10.


Pain stimulates some behaviors (e.g., withdrawal responses) but depresses many other behaviors (e.g., feeding). Pain-stimulated behaviors are widely used in preclinical research on pain and analgesia, but human and veterinary medicine often rely on measures of functional impairment and pain-depressed behavior to diagnose pain or assess analgesic efficacy. In view of the clinical utility of measures of pain-depressed behaviors, our laboratory has focused on the development of methods for preclinical assays of pain-depressed behavior in rodents. The present study compared the effects of a chemical noxious stimulus (IP lactic acid injections) and an opioid analgesic (morphine) administered alone or in combination on the stretching response (a pain-stimulated behavior) and intracranial self-stimulation (ICSS; a behavior that may be depressed by pain) in rats. In the ICSS procedure, rats implanted with electrodes in the lateral hypothalamus responded to electrical stimulation across a range of current frequencies to permit rapid determination of frequency-rate curves and evaluation of curve shifts following treatment. Lactic acid alone produced a concentration-dependent stimulation of stretching and depression of ICSS, expressed as rightward shifts in ICSS frequency-rate curves. Morphine had little effect alone, but it produced a dose-dependent blockade of both acid-stimulated stretching and acid-depressed ICSS. Both lactic acid and morphine were equipotent in the stretching and ICSS procedures. These results suggest that ICSS may be useful as a behavioral baseline for studies of pain-depressed behavior.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Analgesics, Opioid / administration & dosage
  • Analgesics, Opioid / pharmacology*
  • Analysis of Variance
  • Animals
  • Behavior, Animal / drug effects*
  • Biophysics
  • Conditioning, Operant / drug effects
  • Conditioning, Operant / physiology
  • Depression / etiology
  • Depression / therapy*
  • Disease Models, Animal
  • Dose-Response Relationship, Drug
  • Electric Stimulation / methods
  • Lactic Acid / adverse effects
  • Morphine / administration & dosage*
  • Pain / complications
  • Pain Management*
  • Pain Measurement
  • Rats
  • Rats, Sprague-Dawley
  • Self Stimulation / drug effects*
  • Self Stimulation / physiology*


  • Analgesics, Opioid
  • Lactic Acid
  • Morphine