Dopamine D2 receptor plays a role in memory function: implications of dopamine-acetylcholine interaction in the ventral hippocampus.
BACKGROUND
The role of the hippocampal dopaminergic system in mnemonic function has not been clarified yet.


OBJECTIVE
We previously reported that the dopamine D2 receptor (D2R) is involved in the regulation of acethylcholin (ACh) release in the hippocampus. In this study, we further investigated ACh-dopamine (DA) interaction in the hippocampus and its involvement in mnemonic function.


METHODS
For experiment 1, rats fed with Cholin (Ch)-deficient chow were used. We examined the effects of D2R antagonist, raclopride, on cognitive performance using a passive avoidance task. We further carried out in vivo microdialysis to assess the effect of infusion of D2R agonist, quinpirole, into the ventral hippocampus on its capacity to release ACh. For experiment 2, rats fed with normal chow were used. The performance of a radial arm maze task was assessed to examine the effects of hippocampal injection of D2R agonist, quinpirole, on memory impairment induced by scopolamine, a muscarinic ACh antagonist.


RESULTS
In experiment 1, rats fed with Ch-deficient chow showed impaired performances indicated by prolonged latency on retention trials of a passive avoidance task following the hippocampal injection of D2R antagonist, and showed reduced capacity to release ACh following the injection of D2R agonist compared with rats fed with normal chow. In experiment 2, memory impairment induced by the intraperitoneal injection of scopolamine was ameliorated by the injection of D2R agonist into the ventral hippocampus.


CONCLUSIONS
These results indicate the possible involvement of hippocampal ACh-DA interaction in mnemonic processing.
Fujishiro
Hiroshige
H
Department of Geriatrics, Medicine in Growth and Aging, Program in Health and Community Medicine, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Nagoya, Aichi, 466-8550, Japan.
Umegaki
Hiroyuki
H
Suzuki
Yusuke
Y
Oohara-Kurotani
Shinobu
S
Yamaguchi
Yoko
Y
Iguchi
Akihisa
A
D000109:Acetylcholine / Q000502:physiology*; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects; D004298:Dopamine / Q000502:physiology*; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D008297:Male; D018782:Maze Learning / Q000187:drug effects; D008568:Memory / Q000502:physiology*; D017551:Microdialysis; D019257:Quinpirole / Q000494:pharmacology; D020891:Raclopride / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017448:Receptors, Dopamine D2 / Q000502:physiology*
D017448:Receptors, Dopamine D2; D019257:Quinpirole; D020891:Raclopride; D000109:Acetylcholine; D004298:Dopamine