title: Impaired maze performance in aged rats is accompanied by increased density of NMDA, 5-HT1A, and alpha-adrenoceptor binding in hippocampus.
abstract: Using quantitative receptor autoradiography, we assessed binding site densities and distribution patterns of glutamate, GABA(A), acetylcholine (ACh), and monoamine receptors in the hippocampus of 32-month-old Fischer 344/Brown Norway rats. Prior to autoradiography, the rats were divided into two groups according to their retention performance in a water maze reference memory task, which was assessed 1 week after 8 days of daily maze training. The animals of the inferior group showed less long-term retention of the hidden-platform task but did not differ from superior rats in their navigation performance during place training and cued trials. The decreased retention performance in the group of inferior learners was primarily accompanied by increased alpha(1)-adrenoceptors in all hippocampal subregions under inspection (CA1-CA4 and dentate gyrus), while elevated alpha(2)-adrenoceptor binding was observed in the CA1 region and DG. Furthermore, inferior learners had higher NMDA binding in the CA2 and CA4 and increased 5-HT(1A) binding sites in the CA2, CA3, and CA4 region. No significant differences between inferior and superior learners were evident with regard to AMPA, kainate, GABA(A), muscarinergic M(1), dopamine D(1), and 5-HT(2) binding densities in any hippocampal region analyzed. These results show that increased NMDA, 5-HT(1A), and alpha-adrenoceptor binding in the hippocampus is associated with a decline in spatial memory. The increased receptor binding observed in the group of old rats with inferior maze performance might be the result of neural adaptation triggered by age-related changes in synaptic connectivity and/or synaptic activity.
authors.affiliation: Institute of Physiological Psychology, University of Düsseldorf, Düsseldorf, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Topic
authors.forename: I
authors.initials: I
authors.lastname: Willuhn
authors.forename: N
authors.initials: N
authors.lastname: Palomero-Gallagher
authors.forename: K
authors.initials: K
authors.lastname: Zilles
authors.forename: J P
authors.initials: JP
authors.lastname: Huston
authors.forename: R U
authors.initials: RU
authors.lastname: Hasenöhrl
mesh_terms: D018663:Adrenergic Agents / Q000493:pharmacokinetics; D000375:Aging / Q000502:physiology*; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D016291:Dizocilpine Maleate / Q000493:pharmacokinetics; D018690:Excitatory Amino Acid Agonists / Q000493:pharmacokinetics; D018691:Excitatory Amino Acid Antagonists / Q000493:pharmacokinetics; D006624:Hippocampus / Q000378:metabolism*; D008297:Male; D018782:Maze Learning / Q000502:physiology*; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D011869:Radioligand Assay / Q000379:methods; D051381:Rats; D011916:Rats, Inbred F344; D044282:Receptor, Serotonin, 5-HT1A / Q000378:metabolism*; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D018490:Serotonin Agents / Q000493:pharmacokinetics; D018709:Statistics, Nonparametric; D014316:Tritium / Q000493:pharmacokinetics; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000493:pharmacokinetics
chemical_list: D018663:Adrenergic Agents; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D011942:Receptors, Adrenergic, alpha; D016194:Receptors, N-Methyl-D-Aspartate; D018490:Serotonin Agents; D014316:Tritium; D044282:Receptor, Serotonin, 5-HT1A; D016291:Dizocilpine Maleate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid