title: Differential effect of baclofen on cortical and spinal inhibitory circuits.
abstract: OBJECTIVE
  The cutaneous silent period (SP) is a spinal inhibitory reflex, which suppresses activity in spinal motor nuclei. Transcranial magnetic stimulation (TMS) elicits a cortical SP, which represents GABA(B) receptor-mediated inhibition of cortical excitability. Baclofen as a strong GABA(B) agonist effectively reduces muscle hypertonia, however, it is not known whether intrathecal baclofen (ITB) may modulate spinal inhibitory circuits.
  
  
  METHODS
  We evaluated clinical and neurophysiological effects of ITB in ten patients with severe spasticity due to spinal cord injury (n = 9) and chronic progressive multiple sclerosis (n = 1). Neurophysiological assessment included H reflex and cutaneous and cortical SPs, before and 15, 30, 60, 90, 120, and 180 min after ITB bolus administration.
  
  
  RESULTS
  ITB suppressed soleus H reflex as early as 15 min after lumbar bolus injection; MAS scores declined after 1 h. Cortical SP end latency and duration increased progressively with a significant maximum 3h following ITB bolus, whereas cutaneous SP latency and duration did not change significantly.
  
  
  CONCLUSIONS
  The present findings suggest that baclofen does not affect the cutaneous SP, but prolongs the cortical SP.
  
  
  CONCLUSIONS
  The spinal inhibitory circuitry of the cutaneous SP is not modulated by GABA(B) receptor-mediated activity, in contrast to the cortical inhibitory circuitry of the cortical SP, which is subject to powerful GABA(B) control.
authors.affiliation: Department of Neurology, 3rd Medical Faculty, Charles University, Prague, Czech Republic. ivana.stetkarova@fnkv.cz
authors.forename: Ivana
authors.initials: I
authors.lastname: Stetkarova
authors.forename: Markus
authors.initials: M
authors.lastname: Kofler
mesh_terms: D000328:Adult; D001418:Baclofen / Q000008:administration & dosage / Q000494:pharmacology*; D002540:Cerebral Cortex / Q000187:drug effects* / Q000503:physiopathology; D005260:Female; D058786:GABA-B Receptor Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D006181:H-Reflex / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007278:Injections, Spinal; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000150:complications; D009128:Muscle Spasticity / Q000209:etiology / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000294:innervation; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D012018:Reflex / Q000187:drug effects* / Q000502:physiology; D013124:Spinal Injuries / Q000150:complications; D013127:Spinal Nerves / Q000187:drug effects* / Q000503:physiopathology; D013997:Time Factors
chemical_list: D058786:GABA-B Receptor Agonists; D001418:Baclofen