title: Experimentally induced hyperthyroidism disrupts hippocampal long-term potentiation in adult rats.
abstract: BACKGROUND
  Manipulating thyroid hormones has been shown to influence learning and memory. Although a large body of literature is available on the effects of thyroid hormone deficiency on learning and memory functions during developmental or adult-onset hypothyroidism, electrophysiological findings are limited. This limitation is especially notable with respect to thyroxine administration in adult, normothyroid animals.
  
  
  METHODS
  Experiments were carried out on 12 adult male Wistar rats, each 9-10 months of age. Rats were randomly divided into hyperthyroid (0.2 mg/kg/day intraperitoneal thyroxine injection, for 21 days) and control groups (n = 6 animals in each group). Following spatial learning performance tests on hyperthyroid and control groups, rats were anesthetized with urethane and placed in a stereotaxic frame. A bipolar, tungsten electrode was used to stimulate the medial perforant path. A glass micropipette was inserted within the granule cell layer of the ipsilateral dentate gyrus to record field excitatory postsynaptic potentials (fEPSP). Following a 15-min baseline recording of fEPSPs, long-term potentiation (LTP) was induced by four sets of tetanic pulse trains.
  
  
  RESULTS
  Thyroxine-treated rats showed significantly worse performance in the spatial memory task and attenuated input-output relationships in the electrophysiological analyses. Treated rats also showed a lower efficacy of LTP induction when compared with controls.
  
  
  CONCLUSIONS
  The present study provides clear in vivo evidence for the action of L-thyroxine in the impairment of synaptic plasticity and in inducing spatial memory task deficits in adult rats. These findings may explain the complaints of cognitive function reductions in hyperthyroid patients.
authors.affiliation: Department of Physiology, Faculty of Medicine, University of Erciyes, Kayseri, Turkey.
authors.forename: Eylem
authors.initials: E
authors.lastname: Taşkın
authors.forename: A Seda
authors.initials: AS
authors.lastname: Artis
authors.forename: Soner
authors.initials: S
authors.lastname: Bitiktas
authors.forename: Nazan
authors.initials: N
authors.lastname: Dolu
authors.forename: Narin
authors.initials: N
authors.lastname: Liman
authors.forename: Cem
authors.initials: C
authors.lastname: Süer
mesh_terms: D000367:Age Factors; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D004195:Disease Models, Animal; D055724:Electrophysiological Phenomena / Q000187:drug effects; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology; D006980:Hyperthyroidism / Q000097:blood / Q000139:chemically induced* / Q000503:physiopathology*; D017774:Long-Term Potentiation / Q000187:drug effects* / Q000502:physiology; D008297:Male; D018782:Maze Learning / Q000187:drug effects / Q000502:physiology; D008569:Memory Disorders / Q000097:blood / Q000139:chemically induced / Q000503:physiopathology; D051381:Rats; D017208:Rats, Wistar; D013963:Thyroid Hormones / Q000097:blood; D013974:Thyroxine / Q000009:adverse effects* / Q000494:pharmacology
chemical_list: D013963:Thyroid Hormones; D013974:Thyroxine