Muscimol state-dependent memory: involvement of dorsal hippocampal mu-opioid receptors.
In the present study, the effects of subcutaneous (s.c.) injections of morphine, a mu-opioid receptor agonist and intra-dorsal hippocampal (intra-CA1) injections of naloxone, a mu-opioid receptor antagonist on muscimol state-dependent memory were examined in mice. A single-trial step-down passive avoidance task was used for the assessment of memory retention in adult male NMRI mice. Pre-training intra-CA1 administration of a GABAA receptor agonist, muscimol (0.025, 0.05, 0.1 and 0.2 microg/mouse) dose dependently induced impairment of memory retention. Pre-test injection of muscimol (0.05, 0.1 and 0.2 microg/mouse, intra-CA1) induced state-dependent retrieval of the memory acquired under pre-training muscimol (0.1 microg/mouse, intra-CA1) influence. Pre-test injection of morphine (0.5 and 1 mg/kg, s.c.) 30 min before the administration of muscimol (0.1 microg/mouse, intra-CA1) dose dependently inhibited muscimol state-dependent memory. Pre-test intra-CA1 injection of naloxone (0.1 and 0.2 microg/mouse, intra-CA1) improved pre-training muscimol (0.1 microg/mouse)-induced retrieval impairment. Moreover, pre-test administration of naloxone (0.1 and 0.2 microg/mouse, intra-CA1) with an ineffective dose of muscimol (0.025 microg/mouse) significantly restored the retrieval and induced muscimol state-dependent memory. These findings implicate the involvement of a dorsal hippocampal mu-opioid receptor mechanism in muscimol state-dependent memory.
Jafari-Sabet
Majid
M
Department of Pharmacology, School of Medicine, Qazvin University of Medical Sciences, Qazvin, Iran. jafarisa@sina.tums.ac.ir
Jannat-Dastjerdi
Iman
I
D000704:Analysis of Variance; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology; D002404:Catheterization; D004597:Electroshock; D004777:Environment; D018755:GABA Agonists / Q000008:administration & dosage*; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008568:Memory / Q000187:drug effects* / Q000502:physiology*; D011939:Mental Recall / Q000187:drug effects / Q000502:physiology; D051379:Mice; D009020:Morphine / Q000008:administration & dosage; D009118:Muscimol / Q000008:administration & dosage*; D009270:Naloxone / Q000008:administration & dosage; D009292:Narcotic Antagonists / Q000008:administration & dosage; D009294:Narcotics / Q000008:administration & dosage; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*
D018755:GABA Agonists; D009292:Narcotic Antagonists; D009294:Narcotics; C404943:Oprm protein, mouse; D017450:Receptors, Opioid, mu; D009118:Muscimol; D009270:Naloxone; D009020:Morphine