Effects of the α2/α3-subtype-selective GABAA receptor positive allosteric modulator KRM-II-81 on pain-depressed behavior in rats: comparison with ketorolac and diazepam

Behav Pharmacol. 2019 Aug;30(5):452-461. doi: 10.1097/FBP.0000000000000464.

Abstract

This study examined effects of the α2/α3-subtype-selective GABAA receptor positive allosteric modulator KRM-II-81 in an assay of pain-related behavioral depression. Adult, male Sprague-Dawley rats responded for electrical brain stimulation in a frequency-rate intracranial self-stimulation (ICSS) procedure. Intraperitoneal injection of 1.8% lactic acid served as an acute noxious stimulus to depress ICSS. Effects of KRM-II-81 were evaluated in the absence and presence of the acid noxious stimulus. The NSAID ketorolac and the benzodiazepine diazepam were tested as comparators. Neither ketorolac nor KRM-II-81 altered ICSS in the absence of the acid noxious stimulus; however, diazepam produced facilitation consistent with its abuse liability. Ketorolac blocked acid-induced depression of ICSS, and effects of 1.0 mg/kg ketorolac lasted for at least 5 h. KRM-II-81 (1.0 mg/kg) produced significant antinociception after 30 min that dissipated by 60 min. Diazepam also attenuated acid-depressed ICSS, but only at doses that facilitated ICSS when administered alone. The lack of ketorolac or KRM-II-81 effects on ICSS in the absence of the acid noxious stimulus suggests low abuse liability for both compounds. The effectiveness of ketorolac to block acid-induced ICSS depression agrees with clinical analgesic efficacy of ketorolac. KRM-II-81 produced significant but less consistent and shorter-acting antinociception than ketorolac.

Publication types

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

MeSH terms

  • Analgesics / pharmacology
  • Animals
  • Behavior, Animal / drug effects
  • Conditioning, Operant / drug effects
  • Diazepam / pharmacology
  • Electric Stimulation / methods
  • Ketorolac / pharmacology
  • Male
  • Oxazoles / metabolism*
  • Oxazoles / pharmacology
  • Pain / metabolism*
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, GABA-A / drug effects*
  • Receptors, GABA-A / metabolism
  • Self Stimulation / drug effects

Substances

  • Analgesics
  • KRM-II-81
  • Oxazoles
  • Receptors, GABA-A
  • Diazepam
  • Ketorolac