Brain stimulation and morphine reward deficits in dopamine D2 receptor-deficient mice

• Published in: Psychopharmacologia Vol. 182; no. 1; pp. 33 - 44
• Main Authors: ELMER, G. I, PIEPER, J. O, LEVY, J, RUBINSTEIN, M, LOW, M. J, GRANDY, D. K, WISE, R. A
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01-10-2005; Springer Nature B.V
• Subjects: Amphetamine - pharmacology; Amphetamines; Animals; Biological and medical sciences; Brain - drug effects; Brain Mapping; Cocaine; Conditioning, Operant - drug effects; Dopamine; Dose-Response Relationship, Drug; Drug addictions; Drug Synergism; Heterozygote; Hypothalamic Area, Lateral - drug effects; Male; Medical sciences; Mice; Mice, Inbred C57BL; Mice, Knockout; Morphine; Morphine - pharmacology; Motivation; Narcotics; Neuropharmacology; Neurosciences; Pharmacology. Drug treatments; Psychoanaleptics: cns stimulant, antidepressant agent, nootropic agent, mood stabilizer..., (alzheimer disease); Psycholeptics: tranquillizer, neuroleptic; Psychology. Psychoanalysis. Psychiatry; Psychopharmacology; Receptors, Dopamine D1 - deficiency; Receptors, Dopamine D1 - genetics; Receptors, Dopamine D2 - deficiency; Receptors, Dopamine D2 - genetics; Reward; Self Stimulation - drug effects; Stimulants; Toxicology; Oregon; United States > US; Baltimore Maryland; Amphetamine derivatives; Neuroleptic; Psychotropic; Central nervous system; Morphine; Opiates; Stimulation; Narcotic analgesic; Opioid peptide; Encephalon; Depolarization; Gene; Reinforcement; ICSS; Amfetamine; Drug of abuse; CNS stimulant; Rodentia; Opioid; Knockout; Vertebrata; Chemotherapy; Mammalia; D2 Dopamine receptor; Treatment; Amphetamine; Addiction; Mouse; Animal; Mice; Mutation; Reward
• ISSN: 0033-3158; 1432-2072
• DOI: 10.1007/s00213-005-0051-2

The rewarding effects of lateral hypothalamic brain stimulation, various natural rewards, and several drugs of abuse are attenuated by D1 or D2 dopamine receptor (D1R or D2R) antagonists. Much of the evidence for dopaminergic involvement in rewards is based on pharmacological agents with limited or "relative" selectivity for dopamine receptor subtypes. Genetically engineered animal models provide a complementary approach to pharmacological investigations.
In the present study, we explored the contribution of dopamine D2Rs to (1) brain stimulation reward (BSR) and (2) the potentiation of this behavior by morphine and amphetamine using D2R-deficient mice.
Wild-type (D2Rwt), heterozygous (D2Rhet), and D2R knockout (D2Rko) mice were trained to turn a wheel for rewarding brain stimulation. Once equivalent rate-frequency curves were established, morphine-induced (0, 1.0, 3.0, and 5.6 mg/kg s.c.) and amphetamine-induced (0, 1.0, 2.0, and 4.0 mg/kg i.p.) potentiations of BSR were determined.
The D2Rko mice required approximately 50% more stimulation than the D2Rwt mice did. With the equi-rewarding levels of stimulation current, amphetamine potentiated BSR equally across the three genotypes. In contrast, morphine potentiated rewarding stimulation in the D2Rwt, had no effect in the D2Rhet, and antagonized rewarding stimulation in the D2Rko mice.
D2R elimination decreases, but does not eliminate, the rewarding effects of lateral hypothalamic stimulation. After compensation for this deficit, amphetamine continues to potentiate BSR, while morphine does not.