Blockade of the dorsal hippocampal dopamine D1 receptors inhibits the scopolamine-induced state-dependent learning in rats.
In the present study, we investigated the possible role of the dorsal hippocampal (CA1) dopamine D1 receptors on scopolamine-induced amnesia as well as scopolamine state-dependent memory in adult male Wistar rats. Animals were bilaterally implanted with chronic cannulae in the CA1 regions of the dorsal hippocampus, trained in a step-through type inhibitory avoidance task, and tested 24h after training for their step-through latency. Results indicated that pre-training or pre-test intra-CA1 administration of scopolamine (1.5 and 3 μg/rat) dose-dependently reduced the step-through latency, showing an amnestic response. The pre-training scopolamine-induced amnesia (3 μg/rat) was reversed by the pre-test administration of scopolamine, indicating a state-dependent effect. Similarly, the pre-test administration of dopamine D1 receptor agonist, 1-phenyl-7,8-dihydroxy-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SKF38393; 1, 2 and 4 μg/rat, intra-CA1), could significantly reverse the scopolamine-induced amnesia. Interestingly, administration of an ineffective dose of scopolamine (0.25 μg/rat, intra-CA1) before different doses of SKF38393, blocked the reversal effect of SKF38393 on the pre-training scopolamine-induced amnesia. Moreover, while the pre-test intra-CA1 injection of the dopamine D1 receptor antagonist, R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH23390; 0.1 and 0.5 μg/rat, intra-CA1), resulted in apparent memory impairment, microinjection of the same doses of this agent inhibited the scopolamine-induced state-dependent memory. These results indicate that the CA1 dopamine D1 receptors may potentially play an important role in scopolamine-induced amnesia as well as the scopolamine state-dependent memory. Furthermore, our results propose that dopamine D1 receptor agonist, SKF38393 reverses the scopolamine-induced amnesia via acetylcholine release and possibly through the activation of muscarinic receptors.
Department of Biology, Faculty of Basic Sciences, Islamic Azad University, Ardabil Branch, Ardabil, Iran.
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Piri
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Rostampour
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Nasehi
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Zarrindast
D000647:Amnesia / Q000139:chemically induced; D000818:Animals; D056547:CA1 Region, Hippocampal / Q000187:drug effects / Q000378:metabolism*; D018680:Cholinergic Antagonists / Q000008:administration & dosage; D018491:Dopamine Agonists / Q000008:administration & dosage; D018492:Dopamine Antagonists / Q000008:administration & dosage; D007276:Injections, Intraventricular; D007858:Learning / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008568:Memory / Q000502:physiology*; D008845:Microinjections; D051381:Rats; D017208:Rats, Wistar; D017447:Receptors, Dopamine D1 / Q000378:metabolism*; D012601:Scopolamine / Q000008:administration & dosage
D018680:Cholinergic Antagonists; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D017447:Receptors, Dopamine D1; D012601:Scopolamine
1-phenyl-7,8-dihydroxy-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride; ACh; ANOVA; CA1; DA; R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride; SCH23390; SKF38393; acetylcholine; analysis of variance; cAMP/PKA; cyclic AMP/protein kinase A; dopamine; dopamine D1 receptors; dorsal hippocampal; dorsal hippocampus; inhibitory avoidance memory; intra-CA1; intra-dorsal hippocampal; rat; scopolamine; state-dependent memory