Active versus passive cocaine administration: differences in the neuroadaptive changes in the brain dopaminergic system.
There is considerable evidence that chronic exposure to cocaine is associated with low striatal dopamine D2 receptor availability. In the present study we wished to determine whether neuroadaptive changes in densities of D2 receptors were due to direct pharmacological actions of cocaine or they reflected motivational states that were present when cocaine injection depended on active drug-seeking behavior and whether these changes were related to the actual expression of D2 mRNA. To achieve this goal we utilized a "yoked" procedure in which rats were tested simultaneously in groups of three, with only one rat actively self-administering cocaine while the other two received yoked injections of either cocaine or saline. Only passively administered cocaine produced a decrease in dopamine D2 receptor levels in the anterior and central regions of caudate/putamen, and both the shell and core of the nucleus accumbens, as measured by in vitro quantitative autoradiography. In contrast, examination of D2 receptor gene expression using in situ hybridization analysis revealed that there was an increase in D2 receptor mRNA levels in the ventral tegmental area of rats actively self-administered cocaine. We conclude that the reductions in striatal D2 receptor densities may be related to the chronic administration of cocaine per se and not to the motivated process of reinforced responding. Our results also suggest that increases in D2 receptor mRNA levels in limbic regions do not necessarily result in increased receptor densities and these changes likely reflect motivational states that were present when cocaine injection dependent on active drug self-administration.
Stefański
Roman
R
Department of Pharmacology and Physiology of the Nervous System, Institute of Psychiatry and Neurology, Sobieskiego 9, 02-957 Warsaw, Poland.
Ziółkowska
Barbara
B
Kuśmider
Maciej
M
Mierzejewski
Paweł
P
Wyszogrodzka
Edyta
E
Kołomańska
Paulina
P
Dziedzicka-Wasylewska
Marta
M
Przewłocki
Ryszard
R
Kostowski
Wojciech
W
D000222:Adaptation, Physiological / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism* / Q000503:physiopathology; D003042:Cocaine / Q000494:pharmacology*; D019970:Cocaine-Related Disorders / Q000378:metabolism* / Q000503:physiopathology; D004298:Dopamine / Q000378:metabolism*; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D008297:Male; D017072:Neostriatum / Q000187:drug effects / Q000378:metabolism; D009434:Neural Pathways / Q000187:drug effects / Q000378:metabolism; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000235:genetics*; D012054:Reinforcement, Psychology; D012646:Self Administration; D017557:Ventral Tegmental Area / Q000187:drug effects / Q000378:metabolism
D018765:Dopamine Uptake Inhibitors; D012333:RNA, Messenger; D017448:Receptors, Dopamine D2; D003042:Cocaine; D004298:Dopamine