title: Aestivation and hypoxia-related events share common silent neuron trafficking processes.
abstract: BACKGROUND
  The availability of oxygen is a limiting factor for neuronal survival since low levels account not only for the impairment of physiological activities such as sleep-wake cycle, but above all for ischemic-like neurodegenerative disorders. In an attempt to improve our knowledge concerning the type of molecular mechanisms operating during stressful states like those of hypoxic conditions, attention was focused on eventual transcriptional alterations of some key AMPAergic silent neuronal receptor subtypes (GluR1 and GluR2) along with HSPs and HIF-1α during either a normoxic or a hypoxic aestivation of a typical aquatic aestivator, i.e. the lungfish (Protopterus annectens).
  
  
  RESULTS
  The identification of partial nucleotide fragments codifying for both AMPA receptor subtypes in Protopterus annectens displayed a putative high degree of similarity to that of not only fish but also to those of amphibians, birds and mammals. qPCR and in situ hybridization supplied a very high (p < 0.001) reduction of GluR1 mRNA expression in diencephalic areas after 6 months of aerial normoxic aestivation (6mAE). Concomitantly, high (p < 0.01) levels of HSP70 mRNAs in hypothalamic, mesencephalic and cerebellar areas of both 6mAE and after 6 months of mud hypoxic aestivation (6mMUD) were detected together with evident apoptotic signals. Surprisingly, very high levels of GluR2 mRNAs were instead detected in thalamic along with mesencephalic areas after 6 days of normoxic (6dAE) and hypoxic (6dMUD) aestivation. Moreover, even short- and long-term hypoxic states featured high levels of HIF-1α and HSP27 transcripts in the different brain regions of the lungfish.
  
  
  CONCLUSIONS
  The distinct transcriptional variations of silent neurons expressing GluR1/2 and HSPs tend to corroborate these factors as determining elements for the physiological success of normoxic and hypoxic aestivation. A distinct switching among these AMPA receptor subtypes during aestivation highlights new potential adaptive strategies operating in key brain regions of the lungfish in relation to oxygen availability. This functional relationship might have therapeutic bearings for hypoxia-related dysfunctions, above all in view of recently identified silent neuron-dependent motor activity ameliorations in mammals.
authors.affiliation: Comparative Neuroanatomy Laboratory, University of Calabria, 87030 Arcavacata di Rende-CS, Italy. jisly76@yahoo.it
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Giusi
authors.forename: Merylin
authors.initials: M
authors.lastname: Zizza
authors.forename: Rosa Maria
authors.initials: RM
authors.lastname: Facciolo
authors.forename: Shit Fun
authors.initials: SF
authors.lastname: Chew
authors.forename: Yuen Kwong
authors.initials: YK
authors.lastname: Ip
authors.forename: Marcello
authors.initials: M
authors.lastname: Canonaco
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001921:Brain / Q000166:cytology; D004956:Estivation / Q000502:physiology*; D005399:Fishes; D005786:Gene Expression Regulation / Q000502:physiology*; D050884:HSP72 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D000860:Hypoxia / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D020287:In Situ Nick-End Labeling; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D018091:Receptors, AMPA / Q000235:genetics / Q000378:metabolism
chemical_list: D050884:HSP72 Heat-Shock Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger; D018091:Receptors, AMPA; C104722:glutamate receptor ionotropic, AMPA 2