title: Cortisol-induced effects on human cortical excitability.
abstract: BACKGROUND
  Cortisol may fulfill all criteria for a neuromodulator. However, it is not known whether it may rapidly influence motor system activity in humans.
  
  
  OBJECTIVE
  Circulating cortisol levels were manipulated by administration of a single intravenous dose of hydrocortisone or saline solution, on separate days, to study changes in corticospinal and motor cortical excitability.
  
  
  METHODS
  Motor-evoked potentials (MEPs) to single- and paired-pulse transcranial magnetic stimulation from the resting first dorsal interosseous muscle, and cortisol plasma levels were assessed before and after either a bolus of 20 mg of hydrocortisone or saline solution in seven healthy subjects.
  
  
  RESULTS
  Mean cortisol plasma level rapidly rose, peaked between 5 and 10 minutes after hydrocortisone injection, to slowly decay afterward. Mean MEP amplitude significantly increased from preinjection levels, and mean standard deviation of MEPs significantly increased between 8-12 minutes postinjection. Short-intracortical inhibition, tested during the same period, was significantly decreased. No significant changes in the above measures were observed after saline solution administration.
  
  
  CONCLUSIONS
  Our results suggest that high circulating levels of cortisol rapidly increase corticospinal excitability and reduce gamma aminobutyric acid activity, as measured by short-intracortical inhibition, in humans. These effects, lasting about 10 minutes, were observed within 15 minutes from the pharmacological intervention. They are therefore compatible with a nongenomic mechanism. These findings are important in view of the notion that a decrease in intracortical gamma aminobutyric acid activity appears to be a prerequisite for motor learning and plastic processes in the human motor cortex.
authors.affiliation: Sezione di Neurofisiologia Clinica, Dipartimento di Scienze Neurologiche e del Comportamento, Universita' di Siena, Siena, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Milani
authors.forename: Pietro
authors.initials: P
authors.lastname: Piu
authors.forename: Traian
authors.initials: T
authors.lastname: Popa
authors.forename: Raimondo
authors.initials: R
authors.lastname: della Volpe
authors.forename: Marco
authors.initials: M
authors.lastname: Bonifazi
authors.forename: Alessandro
authors.initials: A
authors.lastname: Rossi
authors.forename: Riccardo
authors.initials: R
authors.lastname: Mazzocchio
mesh_terms: D000328:Adult; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D004576:Electromyography; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000187:drug effects / Q000502:physiology; D011712:Pyramidal Tracts / Q000187:drug effects / Q000502:physiology; D050781:Transcranial Magnetic Stimulation / Q000379:methods
chemical_list: D000893:Anti-Inflammatory Agents; D006854:Hydrocortisone