Selective blockade of N-methyl-D-aspartate channels in combination with dopamine receptor antagonism induces loss of the righting reflex in mice, but not immobility

Psychopharmacology (Berl). 2015 Jan;232(1):39-46. doi: 10.1007/s00213-014-3634-y. Epub 2014 May 31.


Rationale: The selective N-methyl-D-aspartate (NMDA) channel blocker MK-801 is known to induce no loss of the righting reflex (LORR) and to stimulate catecholaminergic (CAergic) neurons in rodents, playing a crucial role in arousal.

Objectives: We examined whether MK-801 in combination with CA receptor ligands, which inhibit CAergic neuronal activities, could induce anesthesia including LORR.

Methods: All drugs were administered systemically to mice. To assess anesthesia, three different behaviors were used: loss of nociceptive response (analgesia in the free-moving state without LORR), LORR, and loss of movement in response to noxious stimulation (immobility under LORR).

Results: A very large dose of MK-801 (50 mg/kg) induced neither analgesia nor LORR. In contrast, MK-801 in combination with a small dose of the dopamine (DA) receptor antagonist haloperidol (0.2 mg/kg) dose-dependently produced LORR with a 50 % effective dose (ED50) of 1.6 (0.9-3.0; 95 % confidence limit) mg/kg, but not immobility. The α2-adrenoceptor agonist dexmedetomidine induced not only analgesia, but also immobility in animals treated with MK-801 (5 mg/kg) plus haloperidol (0.2 mg/kg), which then lost their righting reflex. The ED50 value of 0.26 (0.10-0.66) mg/kg (various doses of dexmedetomidine plus a fixed dose of MK-801 and haloperidol) for immobility was approximately three-fold larger than that of 0.09 (0.03-0.23) mg/kg (dexmedetomidine plus vehicle saline) for analgesia. This may occur, as LORR induced by MK-801 plus haloperidol inhibits the pain suppression system. The other ligands had little or no effect.

Conclusions: The DAergic stimulant actions of MK-801 may mask its LORR effects by NMDA channel blockade.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Dizocilpine Maleate / administration & dosage
  • Dopamine Antagonists / administration & dosage*
  • Drug Combinations
  • Excitatory Amino Acid Antagonists / administration & dosage*
  • Haloperidol / administration & dosage
  • Immobilization* / physiology
  • Male
  • Mice
  • Receptors, N-Methyl-D-Aspartate / antagonists & inhibitors*
  • Receptors, N-Methyl-D-Aspartate / physiology
  • Reflex, Righting / drug effects*
  • Reflex, Righting / physiology


  • Dopamine Antagonists
  • Drug Combinations
  • Excitatory Amino Acid Antagonists
  • Receptors, N-Methyl-D-Aspartate
  • Dizocilpine Maleate
  • Haloperidol