α7‐Type Nicotinic Acetylcholine Receptor and Prodynorphin mRNA Expression after Administration of (−)‐Nicotine and U‐50,488H in β‐Amyloid Peptide (25‐35)‐Treated Mice

Abstract

We previously reported that (-)-nicotine and kappa-opioid receptor agonists lessened impairment of learning and/or memory in several animal models. Furthermore, these drugs prevented neurodegenerative damage induced by ischemia or beta-amyloid peptide (25-35). In the present study, we tested whether (-)-nicotine and U-50,488H prevent delayed-memory impairment induced by beta-amyloid peptide (25-35), and changes of expression of alpha7-type nicotinic acetylcholine receptor mRNA and prodynorphin mRNA. Seven days after treatment with beta-amyloid peptide (25-35) (9 nmol/mouse, i.c.v.), memory impairment was observed in the Y-maze test. Memory impairment was prevented when (-)-nicotine (6.16 micromol/kg, s.c.) or U-50,488H (21 micromol/kg, s.c.) was administered 1 h before, but not 1 h after, beta-amyloid peptide (25-35) treatment. There was no change in prodynorphin mRNA or alpha7-type nicotinic acetylcholine receptor mRNA expression in the hippocampus 10 days after beta-amyloid peptide (25-35) treatment alone. Of interest, mRNA expression of not only prodynorphin, but also the alpha7-type nicotinic acetylcholine receptor, was significantly decreased when U-50,488H was administered 1 h before, but not 1 h after, treatment with beta-amyloid peptide (25-35). However, these changes were not observed after the administration of (-)-nicotine. These results suggest that activation of the kappa-opioid system, but not beta7-type nicotinic receptors has a neuroprotective effect on beta-amyloid peptide (25-35)-induced memory impairment, and may be involved in the long-lasting changes in the expression of these mRNAs.