title: Effects of alpha(2)-adrenoceptor agonists on perinatal excitotoxic brain injury: comparison of clonidine and dexmedetomidine.
abstract: BACKGROUND
  A growing number of children have severe neurologic impairment related to very premature birth. Experimental data suggest that overstimulation of cerebral N-methyl-d-aspartate (NMDA) receptors caused by excessive glutamate release may be involved in the genesis of perinatal hypoxic-ischemic brain injury. alpha(2)-Adrenoceptor agonists are protective in models of brain ischemia in adults. The authors sought to determine whether they prevent perinatal excitotoxic neuronal damage.
  
  
  METHODS
  Five-day-old mice were allocated at random to clonidine (4-400 microg/kg), dexmedetomidine (1-30 microg/kg), or saline injected intraperitoneally before an intracerebral stereotactic injection of the NMDA receptor agonist ibotenate; cortical and white matter lesions were quantified 5 days later by histopathologic examination. Cortical neuron cultures exposed to 300 microm NMDA were used to evaluate the effects of clonidine or dexmedetomidine on neuronal death assessed by counting the number of pycnotic nuclei after fluorescent chromatin staining.
  
  
  RESULTS
  In vivo, both clonidine and dexmedetomidine induced significant concentration-dependent reductions in the size of ibotenate-induced lesions in the cortex and white matter. In vitro, the number of neurons damaged by NMDA exposure was significantly decreased by both dexmedetomidine (-28 +/- 12% at 10 microm; P < 0.01) and clonidine (-37 +/- 19% at 100 microm; P < 0.01) as compared with controls. In both models, the selective alpha2-adrenoceptor antagonist yohimbine abolished the neuroprotective effect of clonidine and dexmedetomidine.
  
  
  CONCLUSIONS
  Clonidine and dexmedetomidine are potent neuroprotectors that act by stimulating the alpha(2) adrenoceptors. These results obtained in a murine model of perinatal excitotoxic injury may be relevant to some forms of neonatal brain damage in humans.
authors.affiliation: Laboratoire de Neurologie du Développement, Institut National de la Santé de la Recherche Médicale E9935, Hôpital Robert Debré, Paris, France. vlaudenb@infobiogen.fr
authors.forename: Vincent
authors.initials: V
authors.lastname: Laudenbach
authors.forename: Jean
authors.initials: J
authors.lastname: Mantz
authors.forename: Hugo
authors.initials: H
authors.lastname: Lagercrantz
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Desmonts
authors.forename: Philippe
authors.initials: P
authors.lastname: Evrard
authors.forename: Pierre
authors.initials: P
authors.lastname: Gressens
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D058666:Adrenergic beta-2 Receptor Agonists; D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000187:drug effects*; D003000:Clonidine / Q000494:pharmacology*; D020927:Dexmedetomidine / Q000494:pharmacology*; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity*; D005260:Female; D007051:Ibotenic Acid / Q000494:pharmacology; D051379:Mice; D016202:N-Methylaspartate / Q000633:toxicity; D018696:Neuroprotective Agents / Q000494:pharmacology*; D011247:Pregnancy
chemical_list: D000316:Adrenergic alpha-Agonists; D058666:Adrenergic beta-2 Receptor Agonists; D018690:Excitatory Amino Acid Agonists; D018696:Neuroprotective Agents; D007051:Ibotenic Acid; D016202:N-Methylaspartate; D020927:Dexmedetomidine; D003000:Clonidine