title: Astrocytic adrenoceptors and learning: alpha1-adrenoceptors.
abstract: Noradrenergic receptors are expressed on both on astrocytes and neurons and noradrenergic activation of astrocytic beta(2)- and beta(3)-adrenoceptors are necessary for memory consolidation. In this paper, we marshal evidence for astrocytic alpha(1)-adrenoceptor involvement in memory consolidation. We examine the role of alpha(1)-adrenoceptors in hippocampal and mesopallial (cortical) memory processing using a discriminative avoidance task in the day-old chick. The selective alpha(1)-adrenoceptor agonist, methoxamine, caused the consolidation of weakly-reinforced memory at the time of transition of short-term to intermediate memory and at the time of transition of intermediate to long-term memory. The selective antagonist prazosin prevented memory consolidation at these two times. Blockade of memory by injection of an alpha(2)-adrenoceptor agonist into the LoC could be overcome by mesopallial or hippocampal injection of alpha(1)-, beta(2)- and beta(3)-adrenoceptor agonists. The results of studies where we challenged the ability of methoxamine to promote consolidation by pre-administration of astrocytic metabolic inhibitors of glycogenolysis or oxidative metabolism, suggest that the alpha(1)-adrenoceptor effect is astrocytic. This conclusion is supported by the finding that co-administration of suboptimal doses of methoxamine and thrombin have an additive effect on promoting consolidation. Thrombin causes a calcium response in cultured chick astrocytes but not in neurons. Thrombin, like methoxamine, promotes consolidation at the transition points between short-term, intermediate memory and long-term memory stages. Thrombin enhancement of memory consolidation is blocked by an alpha(1)-adrenoceptor antagonist but not by antagonists of beta(2)- or beta(3)-adrenoceptors. In summary, noradrenaline activation of alpha(1)-adrenoceptors is necessary for consolidation from both short-term and intermediate memory in both the hippocampus and the mesopallium in the chick. Evidence is presented suggesting that the memory consolidating action of alpha(1)-adrenoceptor stimulation results from receptors located on astroctyes and involves an increase in free cytosolic calcium from internal stores.
authors.affiliation: Department of Anatomy and Developmental Biology, Monash University, Clayton, Victoria, Australia. marie.gibbs@med.monash.edu.au
authors.forename: Marie E
authors.initials: ME
authors.lastname: Gibbs
authors.forename: David N
authors.initials: DN
authors.lastname: Bowser
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology*; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D002645:Chickens; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism; D007858:Learning / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008568:Memory / Q000187:drug effects / Q000502:physiology; D008845:Microinjections; D044463:Receptor, PAR-1 / Q000819:agonists; D011941:Receptors, Adrenergic / Q000502:physiology*; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology*; D013649:Taste / Q000187:drug effects / Q000502:physiology; D013917:Thrombin / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D044463:Receptor, PAR-1; D011941:Receptors, Adrenergic; D018340:Receptors, Adrenergic, alpha-1; D006003:Glycogen; D013917:Thrombin; D002118:Calcium