Involvement of Purinergic P2X4 Receptors in Alcohol Intake of High-Alcohol-Drinking (HAD) Rats.
BACKGROUND
The P2X4 receptor (P2X4R) is thought to be involved in regulating alcohol-consuming behaviors, and ethanol (EtOH) has been reported to inhibit P2X4Rs. Ivermectin is an antiparasitic agent that acts as a positive allosteric modulator of the P2X4R. This study examined the effects of systemically and centrally administered ivermectin on alcohol drinking of replicate lines of high-alcohol-drinking (HAD-1/HAD-2) rats, and the effects of lentiviral-delivered short-hairpin RNAs (shRNAs) targeting P2rx4 on EtOH intake of female HAD-2 rats.


METHODS
For the first experiment, adult male HAD-1 and HAD-2 rats were given 24-hour free-choice access to 15% EtOH versus water. Dose-response effects of ivermectin (1.5 to 7.5 mg/kg, intraperitoneally [i.p.]) on EtOH intake were determined; the effects of ivermectin were then examined for 2% w/v sucrose intake over 5 consecutive days. In the second experiment, female HAD-2 rats were trained to consume 15% EtOH under 2-hour limited access conditions, and dose-response effects of intracerebroventricular (ICV) administration of ivermectin (0.5 to 2.0 μg) were determined over 5 consecutive days. The third experiment determined the effects of microinfusion of a lentivirus expressing P2rx4 shRNAs into the posterior ventral tegmental area (VTA) on 24-hour EtOH free-choice drinking of female HAD-2 rats.


RESULTS
The highest i.p. dose of ivermectin reduced alcohol drinking (30 to 45%) in both rat lines, but did not alter sucrose intake. HAD-2 rats appeared to be more sensitive than HAD-1 rats to the effects of ivermectin. ICV administration of ivermectin reduced 2-hour limited access intake (~35%) of female HAD-2 rats; knockdown of P2rx4 expression in the posterior VTA reduced 24-hour free-choice EtOH intake (~20%).


CONCLUSIONS
Overall, the results of this study support a role for P2X4Rs within the mesolimbic system in mediating alcohol-drinking behavior.
Department of Psychiatry, Institute of Psychiatric Research, Indiana University School of Medicine, Indianapolis, Indiana.
Kelle M
KM
Franklin
Department of Psychiatry, Institute of Psychiatric Research, Indiana University School of Medicine, Indianapolis, Indiana.
Sheketha R
SR
Hauser
Department of Psychiatry, University of Illinois at Chicago, Chicago, Illinois.
Amy W
AW
Lasek
Department of Psychiatry, Institute of Psychiatric Research, Indiana University School of Medicine, Indianapolis, Indiana.
Richard L
RL
Bell
Department of Psychiatry, Institute of Psychiatric Research, Indiana University School of Medicine, Indianapolis, Indiana.|Department of Biochemistry, Indiana University School of Medicine, Indianapolis, Indiana.
William J
WJ
McBride
D000428:Alcohol Drinking / Q000503:physiopathology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D057967:Infusions, Intraventricular; D007559:Ivermectin / Q000008:administration & dosage / Q000494:pharmacology; D008297:Male; D058911:Purinergic P2X Receptor Agonists / Q000494:pharmacology; D058920:Purinergic P2X Receptor Antagonists / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D058848:Receptors, Purinergic P2X4 / Q000187:drug effects / Q000502:physiology*; D017557:Ventral Tegmental Area / Q000187:drug effects
D058911:Purinergic P2X Receptor Agonists; D058920:Purinergic P2X Receptor Antagonists; D034741:RNA, Small Interfering; D058848:Receptors, Purinergic P2X4; D007559:Ivermectin
Alcohol Drinking; High-Alcohol-Drinking Rats; Ivermectin; P2X4 Receptor; P2rx4