A single, moderate ethanol exposure alters extracellular dopamine levels and dopamine d receptor function in the nucleus accumbens of wistar rats.
BACKGROUND
The nucleus accumbens (NAc) has been implicated in the neurochemical effects of ethanol (EtOH). Evidence suggests that repeated EtOH exposures and chronic EtOH drinking increase dopamine (DA) neurotransmission in the NAc due, in part, to a reduction in D(2) autoreceptor function. The objectives of the current study were to evaluate the effects of a single EtOH pretreatment and repeated EtOH pretreatments on DA neurotransmission and D(2) autoreceptor function in the NAc of Wistar rats.


METHODS
Experiment 1 examined D(2) receptor function after a single intraperitoneal (i.p.) injection or repeated i.p. injections of 0.0, 0.5, 1.0, or 2.0 g/kg EtOH to female Wistar rats. Single EtOH pretreatment groups received 1 daily i.p. injection of 0.9% NaCl (saline) for 4 days, followed by 1 day of saline or EtOH administration; repeated EtOH pretreatment groups received 5 days of saline or EtOH injections. Reverse microdialysis experiments were conducted to determine the effects of local perfusion with the D(2)-like receptor antagonist (-)sulpiride (SUL; 100 uM), on extracellular DA levels in the NAc. Experiment 2 evaluated if pretreatment with a single, moderate (1.0 g/kg) dose of EtOH would alter levels and clearance of extracellular DA in the NAc, as measured by no-net-flux (NNF) microdialysis. Subjects were divided into the EtOH-naïve and the single EtOH pretreated groups from Experiment 1.


RESULTS
Experiment 1: Changes in extracellular DA levels induced with SUL perfusion were altered by the EtOH dose (p < 0.001), but not the number of EtOH pretreatments (p > 0.05). Post-hoc analyses indicated that groups pretreated with single or repeated 1.0 g/kg EtOH showed significantly attenuated DA response to SUL, compared with all other groups (p < 0.001). Experiment 2: Multiple linear regression analyses yielded significantly (p < 0.05) higher extracellular DA concentrations in the NAc of rats receiving EtOH pretreatment, compared with their EtOH-naïve counterparts (3.96 +/- 0.42 nM and 3.25 +/- 0.23 nM, respectively). Extraction fractions were not significantly different between the 2 groups.


CONCLUSIONS
The present results indicate that a single EtOH pretreatment at a moderate dose can increase DA neurotransmission in the NAc due, in part, to reduced D(2) autoreceptor function.
Franklin
Kelle M
KM
Department of Psychology, Purdue School of Science, IUPUI, Indianapolis, Indiana 46202, USA.
Engleman
Eric A
EA
Ingraham
Cynthia M
CM
McClaren
Joseph A
JA
Keith
Carrie M
CM
McBride
William J
WJ
Murphy
James M
JM
D000704:Analysis of Variance; D000818:Animals; D002492:Central Nervous System Depressants / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D000431:Ethanol / Q000494:pharmacology*; D005260:Female; D016014:Linear Models; D017551:Microdialysis; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D017448:Receptors, Dopamine D2 / Q000187:drug effects*; D013238:Stereotaxic Techniques; D009435:Synaptic Transmission / Q000187:drug effects
D002492:Central Nervous System Depressants; D017448:Receptors, Dopamine D2; D000431:Ethanol; D004298:Dopamine